O & M of DC & UPS Systems

Note: The source of the technical material in this volume is the ProfessionalEngineering Development Program (PEDP) of Engineering Services.

Warning: The material contained in this document was developed for SaudiAramco and is intended for the exclusive use of Saudi Aramco’semployees. Any material contained in this document which is notalready in the public domain may not be copied, reproduced, sold, given,or disclosed to third parties, or otherwise used in whole, or in part,without the written permission of the Vice President, EngineeringServices, Saudi Aramco.

Chapter : Electrical For additional information on this subject, contactFile Reference: EEX21107 W.A. Roussel on 874-1320

Engineering EncyclopediaSaudi Aramco DeskTop Standards

Directing the Operationand Maintenance of DC/UPS Systems

Engineering Encyclopedia Electrical

Directing the Operation and Maintenance of DC/UPS Systems

Saudi Aramco DeskTop Standards

CONTENTS PAGES

DETERMINING WHETHER BATTERIES ARE FUNCTIONINGPROPERLY ............................................................................................................ 1

Preventive Maintenance Requirements .......................................................1Battery Physical Checks .................................................................. 1Battery Voltage Checks ................................................................... 7

Preventive Maintenance Frequency ..........................................................11Preventive Maintenance Records ..............................................................14Problems and Corrective Measures ...........................................................20

Grounding ......................................................................................20Electrolyte Loss ............................................................................. 23Abnormal Specific Gravity ............................................................24

DETERMINING WHETHER DC/UPS SUBSYSTEMS AREFUNCTIONING PROPERLY .............................................................................. 27

Preventive Maintenance Requirements .....................................................27Visual Inspection ........................................................................... 27Cleaning.........................................................................................28Battery Charger Checks and Adjustments ..................................... 31Inverter Checks and Adjustments .................................................. 35

Preventive Maintenance Frequency ..........................................................41Preventive Maintenance Records ..............................................................44Problems and Corrective Measures ...........................................................51

Tripping of Input/Output Breakers................................................. 51Improper Inverter Output ...............................................................53SCR Failures .................................................................................. 54



Saudi Aramco DeskTop Standards

WORK AID 1: MAINTENANCE SPECIFICATIONS AND TROUBLESHOOTING GUIDE COMPILED FROM SADP-P-103 AND ESTABLISHED ENGINEERING PRACTICES FOR DETERMINING WHETHER BATTERIES ARE FUNCTIONING PROPERLYMaintenance Specifications....................................................................... 57Troubleshooting Guide.............................................................................. 58

WORK AID 2: MAINTENANCE SPECIFICATIONS AND TROUBLESHOOTING GUIDE COMPILED FROM ESTABLISHED ENGINEERING PRACTICES FOR DETERMINING WHETHER DC/UPS SUBSYSTEMS ARE FUNCTIONING PROPERLYMaintenance Specifications....................................................................... 59Troubleshooting Guide.............................................................................. 61

GLOSSARY ......................................................................................................... 62



Saudi Aramco DeskTop Standards 1

DETERMINING WHETHER BATTERIES ARE FUNCTIONING PROPERLY

The checks and tests that can be performed to determine whether batteries are functioningproperly include visual observations, service and performance tests, and monitoring ofmetered parameters. This section provides information on the following topics that arepertinent to determining whether batteries are functioning properly:

• Preventive Maintenance Requirements• Preventive Maintenance Frequency• Preventive Maintenance Records• Problems and Corrective Measures

Preventive Maintenance Requirements

Preventive maintenance consists of routine checks and tests that are performed on a piece ofequipment to determine its current condition and to identify and correct degrading equipmentconditions before such conditions result in complete equipment failure. An effectivepreventive maintenance program will help to ensure that batteries meet or exceed themanufacturer's service life.

This section of the Module will discuss the items of a battery that require preventivemaintenance, what maintenance measures are required, and why the maintenance measuresare performed. The items of the battery that require preventive maintenance are divided intothe following general categories:

• Battery Physical Checks• Battery Voltage Checks

Battery Physical Checks

Physical checks should be performed on batteries at regularly scheduled intervals. Thespecific items of a battery that should be checked are specified by the individual batterymanufacturers. The following is a list of the physical checks that generally are specified andthe reasons that the checks are performed. The descriptions also include the methods that canbe used to perform the physical checks.




General Cleanliness - A general cleanliness inspection should be performed to check fordirt, dust, and/or electrolyte accumulation on the battery cells and the floor and for dirtand dust accumulation in the ventilation system filters. The reason that generalcleanliness is checked is that dirt/electrolyte deposits or build-ups on the battery cellscan cause increased cell self-discharge rates, battery grounds and, in severe cases,short circuits. Dirty or wet floors can be slippery, which results in a safety hazard;dirty ventilation filters can decrease the battery room ventilation, which can result inunsatisfactory ambient temperature conditions and in unsafe levels of hydrogen gasaccumulation.

The method that is used to perform the general cleanliness inspection is a visualinspection. If the results of the visual inspection are unsatisfactory, the unsatisfactoryitems must be cleaned. Loose dirt or dust that has accumulated on the battery cells canbe removed through use of a vacuum or a low pressure air sparger. Compacted dirtcan be removed through use of a moderate pressure water hose. Electrolyte residuecan be removed through washing with an appropriate neutralizing solution and thenrinsing with a moderate pressure water hose. The appropriate neutralizing solution forlead-acid batteries is a mixture of one pound of baking soda and one gallon of water.The appropriate neutralizing solution for nickel-cadmium batteries is a 4% solution ofboric acid. Excess water that remains after the washdown should be wiped off with aclean cloth or removed by the air sparger.

Dry dirt or dust that is on the battery room floors should be swept or vacuumed.Electrolyte residue that is on the battery room floors should be removed in the samefashion as electrolyte residue that is on the battery cells.

Reusable-type ventilation filters should be cleaned and air dried. Disposable "one-time" filters should be replaced.

Battery Rack - The battery rack should be checked for loose hardware connections, forchips or cracks in the rack's epoxy paint coating, and for integrity of the rack-to-floormount connection. The reason that the battery rack should be checked is that loosehardware or a loose floor mount connection can result in a structural failure and apossible collapse of the battery rack. Chips and cracks in the epoxy paint can permitexposure of the rack support steel to the highly corrosive electrolyte. Corrosion of therack support steel can also lead to battery rack failure.




The method that is used to perform the battery rack check is a visual inspection. Allloose connections that are found during the visual inspection must be documented, andan immediate repair must be initiated. Cracked and chipped areas of the epoxy paintshould be washed with an appropriate neutralizing solution and rinsed with cleanwater. The appropriate neutralizing solution for lead-acid batteries is a mixture of onepound of baking soda and one gallon of water. The appropriate neutralizing solutionfor nickel-cadmium batteries is a 4% solution of boric acid. After the affected areashave dried, they should be repainted with epoxy paint.

Cell Case Integrity - The integrity of each cell case should be checked to ensure that noleaks exist. The reason that the integrity of each cell case should be checked is that theelectrolyte is both a conductor and a corrosive. Because the electrolyte is a conductor,electrolyte that leaks out of the cell can cause increased cell self-discharge rates,grounds, and shorts. Because the electrolyte is a corrosive, electrolyte that leaks out ofthe cell can corrode any bare metal surfaces that it contacts. The corrosive nature ofelectrolyte also makes it a safety hazard because electrolyte will cause skin burns.

The method that is used to perform cell case integrity checks is a visual inspection.Special attention should be paid to the area that is around the connection terminal(post) seals and around the cover-to-container seals. Each cell also should be visuallychecked for stress cracks and for leaking or missing vent caps/flame arrestors.Cracked or leaking cells should be replaced with a spare cell. Cell replacement will bediscussed in more detail later in this Module.

Vent Caps/Flame Arrestors - Vent caps/flame arrestors should be checked for cracks orother defects, clogging, and tightness. Vent caps/flame arrestors that are cracked orthat are loose can allow electrolyte to leak out of the cell during the gassing phase of acharge. The problems that are caused by these electrolyte leaks are the same as theproblems that are caused by the electrolyte leaks that were discussed previously. Ventcaps/flame arrestors that are clogged will not allow the gases that are formedduring charges and discharges to escape and will in turn cause a buildup of pressureinside of the cell. When the vent cap/flame arrestor is subsequently removed, thepressure that is inside of the cell will be suddenly released. The sudden release ofpressure will cause electrolyte to spray out of the cell and onto the person thatremoved the vent cap/flame arrestor. Such a spray of electrolyte presents a severesafety hazard.




The method that is used to perform vent cap/flame arrestor checks is a combinedvisual/physical inspection. The vent caps/flame arrestors should be visually inspectedfor cracks or other defects and clogging, and they should be physically inspected fortightness (i.e., the vent caps/flame arrestors should be turned by hand to ensure thatthey are hand-tight). Vent caps/flame arrestors that are cracked or that are defectivemust be replaced. Vent caps/flame arrestors that are clogged can be cleaned byagitating them in pure water. Cleaning or neutralizing agents must not be usedbecause these agents tend to further clog the pores of the vent caps/flame arrestorsrather than to clean the pores.

Cell Terminals - The cell terminals should be checked for corrosion, tightness, andterminal resistance. The terminals must be kept free from corrosion because corrosioncan physically weaken the terminal connection and it can cause a high resistanceconnection. The tightness and the terminal resistance of the terminal connections arechecked to ensure that high resistance connections do not exist. High resistanceconnections can reduce the battery voltage and can cause overheating at theconnection.

The method that is used to check the cell terminals for corrosion is a visual inspection.Corrosion normally appears as a white powdery buildup but it may also have a slightlyblue or brown tint. If corrosion is present, it must be removed by wiping the corrodedsurface with a cloth that has been dampened with the applicable neutralization agent(bicarbonate of soda for lead-acid and boric acid for nickel-cadmium batteries). Afterthe neutralization agent has been applied, the surface should be wiped with a cloth thathas been dampened with clean water followed by a final wipe down with a clean drycloth. After the corrosion has been removed, the terminal connection should bechecked for tightness through use of a torque wrench, and a terminal resistance testshould be performed through use of a digital low resistance ohmmeter. After thetightness has been verified and the terminal resistance test has been satisfactorilycompleted, the entire terminal connection should be coated with a thin layer of No-Oxgrease or equivalent. The No-Ox grease is used to inhibit future occurrences ofoxidation or corrosion. If corrosion was not present, the tightness check and theterminal resistance check still should be performed.

Cell Internal Inspection - The internal portion of lead-acid cells should be checked forbuildup of excess sulfate material on the plates, for excess sediment at the bottom ofthe cell container (jar), and for plate damage. Excess sulfate material build-up on theplates is an indication that the cell is being undercharged. Such a condition can limitthe overall capacity of the battery. Excess sediment at the bottom of the cell containeris an indication that the cell is being overcharged. Continuous overcharging willreduce the life of the affected cells. In severe cases, the excess sediment can build upto the point at which it bridges the bottom of the positive and the negative plates,which causes an internal short circuit. Internal short circuits increase the cell's self-discharge rate and limit overall battery capacity. Damaged cell plates can cause a




number of problems, the most severe of which is separator damage, which leads tointernal short circuits.

The method that is used to perform a cell internal inspection is a visual inspection.Sulfate build-up appears as a white scale on the surface of the plates. Sulfateformation is a normal result of discharging a battery; however, if the battery is beingproperly charged, the sulfate material should be converted back into sponge lead andlead peroxide when the battery is charged. If excess sulfate material build-up isobserved, additional tests and inspections should be performed to determine the cause.If excess sulfate material is observed on a single cell, that cell probably has highresistance terminal connections or an electrolyte problem. If excess sulfate material isobserved on a number of cells, the battery charger voltage and/or timer settings areprobably incorrect.

Sediment build-up appears as a combination of white sulfate material and grey activeplate material. Under normal conditions, the sediment build-up will be negligible andit will amount to little more than a thin layer of dust at the bottom of the cell container.The physical size of the space that is below the bottom of the plates is designed toaccommodate all of the sediment that will be formed during battery's designed life. Ifexcess sediment is observed, additional tests and inspections must be performed todetermine the cause and the extent of the damage. The possible causes aremanufacturing defects, excessive electrolyte specific gravity, and excessive batterycharger voltage and/or timer settings.

The visual inspection for plate damage consists of an observation of the plates toensure that they are evenly spaced and that they do not physically interfere with theseparators or the adjacent plates. Bowed and warped cell plates are an irreversiblecondition. If the plates are bowed or warped to the point at which they are in physicalcontact with the separators and/or adjacent plates, the only corrective action is cellreplacement.

Nickel-cadmium batteries are more ruggedly constructed than lead-acid batteries and,as such, they are not susceptible to the same types of internal damage as lead-acidbatteries; therefore, a routine inspection of the internal portion of nickel-cadmiumbatteries is not required.

Cell Operating Parameters - The cell operating parameters include voltage, temperature,electrolyte level, and for lead-acid batteries only, specific gravity. These parametersare checked because they provide an indication of the cell's state-of-charge and of theoverall condition of the cell. The cell's temperature and electrolyte level also are usedto correct the measured value of the specific gravity of lead-acid batteries to a standardtemperature (25oC, 77oF) and level (zero reference point for a particular cell).




The cell's voltage is measured through use of a portable voltmeter. The cell'stemperature is measured through use of a thermometer. The cell's level is measuredthrough use of a ruler or a height stick. The specific gravity of lead-acid cells ismeasured through use of a hydrometer. The corrected value of specific gravity and thecell voltage should be consistent with each other and should be consistent with thecurrent state-of-charge of the cell. If these conditions are not observed, additional testsand inspections must be performed to determine the cause.

Capacity Test Discharge - Capacity test discharges should be performed to check thecurrent capacity of a battery. The reason that capacity test discharges should beperformed is that most batteries are installed to provide an emergency source of powerto critical loads for a specified period of time. If the battery is unable to supply theneeded power for the specified period of time, the critical loads will be lost, whichcould result in damage to personnel, equipment, and/or product.

Before a capacity test discharge is performed, the following initial conditions must bemet:

• The electrolyte level of each cell must be in the normal operational band.

• The terminal resistances must be at or below the manufacturer's specifiedresistance.

• The battery must be in a fully charged condition.

• The temperature of each cell must be a minimum of 25oF (12oC) below themaximum cell temperature that is specified by the manufacturer.

After the initial conditions have been met, the test discharge is conducted throughplacement of a rated load (in amperes) on the battery. The battery is discharged at itsrated load until it reaches the end of charge of 1.75 volts/cell times the number of cellsthat are in series, or until the voltage of any individual cell drops below the end ofcharge voltage of 1.75 volts. When one of these voltage limits is reached, the load isremoved from the battery to stop the discharge and the total length of time that thebattery was discharged is noted. The battery capacity (in percent) is determinedthrough use of the following formula:

%Capacity = 100 (actual ampere-hours discharged / rated ampere-hours)

The battery then must be recharged to a fully charged condition.




Battery Voltage Checks

Battery float voltage, battery equalizing voltage, and battery terminal voltages need to bechecked on a routine basis to help ensure that the battery can perform its design function overits expected service life. The importance of each voltage check and the effect that eachvoltage can have on battery performance and/or battery life are explained below.

Battery Float Voltage - Stationary batteries that are installed to provide standby oremergency power normally are maintained in a float (trickle) charge condition. In thiscondition, the battery charger applies a voltage to the battery that is slightly higherthan the battery's open circuit voltage, which maintains the battery on a continuouslow rate charge. The continuous low rate charge compensates for internal losses andfor intermittent discharges and keeps the battery in a fully charged condition.

Because the float voltage setpoint directly affects battery performance and in the caseof lead-acid batteries, battery life, this value should be checked as part of the routinemaintenance that is performed on batteries. If the float voltage is set too low,restoration of battery capacity lost through internal losses and intermittent dischargeswill not occur; therefore, the battery will always be less than fully charged. A batterythat is not fully charged may be unable to deliver the required amount of standby oremergency power for which it was installed. The long term effect of continuousoperation of lead-acid batteries at low float voltages (i.e., continuous under-charging)is a permanent reduction of battery capacity, which leads to a reduced service life.Nickel-cadmium batteries do not normally suffer any long term effects from operationat low float voltages.

If the float voltage is set too high, the battery will continuously be overcharged. Theproblems that result from continuously overcharging a battery depend on the extent ofthe overcharge. A float voltage that is slightly higher than normal will cause anincreased rate of electrolyte loss and a small increase in the operating temperature oflead-acid and nickel-cadmium batteries.

Provided that the battery room is air conditioned and that the electrolyte levels arechecked on a routine basis, the only real problem that is caused by minor overchargingis that the battery will have to be watered more often.




A float voltage that is significantly higher than normal can be extremely detrimental toperformance and service life of lead-acid batteries. Severe overcharge conditionscorrode the grids of the positive plates into lead peroxide. The corrosion physicallyweakens the plates and increases the resistance of the plates. Severe overchargeconditions also result in continuous battery gassing that will erode the active materialoff of the battery plates. The overall effect of the corrosion and erosion is reducedbattery capacity and reduced service life. In addition to the corrosion and erosion,severe overcharge conditions also can result in a significant increase in operatingtemperature. Operation of a battery at high temperatures, particularly at temperaturesthat are above 55oC, will significantly reduce the service life of the battery. Forexample, 11 days of float operation at 75oC is equivalent in service life to 365 days offloat operation at 25oC.

Overcharging of nickel-cadmium batteries does not generally result in any loss ofperformance or service life. The only problems that are associated with severeovercharge conditions are an increased rate of gassing and electrolyte loss.

The optimum float voltage setpoint for a given battery should be obtained from themanufacturer. Figure 1 shows typical float voltage values for several types of lead-acid and nickel-cadmium batteries that operate at various specific gravities. Duringroutine battery maintenance, the float voltage should be checked directly at the batterypositive and negative terminals through use of an installed or a portable voltmeter.




Float Voltage Per CellLead-Antimony Lead-Calcium Nickel-Cadmium

2.13 - 2.16 @ 1.170 ----- 1.40 - 1.42 @ 1.190 ± .0202.15 - 2.18 @1.215 2.17 - 2.21 @ 1.215 -----

----- 2.21 - 2.25 @ 1.250 ---------- 2.25 - 2.29 @ 1.300 -----

Recommended Float Voltages for Lead-Acid and Nickel-Cadmium Batteries Figure 1

Battery Equalizing Voltage - The battery equalizing voltage is the voltage at which anequalizing battery charge is performed. Because an equalizing charge restores thebattery to a fully charged condition after a discharge or restores any non-uniformitiesthat may have occurred between individual cells, the equalizing voltage is set higherthan the float voltage. The equalizing voltage for lead-acid batteries should be set atthe maximum voltage that the connected system equipment (loads) can tolerate or at2.39 volts per cell, whichever value is highest. The equalizing voltage for nickel-cadmium batteries should be set at the maximum voltage that the connected systemequipment can tolerate or at 1.60 volts per cell, whichever value is highest.

The period of time that the equalizing voltage is applied to the battery is then set,based on the equalizing voltage, at the value that is needed to restore all of the cells toa uniform, full-charge condition; higher equalizing voltages require less charge timethan lower equalizing voltages. The manufacturer's technical literature should beconsulted for the exact values of voltage and time that are required for a given battery.




Because the equalizing voltage value is generally limited by the maximum voltage thatcan be tolerated by the connected loads, and because this voltage is only applied for arelatively short period of time (usually 8 to 24 hours), the overcharge problems thatwere previously described for float voltages are not generally a concern in reference tochecking the setpoint of this voltage during routine maintenance. The major concernof an excessive equalizing voltage is exceeding the voltage limitations of theconnected loads. However, in the case of a failed battery charger voltage regulator,the excessive voltage that would result from such a failure would be detrimental toboth the battery and to the downstream loads.

The condition that is more likely to be detrimental to the capacity and service life oflead-acid batteries is a low equalizing voltage. If the equalizing voltage is too low, thebattery will not be completely restored to a uniform, fully-charged condition at the endof the equalizing charge. Any amount of undercharge that is allowed to persist for aperiod of time will cause a gradual sulphation of the negative plates in lead-acidbatteries with an eventual loss of capacity and reduction of service life. Nickel-cadmium batteries do not suffer any long-term effects from undercharge.

Most lead-acid battery chargers have an equalizing voltage adjustment that rangesfrom about 2.25 to 2.40 volts per cell. Most nickel-cadmium battery chargers have anequalizing voltage adjustment that ranges from about 1.50 to 1.60 volts per cell.During the performance of routine battery maintenance, the equalizing voltage shouldbe checked at the output of the battery charger through use of an installed or a portablevoltmeter.

Battery Terminal Voltages - During the performance of routine battery maintenance,battery terminal voltages should be checked with an installed or a portable voltmeter toverify that the battery is free from grounds and/or high resistance connections. Thefirst voltage that should be measured is the voltage from the positive battery terminalto the negative battery terminal. This voltage should be equal to the float voltage percell multiplied by the total number of cells that are in the battery installation. Theother voltages that should be measured are the voltage between the positive batteryterminal and ground and the voltage between the negative terminal and ground. Eachof these voltages should be equal to one half of the total battery voltage. If theseconditions do not exist, a ground or a high resistance connection is the likely cause.Grounds will be discussed in more detail later in this Module.




Preventive Maintenance Frequency

The overall goal of battery preventive maintenance is to identify and correct minor orimpending problems that, if left unchecked, could result in a reduction of battery capacity, areduction in battery capacity, or a safety hazard. In order for a battery preventivemaintenance program to achieve its goal, the battery systems and equipment must be checkedat regularly scheduled intervals. The regularly scheduled intervals vary dependent upon thetype of battery, the battery manufacturer, the type of intended service, and the environmentalconditions that exist at the installation. The initial battery preventive maintenance inspectionfrequencies are normally established on the basis of the manufacturer's recommendations.These initial frequencies can then be modified (increased or decreased in length) on the basisof local site operating experience and/or governing codes and standards for a particular typeof service.

As an example of how inspection frequencies can be modified on the basis of local siteoperating experience, assume that a particular battery manufacturer recommends that theelectrolyte level of each cell be checked once per month. Also assume that the inspectionresults of two consecutive monthly inspections showed that the electrolyte level in several ofthe cells had dropped below the minimum required level. Based on these results and providedthat no other problem is responsible for the lost level, the frequency of the electrolyte levelcheck for this particular battery should be performed more often. The inspection frequencyfor this particular item would likely be changed from a monthly requirement to a bi-weekly ora weekly requirement.

Figure 2 shows a typical preventive maintenance schedule for stationary storage batteries.The schedule contains the preventive maintenance requirements and the frequency ofperformance. The frequency of performance section is divided into three time categories:routine, quarterly, and annually. The routine column can represent daily, weekly, bi-weekly,or monthly preventive maintenance requirements. The applicable frequency for all of thepreventive maintenance items should be established as previously explained.




Preventive Maintenance Frequency of Performance

Requirement Routine Quarterly

Annually

Battery Physical Checks • General Cleanliness X (1) • Battery Rack X (1) • Cell Case Integrity X (1) • Vent Caps/Flame Arrestors X (1) • Cell Terminals - Corrosion - Tightness - Resistance

X (2)(2)(2)

XX

• Cell Internals * X (1) • Cell Operating Parameters - Specific Gravity * - Cell Voltage - Cell Temperature - Electrolyte Level

X (3)X (3)X (3)X (3)

XXXX

• Capacity Test Discharge X (4)Battery Voltage Checks • Float Voltage Check @ Charger Output X • Equalize Voltage Check @ Charger Output X • Battery Terminal Voltage Checks - Voltage from Positive Terminal to Negative Terminal - Voltage from Positive Terminal to Ground - Voltage from Negative Terminal to Ground

XXX

* Not required for nickel-cadmium batteries

NOTES:(1) Any discrepancies that are found during the check should be corrected.

(2) If corrosion is found, the condition must be corrected. After the corrosion is removed,the tightness and the resistance of the cleaned terminal should be verified.

(3) Routine check of cell operating parameters is only required for the designated pilot cells.

(4) A battery capacity test discharge should be conducted within the first two years ofservice. After the initial capacity test discharge, subsequent capacity test discharges




should be performed at five year intervals until the battery shows signs of degradation oruntil it reaches 85% of its service life expectancy. When one of these conditions is met,annual capacity test discharges should be performed.

Typical Preventive Maintenance ScheduleFigure 2




Preventive Maintenance Records

The results of all of the maintenance and testing that are performed on batteries should berecorded on battery records, and the individual records for each battery installation should bekept in a separate file for the life of the battery. The first step of the record keeping process isto record the baseline data for the battery. The baseline data are the data that were obtainedduring the start-up and commissioning of the battery. (These data were discussed in ModuleEEX 211.06.) Future maintenance records are added as maintenance is performed to providea chronological history of the battery's condition. The chronological history is used toidentify and analyze trends or isolated problems. This information aids the ElectricalEngineer in making future decisions in regard to the operation, maintenance, andtroubleshooting of the battery.

Figures 3 through 5 show typical storage battery maintenance record forms. These formscoincide with the typical storage battery maintenance schedule that previously was shown inFigure 2.

Figure 3 shows a typical storage battery maintenance record form that can be used to recordthe results of routine maintenance. The form is divided into two major parts: IdentificationData and Maintenance Data. The Identification Data section is used to record the pertinentinformation that is needed to identify the particular battery on which the maintenance wasperformed. The Maintenance Data section is used to record the actual results of themaintenance that was performed. A space is provided to record the results of each of theroutine maintenance items that were previously shown on Figure 2.




Storage Battery Maintenance Record - Routine ItemsFigure 3




Figure 4 shows a typical storage battery maintenance record form that can be used to recordthe results of quarterly maintenance. The form is divided into two major parts: IdentificationData and Maintenance Data. The Identification Data section is used to record the pertinentinformation that is needed to identify the particular battery on which the maintenance wasperformed. The Maintenance Data section is used to record the actual results of themaintenance that was performed. A space is provided to record the results of each of thequarterly maintenance items that were previously shown in Figure 2.




Storage Battery Maintenance Record - Quarterly ItemsFigure 4




Figure 5 shows a typical storage battery maintenance record form that can be used to recordthe results of annual maintenance. The form is divided into two major parts: IdentificationData and Maintenance Data. The Identification Data section is used to record the pertinentinformation that is needed to identify the particular battery on which the maintenance wasperformed. The Maintenance Data section is used to record the actual results of themaintenance that was performed. A space is provided to record the results of each of theannual maintenance items that were previously shown on Figure 2. Note that the space that isprovided to record the results of the cell terminal resistance checks and the capacity testdischarge only requires that the overall result of satisfactory or unsatisfactory be entered. Theactual data for these checks are to be recorded on the Individual Cell Terminal ResistanceTest Record and the Battery Acceptance Test Data Sheet, and then these additional recordsare to be attached to the annual maintenance record. The Individual Cell Terminal ResistanceTest Record and the Battery Acceptance Test Data Sheet were previously shown anddiscussed in Module EEX 211.06.




Storage Battery Maintenance Record - Annual ItemsFigure 5




Problems and Corrective Measures

This section of the Module will discuss the following typical battery problems:

• Grounding• Electrolyte Loss• Abnormal Specific Gravity

Grounding

The following aspects of battery grounds will be discussed in this section:

• Problems Caused• Indications• Corrective Actions

Problems Caused - Saudi Aramco Engineering Standard SAES-P-103 requires that thepositive and the negative dc buses of storage batteries that are installed in SaudiAramco industrial facilities be isolated from earth ground; therefore, Saudi Aramcostorage batteries are ungrounded. The possible exception to this requirement is anapplication in which industrial and communications systems must share the same dcbus. In these applications, Saudi Aramco consulting services must be consulted for thegrounding requirements.

Because most Saudi Aramco batteries are ungrounded, a single ground will not causeany protective devices to operate and, from an operational point of view, no abnormalconditions will be present other than a possible increase in the battery's discharge rate.The real problem that is caused by a single ground is an electrical shock hazard topersons who are working on or near the battery.

The potential problems for the battery itself occur when more than one ground existsand the magnitude of the fault current is insufficient to trip the protective devices.This situation can occur when several high resistance ground paths exist between twocells or a group of cells, which effectively creates a short circuit between the effectedcells. The short circuited cells then become a load on the battery and, if the conditionis not corrected, it will lead to permanent cell damage.




Indications - For installations that have permanently installed ground detectors, batterygrounds are indicated through the routine ground checks that are performed by theequipment operators. For installations that do not have permanently installed grounddetectors, battery grounds are indicated through measurement of battery terminalvoltages as was previously discussed. Once a battery ground is detected, the groundcan be isolated to a particular cell or group of cells through use of a technique that isreferred to as half-splitting.

Half-splitting involves the measurement and comparison of the following voltages thatare shown on Figure 6:

• The total voltage that is developed across a string of cells (V1).

• The total voltage that is developed from the beginning of the string to the mid-point of the string (V2).

• The total voltage that is developed from the mid-point of the string to the endof the string (V3).

Voltage V2 and voltage V3 should both be equal to one half of V1. If either voltage isless than one half of V1, the ground is located in the half of the string of cells thatproduced the lower voltage reading. The half-splitting technique can be repeated onsuccessively smaller strings of cells until the exact location of the ground is identified.

Half-Splitting Voltage Measurements




Figure 6




Corrective Measures - Once the location of the ground has been identified, a detailedvisual inspection of the area should be performed to identify the cause of the ground.In most cases, the ground path will be some combination of dirt build-up, electrolyteresidue or leakage, and terminal corrosion. The corrective measures consist ofremoval of the dirt or corrosion and neutralizing the electrolyte.

Electrolyte Loss

The following aspects of electrolyte loss will be discussed in this section:


Problems Caused - Because of the electrolysis that occurs during the battery chargingprocess, some amount of electrolyte loss is anticipated and is normal. The amount ofelectrolyte loss that results from normal battery operations varies with the type ofbattery, the frequency of charging, and the environmental conditions that are at theinstallation site. The anticipated losses are the reason for periodically checking andwatering the battery cells as part of the battery's preventive maintenance program. Ifthe maintenance program is properly implemented, the electrolyte levels will not dropbelow the minimum required level. Provided that the electrolyte levels do remainabove the minimum required level, no problems will result.

If the electrolyte level is allowed to drop below the minimum required level, theproblems that are caused vary dependent upon the actual extent of the level decrease.If the level drops below the bottom of the tube that is on the flash arrestor but remainsabove the plates, the problem that is caused is a slightly increased chance of fire orexplosion. When the electrolyte level drops below the bottom of this tube, the flasharrestor is effectively bypassed. A subsequent removal of the service cap would allowdirect access to the gas space that is at the top of the cell and, if a spark was present,the hydrogen gas that is in the gas space would be more likely to ignite. Becauseseveral events need to occur for the hydrogen to be ignited, the overall likelihood of afire or an explosion is still small.

The most severe problem that can result from a loss of electrolyte is permanent platedamage. If the electrolyte level drops below the top of the plates, the exposed portionsof the plates dry out, become extremely brittle, and completely lose their ability to becharged and discharged.

If the loss of electrolyte is a result of spillage or leaks, other problems such ascorrosion, grounds, and safety hazards also can occur.




Indications - The indications of a loss of electrolyte level are an electrolyte level that isbelow the "Min" level mark on the cell jars or electrolyte that is present on the batteryroom floor.

Corrective Measures - The first corrective measure is to determine and correct the causeof the electrolyte loss. The following are some of the typical causes of electrolyte loss:

• Overcharging.• Leaks.• Spillage.• A drop in ambient temperature.• The battery is approaching the end of its service life (antimony cells).• Improperly scheduled or inadequate preventive maintenance.

If the cause can be corrected (e.g., the cause was not a leak), and if the plates were notexposed and damaged, the affected cells should be filled to their normal level. Afterthe cells have been filled, normal battery operation can resume.

If the cause of the electrolyte loss was a leak, or if plate damage occurred, the batteryshould be placed on open circuit and the affected cell should be drained and removed.Also, the electrolyte that leaked out of the cell must be cleaned up and neutralized. Ifa replacement cell is available, the replacement cell should be installed and normalbattery operation can resume. If a replacement cell is not available, jumpers can beinstalled to re-connect the battery with one less cell. The battery can then betemporarily operated in this condition until a replacement cell can be obtained.

Abnormal Specific Gravity

The following aspects of abnormal specific gravities will be discussed in this section:


Problems Caused - Because specific gravity is a direct indicator of the state of charge ofa lead-acid battery, an abnormally low specific gravity indicates a low state of charge.If all of the cells of a battery have a low specific gravity, the battery is in a low state ofcharge and, as a result, it may not be capable of supplying the required amount ofemergency or standby power for which it was installed.




If only one or several cells have low specific gravities, these particular cells will limitthe overall capacity of the battery. When the battery is discharged, the cells that havethe low specific gravities will reach their low voltage limits (approximately 1.75V)before the rest of the battery. If the discharge is not stopped when the first cell reachesits low voltage limit, cell reversal will occur, which is quickly followed by celldamage.

Because the amount of acid that is in the electrolyte does not change after the cellshave initially been filled, abnormally high specific gravities almost never occur. Ifsuch a condition did occur, the problems that are caused are increased rates of self-discharge and reduced service life.

Indications - Direct indications of abnormal specific gravities can be obtained throughmeasurement of the actual specific gravities with a hydrometer; however, before themeasured specific gravities can be called abnormal, all of the factors that affectspecific gravity readings must be taken into account. Examples of these factorsinclude cell temperature, electrolyte level, whether or not the battery was recentlywatered, and the accuracy of the hydrometer.

Generally, a cell is said to have an abnormal specific gravity when its correctedspecific gravity is more than five points (expressed .005) above or below the averagecorrected specific gravity of all of the cells that are in the installation. The batteryitself is said to have an abnormal specific gravity when one of the following conditionsexist:

• The difference between the highest cell's corrected specific gravity and thelowest cell's corrected specific gravity is more than ten points (expressed .010).

• The difference between the initial and the current average corrected specificgravity of all of the cells that are in the installation is more than ten points (i.e.,.010).

The indirect indications of abnormal specific gravities are abnormal individual cellvoltages or abnormal total battery voltages. If these conditions are observed, a directmeasurement of the specific gravities is normally performed for confirmation.

Corrective Measures - If the abnormal specific gravity is isolated to one or several cells,the first corrective measure would be to recheck the specific gravity readings to verifythe existence of a problem. Once the abnormal specific gravity has been confirmed,the affected cells should be inspected for visible signs of damage and high resistanceconnections. If the results of these inspections are satisfactory, the battery should begiven an equalizing battery charge in attempt to correct the problem. If the problemstill exists at the completion of the equalizing charge, the manufacturer should be




contacted to determine if any special charging procedures can be performed to correctthe problem.

If the problem cannot be corrected, a capacity test discharge should be performed todetermine whether the battery's capacity is still acceptable. If the capacity is stillacceptable, normal battery operation can be resumed; however, the affected cellsshould be more closely monitored for the duration of the service life. If the batterycapacity is unacceptable, the affected cells must be replaced.

If the abnormal specific gravity pertains to the entire battery, one of the followingproblems likely exists:

• The float voltage setpoint is too low.• Too much time has elapsed since the last equalizing charge.• The battery is near the end of its service life

For the above problems, the first corrective measure would be to check and to adjustthe float voltage setpoint and to then perform an equalizing battery charge to correctthe abnormal specific gravities. If the float voltage setpoint was correct, and if theequalizing charge had corrected the specific gravity problem, the frequency of theequalizing charges should be increased to prevent reoccurrence of the problem.

If the equalizing charge did not correct the problem, the battery may be at or near theend of its service life. A capacity test discharge should be performed to determinewhether the battery's capacity is still acceptable. The acceptable range of batterycapacity is from 80% to >.100% of its original rated capacity. However, when thebattery capacity drops below 85% of its original rated capacity, the battery shows signsof degradation, and it should be more closely monitored for the duration of the servicelife. When the battery capacity drops below 80% of its original rated capacity, thebattery has reached the end of its service life, and it must be replaced.




DETERMINING WHETHER DC/UPS SUBSYSTEMS ARE FUNCTIONINGPROPERLY

Because of the advancement of solid-state electronic circuitry, dc/UPS subsystems generallyhave low maintenance requirements. The maintenance of these systems typically onlyincludes routine inspection and cleaning and self-diagnostic testing. This section of theModule provides information on the following topics that are pertinent to determiningwhether dc/UPS subsystems are functioning properly:

• Preventive Maintenance Requirements• Preventive Maintenance Frequency• Preventive Maintenance Records• Problems and Corrective Measures

Preventive Maintenance Requirements

The following preventive maintenance should be performed on dc/UPS subsystems:

• Visual Inspection• Cleaning• Battery Charger Checks and Adjustments• Inverter Checks and Adjustments

Visual Inspection

A visual inspection of dc/UPS subsystems is performed to check the overall condition of thesubsystem components. In general, a definitive pass/fail criterion does not exist for most ofthe items that are checked during the visual inspection. The person who performs the visualinspection must rely on his own personal judgement and experience to determine whether thepresent condition of the dc/UPS subsystem is acceptable or unacceptable. If the inspector isnot comfortable about some aspect of the equipment's condition, he should seek the guidanceof more experienced personnel.

The following types of problems typically can be identified through performance of a visualinspection:

• Physical Damage• Overheating• Loose Connections




Physical Damage - The visual inspection should start with an inspection of the exteriorof dc/UPS equipment enclosures for evidence of physical damage. If physical damageto the exterior of the enclosures is evident, the equipment must have been subjected tosome form of shock since it was last inspected. Because external shock increases thepossibility of physical damage to the internal components, the remainder of theinspections should be performed with extra diligence. The internal inspection forphysical damage should include a check for loose or missing hardware, missinggaskets/seals, broken wires, damaged insulation, and leaking electrical/electroniccomponents (e.g., electrolyte from capacitors or potting compound from transformers).

Overheating - Overheating can occur as a result of elevated enclosure temperatures orcircuitry malfunctions. Enclosure overheating can be caused by a defective ormalfunctioning enclosure ventilation fan or by dirty enclosure ventilation systemfilters. If enclosure overheating is suspected, a more detailed inspection of thefollowing cooling components should be performed to determine the cause:

• Enclosure ventilation fan• Ventilation fan thermostat• Enclosure ventilation filters

All of the interior components and wiring should be inspected for signs of excessiveheat. The typical indications of component overheating are discolorations such asbrowning or charring and/or the presence of ociferous odors. Any components orwires that show signs of excessive heat should be tested to determine whether they arestill serviceable.

Loose Connections - All of the internal terminations should be inspected to ensure thatthey are tight. The most effective method of inspecting for tightness is to apply theappropriate amount of torque to the termination while checking for any movement. Ifany connection is found to be loose, the termination should be further inspected todetermine and correct the cause. The common causes of loose connections areequipment vibration, improper initial torque, cyclic temperatures, and improperconnection hardware.

Cleaning

The interior of the dc/UPS subsystems must be cleaned on a regular basis to prevent theaccumulation of excessive dust and dirt. The accumulation of excessive amounts of dust anddirt can lead to the following problems:

• The formation of high resistance current paths between components or betweencomponents and ground.

• Excessive heat build up.




• The degradation of insulation.




Because both the visual inspection and the cleaning should be performed with the dc/UPSsubsystem deenergized, they often are simultaneously performed. The cleaning can beperformed through use of the following methods:

• Wiping with a clean cloth.• Vacuum cleaning.• Cleaning with low pressure air.• Solvent cleaning.

Wiping With a Clean Cloth - Initial cleaning should be performed by wiping with a clean,dry, lint-free cloth to remove the loose dust and dirt that has accumulated. Rags thatdeposit lint or that leave "stringers" on electrical and electronic components should notbe used. Lint and "stringers" will retain dirt and dust, which defeats the purpose ofcleaning the equipment.

Vacuum Cleaning - Loose dust and dirt that cannot be removed by wiping should beremoved by vacuum cleaning. The vacuum nozzle that is used should be made fromplastic or rubber; metal or other sharp materials can damage electrical components andwiring. The effectiveness of vacuum cleaning can be increased through use of a softbristle brush. The brush can be used to dislodge the dirt and the vacuum can then beused to remove the dirt.

Cleaning With Low Pressure Air - A low pressure jet of air should be used to dislodgedust and dirt from the portions of the equipment that are difficult to reach with a clothor a vacuum nozzle. This method is particularly effective in dislodging the dust anddirt that has accumulated on circuit boards. Cleaning with low pressure air is mosteffective when this method is used in conjunction with vacuum cleaning. The lowpressure air jet is used to dislodge the dirt and the vacuum is used to remove the dirt.

The compressed air that is used for this type of cleaning should not exceed 30 psi;higher air pressures can damage electrical component insulation and coverings. Thecompressed air supply also must be free from contaminants such as moisture and oil.These contaminants can lead to component degradation and short circuits.

Solvent Cleaning - Solvent cleaning is only recommended for use in the removal ofstubborn dirt that cannot be removed by any of the other methods. The followingrecommended solvents are listed in order of effectiveness:

• Isopropyl alcohol• 1,1,1-, trichloroethane (inhibited methyl chloroform)• Freon TF




Cleaning solvents should only be used in a free-air atmosphere and should never beused in an enclosed area. The solvent should be applied to a lint-free cleaning rag andthe rag should then be used to remove the dirt. Any excess solvent should be wipedup before it has a chance to evaporate.

If a solvent other than those that are listed above is used, it must have a flash point inexcess of 37.8oC; therefore, solvents such as gasoline, naphtha, and similarly volatileproducts cannot be used. Another solvent that should never be used is carbontetrachloride. This solvent produces highly toxic fumes that can result in sickness ordeath.

Battery Charger Checks and Adjustments

The following battery charger indicators, controls, and protective devices must be checkedand/or adjusted to ensure that the battery is properly charged and that the equipment operatorswill be alerted to abnormal conditions:

• dc Voltmeter• dc Ammeter• Float Voltage Adjustment• Equalize Voltage Adjustment• Equalize Timer Check• End of Charge Condition Alarm• Ground Detection Alarm• Charger Overvoltage Alarm• Charger Failure Alarm• Enclosure Overtemperature alarm

Because the output of the inverter is the preferred power source for most Saudi Aramco UPSsystems, and because performance of the battery charger checks and adjustments will affectthe input of power to the inverter, the critical ac loads should be switched to the bypass sourcewhile the maintenance is performed.

dc Voltmeter - The accuracy of the dc voltmeter should be checked and/or adjustedduring the performance of preventive maintenance. The accuracy check consists of amechanical zero adjustment and a comparison of the actual meter reading with thereading of a portable, calibrated voltmeter.

The mechanical zero adjustment is performed by opening the ac supply to the batterycharger and by opening the dc battery breaker. After the breakers are opened, themeter indicator should be adjusted to read zero by turning the mechanical adjustmentscrew.




When the mechanical zero adjustment is complete, the dc battery breaker and the acsupply breaker should be closed. A portable, calibrated voltmeter should then beconnected to the output of the battery charger. The reading of the portable, calibratedvoltmeter is compared to the reading of the dc voltmeter; the two readings shouldagree to within _ 2.0%. If the readings do not agree, the dc voltmeter should beadjusted until its reading is within the _ 2.0% tolerance. If the dc voltmeter cannot beadjusted, it should be replaced.

dc Ammeter - The accuracy of the dc ammeter should be checked and/or adjustedduring the performance of preventive maintenance. The accuracy check consists of amechanical zero adjustment and a comparison of the actual meter reading with thereading of a portable, calibrated ammeter.

The mechanical zero adjustment is performed by opening the ac supply to the batterycharger and by opening the dc battery breaker. After the breakers are opened, themeter indicator should be adjusted to read zero by turning the mechanical adjustmentscrew.

When the mechanical zero adjustment is complete, a portable, calibrated ammetershould then be connected in series with the output of the battery charger, and the dcbattery breaker and the ac supply breaker should be closed. The reading of theportable, calibrated ammeter is compared to the reading of the dc ammeter; the tworeadings should agree to within _ 2.0%. If the readings do not agree, the dc ammetershould be adjusted until its reading is within the _ 2.0% tolerance. If the dc ammetercannot be adjusted, it should be replaced.

Float Voltage Adjustment - The float voltage setpoint of the battery charger should bechecked and/or adjusted during the performance of preventive maintenance. Thischeck is performed by dividing the dc voltmeter reading by the number of cells thatare in the installation. The quotient is the float voltage per cell that is being applied tothe battery. This calculated value is then compared to manufacturer's recommendedfloat voltage per cell. Most battery manufacturers specify an acceptable range of floatvoltages. If the actual value of float voltage per cell is outside of the acceptable range,the float voltage setpoint must be adjusted.




Equalize Voltage Adjustment - The equalize voltage setpoint of the battery charger shouldbe checked and/or adjusted during the performance of preventive maintenance. Thischeck is performed by placement of the battery charger in the equalize charge position.After the battery charger is in the equalize charge position, the dc voltmeter reading isdivided by the number of cells that are in the installation to determine the equalizevoltage per cell that is being applied to the battery. This value is then compared tomanufacturer's recommended equalize voltage per cell. Most battery manufacturersspecify an acceptable range of equalize voltages. If the actual value of equalizevoltage per cell is outside of the acceptable range, the equalize voltage setpoint mustbe adjusted. After the adjustments are complete, the battery charger should be restoredto the float charge position.

Equalize Timer Check - The equalize timer is an electromechanical or an electronicdevice that is used to automatically stop the equalize charge after a specified timeperiod has elapsed. The timer is scaled in hours and should be accurate to within _10% of the actual elapsed time. During the performance of preventive maintenance,only the position of the setpoint adjustment is checked and adjusted; the actual elapsedtime should be checked each time that an equalize charge is performed.

End of Charge Condition Alarm - The End of Charge Condition alarm is intended to alertthe equipment operators that the battery has reached its low voltage limit and that thebattery discharge should be stopped. The alarm usually is set at 1.75 volts per cell forlead-acid battery systems and at 1.10 volts per cell for nickel-cadmium batterysystems. The alarm should actuate within _ 5.0% of its setpoint.

The alarm setpoint can be checked by opening the battery charger's dc output breakerand then adjusting the battery charger's output voltage down to the alarm setpoint. Ifthe alarm does not actuate within its _ 5.0% tolerance, its setpoint should be adjusted.After the check is completed, the battery charger's output voltage setpoint should berestored to the float voltage setpoint and the dc output breaker should be closed.

Ground Detection Alarm - The Ground Detection alarm is intended to alert the equipmentoperator that a battery ground exists and to trip the battery circuit breaker to protect thebattery charger from an excessive current flow. The Ground Detection alarm shouldactuate and the battery circuit breaker should trip when the current flow to earthground exceeds 10.0 milliamperes.

The alarm and the circuit breaker trip can be checked by placement of a 2.0k ohmresistance between the positive battery bus and ground or between the negative batterybus and ground. If the alarm fails to actuate or if the circuit breaker fails to trip, theground detection circuit and/or the battery breaker shunt trip device should be adjustedor replaced.




Charger Overvoltage Alarm - The Charger Overvoltage alarm is intended to alert theequipment operator that the battery is being subjected to an excessive chargingvoltage. The alarm usually is set to actuate when the charger's output voltage exceeds10.0% of the nominal cell voltage.

The alarm setpoint can be checked by opening the battery charger's dc output breakerand then adjusting the battery charger's output voltage up to the alarm setpoint. If thealarm does not actuate within 10% of the nominal cell voltage, its setpoint should beadjusted. After the check is completed, the battery charger's output voltage setpointshould be restored to the float voltage setpoint and the dc output breaker should beclosed.

Charger Failure Alarm - The Charger Failure alarm is intended to alert the equipmentoperator that the battery charger is no longer charging the battery. The charger failurealarm usually is set to actuate when the charger's output voltage drops 15% below thenominal cell voltage.

The alarm setpoint can be checked by opening the battery charger's dc output breakerand then adjusting the battery charger's output voltage down to the alarm setpoint. Ifthe alarm does not actuate when the battery charger's output drops 15% below thenominal cell voltage, its setpoint should be adjusted. After the check is completed, thebattery charger's output voltage setpoint should be restored to the float voltage setpointand the dc output breaker should be closed.

Enclosure Overtemperature Alarm - The Enclosure Overtemperature alarm is intended toalert the equipment operator of excessive temperature conditions that requirecorrective action. The Enclosure Overtemperature alarm usually is set to actuate whenthe battery charger enclosure exceeds the recommended maximum operatingtemperature by 10%.

The operation of the alarm's thermostat and contacts can be checked by reducing theenclosure overtemperature alarm setpoint to the actual enclosure operatingtemperature. Because overtemperature alarm devices are fairly linear, successfuloperation of the switch at normal temperature is a reasonable indication that the alarmwill operate satisfactorily at its normal setpoint. If the alarm fails to actuate at normaloperating temperature, the temperature switch must be repaired or replaced. At thecompletion of the check, the overtemperature alarm should be set at its normal value.




Inverter Checks and Adjustments

The following inverter indicators, controls, and protective devices must be checked and/oradjusted to ensure that the inverter properly operates and that the equipment operators will bealerted to abnormal conditions:

• Inverter ac Output Voltmeter• Inverter ac Output Ammeter• Inverter ac Output Frequency Meter• Alternate Source ac Input Voltmeter• High Inverter dc Input Voltage Alarm• Low Inverter dc Input Voltage Alarm• Alternate Voltage/Sync Source Not Available Alarm• Static Switch Position Indication Alarm• Inverter Output Failure Alarm• Auto Synchronization Disconnect Alarm• Static Switch Transfer to Alternate Source Voltage• Static Switch Re-Transfer to Preferred Source Voltage• Static Switch Transfer to Alternate Source Frequency• Static Switch Re-Transfer to Preferred Source Frequency• Enclosure Overtemperature Alarm

Because the output of the inverter is the preferred power source for most Saudi Aramco UPSsystems, and because performance of the inverter checks and adjustments will affect theoutput of the inverter, the critical ac loads should be switched to the alternate source byplacement of the manual bypass switch in the full bypass position while the maintenance isperformed.

Inverter ac Output Voltmeter - The accuracy of the inverter ac output voltmeter should bechecked and/or adjusted during the performance of preventive maintenance. Theaccuracy check consists of a mechanical zero adjustment and a comparison of theactual meter reading with the reading of a portable, calibrated voltmeter.

The mechanical zero adjustment is performed by opening the ac supply to the batterycharger and opening the dc battery breaker. After the breakers are opened, the meterindicator should be adjusted to read zero by turning the mechanical adjustment screw.

When the mechanical zero adjustment is complete, the dc battery breaker and the acsupply breaker should be closed. A portable, calibrated voltmeter should then beconnected to the output of the inverter. The reading of the portable, calibratedvoltmeter is compared to the reading of the inverter ac output voltmeter; the tworeadings should agree to within _ 2.0%. If the readings do not agree, the inverter acoutput voltmeter should be adjusted until its reading is within the _ 2.0% tolerance. Ifthe inverter ac output voltmeter cannot be adjusted, it should be replaced.




Inverter ac Output Ammeter - The accuracy of the inverter ac output ammeter should bechecked and/or adjusted during the performance of preventive maintenance. Theaccuracy check consists of a mechanical zero adjustment and a comparison of theactual meter reading with the reading of a portable, calibrated ammeter.


When the mechanical zero adjustment is complete, a portable, calibrated ammetershould be connected in series with the output of the inverter, and the dc battery breakerand the ac supply breaker should be closed. The reading of the portable, calibratedammeter is compared to the reading of the inverter ac output ammeter; the tworeadings should agree to within _ 2.0%. If the readings do not agree, the inverter acoutput ammeter should be adjusted until its reading is within the _ 2.0% tolerance. Ifthe inverter ac output ammeter cannot be adjusted, it should be replaced.

Inverter ac Output Frequency Meter - The accuracy of the inverter ac output frequencymeter should be checked and/or adjusted during the performance of preventivemaintenance. The accuracy check consists of a mechanical zero adjustment and acomparison of the actual meter reading with the reading of a portable, calibratedoscilloscope.


When the mechanical zero adjustment is complete, the dc battery breaker and the acsupply breaker should be closed. A portable, calibrated oscilloscope should then beconnected to the output of the inverter. The reading of the portable, calibratedoscilloscope is compared to the reading of the inverter ac output frequency meter; thetwo readings should agree to within _ 2.0%. If the readings do not agree, the inverterac output frequency meter should be adjusted until its reading is within the _ 2.0%tolerance. If the inverter ac output frequency meter cannot be adjusted, it should bereplaced.

Alternate Source ac Input Voltmeter - The accuracy of the alternate source ac inputvoltmeter should be checked and/or adjusted during the performance of preventivemaintenance. The accuracy check consists of a mechanical zero adjustment and acomparison of the actual meter reading with the reading of a portable, calibratedvoltmeter.




Before the mechanical zero adjustment can be performed, the critical ac loads must betransferred back to the inverter. After the loads have been transferred, the mechanicalzero adjustment is performed by opening the alternate source ac supply breaker. Afterthe breaker is open, the meter indicator should be adjusted to read zero by turning themechanical adjustment screw.

When the mechanical zero adjustment is complete, the alternate source ac supplybreaker should be closed. A portable, calibrated voltmeter should then be connectedto the alternate ac power source. The reading of the portable, calibrated voltmeter iscompared to the reading of the alternate source ac input voltmeter; the two readingsshould agree to within _ 2.0%. If the readings do not agree, the alternate source acinput voltmeter should be adjusted until its reading is within the _ 2.0% tolerance. Ifthe alternate source ac input voltmeter cannot be adjusted, it should be replaced. Afterthe check is complete, the critical ac loads should be transferred back to the alternatesource.

High Inverter dc Input Voltage Alarm - The High Inverter dc Input Voltage alarm isintended to alert the equipment operators of an inverter condition that requirescorrective action. The alarm usually is set to actuate when the dc input voltage to theinverter rises 5% above the nominal dc input voltage.

The alarm can be tested by opening the dc battery breaker and then raising the batterycharger output voltage. If the alarm does not actuate when the dc input voltageexceeds the nominal input voltage by 5%, the alarm setpoint must be adjusted. Afterthe check has been completed, the battery charger output should be returned to thefloat voltage setpoint and the dc battery breaker should be closed.

Low Inverter dc Input Voltage Alarm - The Low Inverter dc Input Voltage alarm isintended to alert the equipment operators of a problem that is associated with the inputpower supply to the inverter and that requires corrective action. The alarm usually isset to actuate when the dc input voltage to the inverter drops 5% below the nominal dcinput voltage.

The alarm can be tested by opening the dc battery breaker and by then lowering thebattery charger output voltage. If the alarm does not actuate when the dc input voltagedrops below the nominal input voltage by 5%, the alarm setpoint must be adjusted.After the check has been completed, the battery charger output should be returned tothe float voltage setpoint and the dc battery breaker should be closed.

Alternate Voltage/Sync Source Not Available Alarm - The Alternate Voltage/Sync SourceNot Available Alarm is intended to alert the equipment operators of a potential loss ofsystem reliability. The alarm usually is set to actuate when the alternate source voltagedeviates from the nominal system voltage by _ 10.0% or when the alternate sourcefrequency deviates from the nominal system frequency by _ 5.0%.




Before this alarm can be tested, the critical ac loads must be transferred to the outputof the inverter. After the loads have been transferred, the alternate source ac supplybreaker can be opened to check the operation of this alarm. After the check has beencompleted, the ac supply breaker should be closed and the critical ac loads should betransferred back to the alternate source.

Static Switch Position Indication Alarm - The Static Switch Position Indication alarm isintended to alert the equipment operators that the critical ac loads have beentransferred from the inverter to the alternate power source. Before this alarm can bechecked, the critical ac loads must be transferred to the output of the inverter.

After the loads have been transferred, the ac supply breaker for the battery charger canbe opened in conjunction with the dc battery breaker to check the operation of thealarm. Opening of these breakers will cause the static switch to transfer to thealternate power source. This transfer should actuate the alarm. After the check hasbeen completed, the ac supply breaker for the battery charger and the dc batterybreaker should be closed, and the manual bypass switch should be placed back in thefull bypass position.

Inverter Output Failure Alarm - The Inverter Output Failure alarm is intended to alert theequipment operators of a problem that is associated with the preferred power sourceand that requires corrective action. This alarm usually is set to actuate when the outputvoltage of the inverter deviates from the nominal output voltage by _ 10.0% or whenthe output frequency of the inverter deviates from the nominal value of 60 Hz by_5.0%.

The voltage actuation of the alarm can be checked by adjusting the output voltagepotentiometer of the inverter up and down until the alarm actuates. If the alarm doesnot actuate at both +10% and -10% of nominal, the alarm setpoint should be adjusted.The frequency actuation of the alarm can be checked by adjusting the outputfrequency potentiometer that is on the oscillator board up and down until the alarmactuates. If the alarm does not actuate at both +5% and -5% of nominal, the alarmsetpoint should be adjusted. After the check is complete, the inverter's output voltageand frequency should be returned to normal.

Auto Synchronization Disconnect Alarm - The Auto Synchronization Disconnect alarm isintended to alert the equipment operators of a potential loss of system reliability. Thealarm usually is set to actuate when the alternate source frequency deviates from theinverter frequency by _ 5.0%.




Before this alarm can be tested, the critical ac loads must be transferred to the outputof the inverter. After the loads have been transferred, the alternate source ac supplybreaker can be opened to check the operation of this alarm. After the check has beencompleted, the ac supply breaker should be closed and the critical ac loads should betransferred back to the alternate source by placement of the manual bypass switch inthe full bypass position.

Static Switch Transfer to Alternate Source Voltage - When the inverter's output voltage isunsatisfactory, the static switch is designed to automatically transfer the critical acloads from the output of the inverter to the alternate power source. The transfershould occur when the inverter output voltage deviates from the nominal outputvoltage by more than _ 10%.

Before the automatic transfer feature can be checked, the manual bypass switch shouldbe placed in the test bypass position. After the switch is in this position, the inverteroutput voltage potentiometer should be raised to the transfer setpoint. The successfultransfer will be indicated by the actuation of the static switch position indication alarm.If the transfer did not occur when the inverter output voltage exceeded the nominalvoltage by 10%, the transfer setpoint must be adjusted. The check should then berepeated for the low voltage transfer setpoint. When both checks have beensatisfactorily completed, the inverter output voltage should be adjusted to normal andthe critical ac loads should be transferred back to the alternate source by placement ofthe manual bypass switch in the full bypass position.

Static Switch Re-Transfer to Preferred Source Voltage - Because the output of the inverter isthe preferred source of power for the critical ac loads, the static switch is designed toretransfer back to the output of the inverter when the inverter's output voltage returnsto normal. The retransfer should occur when the inverter's output voltage returns towithin _ 2.0% of the nominal output voltage.

The retransfer feature should be checked in conjunction with the transfer feature.After the inverter transfers to the alternate source, the inverter output voltagepotentiometer should be raised to the retransfer setpoint. A successful retransfer isindicated by clearance of the static switch position indication alarm. When the checkhas been satisfactorily completed, the inverter output voltage should be adjusted tonormal and the critical ac loads should be transferred back to the alternate source byplacement of the manual bypass switch in the full bypass position.

Static Switch Transfer to Alternate Source Frequency - When the inverter's output frequencyis unsatisfactory, the static switch is designed to automatically transfer the critical acloads from the output of the inverter to the alternate power source. The transfer shouldoccur when the inverter output frequency deviates from the nominal output frequencyby more than _ 5.0%.




Before the automatic transfer feature can be checked, the manual bypass switch shouldbe placed in the test bypass position. After the switch is in this position, the inverteroutput frequency potentiometer should be raised to the transfer setpoint. Thesuccessful transfer will be indicated by the actuation of the static switch positionindication alarm. If the transfer did not occur when the inverter output frequencyexceeded the nominal frequency by 5.0%, the transfer setpoint must be adjusted. Thecheck should then be repeated for the low frequency transfer setpoint. When bothchecks have been satisfactorily completed, the inverter output frequency should beadjusted to normal and the critical ac loads should be transferred back to the alternatesource by placement of the manual bypass switch in the full bypass position.

Static Switch Re-Transfer to Preferred Source Frequency - Because the output of the inverteris the preferred source of power for the critical ac loads, the static switch is designed toretransfer back to the output of the inverter when the inverter's output frequencyreturns to normal. The retransfer should occur when the inverter's output frequencyreturns to within _ 2.0% of the nominal output frequency.

The retransfer feature should be checked in conjunction with the transfer feature.After the inverter transfers to the alternate source, the inverter output frequencypotentiometer should be raised to the retransfer setpoint. A successful retransfer isindicated by clearance of the static switch position indication alarm. When the checkhas been satisfactorily completed, the inverter output frequency should be adjusted tonormal and the critical ac loads should be transferred back to the alternate source byplacement of the manual bypass switch in the full bypass position.

Enclosure Overtemperature Alarm - The Enclosure Overtemperature alarm is intended toalert the equipment operator of excessive temperature conditions that requirecorrective action. The Enclosure Overtemperature alarm usually is set to actuate whenthe UPS system enclosure exceeds the recommended maximum operating temperatureby 10%.

The operation of the alarm's thermostat and contacts can be checked by reducing theenclosure overtemperature alarm setpoint to the actual enclosure operatingtemperature. Because overtemperature alarm devices are fairly linear, successfuloperation of the switch at normal temperature is a relatively reliable indication that thealarm will operate satisfactorily at its normal setpoint. If the alarm fails to actuate atnormal operating temperature, the temperature switch must be repaired or replaced. Atthe completion of the check, the overtemperature alarm should be set at its normalvalue.




Preventive Maintenance Frequency

The overall goal of dc/UPS subsystem preventive maintenance is to identify and correctminor or impending problems that, if left unchecked, could result in a reduction of systemreliability or in a complete system failure. In order for a dc/UPS subsystem preventivemaintenance program to achieve its goal, the dc/UPS subsystem equipment must be checkedat regularly scheduled intervals. The regularly scheduled intervals vary dependent upon theequipment manufacturers, the type of intended service, and the environmental conditions thatexist at the installation. The initial dc/UPS subsystem preventive maintenance inspectionfrequencies are normally established on the basis of the manufacturer's recommendations.These initial frequencies can then be modified (increased or decreased in length) on the basisof local site operating experience and/or governing codes and standards for a particular typeof service.

As an example of how inspection frequencies can be modified on the basis of local siteoperating experience, assume that a particular UPS manufacturer recommends that the UPSsystem be visually inspected and cleaned once per quarter. Also assume that the results ofthree consecutive quarterly inspections and cleanings showed that no abnormal conditionsexisted and that little or no dirt had accumulated since the previous maintenance. Based onthese results, the interval between the visual inspections and cleanings for this particular UPSsystem could be increased. The visual inspection and cleaning frequency for this UPS systemcould be changed from a quarterly requirement to a semi-annual or an annual requirement.

Figure 7 shows a typical preventive maintenance schedule for a dc/UPS subsystem. Theschedule contains the preventive maintenance requirements and the frequency ofperformance. The frequency of performance section is divided into three time categories:routine, quarterly, and annually. The routine column can represent daily, weekly, bi-weekly,or monthly preventive maintenance requirements. The applicable frequency for all of thepreventive maintenance items should be established as previously explained.




Preventive Maintenance Frequency of Performance

Requirement Routine Quarterly

Annually

Visual Inspection • Physical Damage X • Overheating X • Loose Connections XCleaning XBattery Charger Checks and Adjustments • dc Voltmeter X • dc Ammeter X • Float Voltage Adjustment X • Equalize Voltage Adjustment X • Equalize Timer Check X (1) • End of Charge Condition Alarm X • Ground Detection Alarm X • Charger Overvoltage Alarm X • Charger Failure Alarm X • Enclosure Overtemperature Alarm XInverter Checks and Adjustments • Inverter ac Output Voltmeter X • Inverter ac Output Ammeter X • Inverter ac Output Frequency Meter X • Alternate Source ac Input Voltmeter X • High Inverter dc Input Voltage Alarm X • Low Inverter dc Input Voltage Alarm X • Alternate Voltage/Sync Source Not Available Alarm X • Static Switch Position Indication Alarm X • Inverter Output Failure Alarm X • Auto Synchronization Disconnect Alarm X • Static Switch Transfer to Alternate Source Voltage X • Static Switch Re-Transfer to Preferred Source Voltage X • Static Switch Transfer to Alternate Source Frequency X • Static Switch Re-Transfer to Preferred SourceFrequency

X

• Enclosure Overtemperature Alarm X




NOTE (1) Only the timer setpoint is checked during routine preventive maintenance. Theactual elapsed time should be checked each time that an equalizing change isperformed.

Typical dc/UPS Subsystem Preventive Maintenance ScheduleFigure 7




Preventive Maintenance Records

The results of all of the maintenance and testing that is performed on dc/UPS systems shouldbe recorded on maintenance records, and the individual records for each dc/UPS systeminstallation should be kept in a separate file for the life of the system. The first step of therecord keeping process is to record the baseline data for the system. The baseline data are thedata that were obtained during the start-up and commissioning of the dc/UPS system, whichwas discussed in Module EEX 211.06. Future maintenance records are added as maintenanceis performed to provide a chronological history of the dc/UPS system's condition. Thechronological history is used to identify and analyze trends or isolated problems. Thisinformation aids the Electrical Engineer in making future decisions in regard to the operation,maintenance, and troubleshooting of the dc/UPS system.

Figures 8 through 10 show typical dc/UPS subsystem maintenance record forms. Theseforms coincide with the typical dc/UPS subsystem preventive battery maintenance schedulethat previously was shown in Figure 7.

Figure 8 shows a typical dc/UPS subsystem preventive maintenance record form that can beused to record the results of routine maintenance. The form is divided into two major parts:Identification Data and Maintenance Data. The Identification Data section is used to recordthe pertinent information that is needed to identify the particular dc/UPS subsystem on whichthe maintenance was performed. The Maintenance Data section is used to record the actualresults of the maintenance that was performed. A space is provided to record the results ofeach of the routine maintenance items that was previously shown on Figure 7.




dc/UPS Subsystem Preventive Maintenance Record - Routine ItemsFigure 8




Figure 9 shows a typical dc/UPS subsystem preventive maintenance record form that can beused to record the results of quarterly maintenance. The form is divided into two major parts:Identification Data and Maintenance Data. The Identification Data section is used to recordthe pertinent information that is needed to identify the particular dc/UPS subsystem on whichthe maintenance was performed. The Maintenance Data section is used to record the actualresults of the maintenance that was performed. A space is provided to record the results ofeach of the quarterly maintenance items that was previously shown on Figure 7.




dc/UPS Subsystem Preventive Maintenance Record - Quarterly ItemsFigure 9




Figure 10 shows a typical dc/UPS subsystem preventive maintenance record form that can beused to record the results of annual maintenance. The form is divided into two major parts:Identification Data and Maintenance Data. The Identification Data section is used to recordthe pertinent information that is needed to identify the particular dc/UPS subsystem on whichthe maintenance was performed. The Maintenance Data section is used to record the actualresults of the maintenance that was performed. A space is provided to record the results ofeach of the annual maintenance items that was previously shown on Figure 7.




dc/UPS Subsystem Preventive Maintenance Record - Annual Items




Figure 10




Problems and Corrective Measures

This section of the Module will discuss following typical dc/UPS subsystem problems andtheir corrective measures:

• Tripping of Input/Output Breakers• Improper Inverter Output• SCR Failures

Tripping of Input/Output Breakers

Input and output circuit breakers are employed to protect the system equipment andpersonnel. Each device is designed to trip on excessive current flow. The ac input circuitbreaker is designed to protect the battery charger and the inverter from faults that occurupstream of the output circuit breaker. The battery breaker provides a means to isolate thebattery from the battery charger and the inverter, which, depending on the direction of currentflow, protects the inverter input circuit or the battery. The output circuit breaker protects theinverter in the event of a critical ac load fault or overload condition. The following aspects ofthe tripping of input/output circuit breakers will be discussed in this section:

• Problems Caused• Indications• Corrective Measures

Problems Caused - Because a number of power supply redundancies are designed intothe dc/UPS subsystem, few problems can result from inadvertent tripping of the inputor output circuit breakers. The most serious problem of a loss of power to the criticalac loads cannot occur following a single circuit breaker trip. If only the ac inputcircuit breaker trips, a loss of power to the critical ac loads cannot occur without asimultaneous trip of the battery breaker and the alternate source input breaker. If onlythe ac output circuit breaker trips, a loss of power to the critical ac loads cannot occurwithout a simultaneous trip of the alternate source input breaker. For these reasons,the only real problem that is caused by the inadvertent trip of the input or the outputcircuit breaker is a partial loss of system reliability.

Indications - An inadvertent trip of the input/output circuit breakers will cause a numberof the parameters that are monitored by the dc/UPS subsystem to change. Becausesome of these parameters are monitored by alarms, the first indication of an input or anoutput circuit breaker trip generally is the receipt of an alarm. Other dc/UPSsubsystem parameters also will indicate abnormal values. The following is a list ofindications and/or alarms that occur after an inadvertent trip of the input or the outputcircuit breaker:




Breaker Trip Condition Indication and/or Alarm• AC Input Circuit Breaker

• Inverter Output Breaker

• Charger Failure Alarm

• Static Switch Position Indication Alarm

• DC Ammeter Indicates Zero

• Inverter Output Failure Alarm

• Static Switch Position Indication Alarm

• Abnormal Inverter ac Output Voltage

• Abnormal Inverter ac OutputFrequency

Corrective Actions - Because of the multitude of individual faults or failures that couldcause the input or the output circuit breaker to trip, the various corrective actionscannot be covered in this section. Generally, the corrective actions consist first ofidentifying the cause of the trip. After the cause is known, knowledge of systemoperation must be applied to identify and repair/replace the defective components(s).The following is a list of some of the possible causes of input and output circuitbreaker trips:

Breaker Trip Possible Causes• AC Input Circuit Breaker

• AC Output Circuit Breaker

• Battery Charger Fault

• Inverter Fault

• Defective ac Input Circuit Breaker

• Defective ac Output Circuit Breaker

• Critical ac Load Fault




Improper Inverter Output

The following aspects of improper inverter outputs will be discussed in this section:


Problems Caused - The common inverter output problems are an excessive or aninsufficient inverter output voltage and an excessive or an insufficient inverter outputfrequency. Because the output of the inverter is the preferred source of power for thecritical ac loads, and because many of the critical ac loads are sensitive to powersupply fluctuations, an improper inverter output could cause improper operation of thecritical ac loads. However, as previously discussed in this Module, built-inredundancies and automatic transfers should prevent an improper inverter output frombeing supplied to the critical ac loads; therefore, the only real problem that results fromimproper inverter output is a partial loss of system reliability.

Indications - The indications of an improper inverter output are a combination ofabnormal panelmeter readings and audible alarms. When the inverter output voltageor frequency exceeds its allowable tolerance, the following panelmeter indications andalarms should be present:

• The respective panelmeter (voltage/frequency) will indicate a value that isgreater than the acceptable tolerance.

• The inverter output failure alarm will operate.

• The static switch position indication alarm will operate.

• The inverter output ac ammeter will read zero amps.




Corrective Actions - Many conditions can cause an improper inverter output. Theseconditions can range from an improper dc input, through an inverter malfunction, to astatic switch malfunction. Before corrective actions are initiated, the exact location ofthe malfunction must be determined. If the malfunction occurred as a result of aproblem with the inverter input, additional alarms would occur. Alarms such as LowCharger Output Voltage alarm, Charger Overvoltage alarm, Charger Failure alarm, orLow Battery Current alarm indicate that a problem exists with the battery charger orthe battery that is merely being transferred to the inverter. In these situations, theproblem that must be corrected is "upstream" of the inverter. Knowledge of systemoperation must be applied to identify and repair/replace the defective "upstream"component. When the "upstream" malfunction is corrected, the static switch shouldretransfer to the inverter after verification of proper voltage, frequency, and phaserelationship.

If the inverter input is satisfactory, and if the inverter output is improper, the problemmost likely is in the inverter itself or in the static switch. In this situation, knowledgeof inverter and/or static switch operation must be applied to identify and replace/repairthe defective component. To deenergize the inverter and the static switch fortroubleshooting, the manual bypass switch should be placed in the full bypass position.This position will allow maintenance to be performed on the inverter and the staticswitch with no affect on the critical ac load.

After the necessary repairs are complete, the manual bypass switch should be placed inthe test bypass position to make the necessary output voltage and frequencyadjustments. When the repairs and adjustments are completed, the manual bypassswitch should be placed in the normal position. When the manual bypass switch is inthis position, the static switch should automatically retransfer to the inverter afterproper voltage, frequency, and phase relationship is verified.

SCR Failures

SCR's (silicon control rectifiers) are used in the battery charger, the inverter, and the staticswitch. Battery charger SCR's are used to convert the preferred source ac into rectified dc.

The inverter SCR's are used to produce the 60 Hz ac output to the critical ac loads from the dcinput. The static switch SCR's are used to electronically switch between the inverter outputand an alternate power source. The following aspects of SCR failures will be discussed in thissection:





Problems Caused - Generally, SCR's fail in one of two ways: they open circuit or theyshort circuit. The type of problems that are caused by SCR failures depend on wherethe SCR's are used. If the failed SCR is in the battery charger, the problem that iscaused is a high or a low battery charger output voltage. A short-circuited SCR in thebattery charger will cause a high battery charger output voltage because the short-circuited SCR will continuously conduct. An open-circuited SCR in the batterycharger will cause a low battery charger output voltage because the open-circuitedSCR will not conduct.

If the failed SCR is in the inverter, the problems that will be caused are an improperinverter output voltage, an improper inverter output frequency, an improper inverteroutput phase relationship. Because all of these parameters (voltage, frequency, andphase relationship) are controlled through variance of the firing and conduction timesof the SCR's, all three parameters will be affected by both open-circuited and short-circuited SCR's.

If the failed SCR is in the static switch, the problem that is caused depends on the typeof SCR failure that occurs. An open-circuited SCR in the static switch will cause areduction in the inverter's output because one half of the output ac sinewave will belost. A short-circuited SCR in the static switch may go unnoticed until a transferoccurs because a conducting SCR already is essentially a short-circuit connection.However, when the static switch transfers, a short-circuited SCR will not turn off.

Indications - The indications of an SCR failure also depend on the location of the SCRthat failed. The following are possible indications of an SCR failure in the batteryCharger:

• High or low dc voltmeter reading• High or low dc ammeter reading• Charger overvoltage alarm• Charger failure alarm• High inverter dc input voltage alarm

The following are possible indications of an SCR failure in the inverter:

• Abnormal inverter output voltage reading• Abnormal inverter output frequency reading• Abnormal inverter output ammeter reading• Static Switch position indication alarm• Inverter output failure alarm




The following are possible indications of a SCR failure in the static switch:

• Abnormal inverter output voltage reading• Abnormal inverter output frequency reading• Abnormal inverter output ammeter reading• Static Switch position indication alarm• Inverter output failure alarm• No abnormal indications

Corrective Actions - The first corrective action for an SCR failure is to observe all of thedc/UPS subsystem indications and alarms to determine the location of the SCR failure.Once the location of the failure is known, the dc/UPS subsystem should be completelydeenergized by placing the manual bypass switch in the Full Bypass position and byopening the ac input, battery, and ac output circuit breakers. The suspect SCR'sshould then be tested to determine which SCR has failed. The failed SCR should thenbe replaced.

After satisfactory replacement of the defective SCR, placement of the manual bypassswitch in the test bypass position will permit safe testing of the system withoutdisruption of power to the critical ac loads. After completion of the proper tests, themanual bypass switch should be placed in normal to return the system to normaloperation.




WORK AID 1: MAINTENANCE SPECIFICATIONS AND TROUBLESHOOTINGGUIDE COMPILED FROM SADP-P-103 AND ESTABLISHEDENGINEERING PRACTICES FOR DETERMINING WHETHERBATTERIES ARE FUNCTIONING PROPERLY

Maintenance Specifications

Item/Condition Checked SpecificationsGeneral Cleanliness The battery cells, battery room floor, and ventilation system filters should be free from

excessive dirt, dust, electrolyte residue, and/or water buildup.Battery Rack All battery rack hardware and floor mount connections must be tight. The battery rack's

epoxy coating should be free from chips and cracks.Cell Case Integrity The cell case integrity cannot be breached.Vent Caps/Flame Arrestors The vent caps/flame arrestors should be clean, tight, and free from cracks or other defects.Cell Terminals All cell terminals must be free from corrosion.

All cell terminal connections should be tightened to the torque that is recommended by themanufacturer (usual range is 60-125 inch-pounds).

The terminal resistances should not vary from the previous reading by more than 20%.Also, all terminal resistances should be within 10% or 5__ of the average of all of theterminal resistance readings.

Cell Internals(Lead-Acid only)

The cell plates should be free from excessive sulphation and they should not be bowed orwarped.

The bottom of the cell should be free from excessive sediment.Specific Gravity(Lead-Acid Only)

The corrected specific gravity should be consistent with the battery's current state of charge.

All corrected specific gravity readings should be within 10 points (.010) of the averagecorrected specific gravity readings of all of the cells.

Individual Cell Voltages All individual cell voltage readings should be consistent with the battery's current state ofcharge and with the current float voltage setpoint.

Electrolyte Levels The electrolyte levels must be in the normal operational band (e.g., between the high andlow level marks on the side of the cell case).

Capacity Test Discharge Degradation is indicated by a 10% decrease in capacity from the previous the previous test.

End of service life is indicated by a capacity that is less than 80% of the manufacturer'srating.

Float Voltage The float voltage should be within _1% of the value that is recommended by themanufacturer. The normal range of float voltage per cell for lead-antimony batteries is 2.13-2.18 volts per cell. The normal range of float voltage per cell for lead-calcium batteries is2.17-2.29 volts per cell. The normal range of float voltage per cell for nickel-cadmiumbatteries is 1.40 to 1.42 volts per cell.

Equalizing Voltage For battery chargers that are rated at less than 10 kW, the equalizing voltage should bewithin _1% of the value that is recommended by the manufacturer.

For battery chargers that are rated above 10 kW, the equalizing voltage should be within_2% of the value that is recommended by the manufacturer.

The normal range of equalizing voltage per cell for lead-antimony batteries is 2.24-2.33volts per cell. The normal range of equalizing voltage per cell for lead-calcium batteries is2.29-2.39 volts per cell. The normal range of equalizing voltage per cell for nickel-cadmium batteries is 1.50 - 1.60 volts per cell.

Battery Terminal Voltages The voltage that is measured between the positive terminal and the negative terminal shouldbe equal to the float voltage per cell times the number of cells that are in the installation.

The voltage that is measured between the positive terminal and ground or between thenegative terminal and ground should be equal to one half of the total battery voltage.




Troubleshooting Guide

Symptom Possible Cause(s) Possible Corrective ActionsLow Total Battery Voltage Low float voltage Raise float voltage setting and perform an

equalizing charge.Battery ground Locate and clear the ground.High resistance connections Locate and repair the high resistance

connections.Excess sulphation (lead-acid cells) orbattery is discharged

Perform an equalizing charge.

Battery is nearing the end of its service life. Replace the battery.One or more of the cells is defective orcontaminated.

Locate and repair/replace defective cells.

Undersized battery charger Verify the charger size and if necessary,replace the charger.

Excessive battery temperature Identify and correct the ventilation problem.Low Individual CellVoltage

Grounded cell Clear the ground.

High resistance connection Correct the condition that is causing thehigh resistance.

High cell temperature Determine and correct the cause of the hightemperature.

Excess sulphation (lead-acid cells) Perform an equalizing charge.Damaged or contaminated cell Replace the cell.

Low Specific GravityReadings(Lead-Acid Only)

Low float voltage Raise the float voltage setpoint and performan equalizing battery charge.

High resistance connections Locate and repair the high resistanceconnections.

Excess sulphation or battery is discharged. Perform an equalizing charge.Electrolyte stratification If the battery recently was watered, the

condition is normal and no corrective actionis necessary.

If only one or several cells are affected, mixelectrolyte by drawing it into thehydrometer and then discharging it backinto the cell several times.

If multiple cells are affected, perform anequalizing battery charge.

The battery is nearing the end of its servicelife.

Replace the battery.

Undersized battery charger Verify the charger size and if necessary,replace the charger.

Excessive battery temperature Identify and correct the ventilation problem.High Water Usage/LowElectrolyte Levels

Excessive float voltage Lower float voltage setting.

High ambient temperature and/or lowhumidity

Increase monitoring frequency to preventlow levels.

Battery is nearing the end of its service life. Replace the battery.




WORK AID 2: MAINTENANCE SPECIFICATIONS AND TROUBLESHOOTINGGUIDE COMPILED FROM ESTABLISHED ENGINEERINGPRACTICES FOR DETERMINING WHETHER DC/UPSSUBSYSTEMS ARE FUNCTIONING PROPERLY

Maintenance Specifications

Item/Condition Checked SpecificationsPhysical Damage The equipment should be free from loose or missing hardware, missing gaskets or seals, broken wires,

damaged insulation, and leaking electrical/electronic components.Overheating Components should not show any signs of excessive heat such as browning, charring, or unusual odors.Loose Connections All of the internal termination should be tight.

All internal terminations should be made up using the proper hardware.Cleanliness All equipment should be free from excessive dirt, dust, or other foreign residues.Battery Charger dc Voltmeter Reading should agree with a portable calibrated dc voltmeter to within _2%.Battery Charger dc Ammeter Reading should agree with a portable calibrated dc ammeter to within _2%.Float Voltage Adjustment The float voltage should be within _1% of the value that is recommended by the manufacturer. The normal

range of float voltage per cell for lead-antimony batteries is 2.13-2.18 volts per cell. The normal range offloat voltage per cell for lead-calcium batteries is 2.17-2.29 volts per cell. The normal range of float voltageper cell for nickel-cadmium batteries is 1.40 - 1.42 volts per cell.

Equalize voltage Adjustment For battery chargers that are rated at less than 10 kW, the equalizing voltage should be within _1% of thevalue that is recommended by the manufacturer.

For battery chargers that are rated above 10 kW, the equalizing voltage should be within _2% of the valuethat is recommended by the manufacturer.

The normal range of equalizing voltage per cell for lead-antimony batteries is 2.24-2.33 volts per cell. Thenormal range of equalizing voltage per cell for lead-calcium batteries is 2.29-2.39 volts per cell. The normalrange of equalizing voltage per cell for nickel-cadmium batteries is 1.50 - 1.60 volts per cell.

Equalize Timer The timer should be set at the number of hour that are recommended by the manufacturer.

The actual elapsed time should agree with the timer setpoint to within _10%.End of Charge Condition Alarm The alarm should actuate at 1.75 volts, _5.0%.Ground Detection Alarm The alarm should actuate when the current flow to exceeds 10.0 mA.Charger Overvoltage Alarm The alarm should actuate at 10% above the nominal cell voltage.Charger Failure Alarm The alarm should actuate at 15% below the nominal cell voltage.Enclosure Overtemperature Alarm The alarm should actuate when the temperature reaches the maximum operating temperature that is

recommended by the manufacturer, +10%, -0.0%.Inverter ac Output Voltmeter Reading should agree with a portable calibrated ac voltmeter to within _2%.Inverter ac Output Ammeter Reading should agree with a portable calibrated ac ammeter to within _2%.Inverter ac Output Frequency Meter Reading should agree with a portable calibrated oscilloscope to within _2%.Alternate Source ac Input Voltmeter Reading should agree with a portable calibrated ac ammeter to within _2%.High Inverter dc Input Voltage Alarm The alarm should actuate when the input voltage rises to 5% above the nominal input voltage.Low Inverter dc Input Voltage Alarm The alarm should actuate when the input voltage drops to 5% below the nominal input voltage.Alternate Voltage/Sync Source Not AvailableAlarm

The alarm should actuate when the alternate source voltage deviates from the nominal system voltage by_10%.

The alarm also should actuate when the alternate source frequency deviates from the nominal systemfrequency by _5.0%.

Static Switch Position Indication Alarm The alarm should actuate when the static switch transfers to the alternate power source.Inverter Output failure Alarm The alarm should actuate when the inverter output voltage deviates from the nominal output voltage by

_10%.

The alarm also should actuate when the inverter output frequency deviates from the nominal value of 60 Hzby _5.0%.

Auto Synchronization Disconnect Alarm The alarm should actuate when the alternate source frequency deviates from the inverter frequency by_5.0%.

Static Switch Transfer to Alternate SourceVoltage

Transfer should occur when the inverter output voltage deviates from the nominal output voltage by _10%.

Static Switch Re-Transfer to Preferred SourceVoltage

Re-transfer should occur when the inverter output returns to within _2% of the nominal output voltage.

Static Switch Transfer to Alternate SourceFrequency

Transfer should occur when the inverter output frequency deviates from the nominal output frequency by_5.0%.

Static Switch Re-Transfer to Preferred SourceFrequency

Re-transfer should occur when the inverter output returns to within _2% of the nominal output frequency.

Enclosure Overtemperature Alarm The alarm should actuate when the temperature reaches the maximum operating temperature that is




recommended by the manufacturer, +10%, -0.0%.




Troubleshooting Guide

Symptom Possible Cause(s) Possible Corrective ActionsOverheating Clogged ventilation filters Clean filters.

Inoperable ventilation fan Repair ventilation fan.High/Low InverterOutput Voltage

Improper dc input voltage Adjust the input voltage.

Improperly adjusted or failedvoltage regulator

Replace and/or adjust thevoltage regulator.

High/Low InverterOutput Frequency

Improperly adjusted or failedoscillator board

Replace and/or adjust theoscillator board.

Improperly adjusted or failedsynchronizing circuit

Replace and/or adjust thesynchronizing circuit.

Output WaveformDistortion

Load induced harmonics Identify and filter the problemload.

Improperly adjusted inverter Adjust the inverter.




glossary

baseline data Initially recorded data obtained during startup andcommissioning checks.

equalizing charge A prolonged charge of a storage battery; the charge is designedto correct any inequalities of voltage and specific gravity thatmay have developed between the cells during service.

flash arrestor A cell-venting device that prevents the propagation of anexternal flame into a battery cell.

float charge A continuous, low-rate constant voltage charge of a storagebattery that is designed to maintain the battery in a constant full-charge condition.

mossing To cover over with a moss-like material.

service life The period of useful service of a battery under specifiedconditions. Service life usually is expressed as the time periodor number of cycles that elapses before the ampere-hour capacityof the battery drops to a specified percentage of rated capacity.

stringers Short thread or lint-like strings.

O & M of DC & UPS Systems

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Transcript of O & M of DC & UPS Systems