Transformer Rectifier Unit Monitoring:

1. Purpose:

To determine the pipe to soil potential protection level and efficiency of Transformer Rectifier Unit.

2. Equipment:

Calibrated Multimeter.

Calibrated Clamp meter.

3. How to use Multimeter (or) Clamp meter and its Maintenance:

3.1. First properly check calibration certificate of multimeter.

3.2. Next conduct the continuity test. Continuity test means checking the multimeter’s working condition whether it is good or not. At the time of continuity test, the following procedures will be follow .First choose the continuity option on the multimeter switch, then touch the black(+ve) cable with red(-ve) color cables, at this time one beep sound will appear this shows the cables are in good condition if no beep sound then the cables are in damage condition .3.3. Since sunlight easily affects multimeter display, Multimeter should not be shown directly in sunlight. 3.4. Note all options (AC voltage & Current and DC voltage & current, Resistance and Temperature) change the switch option accordingly.3.5. After measurement switches off the multimeter.

4. Safety Measures while taking Transformer Rectifier Unit Monitoring:

4.1. Wear safety shoes, helmet, hand gloves etc.

4.2. Before TRU door open, should be check AC current using tester and carefully open to the TRU door. While taking this kind of measurements compulsorily use hand gloves and safety shoes.4.3. Open TRU door carefully (you may find some small insects) with the TRU key. Once the door is open then start taking the TRU readings.

5. Standard Safety Factors of Transformer Rectifier Unit Monitoring:

5.1. CP rectifiers have exposed electrical AC and DC terminals on the panel of the rectifier. The voltage exposure varies with the rectifier rating and design. Do not make body contact with any electrical terminal when the rectifier is energized and protect yourself from this hazard.5.2. Take measurements with insulated meter probes intended for that purpose using a one-hand method while avoiding contact to the probe end. Never press a probe end and a terminal or wire between your fingers to make a contact.5.3. Turning off the circuit breaker in the rectifier will render the front of the panel safe but will not make the back or inside of the rectifier safe!

5.4. The AC disconnect outside the rectifier must be OFF (locked out/tagged out) before the entire rectifier is safe to work on.5.5. Confirm that the AC power is off by testing as breaker contacts can fuse together thus making contact in the tripped position.5.6. Lock out and tag the rectifier breaker or AC disconnect after turning OFF when installing an interrupter, changing taps, replacing components, or installing and removing the rectifier.This is a good habit to form and is required by code in many areas.5.7. There is no testing that is required behind the panel with the rectifier energized with the exception of measuring the input AC supply voltage. This AC voltage measurement is only to be completed by persons properly trained and is only to be measured if the terminals are readily accessible at the side of the rectifier. Remember that even with the rectifier breaker OFF; AC line voltage still exists up to the rectifier circuit breaker.5.8 Remember to turn OFF, lock out and tag the AC disconnect when working on or removing rectifier components. No one else can then inadvertently turn the AC on before it is safe.

6. General Precautions:

6.1. Wear protective eyewear, gloves, shoes and other clothing.6.2. Avoid open flames.6.3. Avoid causing electric sparks especially in areas that may contain a hydrocarbon.6.4. Know the handling/storage procedures for chemicals or other hazardous materials or equipment.6.5. Working at heights.6.6. Animals, reptiles and insects6.7. Vehicles: Drive defensively and be aware of hazard situations that could occur.

7. Common Procedure of Transformer Rectifier Unit Monitoring and Maintenance:

7.1. First arrange all safety tools equipments and wear safety shoes, hand gloves and helmets.

7.2. Properly check calibration certificate of multimeter and clamp meter.7.3. Properly check working condition and continuity check of multimeter and clamp meter.7.4. Next open the TRU door carefully then pre-check all display readings and note the readings of pipeline soil potential, TRU input voltage & current value, TRU output voltage & current value, etc.7.5. Should check the anode header cable voltage & current readings using the clamp meter then compare the readings with TRU output display readings.7.6. Clamp meter reading should be equal to the TRU display readings. Sometimes readings will change, at this time calibrate all the display meters.7.7. Note all the following measurements,

Pipeline PSP. Reference cell PSP (Ref-1, Ref-2 & ref-3). Pipeline protection level (Over protection or under protection). TRU operating mode (Auto reference mode, Manual mode & CVCC mode). Reference cell voltmeter selector.

Reference cell electrode selector.7.8. If the Pipeline PSP is in over protection level, at this time decrease the input current value using adjustable switch.7.9. If the Pipeline PSP is in under protection level, at this time increase the input current value using adjustable switch.7.10. Sometimes if TRU display meter is in off condition then check the meter fuse working condition otherwise replace with new fuse.7.11. If the TRU display meter is not working properly at this time calibrate the meter immediately.7.12. Should check the inbuilt interrupter working condition.7. 13. Properly check the anode and cathode header cable connection for TRU output side. Should maintain the tight connection and place the insulation tap.7.14. After TRU monitoring finally close the TRU door properly.7.15. Calculate the total anode bed resistance value. The resistance of anode ground bed to earth as measured should be less than 1.0 Ohms. If the resistance is more than 1.0 Ohm, at this time pour some salt water on the anode bed and reduce it.7.16. AC power supply should be available 24 hours for TRU.7.17. TRU monitoring will be conduct once in every week.

8. Rectifier Testing:

8.1• CAUTION: Only qualified personnel are to test and work on a rectifier. Safety is of the utmost importance when working on an electrical device.8.2• Determine if the rectifier or any associated electrical equipment is in an electrically hazardous area. Do not open any explosion proof junction boxes unless otherwise qualified and then only if the circuits are turned off and locked out/tagged out.8.3• Do not work on or remove any rectifier component without first turning the upstream power off and locking/tagging out.8.4• When first approaching the rectifier confirm that the case is not electrically “hot” either by taking an AC voltage-to-ground measurement or with a voltage alert device.8.5• On first opening the rectifier identify any exposed terminals that will have a voltage and take measures to protect yourself from them.It is important to ensure that the power source in an impressed current system, such as a rectifier, remains operational and that the cathodic protection system is connected with proper polarity. The negative (–) terminal of the power source must be connected to the structure and the positive (+) terminal must be connected to the anode bed (see Below Figure).The proper connection of a rectifier is CRITICAL and if done improperly can result in catastrophic damage to the structure that is supposed to be protected, resulting in loss of product, structural damage, property damage, environmental damage, or loss of life. Often the cathodic protection cables are either not identified or are incorrectly identified. It is therefore mandatory to verify the proper connection polarity. This can be accomplished by measuring the structure-to-electrolyte potential near the power source both before and after the source is activated. A shift in potential in the electronegative direction with the power source energized, confirms the correct polarity. For this test the cable connected to the negative terminal of the rectifier should not be used as the test lead for the structure-to-electrolyte potential measurement. When connecting a

rectifier to an AC power supply, the AC supply circuit should be dedicated and separately fused. The rectifier should never share an AC circuit with normally interruptible facilities such as lighting and pumps.The voltage and current output of the power source should be monitored regularly to ensure that the unit remains operational.Basic rectifier operational data includes:• AC input voltage• DC output voltage and DC output current• Tap settings and/or potential set point (if constant potential) or current set point (if constant current)• Anode-to-structure resistance.

9. Routine & Preventive Maintenance of Transformer Rectifier Unit

9.1. Check calibration of the system every six months.

9.2. Check tightness of all electrical connections periodically.

9.3. Keep the inside of the control enclosure clean and check that gasketting and fastening are in good order.

9.4. Check that all connections, particularly those carrying high current are tight.

9.5. Maintain oil level. Check the input voltage to ensure that the desired voltage level is fed into TR at all times.

9.6. Check the effectiveness of equipment earthing periodically.

10. Operating Procedure of Transformer Rectifier Unit

10.1. Inspect the connections made following the installation procedures.

10.2. Carry out megger and resistance tests using appropriate meters.

10.3. Make sure the interrupt switch (on/off) on the front panel is off.

10.4. Make sure output adjustment knob is at zero (minimum).

10.5. Check oil level and make sure it is full. ON the A.C supply to the Transformer-Rectifier.

10.6. Check the mains input voltage cables on the circuit breaker and make sure they are strongly fitted.

10.7. Turn ON the power switch (i.e. circuit breaker) on the left side of the control panel.

10.8. Gradually adjust the output adjustment knob until the required voltage and current output level is achieved.

10.9. Then record readings obtained.

11. Fault Finding of Transformer Rectifier Unit

In the event of no indicated d.c. output:-

11.1. Check supply volts, if ok, check fuses. Replace if necessary.

11.2. If there is still no d.c. output, check position of output adjustment knob to be sure it is not in zero. Check primary volts into the TR, if o.k. check primary volts into main step down transformer.

11.3. If there is still no d.c output, check the semi-conductor bridge diodes and SCRs.

11.4. This may necessitate the removal of the rectifier stack for checking. In the event of no d.c. Voltage being indicated, but current is: - Check voltmeter. Check on voltmeter terminals if voltage there but no readings then replace voltmeter.

11.5.Top quality: for universal use Cena Summit Mesa 10 In the event of no indicated d.c. output current, but voltmeter is reading d.c. Voltage: - Check on ammeter terminals if millivolts present replace ammeter, if not proceed as below.

11.6. Check d.c. output fuse. Check that external output circuit (groundbed and structure connections) for open circuit. Check shunt signal by connecting milli-voltmeter on mV d.c. Across shunt at and check mV is proportional to current. Shunt rating in amps Let this =A, then 0.075/A * OUTPUT AMPS =mV READING.

12. Cathodic Protection Transformer Rectifier:

Cathodic Protection Transformer Rectifier unit (TRUs) comprise of Automatic, Manual & CVCC controlled. CP-TRU is

used for cathodic protection of buried pipelines across the country, storage tanks at terminals /refineries and other

buried structures.

12.1. Applications:

12.1.1. TRUs are used to prevent submerged (Soil or water) metallic structures from corrosion. All submerged

Pipelines (Oil, water etc.), concrete structure of bridges/ buildings / sea ports etc can be protected from corrosion by

doing CP.

12.1.2. TRUs impress DC Currents in to the Carbon-steel/steel structure to be protected in opposite direction to the

galvanic corrosion currents & protect the structure from corrosion.

12.1.3. To obtain the optimum level of protection under varying conditions, it is necessary to vary the impressed

current continuously so as to maintain a constant level of protective potential at the structure. This continuous

monitoring and control can be achieved by providing an automatic control for the cathodic protection system.

12.1.4. HIRECT offers several types of TRU which are designed, manufactured and tested under strict quality

assurance system to achieve highest quality standards.

12.2.Transformer:

All the Transformers used in TRUs are designed to give high efficiency with low loss. The coils are wound with high

conductivity, annealed, insulated electrolytic copper and core material is high permeability, low loss CRGO/CRNGO.

The insulation material used is of high standard Class F. Designed and tested as per IEC 76/IS 2026 standards.

12.3. Rectifier:

Rectifiers are based on internal quality standards and our own make Diodes / Silicon Controlled Rectifiers. Rectifier

circuits have different topology depending upon the load requirements.

12.4Modes of Operation

12.4.1. Auto Reference Mode

The operation of the TRUs in this mode will be fully automatic and will be controlled by reference electrode feedback.

The unit will automatically maintain reference voltage or P.S.P. within ± 15 mv of the set value under all conditions.

12.4.2. Manual Mode

The DC output voltage of TRU will be controlled in 24 symmetrical steps by means of a separate Autotransformer

with Coarse & Fine tapping.

12.4.3CVCC Mode

The unit will be operated in Constant Voltage or Constant Current mode. In constant voltage mode the DC output

voltage will be settable from 0 to rated value in step less manner by means of voltage adjustable pot.

In constant current mode the DC output current will be settable from 0 to rated value in step less manner by means of

current adjustable pot.

12.5.1. Features and Benefits

Types Of Unit Natural/Forced Air Cooled, Oil Cooled | Indoor or Outdoor type.

Control Element The DC Output will be controlled through latest solid state Silicon Controlled Rectifiers

(SCRs) with plug in type control card of electronic circuits.

AC Inputs Single phase or three phase, 50 Hz/ 60 Hz

DC Outputs DC output Voltage - Unto 200V

DC output Current - Up to 500A

Meters 48 x 96 mm, 3 ½ Digit Digital meters as under

Input Voltage:0 to 750 V AC

Input current: Ammeter with suitable CTs

Output Voltage :As per output rating

Output Current: Ammeter with suitable shunt

PS.P: 0 to ± 19.99 V DC

Indications Mains ON , Auto Mode , Manual Mode , Auto Ref. mode , CVCC mode , under protection,

Over protection , All Ref. Fail , Current Limit.

Protection Normally we provide following protections 

MCBs with HRC Fuses in AC Input & DC Output

Over current limit & short circuit protection through electronic controller

Glass cartridge fuses in the all auxiliary power lines to control circuit

Operational Climatic

condition

TRUs are designed to work under severe environmental conditions with ambient

temperature of 50 ° C and humidity of 95 % (non condensing). Enclosure confirming to

class IP 55 degree of protection.

Enclosures Enclosures are fabricated from 2.5 mm/2.0mm/1.5 mm CRCA sheet and confirming to

IP55 degree of protection. Stainless Steel Cabinets for corrosive atmosphere. Lockable

doors shall be provided in the Front and Back. Polycarbonate window is provided viewing

meters and indications.

Finish Powder coating /Paint of required shade and thickness with proper treatment to suit

corrosive/site conditions.

12.5.2. Additional Features

Following additional features can be provided as per Specifications along with Rectifiers

12.5.2.1. Interrupter Timer

The Interrupter timer is used for carrying out ON/OFF CP survey using the current interruption technique.

Stand Alone Interrupter Timer

GPS synchronizable Interrupter Timer

12.5.2.2.SCADA Monitoring Facility

Isolated 4- 20 m A are provided for DC output voltage, DC output current and pipe to soil potential (PSP)

Remote Monitoring through GSM Data Logger

The parameters values can be remotely monitored using the GSM based remote monitoring systems

13. General Safety Factors of Cathodic Protection:

The works shall be carried out on a cross country pipeline and within the AGIs and terminals. The relevant Statutory Indian Legislation for conducting work on the pipeline and within operational gas terminals shall be strictly adhered to, together with any other local rules/legislation that may be applicable to the work.

Personnel Protective Equipment (PPE) shall be worn all the times when the work is performed.This shall include safety helmet, safety shoes, reflective jackets and coveralls where applicable.The work shall be carried out on a pipeline spread and other construction activities may also be occurring at the same time as the survey. The other activities shall be co-ordinated so as to avoid risk to personnel working on the interference survey.

Personnel shall also be advised that there may be hazardous AC voltages present on the pipeline under certain circumstances due to parallelism with overhead power lines or if there is a fault on the overhead power line. Operators shall therefore treat the pipeline a potential “live” conductor until tests proved otherwise. It is also important that no work takes place on the pipeline should there be the possibility of lightning in the area or weather conditions are unfavorable.

When taking CP readings fused test leads should be used where possible and operators should have rubber lines hand glues and safety shoes to ensure a ground contact resistance is high. If there is any significant AC current discharge through the zinc earth electrodes installed at the Motor Operated Valve (MOV) locations, this may pose a safety risk. Appropriate safety precautions should always be considered.

No work shall be undertaken on Railway property without the written authorization and Indian Railway Authority safe working procedures for work within the vicinity of railway lines shall be obtained.