AC HIGH-POTENTIAL TESTING - ccj-online.com · AC HIGH-POTENTIAL TESTING ... recommendations were...

© 2015 Doble Engineering Company – 82nd International Conference of Doble Clients All Rights Reserved

AC HIGH-POTENTIAL TESTING

James E. Timperley Doble Engineering

ABSTRACT This tutorial provides the development history and case studies for the application of ac overpotential testing to provide proof of suitability for service of large high voltage 2-pole and 4-pole generators. The types of test sets available, power frequency and very low frequency and their application are discussed. A method for estimating remaining generator stator service life is presented. INTRODUCTION The search for stator insulation testing techniques that can assure against in-service failures of large rotating electric machines has continued for more than 120 years. The goal of this test is to determine the dielectric strength of a winding without weakening or destroying that insulation. A proof test of dielectric strength is required that will provide some confidence of suitability for service for a certain time. Overvoltage tests are the only known means for providing assurance that a winding has a specified minimum dielectric strength. Two proof tests are often applied, ac and dc overpotential. Both have merits and disadvantages. The debate surrounding which is best has been known to raise the voice of more than one normally well-mannered engineer. The following will discuss the application of ac overpotential tests to large generator stators. Application of an ac test to rotating fields, power cables, bus and switchgear will not be discussed. BACKGROUND The American Institute of Electrical Engineers, AlEE, began the standardization of testing electrical apparatus at the January 26, 1898 meetings, held simultaneously in New York and Chicago [1]. The initial committee of 7 consisted of industry pioneers such as Thomson, Crocker and Steinmetz. Their recommendations were presented in 1899. At the beginning of the 20th century, the duration and amplitude for an over-potential test (Hipot) voltage that was applied was often arbitrary. A variety of values and times were considered satisfactory. In the beginning of the 20th century, the German standards mentioned hipot tests at 130% of the rated voltage for 5 minutes. Different values and times were used in England and the United States. There was no fundamental principle at work, except to "prove the windings were suitable for service." A Hipot test is often called a "Proof Test". Revisions and expansion occurred in 1902, 1905 and 1910. Committee size increased to 52 active members and in 1911 a "radical" revision began. This work resulted in a document on "Standardization Rules of the AIEE" [2]. These documents describe hipot tests for electric machinery under "Tests of Dielectric Strength of Machinery, Values of a-c Test Voltages". Paragraph 485 of the Standardization Rules specifies a 60 second test. Paragraph 500 states: “The standard test for all classes of Apparatus, except as otherwise specified, shall be twice the normal voltage of the circuit to which the apparatus is connected, plus 1000 volts”. Paragraphs 501 to 510 list the exceptions to this test value. This value, 2E+l, was only one of several values listed. Machinery in 1914 meant all electrical equipment, motors, generators, transformers, household devices, switches and control apparatus. Test values listed in the exceptions were 2.73E+l, 10 E but no less than 1.5 kV or more than 3.5 kV, 4E+l, 2.25E+2 and the fixed values of 500 V, 900 V, 5 kV, 8 kV and I0 kV. The 2E + 1 ac test value has survived unchanged for more than 100 years. Why? Perhaps because experience shows it to be a good reliable benchmark for both manufacturer and user.


2-16

In 1914, Steinmetz (GE) and Lamme (Westinghouse) reached a compromise and agreed on 60-seconds. This was first published in the 1914 Standards report - AIEE Trans Vol. XXXIII, 1914, Part II pp. 1787-883. and page 1829, Duration [2]. Power frequency over potential (Hipot) tests on machines have been performed throughout the 20th century and continue today. As the machines became larger, the ac supplies increased in size to supply the necessary capacitive charging current. DC high voltage testing was not possible until the 1930s when Kenetron supplies with vacuum tube rectifiers became available [3]. This reference also explains the fear that ac testing can be destructive to machine insulation. The 20 to 30 year old shellac mica-folium systems tested in 1938 often had measured power factors of from 10 to 30%. Dielectric heating and the resulting loss of insulation strength were measurable if there was repeated application of high ac test voltages. With the asphalt, epoxy or polyester bonded systems in use today this deterioration is no longer true. Factory Proof Hipot The final factory ac one minute acceptance test of 2E+1 is required by the standards for all new generator stator windings. This is the suitability for service test and is intended to verify manufacturing procedures were successful. During the factory process there are several other proof tests applied to winding bars and coils during manufacturing. These are applied at voltages higher than 2E+1 and depend on the factory culture. In most cases the earlier in the process the higher the applied process proof voltage. The time voltage is applied is frequently shorter than one minute for these earlier manufacturing QA tests. This testing is used to catch process defects early in the production run so they can be corrected. The final factory high-potential stator test as specified by standards are performed with ac voltages (50/60 Hz) for 1 minute. According to standards [4, 5], the stator hipot ac voltage shall be 2E + 1 kV ac, where E is the stator rated line-to-line ac voltage (in kV rms). Maintenance Testing Few utilities perform routine generator maintenance Hipot tests [6, 7]. A maintenance hipot is usually performed as part of scheduled major work along with an inspection and repairs. Never test unless you are prepared for a failure. This includes having spare bars, winders, time and money available to perform any repairs that may be required. Before deregulation, most generator manufacturers recommended inspection and hipot after the first year of operation and then at intervals of no more than 5 years. After deregulation these inspection/testing intervals have continued to increase. A major outage in the 8 to 10 year range is not unusual in today’s industry. The risk of in-service failures has increased as a direct result. It all relates to risk management. If there is a test, the generator may fail and the outage extended while repairs are implemented. If there is no Hipot test the generator may fail in service. Usually a test failure is not covered by insurance. An in service failure is often covered by insurance. There is the cost of performing a test. A test set needs to be rented since only very large companies have ac high voltage test sets. A trained person must be available and again few companies have maintained this skill set in house. Critical path outage time is needed. Outage time is extended if repairs are required.


3-16

APPLICATION OF A 50 Hz or 60 Hz HIPOT

A transformer type 60 Hz test set from the 1960’s Figure 1

The high voltage 60 Hz test set in figure 1 is typical of a “compact Hipot” available in the 1960’s. It is a brute force 200 kVA step-up transformer 550 V, 200 amps input and 0-50,000 volt output. Weight was 6850 pounds (3100 kg). Maximum capacity was 2 amps @ 50 kV for one minute, followed by an hour of cooling. High transformer reactance helped balance the stator capacitance load. The right photo shows the control panel. There are condition indicator lamps, the output voltmeter, raise and lower controls, timer and output current meter. All are basic analog controls. This set remains in frequent use today after 50 years. One modification has been the addition of terminal blocks to attach digital instrumentation.

A resonant test set from the 1980’s Figure 2

Figure 2 shows one of the early designs of a large capacity resonant test set; now preferred for ac hipot testing. The control voltage regulator is on the right and the high potential source transformer in the center. The tunable shunt reactor is on the left. This set has an input of 550 V @ 52 amps or 480 V @ 63 amps and an output of 0-30 kV or 0-50 kV @ 300 kVA. Weight was 5,500 pounds. Controls have many features including an arc detector, figure 3. Reactor air gap, input voltage, output voltage and current are all displayed.


4-16

Besides the reduction in physical size another advantage of the resonant test set is the rapid collapse of voltage after a dielectric failure. High test voltage is developed by a resonance between the set reactor inductance and the generator stator capacitance. This is achieved by changing the reactor core air gap and tuning the set and load at the power frequency. Stored energy in the L-C resonant circuit collapses when a dielectric failure occurs. There has always been the rumor that a dielectric failure will damage stator iron. There is less total fault energy available in a resonant set than a transformer type source. This reduces the chance of a fire and collateral damage. In the authors experience and hundreds of ac Hipot failures there has never been a documented case of stator lamination insulation damage resulting from a stator test failure. Both transformer and resonant test sets were employed.

A resonant test set control panel Figure 3

APPLICATION OF 0.1 Hz (VLF) The DC Hipot test does not subject stator insulation to the same voltage distribution as AC voltage in service. Yet many proponents of DC testing did not like the size and expense of the power supply required for AC testing. The previous examples show AC test sets can often weigh several tons. This resulted in 0.1 Hz testing (very low frequency or VLF ) developement in Sweden and proposed in early 1960s [7,8]. IEEE Standard 433 on VLF testing machines was first published in 1974 and later updated in 2009 [9]. Since the applied voltage has a much lower frequency than 50 or 60 Hz, the capacitive charging current is likewise much smaller at 0.1 Hz, resulting in a smaller test set. The quality of the AC waveform in early 0.1 Hz power supplies was poor. In the 1970s and 1980s, resonant 50 Hz and 60 Hz AC power supplies became available and the size of the supplies required to provide capacitive current to large stator windings became manageable. One problem with VLF testing is output current is often only a few ma. This prevents the use of VLF with large water cooled windings unless the water is removed and the stator dried.


5-16

A 0.1 Hz test set from the 1960’s and setup for a stator test Figure 4

Available from Sweden since the 1960’s, this 0.1 Hz test set had a peak voltage of 70,000 and could charge 0.7 microfarad capacitance, weight is 530 pounds (240 kg) and it is powered from a standard welding outlet. Today the use of 0.1 Hz Hipot tests for generator stators is uncommon. VLF (0.1 Hz) is widely used for testing long power cable runs of several km, in Europe. Partial Discharge and Power Factor data can now be collected during a VLF test. With the availability of new and better quality supplies, there appears to be some renewed interest in trying 0.1 Hz voltages for machine insulation tests. The ability to test large capacitances with very lightweight equipment is the major advantage. One modern VLF set weighs only 44 lbs. (20 kg), input is 120-240 volts, 300 VA and output 14 ma, 34 kV peak. This is sufficient to test up to 4kM of shielded power cable. DOES THE HIPOT TEST DAMAGE A WINDING No one wants to cause a failure by testing. The question “will this test damage a good winding” is frequently asked when engineers want to apply an overpotential test, most often by asset managers who do not want a failure during their watch. The answer is NO. Maintenance Hipot testing does not damage or degrade a good insulation system. Several EPRI reports note machines that have failed a hipot test have always been found to have seriously deteriorated insulation systems. [10, 11, 12]. There was a high probability the machine would have failed in-service, especially if an overvoltage from surges or a power system fault were to occur. Experience has shown, only machines with deteriorated or marginal insulation systems are likely to fail during the hipot test. A good system will not fail. Stator coils and bars used in modern machines have the capability to pass a voltage endurance test [13]. Typically coils for a 13.8 kV winding are expected to survive for 400 hours at 30 kV and 100o C. If this 400-hour test at 30 kV represents 25 years of life in-service, then a one minute 2E+1 or 29 kV over potential test ages the insulation by nine hours (see IEEE Standard 930 for the relationship between voltage and insulation life) [14]. Testing is often at “room temperature” while the IEEE 1553 voltage


6-16

endurance test applied at operating temperatures of 100o C or higher. When this is included in the aging process the maintenance test removes only minutes of expected remaining service life. Maintenance test voltages are usually much lower than 2E+1 so the “electrical aging” is only a matter of minutes, out of decades of remaining service life. In the authors experience of over 100 ac overpotential tests only severely deteriorated windings failed. Not Testing in Air The usual procedure for Hipot testing hydrogen cooled generators requires hydrogen be removed to prevent a hydrogen explosion. This process can require days of critical path outage time to degas then refill with CO2,

then air, then remove the generator end shields. At some locations a maintenance Hipot has been routinely performed without opening the generator and if there were no failure the generator would not be opened or inspected. Needless to say this required a progressive management approach at those plants and a faith in engineering judgment. A first look, testing at high voltages by filling a generator with CO2 to displace the hydrogen as shown in Table 1 is possible.

Table 1 Dielectric Strength Comparison

One ATM Dielectric Strength

Ambient Density Two ATM Three ATM

15 PSIG 30 PSIG

Air 1.00 2.00 3.00

Hydrogen 0.07 1.52 2.16

CO2 1.52 2.2 3.15

The table shows a generator with a slight + pressure of CO2 has a higher ambient dielectric strength than when tested in air. There can be no explosion or fire in the CO2 environment. ATM is one standard atmosphere of pressure, (76 cm of mercury and 25o C). The Sphere Gap An essential part of a Hipot test is a sphere gap as shown on Figure 5. It serves two important functions. The gap is set at a specific voltage to verify the test set voltage indication is accurate. Then the gap is opened slightly to serve as over voltage surge protection during the test. Corrections for ambient air pressure, temperature, sphere diameter and test voltage are needed. All this basic text book high voltage physics had been used for over 100 years. Arcing over the sphere gap before a test is shown in Figure 6. There is no arc flash hazard since the current and total energy are limited by the series resistor. This also prevents damage to the polished sphere surfaces. Typical arc current is limited to less than 2 amps.


7-16

A 0.1 Hz test set from the 1960’s and setup for a test Figure 5

A sphere diameter of 6.25 cm is typically used for the test voltages ranging from 10 kV to 50 kV as typically applied to generator stators. A General Electric Service Manual [15] provides excellent details on the use, calibration and adjustment of sphere gaps

Checking gap spark over voltage before a test Figure 6

Figure 6 shows the arc over of a sphere gap to set the over voltage protection limit during a maintenance Hipot.


8-16

DETERMINING REMAINING SERVICE LIFE One major utility operated a large number of mature asphalt mica generator stators. Some (20) had been high maintenance with a few in-service failures and several stator bars replaced and others (22) had been trouble free. The question of remaining service for these mature generators was a vital question for asset managers. In-service failures are to be avoided, but it is uneconomical to rewind a machine if the plant and unit were to be retired within a few years. Large sums had been invested on pollution controls on some units and another 20 years of service was planned. Overpotential testing with a carefully selected test voltage can be an accepted method to determine the suitability for continued service of questionable equipment. Several generators were scheduled to be rewound and were tested to destruction before the stator bars were removed. Results were educational. Some circuits withstood 3E while others failed below rated stator phase to phase voltage. Based on this experience and a paper published in 1970 [16], a methodology was developed based on original stator dielectric strength of 4E and a linear insulation deterioration model [17, 18]. Figure 7 shows a typical evaluation as applied to a 37 year old stator. Eighteen steam turbine generators ranging from 100 to 125 MW and four 20 MW hydro electric generators were not rewound due to favorable 2E+l test results, even after 35 to 55 years of service.

Estimating service life from a 2E+1 HiPot Figure 7

The approach was that the results of an ac overpotential test will provide a good indication of generator stator dielectric strength and remaining service life. With this test data, a low risk decision based on actual conditions can be made for a given generator. Is the expected generator life much less than the remaining site life? Should the machine be repaired or should a full stator rewind be scheduled? In a dozen cases the major expense of a stator rewind was successfully postponed for many years until the plant site was retired. The decision to rewind stators was effectively based on ac overpotential test results.


9-16

BACKGROUND A paper suggesting a method of ac overpotential testing to assure a reliable short-term service life of steam turbine generators was published by Clyde Maughan in 1970. [16]. This idea was successfully applied to postpone stator rewinding and expanded to cover hydro-generators as well as steam turbine generators in 1994. [17, 18] The basic premise is that for asphalt/mica-flake high voltage insulation systems deterioration is linear with time. Loss of dielectric strength results from thermal and mechanical deterioration. With some synthetic resin/mica–paper insulation systems partial discharges are not a life limiting parameter. In these cases thermal and mechanical deterioration frequently limit useful service life [19] ASSUMPTIONS Several assumptions were made for the application of this procedure. It can be argued that there may not be sufficient information to confirm some of these assumptions but the limited data collected and successful application has, to date suggested the technique is valid. • The initial dielectric strength of an insulation system was approximately 4 times rated voltage. • Properly applied ac overpotential testing will not shorten the remaining service life of a winding. • If mechanical looseness and partial discharges are not present, then stator insulation deterioration is a function of thermal aging and load cycling. • Loss of dielectric strength is linear with time if the type of operation remains constant. • Remaining stator dielectric strength is an indication of remaining service life. • This technique is applicable to asphalt, polyester, and epoxy binders as well as mica-flake and mica-paper systems. • Projected failure is chosen to be at rated line-to-ground voltage. No over voltages or surges are considered.


10-16

Application of a Hipot for risk management.

Figure 8 IS IT SAFE TO HIPOT A STATOR WINDING Minimum insulation resistance Periodic insulation resistance readings are an important part of determining the condition of insulation. But there is no indication that insulation resistance has any relationship to dielectric strength. Contamination and moisture can be detected and is often trended to indicate when cleaning is needed. Modern windings with synthetic resin binders may have such high readings as to be of little practical value [20]. IEEE P43 states that readings over 5000 meg ohms may not be meaningful (12.2.20. However very low readings do not necessarily indicate a Hipot cannot be performed. Testing water cooled windings, with the water system in service, is possible with an AC test but not practical with DC or VLF. Insulation resistance for a phase to ground may be much less than 1 meg ohm when the water is still in the stator bars. The resistance is determined by the number of water hoses and stator water conductivity. Machines with single pass cooling and a large number of stator bars can have very low insulation resistances even when the stator water conductivity is at normal levels. A range of insulation resistance, from actual test data, for several generator stators tested is given in Table 2.


11-16

Table 2 Typical ac Hipot Stator Loads, 60 Hz

Generator Stator Test Requirements for each Phase

Rated Voltage kV

MVA Cooling Applied Voltage kV

Charging current Amps each

phase

Insulation Resistance* Meg ohms

24 568 water 130% 31.2 3.2 9.5 (wet)

26 907 water 115% 29.9 2.6 1.8 (wet)

26 1333 water 180% 46.8 10.5 0.065 (wet)

16.5 292 water 130% 21.5 2.2 700 (dry)

15.5 100 hydrogen 2E+1 32.0 3.1 2150

15.5 118 hydrogen 2E+1 32.0 2.8 2000

13.8 111 hydrogen 2E=1 28.6 1.25 1000

* Stator insulation resistance readings are the one minute reading, usually at 2500 volts. Stator water pumps are running and conductivity is in the normal operation range. Table 2 shows data from 2-pole and 4-pole machines with asphalt-mica as well as epoxy-mica insulation systems. Technical details of the stators are not provided to keep the table size reasonable. The goal was to present real data to help describe the conditions when testing large generator stators.


12-16

APPLICATIONS OF REMAINING SERVICE LIFE PREDICTION Case Study 1 Application of ac overpotential testing to determine suitability for extended service began in 1989 at a four unit hydro-electric plant. These asphalt-mica flake insulated machines began operation in 1939. The original stator windings had experienced no coil failures and inspections found no indication of serious physical deterioration. A full set of stator windings was available if test results indicated replacement was necessary or a failure occurred. A generator was then tested each year at 2E+1 for one minute until all machine circuits had been tested. No stator failed the one-minute test level usually reserved for new windings. See Figure 1 for an example of typical test results.

Remaining service life for a 50 year old Hydrogenerator Figure 9

Figure 9 –This curve shows the plot of projected life for the oldest series of generators in the program. These asphalt/mica 11 kV hydro generators began service in 1939. The projected operating life is almost 100 years. At the time this was written in 2015 these four generators remain in service. There has been an additional 26 years of service after the 2E+1 test of a 50 year old stator winding. Case Study 2 At a pump-storage site units 1&5 are 69 MVA pump-generators with severe operating duty cycles. There can be no operation for days then numerous generator or pump starts within 24 hours. The original asphalt/mica-flake windings were replaced in 1972 and 1973 with a B-Stage epoxy/mica-flake insulation system. Minor maintenance had been necessary but no serious partial discharge problems or coil looseness developed. In 2002 during a maintenance test before rewedging, Unit 1 failed near the rated voltage of 13 kV. See Figure 10. A 130% ac test had been planned before stator rewedging. The failed coils were bypassed and rewedging cancelled; the unit was returned to service. Stator winding replacement was scheduled for both Units 1&5 since the design, age, and operating conditions are the same for both machines. Unit 5 did experience an in-service failure in May 2003 while in the pumping mode. After evaluation, the failed coil was bypassed and the unit returned to service. The Unit 5 stator was scheduled for rewind first, in the fall of 2003. Unit 1 rewinding followed the next year.


13-16

Generator at the end if service life Figure 10

Figure 10 – This plot of the expected life of an epoxy/mica 13 kV insulated pump-generator was the newest insulation system evaluated. Machine operation can be severe with several load and speed cycles each day. Winding replacement was scheduled. PROJECT RESULTS Application of 2E+1 to steam turbine generators began in 1990. Over thirty generators were tested and the rewinding of 12 of these machines ranging up to 150 MW and 55 years old were confidently postponed. As of 2015 there has been no failure of any of the stators tested at the 2E+1 level. Application of 130% to 150% of rated voltage, rather than 2E+1, can also be considered sufficient to determine the remaining short term service life, just as proposed in the 1970 paper. About ½ of the generators tested, where the stator rewinds were postponed, have remained in service until the plant sites were retired by the close of 2015. The other machines remain in service or have been rewound as part of a plant life extension package. Most of the large generators in this utility have been tested at ac voltages above 130% of rated voltage over the past three decades. This program has reduced the risk of an in-service stator failure substantially. There have been only three in-service failures due to groundwall deterioration within the past 4000 generator years of operation. In all cases, those machines had not been ac overpotential tested as part of this program. CONCLUSION The application of an AC overpotential test has been applied to stators of rotating electric machines for 100 years to prove suitability for service. The test does not damage windings, does not reduce remaining service life by more than a few minutes and can provide valuable information for condition assessment. Estimating remaining service life can be estimated. ACKNOWLEDGEMENTS Many thanks to my friends in EPRI, IEEE and at American Electric Power for their help with this paper. Special thanks in particular to Daniel Shriver who performed many of the tests referenced in this paper.


14-16

REFERENCES [1] “Report of the Committee on Standardization,” in Transactions of the American Institute of Electrical Engineers, vol. XVI-XIX. New York, NY: American Institute of Electrical Engineers, 1899–1902. [2] “Standardization rules of AIEE,” in Transactions of the American Institute of Electrical Engineers, vol. XXVI- XXXVII. New York, NY: American Institute of Electrical Engineers, 1907–1918. [3] Van Ness, B., "Generator Insulation Tests," Edison Electric Institute Bulletin," Vol. 6, January - December, 1938, pp. 204-206 & 231 [4] C50.12-2014 “IEEE Standard for Salient-Pole 50 Hz and 60 Hz Synchronous Generators and Generator/Motors for Hydraulic Turbine Applications Rated 5 MVA and Above” [5] C50.13-2014 “IEEE Standard for Cylindrical-Pole 50 Hz and 60 Hz Synchronous Generators Rated 10 MVA and Above” [6] Guide for Rotating Electrical Machine Hipot Testing, EPRI Report 100666, EPRI, Palo Alto, Calif., 2000. [7] Virsberg, L. G., “The high voltage testing of large electrical machines at 0.1 c/s,” ASEA Journal (Sweden), vol. 40, no. 5, pp. 71–75, 1967. [8] Bhimani, B. V., “Very low frequency high potential testing,” AIEE Transactions on Power Apparatus & Systems, vol. 80, pp. 148–155, 1961. [9] IEEE Standard 433-2009, IEEE Recommended Practice for the Insulation Testing of AC Electric Machinery with High Voltage at Very Low Frequency, New York, N. Y., 2009 [10] Guide for Rotating Electrical Machine Hipot Testing, EPRI Report 100666, EPRI, Palo Alto, Calif., 2000. [11] Guide for Rotating Electrical Machine Hipot Testing: 2007 Update, EPRI Report 1014908, EPRI, Palo Alto, Calif., 2008. [12] (Hipot) Testing: A Tool to Assess Stator Winding Condition, EPRI report 1014908, Palo Alto, Calif., 2009 [13] IEEE Standard 1553-2002, Standard for Voltage Endurance Testing of Form Wound Bars and Coils for Hydrogenerators, Institute of Electrical and Electronics Engineers, New York, N.Y., 2002. [14] IEEE std. 930-2004 - (Replaced) IEEE Guide for the Statistical Analysis of Electrical Insulation Breakdown Data [15] General Electric Service Shops Department, GEI- 41580, Sphere Gaps 2-150 centimeters [16] Maughan, C. V. and Bristor, A. F.”High-Potential Testing of Large Turbine-Generator Stator Insulation” IEEE Conference Paper 70 CP196-PWR [17] Timperley, J. E. and Michalec J. R., “Estimating the Remaining Service Life of Asphalt-Mica Stator Insulation”, IEEE Transactions on Energy Conversion, December 1994, Vol. 9, No. 4, pp. 686-694. [18] Timperley, J. E. “Power Frequency Overpotential Tests on Installed Stator Windings of Rotating Electric Machines”, IEEE/PES Panel Session on “High Voltage Testing of Rotating Machines”, IEEE Publication 97TP119-0, pp 14-17.


15-16

[19] Maughan C. V., “Testing of large electric generators for suitability of service,” presented at the Iris Rotating Machines Conference, San Antonio, TX, Jun. 2002 [20] IEEE std. P43-2013, Recommended Practice for Testing Insulation Resistance of electric Machinery, New York, NY: IEEE


16-16

BIOGRAPHY James E. Timperley is currently a Sr. Principle Engineer with Doble Engineering near Columbus, Ohio. He has 45 years experience in the power industry with an emphasis on large electrical rotating machinery and isolated phase bus. Jim has authored more than 80 technical papers in the areas of applied research, advanced insulation systems, diagnostic testing, failure investigation, inspecting, maintaining and specifying rotating machinery for IEEE, Doble, ASME, CIGRE, EPRI, DEIS, PCIC and the American Power Conference. His work involves root cause analysis of equipment failures, insulation deterioration, and developing repair procedures for use at petrochemical and industrial sites as well as in fossil, nuclear and hydroelectric power plants. Mr. Timperley is a Life Fellow of the IEEE and received the 2006 DEIS Dakin Award for the development of EMI Diagnostics for power equipment. He is active in IEEE standards committees, holds a BS degree in electrical engineering from Oklahoma State University and is a registered Professional Engineer in the State of Ohio. He has completed Basic Offshore Safety Induction & Emergency Training (BOSIET) for working on off shore rigs.

AC HIGH-POTENTIAL TESTING - ccj-online.com · AC HIGH-POTENTIAL TESTING ... recommendations were...

Documents

Transcript of AC HIGH-POTENTIAL TESTING - ccj-online.com · AC HIGH-POTENTIAL TESTING ... recommendations were...