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HOW SAFE IS THE INSULATION SYSTEM OF ROTATING MACHINES OPERATING IN GAS GROUPS B, C & D?

Copyright Material IEEE

Paper No. PCIC-2011-36

Saeed Ul Haq, P.Eng Bharat Mistry, P.Eng Ramtin Omranipour GE Energy GE Energy GE Energy 107 Park St N. 107 Park St N. 107 Park St N. Peterborough, K9J 7B5 Peterborough, K9J 7B5 Peterborough, K9J 7B5 Canada Canada Canada Saeed.haq@ge.com Bharat.Mistry@ge.com Ramtin.Omranipour@ge.com

Abstract - The safe operation of electrical rotating machines in Chemical, Oil and Gas industrial environments where hazardous gas may be present is of primary concern. There are numerous publications available on the subject of arc and spark at various locations within rotating electric machines. Various techniques have been used to minimize corona discharge activity in high voltage stator windings. To understand the impact of discharge activity in a hazardous environment, few manufacturers have tested or provided such data. To ensure safe operation of machines in these environments, it is necessary to determine and understand the levels of partial discharge (PD) and corona discharge activities. PD and corona discharge activities are phenomena related to the applied voltage. There are many other design and environmental related factors that can cause variation in the level of discharge activity. It is believed that if the PD or corona discharge activity exceeds certain limits, it may ignite a specific explosive gas or vapor of gas as defined in the IEC Std. 60079-15. To assess the safe operation of insulation systems of 6.6 kV to 13.8 kV, the steady state ignition tests, called Incendivity testing was performed on stator windings in gas groups B, C, and D as specified in IEC Std. 60079-15. The contributing factors and mitigation of discharge activity will also be discussed in this paper.

Index Terms — Corona, Ignition, Incendivity, Partial

discharge, Surface discharge, Sparking.

I. INTRODUCTION

In North America, classification of locations for machines running in hazardous gas or vapor environments are defined in the NEC [1] or CEC [2]. These classified locations are Division 1 & 2. High voltage rotating machines installed in Division 2 locations are generally open machines; whereas, in Division 1 they are specifically designed to avoid contact with hazardous gas. As the majority of machines operate in a Division 2 hazardous gas environment; therefore, it is necessary to understand the behavior of stator insulation systems in three different gas groups, as specified in IEC Std. 60079-15 [3]. The presence of explosive gas in an enclosure during the start or continuous operation of high voltage machines could create an explosion, if PD or corona discharge activities are not within acceptable limits. Some explosions have occurred on oil platforms in the North Sea and other remote locations in the petro-chemical industry; however, the causes of these

explosions were not all specifically related to PD or corona activities [4, 5]. In response to these explosions, a series of meetings were organized to determine the root cause(s) and to devise practical solutions that could be implemented to ensure the safe operation of electrical rotating machines. It was also realized that motors driving centrifugal and screw compressors in hydrocarbon service are particularly vulnerable to gas ingress during the start sequence [5].

Review of North American standards suggest that no test method has yet been developed for testing the stator insulation system under hazardous gas environment. The only available standard is IEC 60079-15 [3] for Ex”n” motors, operating in an environment equivalent to Division 2 area.

In this paper, practical aspects of hazardous gas environment testing are explored. In addition, the test method, sample preparation and possible conditions leading to high PD and corona activities are discussed.

II. HAZARDOUS GAS GROUPS

Table I lists hazardous gas groups. Gas groups C and D are considered less severe, but may also ignite the surrounding gas depending on the energy developed by a discharge. Therefore, an attempt has been made by NFPA 497 [6] to develop a relation of each explosive gas group with respect to the minimum ignition energy. The minimum ignition energy levels described by standard NFPA 497 are listed in Table I. The authors have not considered the gas group A of Acetylene during testing since operation of machines in that gas group is rare. The following tables provide the gas group designations as defined in NEC [1] and IEC [2].

TABLE I GAS GROUPS/MINIMUM ENERGY

Typical Explosive

Gas

Gas Group Designation by

NEC [1]

Gas Sub Group

Designation by IEC [3]

Minimum Ignition Energy

(MIE) in mJ

Hydrogen B IIC 0.019 Ethylene C IIB 0.070 Propane D IIA 0.250

IEC Std. 60079-0 [7] also specifies the relation of each gas

group with respect to the minimum static discharges in “nC”. These data are provided in Table II. Static discharge data suggest that for safe operation of electrical equipment the

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magnitude of discharge should be less than 10 nC for gas group B (Hydrogen).

TABLE II GAS GROUPS/MINIMUM STATIC DISCHARGE

Typical Explosive Gas

NEC Gas Group

Designation

Gas Group Designation by

IEC [2]

Minimum Static Discharge in nC

Hydrogen B IIC 10 Ethylene C IIB 30 Propane D IIA 60

III. TEST SAMPLE REQUIREMENTS ACCORDING TO

IEC STD. 60079-15

According to the IEC Std. 60079-15 [3] incendivity tests can be carried out on any of the following:

• a complete fully wound and vacuum pressure

impregnated (VPI’d) stator; • a stator with motor enclosure; • a complete assembled motor; • a partially wound and VPI’d stator • a section of stator, referred to as a “statorette”, fully

wound and VPI’d; • a group of coils.

As it may be quite expensive and not physically practical to

perform testing on a complete, fully wound and VPI’d stator, incendivity testing on a partially wound stator or on a section of stator (“Statorette”) is often preferred to understand the behavior of an insulation system in explosive environments.

There are three major gas groups - D (Propane), C (Ethylene) and B (Hydrogen) – in which incendivity testing is performed to meet the IEC standard requirements. For steady state ignition testing, a special setup is required with an accurate measurement of the mixture by volume of explosive gas mixtures. The tests also require the use of high voltage test equipment to perform the incendivity testing at high voltages. There are a limited number of laboratories around the globe capable of performing such complex tests.

Among the three different gas groups described earlier, gas group B is considered the most challenging in the petrochemical industry. It is the most ignitable gas of all the gas groups. If the equipment under test can pass the gas group B tests, then it is considered acceptable for all other gas groups without further testing; however, to better understand the performance of the insulation system, it is considered prudent to complete the test in all gas groups starting from the least severe to the most severe. In general the installation of electrical rotating machines in gas group B is limited to only 5% to 10% of all Zone 2/Division 2 applications. The steady state ignition test by itself is considered sufficient to understand the behavior of insulation systems for Zone 2/Division 2 hazardous atmospheres.

The behavior of insulation systems related to high frequency PWM drives is well explained in reference [10]. If the insulation system is not properly designed to suit high frequency application, there could be extra dielectric heating, leading to hot surfaces at the junction of the grading and conductive tapes or between the conductive tape and the iron core. Therefore, further research work is recommended to understand the

behavior of insulation systems in gas groups B, C and D when operated under PWM-VSC application.

In this paper, the influence of hazardous gas environments, listed in Table III, has been investigated when stator winding insulation is subjected to 60 Hz AC voltage waveform. In addition, available options to reduce the extent of surface discharge activity to ensure reduced risk of detonation of the gases are described.

TABLE III EXPLOSION TEST MIXTURES [3]

Typical Explosive Gas

IEC Equipment

Group (NEC)

Test mixture in air v/v

Hydrogen IIC (B) (21 ± 5) % hydrogen Ethylene IIB (C) (7,8 ± 1) % ethylene Propane IIA (D) (5,25 ± 0,5) % propane

IV. RATED VOLTAGE REQUIREMENTS FOR

INCENDIVITY TESTING

IEC Std. 60079-15 [3] specifies an application of a sinusoidal voltage with a magnitude of 1.5 times the rated voltage of the machine during incendivity testing. The voltage is applied between one phase and ground with the other phases grounded. In a wound and VPI’d stator, the voltage distribution among the coils varies depending on the location of the coils inside the wound core. The surfaces of coils located inside the slots will be at ground potential while the surfaces of coils outside the slots will have varying degrees of static voltages along their length, depending upon the voltage grading system used. Phase-to-phase voltage stresses exist at the cross-over of two coils that belong to different phases. It is imperative to observe PD and corona activities at the cross-over and end regions of these coils, including cable connections, at the specified elevated voltage.

For stators with high operating voltages, incendive surface discharges can occur, particularly if the stator end-winding surfaces are contaminated. Since the corona discharge could potentially be a continuous ignition source, this effect must be considered during normal machine operation.

Industry experience suggests that properly maintained electrical machines with rated voltages up to and including 4160 V does not present an unacceptable risk of ignition due to winding surface discharge; therefore, machines rated for higher voltages should be considered to understand whether with the requirements of Ex “nA”.

V. PARTIAL DISCHARGE, CORONA OR SURFACE DISCHARGES

A. PD or Corona Discharges

PD is a localized dielectric breakdown within a solid or liquid insulation under a high electrical stress. Corona discharges occur in the fluid surrounding a conductor. Corona is a form of PD that occurs in gaseous media around conductors and exhibits a certain discharge magnitude and energy. Generally, PD and corona discharges appear as short duration pulses having duration of much less than 1 μs. Both PD and corona discharge activities are often accompanied by emission of sound, heat and chemical reaction. Corona discharges will also emit light when the electrical stress is sufficiently high. The

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magnitude of discharges depends on the size of the voids within a dielectric or the gap between conductors at different potential. The quantity of discharges is related to the number of voids. Corona discharges in the external environment will be of main concern with respect to ignition of the hazardous gases.

To determine the magnitude of discharge activity, PD measurements were performed using an ICM++ instrument with RPA2 filter. The frequency bandwidth used for RPA2 is in the range of 2 MHz to 20 MHz and has an input sensitivity of 200 μV, 0.15 pC.

B. Wound Stator – Areas of Concern with Respect to Corona

Discharge

Corona discharges occur in stator windings due to high potential differences in the endwindings. The discharge may occur at the grading system, phase breaks, coil crossovers and between coil top and bottom legs sharing the same slot.

Major gas groups B, C and D maybe ignited by presence of corona discharge activity and oxygen. Research work presented in [9] and also reported in [5] suggests that a discharge magnitude of 10 nC is still safe for type B gas environment.

IEC Std. 60079-15 recommends that surface discharges be minimized for all high voltage windings. For windings with a rated voltage of 6.6 kV or greater, the use of PD suppressant materials, i.e. a stress grading system is highly recommended. In order to prevent corona discharge activity, detailed attention must be focused on the following areas:

1) Performance of Stress Grading System: Form wound high voltage stator coils utilize a stress grading system in the endarm region and a semi-conducting armour material in the slot portion, as shown in Fig. 1. A good contact between the coil surface and the slot wall avoids PD activity and protects the main or groundwall insulation from degradation. To avoid shorting the stator core laminations, a material with constant conductivity (10-2 to 10-5 S/m), which shows little or no electric field dependence, is normally used [10, 11]. Stress grading composites are applied to the overhang portion of the stator coils with an overlap on the semi-conducting armour coating or tape. These composites typically contain silicon carbide (SiC) fillers that exhibit electric field dependency; a higher conductivity exists where the electric stress is high, and a lower conductivity exists where the field is low [12, 13]. The stress grading system reduces the local surface stress where the field exceeds the breakdown strength of the surrounding medium. This reduction is obtained by modifying the surface impedance of the mainwall insulation. Surface potential distribution for a typical high voltage coil is illustrated in Fig. 2.

In high voltage rotating machines with improper or no stress grading system, the electric field in the endarm region will intensify and very likely lead to corona discharge activity. The energy of the discharge activity may be sufficient to ignite the major gas groups. Therefore, an optimized design of the stress grading system is vital, see Fig. 3.

2) Influence of Endwinding Contamination: One of the causes of corona discharge on the stator winding is the presence of surface contamination, which shorts out the grading system applied to the stator endarms of high voltage machines. Any type of metallic or conductive contamination can set up conditions for either surface discharges to ground or even point discharges between coil endarms. In addition,

excessive surface contamination can increase the intensity or energy of the discharge activity at the outboard end of the grading system.

Fig. 1 A Sample Coil After VPI Treatment

If the surface contamination is uneven, the voltage stress on the insulation can reach levels well in excess of hi-pot values and insulation deterioration will occur as discussed by Weber et al. [14]. To prevent winding discharges and ignition of B, C or D gas groups, surface contamination must be minimized by placing the machines in a clean environment or by cleaning the stator winding frequently, e.g. during periodic maintenance [15].

0

1.00

0.42

0.85

0.71

0.57

0.28

Normalized Surface Potential

Distance from slot exit

0.14

Fig. 2 Measured Surface Potential along the Stress Grading System [16]

3) Sparking/Discharge Activity Between Stator Windings

and Stator Windings to Frame: Other areas where electrical discharge can occur are between adjacent endarms of coils of differing phases, at the crossover points of coils of different phases, or between coil endarms and grounded metal baffles. If the radial clearance between adjacent coils endarms is insufficient, there will be a discharge at this location. Where the clearance between the coil endarm and a ground plane such as a metal baffle or the rotor rings is too small, the potential difference between the two planes will result in discharges. Therefore, establishing proper electrical clearances in the overhangs at the design phase, adhering to minimum clearances at the manufacturing stage, and maintaining the windings in a clean condition are essential if surface discharges

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on the stator winding are to be eliminated [15].

Fig. 3 Corona Discharge Activity at the Stress Grading System

4) Lead Connections and Spacing: lead (cable or bus bar)

connections must have sufficient clearance between individual phases and to the ground. Cable contact with the grounded enclosure must be avoided as this condition can result in strong localized electrical fields that can cause ionization of the surrounding medium, eventually leading to electrical discharges.

VI. SAMPLE PREPARATION AND INCENDIVITY TESTING

A. Statorette Design of 6.6 kV & 13.8 kV used for

Incendivity Testing As described in Section III of this paper, in all cases the test model shall be representative of a complete stator with, where appropriate, corona shield, stress grading, packing and bracing, impregnation and conductive parts such as the stator core. All exposed conductive parts shall be earthed [3]. Based on these criteria, two statorettes with a system rating of 6.6 kV and 13.8 kV were manufactured and VPI’d. Both statorettes consist of two phases with 3 coils in one phase, 5 coils in second phase. Three slots of the statorette share the coil legs from each of the two phases to demonstrate top-to-bottom leg and crossover clearances.

B. Steady State Ignition Test IEC 60079-15 Ed. 4 (Paragraph 22.13.2.3) specifies the following steady state ignition test, which is intended to check for sparking during normal operation:

1) Insulation systems and connection cables shall be tested in an explosive test mixture comprised of (21± 5)% hydrogen-in-air, v/v (by volume) with a sinusoidal voltage of 1.5 times the rated r.m.s. line voltage for at least 3 min. The maximum rate of voltage rise shall be 0.5 kV/s. The voltage shall be applied between one phase and earth with the other phases earthed.

2) No ignition of the explosive test mixture shall occur.

C. Experimental Setup and Test Procedure

Both statorettes 6.6 kV and 13.8 kV were installed individually on a work surface in an explosion test room (see Fig. 4). All normally grounded portions of the assembly were connected to a solid earth ground. To achieve the required homogeneous gas mixture, a non-sparking mixing fan was placed in the core section of the test sample. A flexible plastic tube with internal dia of approx. 0.25” was used to discharge gas into the test enclosure from a compressed gas cylinder, situated in a separate safe area. Three different tanks containing propane, ethylene and hydrogen were used. A second flexible plastic tube of similar size was connected to a sampling pump, such that the sample pump continuously drew gas from the test enclosure and discharged it via connected tubing to a gas analyzer, also located in a safe area.

The statorette assembly was enclosed using a PVC sheet material, which served to contain the explosive fuel-air mixture. The enclosed volume, containing the unit under test was tested following sequence listed below:

1) The volume enclosing the statorette was filled with the

required explosive fuel-air mixture and then purged with the same mixture for a certain time.

2) The sample pump was turned on so that a gas sample stream from the test enclosure was pumped through to the appropriate gas analyzers.

3) Gas analyzers used were calibrated prior to each test run. Both analyzers were able to provide a stable reading within the test specification as shown above in the extract from IEC 60079-15 (Table III). When the fuel-air mixture reached the desired concentration, the gas pump was turned off along with the mixing fan.

4) Individual phases of the 6.6 kV statorette under test were energized at voltage of 10.4 kV (considering system voltage of 6.9 kV x1.5 = 10.35 kV) and for 13.8 kV statorette at voltage of 20.7 kV (13.8 kV x1.5 = 20.7 kV), respectively using the specified rate of rise of 0.5 kV/s. The test voltage was maintained for a period of at least 3 minutes.

5) If no ignition occurred within the 3 minutes, the high-voltage power supply was de-energized.

6) The explosive gas environment was diluted with air until the atmosphere was rendered safe. The testing for 6.6 kV statorette was started with gas Group B; whereas, for 13.8 kV statorette the sequence of testing used was Group D, C and then B.

D. Incendivity Test Results in Explosive Gases The 6.6 kV and 13.8 kV statorettes were tested at 10.4 kV and at 20.7 kV, respectively. After the first phase had been tested for 3 minutes the same procedure was repeated on the second phase. Failure of one phase naturally means that the test as a whole is failed. Experience has shown that ignition does not necessarily occur at the beginning of the test and an explosion can occur at any time during the test duration. After successfully passing the incendivity testing the voltage was then increased on one of the Phases to determine the level at which the B gas mixture would detonate. Complete test results are shown Tables IV and V.

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Fig. 4 Statorette Undergoing Incendivity Testing

TABLE IV TEST RESULTS – STATORETTE 6.6 KV

TEST PERFORMED ON AS-IS SAMPLE IN GAS GROUP “B” – NO REMEDIAL WORK PERFORMED

Test # Phase* Voltage (kV) Duration (sec) Result 1 1 9.9 195 sec Pass 2 1 10.4 195 sec Pass 3 2 9.9 195 sec Pass 4 2 10.4 195 sec Pass 5 2 11.0 185 sec Pass 6 2 11.5 185 sec Pass 7 2 12.0 8 sec Fail 8 1 11.0 190 sec Pass 9 1 11.6 60 sec Fail

*Phase 1: (T1-T2) 3 coils; Phase 2: (T3-T4) 5 coils.

TABLE V TEST RESULTS – STATORETTE 13.8 KV

TEST PERFORMED ON AS-IS SAMPLE – NO REMEDIAL WORK PERFORMED

Test # Gas Type

Phase Tested

Voltage (kV)

Duration (sec) Result

1 D 1 20.7 195 Pass 2 C 1 20.7 195 Pass 3 C 2 20.7 195 Pass 4 B 1 16.5 195 Pass 5 B 1 18.8 195 Pass 6 B 2 16.5 195 Pass 7 B 2 18.8 195 Pass 8 B 2 20.7 195 Pass 9 B 1 20.7 195 Pass 10 B 1 22.5 10 Fail 11 B 2 22.5 0 Fail

*Phase 1: (T1-T2) 3 coils; Phase 2: (T3-T4) 5 coils.

VII. PD DATA ACQUISITION AND INTERPRETATION

PD measurements were performed on both statorettes using an ICM++ (RPA2) instrument. As shown in Tables VI and VII, the peak magnitude (Qm) of the pulses that has a repetition rate of 10 pulses per second are listed. The acquired PD data for individual phases showed positive pulse predominance. The extracted Qm data from several PD fingerprints indicated that the discharge activity was close to the surface and had positive

predominance at Incendivity test levels of 10.4 kV and 20.7 kV. Based on the acquired PD data, the discharge magnitude (Qm) of greater than 7.9 nC, if related to the surface activity, appears as a critical level for the ignition of gas group “B”. As an example in 13.8 kV statorette when voltage was increased from 20.7 kV to 22.5 kV detonation of explosive gas from Group B occurred. This is possibly due to increase in the surface discharge activity from 7.9 nC to a higher level.

TABLE VI PD MEASUREMENTS (6.6 KV STATORETTE) – ICM++

Test Voltage (kV)

T1-T2 (nC) T3-T4 (nC) Qm (+) Qm (-) Qm(+) Qm (-)

6.9 0.30 no activity 0.26 0.08 10.4 0.30 0.10 0.30 0.11

TABLE VII

PD MEASUREMENTS (13.8 KV STATORETTE) – ICM++ Test Voltage

(kV) T1-T2 (nC) T3-T4 (nC)

Qm (+) Qm (-) Qm(+) Qm (-) 13.8 3.6 no activity 3.1 1.1 20.7 7.9 no activity 4.0 1.2

VIII. CONCLUSIONS

In this paper, critical areas in a stator winding insulation system were identified as potential contributors to corona discharges. The magnitudes of PD associated with detonation of explosive gas from Group B were correlated. It was demonstrated that the insulation system of the medium voltage ac stator can operate in explosive atmospheres without causing detonation of the gases.

A stator insulation system, operating at or above its nominal line-line and line-ground voltages will have a certain level of PD and corona activity. Present study suggests that PD magnitudes greater than 7.9 nC, if related to surface activity, may be a critical level for the ignition of gas group B. Therefore, it is vital that insulation systems of stator windings be designed and constructed such that the level of PD and corona discharge is less than the critical level. This will ensure that explosive mixtures of various gases will not be detonated even if the gases are in intimate contact with the stator winding.

IX. ACKNOWLEDGEMENTS

The authors would like to thank the GE Peterborough Technology, Manufacturing and laboratory teams for manufacturing and testing of the statorettes. Thanks are also extended to George Lobay of Canada Dept. of Natural Resources CANMET, Ottawa, Ontario, for performing the Incendivity testing and to Domenic Somma of CSA for witnessing all of the tests.

Thanks also to D. H. Messervey, without whose project support we could not have completed this study.

X. REFERENCES

[1] ANSI/NFPA 70 (2011), National Electrical Code® (NEC®) 2011, National Fire Protection Association.

[2] CSA C22.1 (2009), Canadian Electrical Code (CEC) Part 1 Canadian Standards Association.

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[3] International Electrotechnical Commission (IEC) IEC 60079-15, 2010 Ed. 4: Electrical Apparatus for Explosive Gas Atmosphere - Part 15: Construction, Test and Marking of type of Protection “n” Electrical Apparatus.

[4] Bharat Mistry, William G. Lawrence, Evans Massey, Paul S. Hamer, “Proposed Revisions to IEC 60079-15: How has Harmonization Affected Ex “nA” Motors?”, IEEE/PCIC Europe 2009.

[5] Jussi Rautee, Frank Lienesch, Tom Liew, “Safety improvements of non-sparking and increased safety motors”, IEEE Petroleum and Chemical Industry Conference Europe - Electrical and Instrumentation Applications, PCIC Europe 5th, 2008.

[6] NFPA 497, 1997 Recommended Practice for Classification of Flammable Liquids, Gases, or Vapors and of Hazardous (Classified) Locations for Electrical Installations in Chemical Process Areas.

[7] International Electrotechnical Commission (IEC) IEC 60079-0, 2007 Explosive Atmospheres - Part 0: Equipment - General Requirements.

[8] Meredith K.W Stranges, Greg C. Stone, Dennis L. Bogh, “Voltage Endurance Testing: Stator Insulation Systems for Inverter-fed Machines” IEEE IAS, Vol. 15. No.6.ISSN 1077.2618, November/December 2009.

[9] Von Pidoll, U. Brzostek, E. Froechtenigt, H.-R Determining the incendivity of electrostatic discharges without explosive gas mixtures. IEEE Transactions on Industry Applications, Vol. 40, Issue 6, pp 1467- 1475, 2004.

[10] F. P. Espino-Cortes, E. A. Cherney, S. Jayaram, “Effectiveness of Stress Grading Coating on Form Wound Stator Coil Groundwall Insulation under Fast Rise Time Pulse Voltages”, IEEE Transactions on Energy Conversion, Vol. 20, pp. 844- 851, 2005.

[11] J.A. Allison, “Understanding the need for Anti-corona materials in High Voltage Rotating Machines”, 6th International Conference on Properties and Applications of Dielectric Materials, pp. 860-863, 2000.

[12] R. Malamud, I. Cheremisov, “Anti-Corona Protection of the High Voltage Stator Windings and Semi-Conductive Materials for its Realization”, IEEE International Symposium on Electrical Insulation, pp. 32 –35, 2000.

[13] J. P. Mackevich, J. W. Hoffman, “Insulation Enhancement with Heat-Shrinkable Components Part III: Shielded Powder Cable”, IEEE Electrical Insulation Magazine, pp. 31-40, 1991.

[14] K. Weber, M. Stutt, R. Rehder, and J. Dymond, “Finite Element Field Analysis of Non-uniform Surface Contamination on High Voltage Winding of Electric Machines”, IEEE-CEIDP, Oct. 1996.

[15] J. Dymond, “Sparking, Electrical Discharge, and Heating in Synchronous and Induction Machines: Can it be Controlled?”, IEEE Trans. On Industry Applications, Vol. 34. No. 6, Nov. 1998.

[16] R. Omranipour and S. U. Haq, “Evaluation of Grading System of Large Motors AC Stator Windings”, IEEE-ISEI, 2008.

XI. VITA

Saeed Haq received his B.Sc. degree in Electrical

Engineering from UET, Peshawar, Pakistan, in 1991, M.A.Sc. degree from the University of Windsor, Windsor, ON, Canada, in 2001, and his Ph.D. degree from the University of Waterloo, Waterloo, ON, in 2007. During his Ph.D. program, his main research interest was to study the insulation problems in drive-fed medium-voltage motors. Dr. Haq is a registered Professional Engineer in the Province of Ontario, Canada. In the past, he was involved in extensive volunteer work for the IEEE Conference on Electrical Insulation and Dielectric Phenomena (CEIDP) and International Symposium on Electrical Insulation. In 2007, he joined the GE Large Motors & Generators Technology team at Peterborough, Ontario, Canada, as an Insulation Engineer. His area of interest is in the development of insulation systems for large rotating electric machines.

Bharat Mistry received his B.E degree in Electrical

Engineering from South Gujarat University, Surat, India in 1972. He has been a practicing Professional Engineer in Ontario since 1988. He has served industry in many areas including quality, maintenance and design and application. During the past 15 years, he has devoted his time to the design and application of large rotating electrical machines for hazardous and non-hazardous locations built to national and international standards. He has published many technical papers in “Electrical India”. He has also been author and co-author of many IEEE/PCIC papers. He is a technical adviser for the development of NEMA MG-1 (Global standard), IEEE 1349, TC31/WG27- IEC 60079 series standards of explosive gas atmosphere.

Ramtin Omranipour graduated with a B.Sc. in Electrical

Engineering from the University of Science and Technology, Tehran, Iran, in 1991. Between 1991 and 1999, he worked as an Electrical Engineer for multiple organizations where he was in charge of maintenance and repair of electrical systems and equipment including high voltage transformers and rotating electric machines. In 2000, he began graduate studies at the University of Waterloo, Ontario, Canada, where he conducted research on high voltage insulating materials, mainly silicone-based products. In 2002, he joined the GE Large Motors & Generators Technology team at Peterborough, Ontario, Canada, as an Insulation Engineer. His area of interest is the design and development of large AC motors and generators, with specific emphasis on the development of insulation systems for large rotating electric machines.