Study on the Wetting Process and Its Influencing Factors of Pollution Deposited on Different Insulators Based on Leakage Current

678 IEEE TRANSACTIONS ON POWER DELIVERY, VOL. 28, NO. 2, APRIL 2013

Study on the Wetting Process and Its InfluencingFactors of Pollution Deposited on DifferentInsulators Based on Leakage Current

Zhijin Zhang, Xingliang Jiang, Haizhou Huang, Caixin Sun, Jianlin Hu, and David Wenzhong Gao

Abstract—Pollution-induced flashover has a serious threat onthe safe and reliable operation of power systems. It is known thatthe pollution flashover voltage is directly related to the wetting de-gree of the pollution layer. But the wetting performance character-istics and control method of pollution layer on insulators have notbeen properly specified in the existing pollution test standards. Inthis paper, the wetting processes of the pollution layer on differenttypes of insulators have been studied in an artificial fog chamber.In our test studies, the leakage current on the surface of pollutedinsulators under a different test environment is measured and thenthe curves of leakage current varying with time are plotted. Fur-thermore, the main influencing factors of the wetting process ofthe pollution layer have been analyzed in this paper. Test resultsshow that the wetting process of the pollution layer can be charac-terized well through the change of leakage current, and when theleakage current reaches the maximum value, the pollution layeris saturated with fog. Specifically, during the wetting process, theleakage current gradually increases until the maximum value andthen decreases; the time for the pollution layer to become satu-rated is dependent on the salt-deposited density (SDD), the steamfog input rate, the temperature in the artificial fog chamber, andthe type of insulators. It is found that with the increase of SDD andthe decrease of the steam fog input rate and the temperature inthe climate chamber, the necessary wetting time will increase, andthe more complex the insulator structure is, the longer the wettingtime will be.

Index Terms—Influencing factors, insulators, leakage current,pollution, wetting process.

I. INTRODUCTION

U NDER FOG, dew, drizzle and other adverse weatherconditions, polluted insulators may flashover under a

lower applied voltage. So far though, the flashover accidentcaused by pollution is second to the most harmful one causedby lightning–the loss caused by pollution flashover accidents is

Manuscript received December 06, 2011; revised May 14, 2012; acceptedOctober 19, 2012. Date of publication February 26, 2013; date of current versionMarch 21, 2013. This work was supported by the Fundamental Research Fundsfor the Central Universities (No. CDJZR12110020). Paper no. TPWRD-01034-2011.Z. Zhang, X. Jiang, H. Huang, C. Sun, and J. Hu are with the State Key Lab-

oratory of Power Transmission Equipment and System Security and New Tech-nology, Chongqing University, Chongqing 400044, China (e-mail: [email protected]; [email protected]; [email protected]; [email protected];[email protected]).D. W. Gao is with Department of Electrical and Computer Engineering, Uni-

versity of Denver, Denver, CO 80208 USA (e-mail: [email protected]).Color versions of one or more of the figures in this paper are available online

at http://ieeexplore.ieee.org.Digital Object Identifier 10.1109/TPWRD.2012.2226758

ten times that caused by lightning [1], [2]. So great attention hasbeen paid to the research of pollution flashover performanceand its mechanism, and a lot of research work has been carriedout [1]–[28].The studies on flashover performance of polluted insulators

are mainly conducted experimentally in order to analyze the re-lation between flashover or withstand voltage and pollution de-gree and the influencing factors of pollution flashover perfor-mance [1]–[9]. For an investigation of the pollution flashoverperformance and mechanism, it is very important to choose arational test method. Research results indicate that the wettingmethod and wetting degree of the pollution layer have a signifi-cant influence on the flashover voltage. And many studies aboutthis have been carried out worldwide.Currently, the wetting methods for the pollution layer on in-

sulators are mainly cold fog, warm fog, and steam fog methods[1], [2], [10]–[12]. The influence of different wetting methodson the wetting process and the wetting degree of pollution layeris different. And this difference will influence the flashover per-formance of the polluted insulators.Studies in paper [1] indicate that in order to evenly wet the

pollution layer on the surface of the entire insulator string, thedifference in temperature between the insulator and fog chambershould not exceed 2 C and the temperature gradient should notexceed 1 C m. It is shown in paper [2] that in order to ob-tain the stable withstand voltage, the maximum water contentin fog should be in the range of 3.5–10 during the wet-ting process. The influence of concentration and particle sizeof fog and the temperature in the fog chamber on the pollutionflashover voltage have been studied in [13] and [14]. The ap-propriate condition for the pollution flashover test is proposedto be as follows: the concentration of fog shall be 3–7 ;the particle size of fog 5–20 ; the difference in temperaturebetween test sample and fog chamber 6–7 C.The measurement of resistivity of pollution layer is com-

plicated and time-consuming. When test samples were appliedwith a low voltage (LV), the changes of leakage current duringthe wetting process of pollution layer can be measured andmon-itored. As soon as the leakage current reaches the maximumvalue, the pollution layer is saturated [15].The changes of leakage current on the insulator surface

wetted by different types of fog have been studied. The studiesin [16]–[18] indicated the following: the time needed fromthe beginning of wetting to saturated wetting is the shortestwhile the rising and descending gradient of leakage currentis the highest if cold fog is used; the leakage current changes

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Fig. 1. Schematic diagram of the tested circuit.

slowly and has a higher peak value if warm fog is used; foran insulator wetted by steam fog, the rising and descendinggradient of leakage current is smaller and the washing effect ofsteam fog upon the pollution is not significant. Through pollu-tion flashover tests, it was found [16]–[18] that the flashovervoltage is the highest on the insulator strings wetted by coldfog and the lowest by steam fog, while the flashover voltageis in between for the case of warm fog. Similar results werefound in [19]–[23]. Based on research results of many researchinstitutes, the standards of IEC 60507 and GB/T 4585 providea recommendation for the input rate of steam fog and testtemperature in pollution tests.Based on the aforementioned text, the wetting status of the

pollution layer on the insulator surface has an influence on theelectrical performance of the polluted insulator, and there aremany complicated factors that influence the wetting process.Up until now, pollution flashover accidents have continuouslyremained as big concerns for the power grid despite the factthat many technical and management measures had been takento prevent pollution flashover in many countries. The safe op-eration of the grid still bears the risk of large-area pollutionflashover. From the perspective of improving experimental testmethods, different types of porcelain, glass, and polymeric in-sulators were taken as test samples in this paper to study thewetting process of pollution layers and their influencing factors.Our test results provide some useful recommendations for arti-ficial pollution testing.

II. TEST FACILITIES, SPECIMENS, AND TEST PROCEDURES

A. Test Facilities

All tests were carried out in a chamber made of glass. Thischamber has a diameter of 65 cm and a height of 100 cm. Thepressure and humidity can be controlled in the range of 98.6kPa 10 kPa and 30% 100%, respectively. The steam fogwas generated by an automatic electric heating steam generatorHX-7.5D with a rated capacity of 1.0 kg/h. The flow of steamfog can be regulated through a valve. The test voltage was sup-plied by the YDW-50/50 ac test transformer with a rated voltageof 50 kV and a rated current of 1 A. The partial discharge of thistransformer is less than 10 pC.The test circuit is shown in Fig. 1, where ac denotes the ac

power supply, denotes the protection resistor, F denotes thecapacitive divider, H denotes the bushing, E denotes the testchamber, S denotes the test insulator, denotes the samplingresistor, G denotes the control panel, and Z denotes the steamgenerator.

TABLE IDIMENSIONS AND PROFILES OF TESTED INSULATORS

During the test, the temperature and humidity were mea-sured by a temperature and humidity measuring instrument,respectively; the voltage was measured by a voltmeter and theSGB-200 ac capacitive divider with a precision of 2%. Througha data-acquisition (DAQ) card, the voltage waveform obtainedfrom the LV side of the capacitive divider and the leakage cur-rent waveform obtained from a precision noninductive resistorwere recorded by a computer in real time. The resistor is woundnoninductively and two such resistors each with a resistanceof 50 were connected in series to obtain a resistance of 100. The power and the maximum withstand leakage of eachresistor are 100 W and 2 A, respectively. In order to reduce theinterference coming from the test circuit and outside noise, adouble-shielded cable was taken as the signal transmission line.

B. Test Specimens

The specimens are five types of porcelain, glass, and poly-meric insulator (types A, B, C, D, and E). The specific parame-ters and profile of these insulators are shown in Table I, whereH (in millimeters) is the configuration height, D (in millime-ters) is the shed diameter, and L (in millimeters) is the creepagedistance.

C. Wetting Test Procedures of the Pollution Layer onInsulators

According to rational standards [11], [12], the test proceduresare as follows.1) Preparation of specimens: First, every specimen wascleaned using the solution so that all traces ofdirt and grease were removed. And then they were washedby water until a large area of water films appeared ontheir surface. The specimens are then dried naturally. Forpolymeric insulators, the surfaces of the samples werecoated by a very thin layer of dry kieselguhr to destroy thehydrophobicity.


Fig. 2. Condensed waveform of leakage current.

2) Polluting: The insulators were polluted by the quantitativecoating with pasting method. First, the required amountof sodium chloride and kieselguhr were calculated andweighed according to the specified SDD, NSDD, and thesurface areas of the specimens. Then, the sodium chlorideand kieselguhr were mixed to slurry with an appropriatevolume of deionized water . At last,these specimens were polluted uniformly.

3) Drying: These polluted insulators were dried naturally for24 h.

4) Voltage applying: Specimens were suspended vertically inthe test chamber and applied a constant voltage. Mean-while, the steam generator was started, and wetting of thepollution layer was accomplished by steam fog. Duringthe test, the flow of steam fog, the temperature of the fogchamber, and the leakage current on the insulator surfacewere measured and recorded. The change of leakage cur-rent is monitored; when it reaches the maximum value, thepollution layer is considered to be saturated. At this mo-ment, the time needed for reaching saturation and the cor-responding value of leakage current were recorded. Theleakage current waveform is shown in Fig. 2.

III. TEST RESULTS AND ANALYSIS

A. Influence of SDD on Saturated Wetting of the PollutionLayer

The wetting processes of types A, C, and E insulators withdifferent salt-deposited densities were studied through tests (thetest condition is as follows: NSDD 0.2 , temperaturein the fog chamber is 20 , and input velocity of steam fogis ). During the wetting process, the type Ainsulator and the type C insulator were applied with a constantvoltage of 1 kV, while the type E polymeric insulator was ap-plied with a constant voltage of 4 kV. The leakage current wave-forms were recorded and the curves of leakage current varyingwith time are plotted in Fig. 3.From Fig. 3, we can obtain the following conclusions: SDD

has some influence on the wetting process of pollution on theinsulator surface. The time from the beginning of the wettingprocess to the point when the pollution layer is saturated will

Fig. 3. Leakage current waveform under different SDDs: (a) type A, (b) typeC, and (c) type E.

increase with increasing SDD. Taking the type A insulator asan example, when the value of SDD is 0.05 , 0.10

, 0.15 , and 0.25 , the time from thebeginning of the wetting process to the point when the pollutionlayers are saturated wet is 5.8, 6.8, 7.4, and 8.2 min, respec-tively. The reason is that there is a thicker pollution layer onthe insulator with a higher value of SDD. So this pollution layerwill need more time to be wetted.

B. Influence of the Flow Rate of Steam Fog on the WettingProcess of Pollution

Tests on the wetting processes of the pollution layer on typeA, C, and E insulators were carried out in the fog chamber


Fig. 4. Leakage current waveform under different steam fog input rates: (a)type A, (b) type C, and (c) type E.

with a different flow rate of steam fog (test condition NSSD, SDD , and the temperature of

the fog chamber is ). The test procedure is the sameas that described before. The curves of leakage current varyingwith time are plotted in Fig. 4.According to Fig. 4, the following conclusions can be

obtained:1) With the increasing input rate of steam fog, the decreasingwetting time is nonlinear. When the input rate is relativelysmall, the wetting time will decrease significantly with theincrease of an input rate of steam fog. But when the inputrate is increased to a certain high value, with further in-creasing the input rate, there is very little change in the

wetting time. The reason is that the absorption of water andthe wetting process of the pollution layer need more time.

2) The influence of the input rate of steam fog on the max-imum value of leakage current on the pollution layer whenit is saturated is not significant. For the type A insulator,when the input rate of steam fog is ,

, , and ,the maximum value of leakage current is 4.2, 4.3, 4.2, and4.1 mA, respectively.

C. Influence of Temperature in the Fog Chamber on theWetting Process

Under the condition that NSDD is 0.2 , SDD is 0.1and the input rate of steam fog is ,

the wetting processes of pollution on type A, C, and E insulatorswere studied in fog chamber with different temperature. Theprocedure to apply voltage on insulators is the same with thecase described before. Under different temperatures, the curvesof leakage current varying with time are plotted in Fig. 5.Fig. 5 indicates the following:1) The temperature has a significant influence on the wettingprocess of pollution on the insulator surface. The wettingtime of all three types of insulators increases with the in-creasing temperature. For the type A insulator, when thetemperature is C, C, and C, thewetting time from the beginning of the wetting process tothe point when the pollution layers are saturated is 5.2, 6.8,and 10.2 min, respectively. The reason is that with the sameinput rate of steam fog, the liquid water content decreaseswith the increasing of temperature. The decreasing liquidwater content in the fog chamber makes the wetting timebecome longer. During the test, it is found that when thetemperature is higher than 35 C, the liquid water contentof fog decreases. It is also found that the high temperaturehas a drying effect on the pollution layer and that thereis nonuniform wetting between the upper and lower sur-face of the insulator. The high temperature is not good forthe wetting of the pollution layer. So for artificial pollutiontests, the temperature in the fog chamber should be keptlower than 35 C during the wetting process of pollution.

2) The temperature in the fog chamber has some influence onthe leakage current. With the increasing temperature, themaximum value of leakage current first increases and thendecreases. When the temperature is C, C,and C, for the type A insulator, the maximum valueof leakage current is 4.1, 4.2, and 3.6 mA, respectively; forthe type C insulator, it is 3.5, 3.7, and 3.2 mA, respectively;for the type E insulator, it is 4.5, 4.6, and 4.3 mA, respec-tively. The reasons could be expressed as follows: first,the positive temperature coefficient of the conductivity ofthe pollution layer makes the conductivity increase withthe increasing temperature. And then because of the effectof leakage current and the drying effect of ambient tem-perature, the conductivity of the pollution layer decreases.When the temperature is low, the first reason dominates thechange of conductivity and makes the maximum leakagecurrent increase gradually. On the other hand, when the


Fig. 5. Leakage current waveform under different temperature. (a) Type A; (b)type C; (c) type E.

second reason plays the major role, the maximum value ofleakage current decreases gradually in the chamber withthe higher temperature.

D. Influence of the Insulator Type on the Wetting Process ofthe Pollution Layer

Under the test condition that NSDD is 0.2 , SDD is0.1 , the temperature is , and the input rate ofsteam fog is , the wetting processes of the pol-lution layer on five types of insulators were studied in the fogchamber. The procedure to apply voltage on insulators is thesame with cases described before. For different types of insula-tors, the curves of leakage current varying with time are plottedin Fig. 6.From Fig. 6, the following conclusions can be obtained:

Fig. 6. Leakage current waveform of various insulators.

1) Under the same condition, the values of leakage current ondifferent types of insulators are very different. The reasonscould be expressed as follows.The surface resistance of the pollution layer is

(1)

where is the equivalent diameter of the polluted in-sulator and is the surface conductivity. The equivalentdiameter of the insulator, which is expressed in centime-ters, is defined [26] as

(2)

where is the form factor of the insulator

(3)

where is the insulator diameter as a function of theposition on the insulator.Different types of insulators have different values of ,, and . So the resistance values of pollution layer ondifferent types of insulators are different despite the factthat the conductivity keeps a constant. Hence, when ap-plied with the same voltage, the values of leakage currentof different types of insulators are different.

2) The wetting time of the pollution layer on different typesof insulators is very different. The wetting of the pollutionlayer on the type B insulator takes the shortest time at 5.6min. And the wetting of the pollution layer on the type Einsulator takes the longest time at 23.8 min. The reasonsare related to the structure of insulators. For the type Binsulator with a simple structure, there are no under-ribsand the upper and lower surfaces are smooth. So the pollu-tion layer on its surface will be easily wetted. While for thetype E polymeric insulator, because of the hydrophobicity,water is not easily absorbed by pollution. Hence, the wet-ting time of the type E polymeric insulator is longer. Fortypes A, C, and D insulators, despite the fact that their sur-faces are hydrophilic because their structure is complicatedand there are many edges which are not easily wetted on


TABLE IIWETTING TIME OF THE POLLUTION LAYER ON

INSULATORS WITH DIFFERENT SDDS (MIN)

their lower surface, the wetting time of the pollution layerof types A, C, and D insulators is between that of type Band type E insulators.

IV. DISCUSSIONS AND ANALYSIS

For the artificial test research on flashover performance of in-sulators, the wetting state and wetting degree have a direct influ-ence on the test results. It is necessary to take a reasonable testprocedure in artificial pollution tests. The related standards [15],[24] provide the recommended test procedures without specificdetails.Under the condition that NSDD is 0.2 , temperature

is , the input rate of steam fog is ,we repeat the wetting tests of the pollution layer on three typesof insulators with different SDDs five times. Using the samemethod with that mentioned before to apply voltage on insu-lators, we obtain the wetting time from the beginning of wet-ting to the point when the pollution layer on insulators with dif-ferent values of SDD becomes saturated. Test results are shownin Table II.From Table II, the wetting time of the pollution layer on the

insulator with different values of SDD is in the range of 6–10min for the type A and C insulator. While for the type E insu-lator, it is in the range of 13 20 min. In standards [15] and[24], the test procedure for the type A insulator stipulates thatbefore and during the insulators are applied voltage, the inputrate of steam fog should be high enough to make the conduc-tivity of the pollution layer reach the maximum value in 2040min. The test procedure for the type B insulator stipulates thatthe input rate should be and then be adjustedaccording to the wetting state. According to our test results, itis found that the pollution layer of insulators almost becomessaturated under the effect of steam fog in 30 min. Hence, whenthe up and down method or the withstand method are used tocarry out the tests of pollution flashover performance, the input

TABLE IIITEST RESULTS OF POLLUTION FLASHOVER PERFORMANCE

FOR DIFFERENT TYPES OF INSULATORS

rate should be at least and the duration thatinsulators are applied voltage should not be less than 30 min.For the control of temperature in the fog chamber, the stan-

dards [15], [24] recommend controlling the temperature in therange of 5 to 40 . Research results in this paper indicate thatthe temperature has some influence on the wetting process ofpollution layers. Other research results [5], [27], [28] also in-dicate that the temperature has an influence on the pollutionflashover voltage. Hence, based on the related research results,it is suggested that the temperature in the fog chamber should bekept at 35 C during the wetting process of pollution. In addi-tion, the temperature should remain consistent in each test. Oth-erwise, the temperature correction of pollution flashover voltageneeds to be carried out.According to the analysis from before, we studied the 50%

flashover voltage of type A, C, E insulators with different pollu-tion degrees. Tests were carried out in a artificialfog chamber. Test power was supplied by a 150-kV/900-kVAtest transformer. The specific parameters and principles of testequipment are introduced in paper [6]. During each test, theinput rate of steam fog is , the temperatureis , and the value of NSDD is 1 . We usedthe up and down method to apply voltage on insulators, and se-lected 20 effective test data points to calculate the 50% flashovervoltage. The detailed test procedures are introduced in [29]. Thetime duration that insulators were applied voltage is 30 and 60min, respectively. Test results are shown in Table III.From the test results in Table III:1) using the method proposed in this paper to carry out pollu-tion flashover tests, the dispersion of results is small, andthe relative errors of all test results are less than 6%;

2) when applied a withstand voltage for 30 min, the 50%flashover voltage of insulators is very close to that of theinsulator when applied a withstand voltage for 60 min; therelative error between tests with the two different time du-rations is less than 2%;


3) with the increase of SDD, the pollution flashover voltagedecreases; and the relationship between flashover voltageand SDD satisfies the following formula [1]–[6]:

(4)

where is a coefficient related to the shape of the insulatorand the type of voltage; SDD is the salt-deposited density,in ; is a characteristic exponent characterizingthe influence of SDD on and is related to the config-uration and material of insulators and the type of voltage.From Table III, the relationships between of the insu-lators when applied a withstand voltage for different timedurations and SDD can be expressed as in (5)–(7).

For the type A insulator

(5)

For the type C insulator

(6)

For the type E insulator

(7)

To summarize, for each sample in this test, it is found thatthe value of and the relationship between and the SDDof the insulator when applied a withstand voltage for 30 minare basically the same as that of the insulator when applied awithstand voltage for 60 min. Hence, for test research on theflashover performance of polluted insulators, it is acceptable toapply the withstand voltage on test samples for just 30 min.

V. CONCLUSIONS

1) For porcelain- and glass-type insulators, the wetting timefrom the beginning of the wetting process to the point whenthe pollution layers are saturated wetting is in the range of5 20 min. And it is in the range of 15 25 min for poly-meric insulators. The wetting time is dependent on SDD,the input rate of steam fog, temperature in the fog chamber,insulator shape, and so on. For the withstand voltage test ofpolluted insulators, it is suggested that the steam fog shouldflow into the fog chamber after the insulator is applied to apredetermined voltage and that insulator should be applieda withstand voltage for 30 min.

2) Temperature has an influence on the wetting time of thepollution layer. When the temperature in the fog chamberis higher than 35 C, the liquid water content of steamfog decreases significantly, the wetting process becomesslow, and the insulator surface could be dried by the hightemperature. Hence, the temperature in the fog chambershould be controlled below 35 C in the artificial pollutiontest.

3) It takes some time for the pollution on insulator to absorbwater under steam fog. If the input rate of the steam fog istoo small, the wetting time of the pollution layer increasessignificantly, thus causing the efficiency of the test to de-crease. On the other hand, if the input rate of the steam fogis too high, the washing effect of liquid water of fog on thepollution layers increases. Hence, it is recommended thatthe input rate of steam fog should be controlled in the rangeof in the artificial pollution test.

ACKNOWLEDGMENT

The authors would like to thank all members of the externalinsulation research team at Chongqing University for their hardwork to obtain the experimental data in this paper.

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[29] Z. Zhang, X. Jiang, C. Sun, J. Hu, andH.Huang, “Study of the influenceof test methods on DC pollution flashover voltage of insulator stringsand its flashover process,” IEEE Trans. Dielectr. Elect. Insul., vol. 17,no. 6, pp. 1787–1795, Dec. 2010.

Zhijin Zhangwas born in Fujian Province, China, inJuly 1976. He received the B.Sc., M.Sc., and Ph.D.degrees in electrical engineering from ChongqingUniversity, Chonqing, China, in 1999, 2002, and2007, respectively.He is a Professor of the College of Electrical

Engineering, Chongqing University, Chonqing,China. His main research interests include highvoltage, external insulation, numerical modeling,and simulation. He is the author or coauthor ofseveral technical papers.

Xingliang Jiangwas born in Hunan Province, China,on July 31, 1961. He received theM.Sc. and Ph.D. de-grees in electrical engineering from Chongqing Uni-versity, Chongqing, China, in 1988 and 1997, respec-tively.He was with Shaoyang Glass Plant, Shaoyang,

Hunan Province; Wuhan High Voltage ResearchInstitute, Wuhan, Hubei Province; and the Collegeof Electrical Engineering, Chongqing University.His special fields of interest include high-voltageexternal insulation as well as transmission-line icing

and protection.

Haizhou Huang was born in Chongqing, China, inApril 1986. He received the B.Sc. degree in automa-tion from Qingdao University of Science and Tech-nology, Shandong, China, in 2009 and is currentlypursuing the M.Sc. degree in electrical engineeringat Chongqing University, Chonqing, China.His main research interests include high voltage

and external insulation.

Caixin Sun was born in Chongqing, China, onDecember 13, 1944. He Graduated from ChongqingUniversity, Chonquing, China. He received theB.Sc. degree in power system and automation fromChonqing University, Chonqing, China, in 1969.He is a Professor andDoctorate Advisor of the Col-

lege of Electrical Engineering, Chongqing Univer-sity. His current research interests include externalelectrical insulation technology in complex climaticenvironments, online detection of insulation condi-tions, and insulation fault diagnosis for high-voltage

apparatus and high-voltage techniques applied to biomedicine.Prof. Sun is a member of the Chinese Academy of Engineering.

Jianlin Hu was born in Hubei Province, China, inJanuary 1978. He received the B.Sc. and M.Sc. de-grees in electrical engineering from Chongqing Uni-versity, Chongqing, China, in 2001 and 2003, respec-tively, where he is currently pursuing the Ph.D. de-gree in electrical engineering.He has been a Teacher in the College of Electrical

Engineering, Chongqing University, since 2003. Hismain research interests include high-voltage externalinsulation.

David Wenzhong Gao received the M.S. and Ph.D.degrees in electrical and computer engineering fromthe Georgia Institute of Technology, Atlanta, in 1999and 2002, respectively.His current teaching and research interests include

renewable energy and distributed generation, powerdelivery, power-electronics applications, powersystem protection, power system restructuring, andhybrid electric propulsion systems.

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