• Title/Summary/Keyword: Insulation deterioration

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A Study on Monitoring Means of Insulation deterioration of Electric Power Cable (전력케이블 열화 감시방안에 관한 연구)

  • Han, Hag-Su;Min, Kyung-Yun;Ryu, Ki-Son
    • Proceedings of the KSR Conference
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    • pp.1522-1528
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    • 2007
  • Electric Power cable is the apparatus that receives electric power from the Korea Electric Power Corporation and supplies electric power to electric train and annex facilities of each railway station. With substantial ripple effect during power blackout accidents, such power blackout accidents must be coped with by discriminating the status of insulation deterioration of electric power cable in advance. Discrimination of insulation deterioration of the electric power cable is normally executed while the power is disconnected and it is very difficult to discover, at early stage, the insulation deterioration of the power cable in operational state since the duration of inspection is limited. This research aims to consider method of diagnosing the insulation deterioration of electric power cable in On-Line state rather than diagnosis in Off-Line state in order to secure reliability of power supply by reducing duration of power blackout (accidental blackout and blackout during works) and by seeking reduction in equipment and manpower used in diagnosis of deterioration through prevention of the accident itself prior to occurrence through early restoration of accident due to insulation deterioration of the electric power cable and assessment of performance of the cable under operation.

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Insulation Deterioration of AC/DC Section Insulators for Electric Railroad Catenary. (전기철도 교/직 절연구분장치의 절연열화 현상)

  • 최규형
    • The Transactions of the Korean Institute of Electrical Engineers B
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    • v.52 no.1
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    • pp.16-22
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    • 2003
  • While passing through the AC/DC section insulators installed at electric railroad catenary, some electric trains undergo mis-operation of main circuit breaker after AC/DC change-over operation. This paper provides insulation resistance measurements of AC/DC section insulators, which confirm the insulation levels of section insulators are below the standard of insulators. The insulation deterioration and pantograph arrangement on the electric train can produce voltage impression on section insulator which induces mis-operation of main circuit breaker To mitigate the insulation deterioration of the section insulator installed at underground railroads, the section insulators have been cleaned periodically, but section insulator structure should be modified to make the section insulator performance perfect. Based on the above analysis, effective modification method of AC/DC section insulator is provided.

Assessment of Insulation Deterioration in Stator Windings of High Voltage Motor (고압전동기 고정자 권선의 절연열화 평가)

  • Kim, Hee-Dong;Kong, Tae-Sik
    • The Transactions of The Korean Institute of Electrical Engineers
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    • v.61 no.5
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    • pp.711-716
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    • 2012
  • To assess the insulation deterioration of stator windings, diagnostic and AC breakdown tests were performed on the eleven high voltage (HV) motors rated at 6kV. After completing the diagnostic tests, the AC overvoltage test was performed by gradually increasing the voltage applied to the stator windings until electrical insulation failure occurred, to obtain the breakdown voltage. Stator winding of motors 1, 3, and 8 failed at above rated voltage at 14 kV, 13.8kV, and 16.4kV, respectively. The breakdown voltage of three motors was higher than expected for good quality windings in 6kV motors. Based on deterioration evaluation criteria, the stator winding insulation of eleven HV motors are confirmed to be in good condition. The turning point of the current, $P_{i2}$, in the AC current vs. voltage characteristics occurred between 5kV and 6kV, and the breakdown voltage was low between 13.8kV and 16.4kV. There was a strong correlation between the breakdown voltage and various electrical characteristics in diagnostic tests including Pi2.

Characteristics of Insulation Diagnosis and Failure in Gas Turbine Generator Stator Windings

  • Kim, Hee-Dong
    • Journal of Electrical Engineering and Technology
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    • v.9 no.1
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    • pp.280-285
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    • 2014
  • In order to evaluate the insulation deterioration in the stator windings of five gas turbine generators(137 MVA, 13.8 kV) which has been operated for more than 13 years, diagnostic test and AC dielectric breakdown test were performed at phases A, B and C. These tests included measurements of AC current, dissipation factor, partial discharge (PD) magnitude and capacitance. ${\Delta}I$ and ${\Delta}tan{\delta}$ in all three phases (A, B and C) of No. 1 generator stator windings showed that they were in good condition but PD magnitude indicated marginally serviceable and bad level to the insulation condition. Overall analysis of the results suggested that the generator stator windings were indicated serious insulation deterioration and patterns of the PD in all three phases were analyzed to be internal, slot and spark discharges. After the diagnostic test, an AC overvoltage test was performed by gradually increasing the voltage applied to the generator stator windings until electrical insulation failure occurred, in order to determine the breakdown voltage. The breakdown voltage at phases A, B and C of No. 1 generator stator windings failed at 28.0 kV, 17.9 kV, and 21.3 kV, respectively. The breakdown voltage was lower than that expected for good-quality windings (28.6 kV) in a 13.8kV class generator. In the AC dielectric breakdown and diagnostic tests, there was a strong correlation between the breakdown voltage and the voltage at which charging current increases abruptly ($P_{i1}$, $P_{i2}$).

Analysis of Insulation Quality in Large Generator Stator Windings

  • Kim, Hee-Dong;Kong, Tae-Sik;Ju, Young-Ho;Kim, Byong-Han
    • Journal of Electrical Engineering and Technology
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    • v.6 no.3
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    • pp.384-390
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    • 2011
  • To evaluate the condition of stator winding insulation in generators that have been operated for a long period of time, diagnostic tests were performed on the stator bars of a 500 MW, 22 kV generator under accelerated thermal and electrical aging procedures. The tests included measurements of AC current (${\Delta}I$), dissipation factor ($tan{\delta}$), partial discharge (PD) magnitude, and capacitance (C). In addition, the AC current test was performed on the stator winding of a 350 MW, 24 kV generator under operation to confirm insulation deterioration. The values of ${\Delta}I$, ${\Delta}tan{\delta}$, and PD magnitude in one stator bar indicated serious insulation deterioration. In another stator bar, the ${\Delta}I$ measurements showed that the insulation was in good condition, whereas the values of ${\Delta}tan{\delta}$ and PD magnitude indicated an incipient stage of insulation deterioration. Measurements of ${\Delta}I$ and PD magnitude in all three phases (A, B, C) of the remaining generator stator windings showed that they were in good condition, although the ${\Delta}tan{\delta}$ measurements suggested that the condition of the insulation should be monitored carefully. Overall analysis of the results suggested that the generator stator windings were in good condition. The patterns of PD magnitude in all three phases (A, B, C) were attributed to internal discharge.

A Study on Site Application Techniques for Insulation Reliability of Rotating Machine (고압회전기 절연열화진단의 현장적용기술연구)

  • Kim, K.Y.;Jo, K.H.;Kim, T.S.;Han, S.O.;Lee, H.S.
    • Proceedings of the KIEE Conference
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    • pp.286-291
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    • 1991
  • Most of the failures of rotating machine are stator coil insulation failures. The insulation diagnostic testing for high voltage motors and generators are only megger test and P. I Test which is applied DC voltage until now. But it was impossible to judge insulation deterioration status of high voltage rotating machinery by above testing. In other words, even though the megger measurement values are fairly high, they used to be failed from time to time. Therefore in order to excute reliable and detailed diagnosis of insulation deterioration for rotating machinery, the tangent delta test, the alternating current test and the partial discharge test shall be applied to the insulation diagnostic testing on site.

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A study on the Analysis of Insulation Aging for Generator stator windings (수력발전기 고정자권선의 절연열화 분석)

  • Byun, D.G.;Oh, B.K.;Kang, D.S.;Lim, K.J.
    • Proceedings of the KIEE Conference
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    • pp.2072-2074
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    • 2005
  • This test was performed to assess the insulation condition of the stator winding of 3.45kV hydro generator in insulation deterioration condition which was due to long service period(30years) since installed We extracted 12 stator wingdings from the hydro generator core, cut the stator windings into three parts(Middle winding part, slot winding part, end wingding part), and evaluated the insulation condition to know the deterioration condition of each parts. This insulation diagnostic tests include AC current, dissipation factor, and partial discharg test.

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Diagnostic method of Insulation Deterioration for CV cable Using D.C. Potential Decay Components (직류전압 감쇄성분 측정에 관한 CV케이블의 절연열화 예측)

  • Yoo, Hyeong-Ho;Han, Min-Koo
    • Proceedings of the KIEE Conference
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    • pp.323-328
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    • 1989
  • In this paper, we studied the diagnostic method of insulation deterioration for 22.9kV CNCV cable using D.C potential decay component. At first, arbitrary D.C high voltage is appeied the CNCV cable for two minutes and switched off in vacuum. And then D.C potential decay components is measured for ten minutes. It is detecting source for cable insulation deterioration that its gradient is. Provisionally, we decided the criterion voltage and select the high voltage meter and S.W.

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Condition Monitoring Technique for Heating Cables by Detecting Discharge Signal (방전신호 검출에 의한 히팅 케이블의 상태감시기술)

  • Kim, Dong-Eon;Kim, Nam-Hoon;Lim, Seung-Hyun;Kil, Gyung-Suk
    • Journal of the Korean Institute of Electrical and Electronic Material Engineers
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    • v.34 no.2
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    • pp.136-141
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    • 2021
  • Heating cables, widely used in office buildings, factories, streets and railways, deteriorate in electrical insulation during operation. The insulation deterioration of heating cables leads to electric discharges that can cause electrical fires. With this background, this paper dealt with a condition monitoring technique for heating cables by the analysis of discharge signals to prevent electrical fires. Insulation deterioration was simulated using an arc generator specified in UL1699 under AC operation, and the characteristic and propagation of discharge signals were analyzed on a 100 meter-long heating cable. Discharge signals produced by insulation deterioration were detected as a voltage pulse because they are as small as a few mV and they are attenuated through propagation path. The frequency spectrum of discharge signals mainly existed in the range from 70 kHz to 110 kHz, and the maximum attenuation of the signal was 84.8% at 100 meters away from the discharge point. Based on the experimental results, a monitoring device, which is composed of a high pass filter with the cut-off frequency of 70 kHz, a comparator, a wave shaper and a microprocessor, was designed and fabricated. Also, an algorithm was designed to discriminate the discharge signal in the presence of noise, compared with the pulse repetition period and the number of pulse counts per 100ms. In the experiment, the result showed that the prototype monitoring device could detect and discriminate the discharge signals produced at every discharge point on a heating cable.

Estimation of Insulation Diagnosis and Dielectric Strength in 6.6 kV Motor Stator Windings (6.6 kV 전동기 고정자 권선의 절연진단과 절연내력 평가)

  • Kim, Hee-Dong;Kong, Tae-Sik
    • The Transactions of The Korean Institute of Electrical Engineers
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    • v.63 no.6
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    • pp.780-785
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    • 2014
  • To assess the deterioration condition of stator insulation, diagnostic and AC dielectric strength tests were performed on five high voltage (HV) motors (2,000 HP, 6.6 kV) for boiler feed-water pump (BFP). Two HV motors for BFP were installed per unit. Following the long term rewinding program, the diagnostic test was performed on five 6.6 kV motors during the planning maintenance period. After completing diagnostic test, AC dielectric strength test was done on the stator windings of HV motors. The AC dielectric strength test was conducted at 15 kV for one minute. Dielectric strength test and diagnostics test results confirmed that the stator insulation was judged to be in serviceable condition in the five 6.6 kV motors.