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Effect of Humidity on Partial Discharge Characteristics

Effect of Humidity on Partial Discharge Characteristics. Zainuddin Nawawi* Yuji Muramoto Naohiro Hozumi and Masayuki Nagao Proceedings of the 7 th International Conference on Properties and Aplications of Dielectric Materials 1-5 June 2003 장 성 수. Abstract.

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Effect of Humidity on Partial Discharge Characteristics

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  1. Effect of Humidity on Partial Discharge Characteristics Zainuddin Nawawi* Yuji Muramoto Naohiro Hozumi and Masayuki Nagao Proceedings of the 7th International Conference on Properties and Aplications of Dielectric Materials 1-5 June 2003 장 성 수

  2. Abstract • The effect of humidity on Partial Discharge (PD) characteristics in a void with insulation-insulation configuration • Test Configuration • CIGRE Method-II specimen with various levels of relative humidity • The statistical time lag under periodical square HV pulses • With related to the change of relative humidity • The relation among surface resistance of samples • PD characteristics and the discharge time lags

  3. Introduction • Partial Discharge (PD) characteristics • One factor for the improvement and the diagnosis of insulating materials • Affected by contamination, particularly absorbed moisture, nature of the ambient medium, temperature and humidity • The purpose of this paper • To clarify the effect of relative humidity on the PD characteristic in a air gap with insulation-insulation configuration • Investigation of the PD behaviors and the effect of humidity through measurements of PD Vi and Ve, PD patterns and the discharge time lags

  4. Experimental Methods • Test Specimen and Humidity Control (Fig. 1) • Specimen : CIGRE method II type • Insulation material : Polymethyl methacrylate (PMMA) sheet of 1mm thick • Polyimide spacer of 125 μm thick (to form a gap where discharge takes place) • Two slits with 10 mm wide to control relative humidity • Saturated salt solution for humidity conditioning of the air surrounding specimens Fig. 1 Schematic diagram of the specimen

  5. Experimental Methods • Measurement of PD patterns (Fig. 2) • Function Generator • High Voltage Amplifier - Amplified the output of the function generator - Generated the sinusoidal high voltage waveform - Applied to the spherical electrode of the specimen • PD inception voltage (Vi) • The applied ac voltage was raised at a rate of 70 V/sec until the discharge occurred • PD extinction voltage (Ve) • The applied voltage was decreased at the same rate until the discharge disappear

  6. Experimental Methods Fig. 2 Schematic diagram of the measurement system

  7. Experimental Methods • Measurement of Discharge Time Lag • Test configuration for discharge time lag • Same setup as shown in Fig. 2 • Applied square HV pulses with 10 ms in pulse width, 20 ms interval of pulses • Discharge time lag • The time between the leading edge of square pulse and the discharge pulse • The measurements through 64 pulses were performed • The test was performed under 33, 75 and 98% of relative humidity

  8. Experimental Results and Discussion • Surface Resistance of Sample • To evaluate the effect of humidity on surface resistance of void • The surface current measurement • At 10 minutes after 10KV dc voltage was applied to the main electrode using electronic pico ammeter • Results : Fig. 3 • The surface resistance decreases with increasing relative humidity Fig. 3 Surface resistance as a function of RH

  9. Experimental Results and Discussion • The PD Inception and PD Extinction Voltages • The effect of relative humidity on the Vi and Ve • With increasing of relative humidity • Vi decreased, and Ve increased • Major factors to determine the Vi and Ve • Geometry, spacing between electrode • The type and homogeneity of the insulation • The type of the contamination on the surface of the insulation and the ambient condition • Ve at 33, 75 and 98% of RH are about 0.7Vi, 0.8Vi and 0.9Vi, respectively • At humid condition, Vi occurred at lower voltage Fig. 4 PD inception voltage and PD extinction voltage as a function of relative humidity

  10. Experimental Results and Discussion • The effect of humidity on PD magnitude • The average of PD magnitude Qave decreases with increase of relative humidity • In positive cycle • 33% RH is about 530pC, at 75 and 98% RH are 240pC and 120pC • In negative cycle • At 33% RH is about 640pC, at 75 and 98% RH are similar to PD magnitude in positive cycle Fig. 5 The average of PD magnitude as a function of relative humidity

  11. Experimental Results and Discussion • The plots (Fig. 6) of charge intensity in positive and negative half cycles, to clarify the effect humidity on PD magnitude; • Fig. 6 shows the plots of charge intensity and cumulative probability • The charge intensity shift to smaller value with increase of RH • A slight difference between positive discharges and negative ones; • it seems that the effect of humidity on the PD magnitude was significantly Fig. 6 Plots of charge intensity in positive and negative half cycles

  12. Experimental Results and Discussion • The plots (Fig. 7) of number of discharge pulses as a function of charge intensity, to clarify the effect humidity on PD magnitude; • Fig. 7 shows the plots of the number of PD pulses as a function of charge intensity • The number of PD pulses; • Increased with increase of RH • For positive PD, charge intensity becomes too small to be detected • In the experiment, the PD magnitude was measured 1 min after 10KVrms was applied to avoid degradation effect of sample material Fig. 7 Charge intensity of negative and positive cycle as a function of discharge pulses

  13. Experimental Results and Discussion • The Effect of Humidity on Discharge Time Lag • Fig. 8 shows the Laue plots of the discharge time lags with various levels of relative humidity • The discharge time lag becomes shorter with increase of RH • The statistical discharge time lag at 37% of residual probability • For positive PD at 33, 75 and 98% RH are about 2.8, 1.6 and 0.41ms • For negative PD at 33, 75 and 98% RH are about 2.9, 1.6 and 0.42ms, respectively Fig. 8 Laue plots of the discharge time lag for PD in negative and positive cycles at 20KVp-p

  14. Experimental Results and Discussion • The Effect of Humidity on Discharge Time Lag • Fig. 9 shows the discharge time lag under the same applied voltage the different levels of RH • The reduction on the discharge time lags; • The RH plays in determination of the PD magnitude • Based on experimental results; 1) Increase of the RH 2) Lower of the surface resistance of the void 3) Easier release of initial electron to decrease discharge inception voltage and leading to a large number of small discharge Fig. 9 The discharge time lag as a function of relative humidity under step voltage 20KVp-p

  15. Conclusions • Measurement of the PD patterns in a void of insulation-insulation configuration with various level of RH • The PD characteristics in positive and negative cycles • Increase of RH in the void • Significant change of the PD characteristics • The decrease of the discharge time lags • Based on experimental results • Increase of the RH • Decrease of the surface resistance of the void • Easier release of initial electron from surface of void • At humid condition, • PD inception voltages decrease • PD extinction voltages increase • Leading to decrease in PD magnitude

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