Research on the Micro-void Discharge in Power Frequency and High Frequency

Qifu Lu1, Qizheng Ye2, Hong Lv1, Xingwang Li1, Chu Yang2, Siyang Wu2

1Electric Power Research Institute of Guangdong Power Grid Corporation, Guangdong, 510080, China. 2State Key Laboratory of Advanced Electromagnetic Engineering and Technology,

College of Electrical and Electronic Engineering, Huazhong University of Science and Technology, Wuhan, 430074, China

Abstract- In this paper, a type of typical PD source, micro-void discharge, is designed and fabricated to imitate the defects in GIS online. The void in solid insulation is carved by the laser inside-carving machine and the machining operation, respectively. Comparing these two kinds of void discharge, a single void discharge form can be obtained using the void carved by the laser inside-carving machine. The void discharge characteristics in power frequency and high frequency are also compared and analyzed. The singleness of discharge forms in high frequency is better. The experimental results will be applied in PD monitoring and materials testing.

I. INTRODUCTION

Gas-insulated switchgear (GIS) plays an important role in power systems, not only because it is maintenance free and has less of an influence on environmental and industrial conditions, but also due to its low space requirements and high reliability. The statistic of GIS reliability show that the most common cause of electrical failure is the Partial Discharge (PDs), such as a particle, floating shield, void and so on [1-2]. In order to distinguish different types of PDs, some different discharge models are needed to be manufactured and researched [3]. For the void discharge, the influence of the manufacturing techniques of the void on the discharge characteristics is lack of research. In this paper, a type of typical PD source, void discharge, is designed and fabricated to imitate the defects in GIS online.

� EXPERIMENTAL SET UP

The discharge device is shown in fig.1 and the experimental set-up is shown in fig.2. The high-voltage electrode is a column-type electrode inlayed in a column-type Plexiglas, and the lower electrode is a plate electrode inlayed in this column-type Plexiglas also. The void is embedded in the Plexiglas between two electrodes, and carved by the laser inside-carving machine and machining operation, respectively. The gap is fixed at 5 mm in all experiments. An AC high voltage is applied to the electrodes. Its frequency is 50Hz or 8.48 kHz. A high voltage probe (Tektronix P6015A) is used to measure the applied voltage. The resistor is used to measure the current.

� EXPERIMENTAL RESULTS

The voltage-current waveforms in 50Hz are shown in fig.3. We can find that there is one current pulse in per half cycle, and there is no difference between positive and negative half cycle. This means that there is only one single discharge produced in the void. It is a typical void discharge.

The voltage-current waveforms in high frequency are shown in fig.4. We can find that there is one current pulse in per half cycle, and there is no difference between positive and negative half cycle. It is also a typical void discharge.

void

Figure 2. Experimental set-up.

Oscilloscope

HV probe

R

Figure 1 Discharge device.

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Compared with the discharge in power frequency, the onset voltage in high frequency is lower than that in power frequency.

The voltage-current waveforms of the void carved by the machining operation in 50Hz are shown in figs.5 and 6. Compared with the discharge of the void carved by the laser inside-carving machine, we can find there is a group of disordered current pulses in per half cycle. However, the current waveforms produced by the void carved by the laser show that the phenomena of the single current pulse remain almost constant with the voltage increasing from 27.5 to 36.6kV, as shown as in figs. 7 and 8. It means that the fabrication technique is important.

��CONCLUSION

The manufacturing technique of the laser inside-carving machine is better than that of the machining operation. We can get one single discharge in void. Compared with the discharge in power frequency, the onset voltage in high frequency is lower than that in power frequency. .

ACKNOWLEDGMENT

Figure 8. The voltage-current waveforms (50Hz, Upp=36.6kV) for void carved by the laser.

Figure 7. The voltage-current waveforms (50Hz, Upp=27.5kV) for void carved by the laser.

Figure 3. The voltage-current waveforms (50Hz) for the void carved by the laser.

Figure 4. The voltage-current waveforms (8.48 kHz) for the void carved by the laser.

Figure 5. The voltage-current waveforms (50Hz, Upp=25.9kV) in void carved by the machining operation.

Figure 6. The voltage-current waveforms (50Hz, Upp=31.0kV) in void carved by the machining operation.

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The research reported in this paper was supported by the grant from the National Nature Science Foundation of China, Grant No 51177059.

REFERENCES

[1] Pearson J S, Farish O, Hampton B F, et al. “Partial Discharge Diagnostics for Gas Insulated substations,” IEEE Trans. On DEI, vol. 2, pp.893-905, May 1995.

[2] Tenbohlen, S.; Denissov, D.; Hoek, S.; Markalous, S.M. “Partial discharge measurement in the ultra high frequency (UHF) range,” IEEE Trans On Diel. Elec. Insul., vol. 15, pp.1544- 1552, June 2008.

[3] Wensheng Gao, Dengwei Ding, and Weidong Liu, “Research on the typical partial discharge using the UHF detection method for GIS,” IEEETrans On Power Delivery, vol. 26, pp. 2621-2629, April, 2011.

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