Chang Wenzhi

Experimental study on the development characteristics of point discharge in GIS

Studying the characteristics of partial discharge development is conducive to make an accurate assessment of the severity of discharges and give a reasonable maintenance strategy for the equipment. Point discharge is a typical failure discharge fault occurred in GIS equipment, the differences of the characteristics of the PRPD patterns produced by UHF partial discharge enveloped signals in different development stage is studied and the variation with the test time of the average amplitude and number of discharges in each sampling period, the max discharge amplitude ratio and discharge frequency ratio of positive and negative half-cycle is discussed in this paper. It provides a basis for assess the severity of partial discharge. The results show that, with the extension of the test time, the average amplitude and number of discharges increase first, and then decreased, while the ratio of maximum discharge amplitude on the positive half-cycle to the maximum discharge amplitude on the negative half-cycle and the ratio of the number of discharges on the positive half-cycle to the number of discharges on the negative half-cycle increase gradually, and the decrease rate with the discharge amplitude of the number of discharges which is defined in this paper becomes faster and faster.

Multi-PD sources location by UWB RF detection on power transformers and a case study on-site

Ultra-wideband (UWB) RF sensor-array PD location is a novel technology based on antenna array detection and time-difference algorithm for power transformers. It has demonstrated high sensitivity and accuracy for single PD source by experiments in laboratory. In this paper, a further study has been carried out for multi-PD sources location using the UWB RF sensor array PD location method. Moreover, a practical location case is given on a real transformer. The results indicate that the method presented in the paper is effective for multi-PD source location and has promising future in real transformers.

The design of temperature monitoring system for power cable joint

Power Cable Joint is the area where the faults are often happening on the power cable. Real-time monitoring of Power Cable Joint temperature can discover the joint overheating, and can evaluate insulation aging degree, and then, potential safety hazard of the cables will be removed timely. In this paper, a temperature measurement method based on embedded sensors inner Power Cable Joint has been proposed, and a set of temperature monitoring system for Power Cable Joint has been developed. The temperature monitoring system was composed of embedded sensors, data acquisition unit, current induction power supply, data transmission based on combination of ZigBee and GPRS, data analysis software. The temperature measurement system has the advantages of high reliability, real-time and highaccuracy, the long-distance temperature measurement for Power Cable Joint has been achieved.

A novel sensor for UWB RF PD location and experimental investigation on a 220kV transformer

Ultra-Wideband (UWB) RF partial discharge (PD) location technique is a new method for PD source location on power transformers, which is based on multi-antenna PD detection and Huygens-Fresnel principle. In this paper, a novel sensor with 2GHz–8GHz bandwidth for UWB RF detection has been designed. A new location algorithm named Space-Grid-Search Algorithm has been proposed which greatly eliminate the divergent effect of analytical method. Four typtical artificial PD models are applied to a real 220kV transformer. Then experiments have been carried out for PD location on the transformer using UWB RF technique. The test results indicate that the average error of the pre-set PD sources was about 30 centimeters.

A communication interference suppression method for ultra high-frequency partial discharge detection

Because of its favorable corona resistant ability, ultra high-frequency (UHF) technique based partial discharge (PD) detection is widely applied in partial discharge detection of such power equipment as power transformer and gas insulated switchgear (GIS). However, in complicated electromagnetic environment of the substation, a great variety of UHF interference signals caused by communication such as mobile phone signals cause difficulties to on-site detection and diagnosis of the PD faults, thus it is hard to diagnose the test results accurately. According to the frequency domain features and characteristics of envelope waveform of partial discharge UHF signals, a comprehensive anti-interference approach, which is based on notch filter and cross-correlation analysis, is proposed in this paper. Analysis and test results show that the proposed anti-interference approach can suppress the interference caused by communication signals which is common in PD UHF detection, the detection sensitivity and accuracy of discharge pattern recognition can be improved.