Zheng Shusheng

Experimental study on the relationship between partial discharge and gas decomposition products in SF6 insulated electrical equipments

SF6 decomposition serves as an effective means for online fault detection and diagnosis of SF6 insulated equipments. The relationship between SF6 decomposition products and partial discharge (PD) in SF6 insulated equipments remains a significant theoretical and practical issue to be addressed. Based on the simulations of protrusion discharge, floating discharge and surface discharge in SF6 insulated equipments, the present experiment studied the impacts of differentiated PD patterns, PD severities and SF6 pressures on the concentrations of SF6 decomposition products as well as the change in concentrations over time. The experimental results indicate that three kinds PD pattern discharges produce SOF2+S02 and HF, the concentration of the SOF2+S02 being always higher than HF. Generation of both gases increase with voltage application time; The concentrations of SOF2+S02 and HF differ from differentiated PD discharge strength, and increase as discharge strength ascends; A negative relationship exists between SF6 gas pressure and the generation speed of SOF2+S02 and HF. It is concluded that SF6 decomposition products, SOF2+S02 and HF in particular, could be used as a means for on-line PD faults detection and diagnosis.

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.

Study on the Disc Sensor Based on the Cavity Mold Theory

Ultra-high-frequency (UHF) sensor is the vital component of a partial discharge detection system and its coupling performance is affected by structural parameters. On the basis of the cavity model theory, this paper studied the influence of the disc electrode diameter, the thickness, the dielectric constant of the dielectric substrate, and the position of the coaxial connection on the performance of the disc-type UHF sensor with the application of the XFdtd software. The simplified finite-difference time-domain simulation model for the gigahertz transverse electromagnetic (GTEM) cell has been established, and the influence of the coaxial feed position on the performance of the disc-type UHF sensor is studied via the frequency domain effective heights in the simulation. The result shows that as the disc electrode diameter, the thickness, and the dielectric constant of the dielectric substrate increase, the working frequency band shifts toward the reducing direction. The position of the coaxial connection has an obvious effect on the resonant mode of sensor, too.

Development and application of data analysis software for transformers PD UWB RF location

Ultra-Wideband (UWB) RF partial discharge (PD) location technique is a new method for PD sources location in power transformers, which is based on multiple sensors array detection and Huygens-Fresnel principle of PD electromagnetic radiation signal. In this paper, a classification algorithm of multi-PD sources has been proposed, which is based on dynamic search in the TDOA (time difference of arrival) sample space, it is able to distinguish multiple PD sources and complete the TDOA classification of every PD source automatically when there are multiple PD sources has been detected simultaneously. Based on the classification algorithm of multi-PD sources and location algorithm based on Huygens-Fresnel principle, a set of data analysis software used for PD UWB RF location system has been developed based on Labview8.5. It manages multiple test projects using Access Database, and establishes the TDOA sample space for every testing program, finishes the multiple PD sources classification and location calculation for every PD source finally. Meanwhile, multiple functions have been integrated into the software, such as signal processing, report generation, human interface design and so on. Finally, an illustrative example has proved that the softwares validity.