Shen Qinghe

Cluster analysis on signals from XLPE cable partial discharge detection

XLPE cables have had a large number of applications in the power grid, with good insulation properties, reliable power supply and easy to manufacture and install, however partial discharges caused by insulation defects would have serious consequences, such as insulation breakdown. Therefore, the cable partial discharge detection is of great significance. Since the partial discharge signal is weak and complex, it can easily be interfered by background noise or electromagnetic interference from outside, mainly from the radio signal propagation, a variety of spark discharge near the test site, discharge welding and high-voltage equipment, over-voltage pulse, corona discharge caused by poor contact, inductive discharge caused by a grounded metal object. These signals are random, whose unpredictable nature often have a great interference on partial discharge detection. In this paper, high-frequency current method is used for partial discharge detection. High-frequency current sensors are coupled to a large number of interfering signals. Cluster analysis starting from the distance matrix, selects the magnitude, rise time, fall time and frequency as variable, gets the data matrix and differentiation matrix of four-dimension and calculates using the consolidation method. Clustering results show that the cluster analysis method is effective to separate the signal from each other. In this paper, signals coupled by high-frequency current sensor can be attributed to three categories, namely, partial discharge signals, noise interference signals and corona discharge interference signals. Further study finds that the waveform, magnitude and rise time of above three signals each have significant differences. Basing on the results of the clustering method, frequency domain analysis of partial discharge signal, noise signal and corona discharge interference shows different spectral distribution, and this could be used to distinguish these signals more effectively.

Detection and processing for ±660 composite insulator abnormal discharge

Composite insulators are used greatly in±660kV DC transmission line, which influenced by external factors such as strong electric field, acid rain or mist, wire load and temperature shock, leading to the degradation of insulator, hydrophobic performance decline and mechanical strength reduction, and furthermore insulator abnormal discharge and other issues are also increasing year by year. In this paper, multi-spectral detection technology is presented firstly, containing visible light, infrared and ultraviolet detection technology. Visible light, infrared and ultraviolet detection technology each has its advantages and disadvantages, and multi-spectral method combine the three effectively, to improve the detection accuracy of composite insulator abnormal discharge obviously through the horizontal and vertical contrast. Discussions from detection principle to conditions are continued. Detecting instrument selection and configuration should be based on unit, equipment, management scope, voltage level and other actual situation, to meet the requirements of accurate detecting. Ideal detection should be carried on at clear night, while the wind speed is 0.5 m/s or less and humidity 85% or less, without electromagnetic interference or background radiation interference, focusing on the umbrella and sheath of composite insulator close to wire. Practice shows that the method can detect abnormal discharge effectively, which are more accurate than signal detection technology. For actual abnormal insulator detected, characteristics of visible image, infrared imaging and UV imaging are described, which are closely interrelated from each other. Composition analysis of surface contamination indicates the presence of water soluble ions in high concentration is primary factor in abnormal discharge. For abnormal discharge problem of composite insulators, the paper also presents a new type of DC composite insulator that uses large-floral-umbrella type, which improves electric field distribution of insulator surface, but also improves the creepage distance. Actual operation shows that such insulators operate in good condition, without abnormal discharge situation.