Zhu Wenjun

Influence of the injected current on dynamic contact resistance measurements of HV circuit breakers

Dynamic contact resistance measurement (DRM) is an effective technique for assessing the condition of power circuit breaker main contacts and arcing contacts. However, DRMs are easily affected by measurement condition, and they vary widely with changes of measurement condition, which is likely to lead to misjudgments. The problem can be relieved by increasing the injected current value. The proposed paper researched the influence of the dc injected current on dynamic contact resistance, and discovered that the average main contact resistance, the average arcing contact resistance, and the standard deviation of DRM curve decreased with the increase in the current value. At the same time, the reproducibility of parameters above improved. Besides, this paper also proposes a proper DRM strategy for the tested breaker.

Pattern identification method of partial discharge based on the features of UHF envelope signals

To determine the relationship between partial discharge type and envelope signal of partial discharge is important to evaluate the insulation state of gas-insulated switchgear (GIS). In this paper, discretization and differential matrix reduction is first conducted over the feature matrix composed of feature vectors characterizing UHF PD envelope signals using rough set theory for dimensionality reduction. Then the reduced feature vectors are used for pattern identification of four different types of UHF PD envelope signals in combination with BP neural network classifier. The results show that this method has a high identification rate.

Phase angle calculation for UHF partial discharge detection in segment acquisition mode

Phase angle of PD pulse is an important parameter of PD pattern, and its accuracy determines the effectiveness of PD pattern recognition based on phase-resolved distribution analysis. In this paper, a novel phase angle calculation method for UHF PD detecting systems in segment acquisition mode is proposed. This method use a synchronous circuit to output UHF marker signals with certain frequency characteristics to represent the rising edge of zero-crossing points of power frequency signal. The UHF PD detection system receives both marker signals and PD pulses, and records the occurrence time of all of the UHF pulse signals. Those two types of signals could be separated and marked by calculating their different time-frequency characteristic parameters using fuzzy clustering method. Then the phase angle of PD pulses could be calculated from the time difference between the UHF PD pulses and the neighboring zero-crossing points of power frequency signal. This method realizes the phase angle calculation of UHF PD signals without sampling power frequency signal, which greatly simplifies the structure of the system and reduces its requirements for data processing. The validity of the method is verified by experimental application in Laboratory.