Study Of PT Resonance Detection Method In Distribution Network

PT resonance is a common form of the power system PT resonance has occurred in various voltage levels and different structure of the grid in the actual operation of220kv and below. PT resonance occurs in the neutral point ungrounded system of electric distribution network frequently. The root cause of PT resonance is the nonlinear characteristics of the electromagnetic voltage transformer. PT resonance is caused due to the saturation of the electromagnetic voltage transformer in the neutral point ungrounded system. The overvoltage and over current seriously affect the security and stability operation of the system. PT resonance that lasts long time lead to fusing of the high voltage, burn of the transformer body, flashover of porcelain insulation, explosion of arrester and other accidents.This paper mainly studies detection method of the PT Resonance of the neutral point ungrounded system. The purpose is to find a simple and practical resonance detection algorithm for power system. Using the real-time recorded data gives early warning information in a timely manner, improves the safe operation of the power system level. First, the paper introduces the research status of PT resonance, and analyzes the different methods for the detection of PT resonance. Therefore, find an accurate detection method of PT resonance to avoid the failure to expand, improve the reliability and stability of the system, these have a relatively long term practical significance.Firstly, the paper analyzes the causes of PT resonance overvoltage in the neutral point ungrounded system, the nonlinear characteristics of the electromagnetic voltage transformer, different types and characteristics of the PT resonance. Then, the paper establishes the equivalent circuits of electromagnetic voltage transformer and10kv neutral point ungrounded system based on the related theoretical analysis. The paper establishes the model of lOkv neutral point ungrounded system using the electromagnetic transient simulation software which is called ATP. Using the software does a large amount of simulation experiments, just by changing the line capacitance, changing the moment of the disappearance of the single-phase ground fault and changing the initial phase of power. The simulation results include the sub-frequency resonance, base-frequency resonance and high-frequency resonance, providing simulation data for the detection method of PT resonance. At the same time, do simulations of the single-phase ground fault in order to compare with the base frequency resonance.On this basis, the paper proposes a detection method of PT resonance combined of wavelet transform, Fourier transform and the energy method. The method mainly picks up the neutral point voltage of single-phase ground fault and deal with it. Using MALLAT algorithm achieves one-dimensional discrete wavelet decomposition of the neutral point voltage. Sub-band signals are obtained by the decomposition. Then fast Fourier transform is used to deal with the sub-band signals. After the transformation, the spectrum of each sub-band signal has been achieved. When the frequency of the signal is sub-frequency or high-frequency, judge that there is a sub-frequency resonance or high-frequency resonance. When the frequency of the signal is baseband, go to the next step. Distinguish the base-frequency resonance with single-phase ground fault using the energy method. Finally, the simulation data and the actual data are used to the method. The results show that the method can effectively detect the occurrence of PT resonance and determine the type of PT resonance. Thereby, the method achieves the detection of PT resonance and has a certain practicality.