Multi-Terminal Detection And Location Analysis Method Of Partial Discharge Pulse Current In Transformer

Partial discharge is the dominant factor causing transformer insulation problems.Traditional high-frequency current sensors are generally installed on iron core grounding lines,which cannot meet the requirements of partial discharge positioning and anti-interference.With the development of ultra-high voltage and ultra-high voltage transformers,the existence of transformer scale effect poses new challenges to partial discharge detection.In this paper,the engineering problems of partial discharge multi-terminal detection and location analysis are studied.The main work is as follows:A broadband partial discharge detection system with an effective detection frequency range of 100kHz-30MHz was built,and a 110kV transformer and a 500kV converter transformer were measured at multiple ends.The calculation results show that as the pulse injection position moves down,the overall trend of the amplitude ratio of the first and the end is gradually reduced;the equivalent time increases with the increase of the distance between the detection end and the pulse source.The equivalent bandwidth decreases with the increase of the distance between the detection end and the pulse source.With the increase of winding scale,the attenuation degree of 500 kV winding signal is about 12.050～37.725 times that of 110 kV transformer winding signal.Through the positioning analysis of pulse measurement results at both ends of each winding,it can be judged that the pulse comes from a certain winding or its head and end leads.The multi-conductor transmission line model of discharge pulse propagating in the windings of 110kV three-phase two-winding transformer and 500kV single-phase three-winding converter transformer is established.In the 110 kV simulation,the two cases of winding turn-to-ground discharge and cake-to-cake discharge are simulated and analyzed.By using the method of lumped parameter simulation,the calculation port of the multi-conductor transmission line model is expanded from the first and last ends of the high-voltage winding to the first and last ends of the high and low-voltage winding,the core and the shell,a total of six ports,to realize the simulation calculation of multi-terminal transmission characteristics;in the 500 kV transformer,the large-scale spiral winding on the valve side is modeled and analyzed,and the transmission characteristics are calculated by changing the boundary conditions of the turns for different winding modes of the continuous winding of the 110 kV transformer.The errors of the 110kV single-winding model and the 110kV multi-port model in the range of 100kHz～6MHz are 18.2%and 16.7%respectively,and the error of the 500kV model in the range of 100kHz～5MHz is 21.4%.Comparing the frequency domain simulation results of 500 kV transformer and 110 kV transformer,it is found that the signal attenuation range is 28.1%～61.9%with the increase of transformer scale.Based on the multi-winding model,the interference identification and location analysis of partial discharge are carried out.In terms of interference identification,with the increase of winding turns,the amplitude of the first wave decreases compared with the waveform amplitude(K value),and the maximum decrease is 13.9%,but the first wave can still be detected.A pulse clustering and positioning analysis method based on equivalent duration-equivalent bandwidth parameters is developed.Compared with the existing energy ratio curve method,the existence of transformer scale effect makes the positioning errors of the above two methods increase by 14.7%and 10.4%respectively.This paper analyzes the practicability of the existing partial discharge detection methods in ultra-high voltage and ultra-high voltage transformers,which has important practical engineering significance.