Research On Frequency Reduction Processing Of Radio-frequency Signal Produced By Partial Discharge In Oil And Acousto-electrical Joint Detection

Normal operation of high voltage electrical equipment is the basis of safe and stable operation of power system,high voltage power cable is an indispensable part of power system,It shoulders the responsibility of transmitting and distributing electric energy.Partial discharge is one of the important reasons for insulation failure of power cable,therefore,it has received extensive attention and research.Partial discharge monitoring of power cables can detect microdischarges in cables in time,It also prompts operators to remove the faults before serious faults occur,and improving the reliability and economy of power system operation.In this paper,the generation and propagation mechanism of UHF and UHF signals of partial discharge are briefly introduced.Then,the advantages and disadvantages of UHF and Ultrasound methods for detecting partial discharge are analyzed in detail.A method of combining the two methods is proposed,which uses UHF method to indicate the existence of partial discharge nearby,and then uses ultrasonic method to locate it.At the same time,in order to save the cost of detection,UHF and ultrasound signals acquisition using low-cost data acquisition card,an envelope demodulation and frequency reduction circuit is designed and manufactured.Through software simulation and actual testing,It is proved that the circuit can reduce the frequency of UHF signals from 300 MHz to 800 MHz to less than 3kHz.,and it can be collected by low-cost data acquisition card.It can reflect the partial discharge sensitively and reduce the detection cost.In the detection process,the first step is to measure partial discharge by pulse current method,study on the correlation between signal amplitude and discharge quantity by combining UHF method and ultrasonic method.It is proved that the amplitude of UHF signal can better reflect discharge quantity than that of ultrasonic signal.The proportional relationship between the signal amplitude after frequency reduction and the original signal amplitude is established.Then,the needle-plate discharge model is taken as an example,combining UHF method with ultrasound method.UHF method is used to determine the range of the partial discharge signal which can be measured by using the reduced frequency circuit is 1.2m.Then four ultrasonic sensors are used to locate the exact position of partial discharge source,high positioning accuracy has been achieved.