Research On Lightning Intruding Wave Overvoltage In Substation Measurement Technique Based On CVT

Thunderstorm accidents occur frequently in substations.The existing accident statistics summary and experimental research exploration are the main control methods for rationally configuring the insulation scheme in substations and formulating corresponding lightning wave overvoltage protection measures.The lightning wave used today for lightning protection has been the standard lightning waveform,which is developed by the IEC in the1920 s.However,the topology of the transformer substation actually changed due to the introduction of new and new electrical equipment.As a result,the actual lightning wave intrusion into the substation equipment is different from the standard waveform before.Therefore,the accurate measurement of the lightning surge overvoltage received by the equipment in the substation by using the different measurement technologies is the primary task of correcting and revisiting the standard lightning waveform.The Capacitor Voltage Transformer(or called CVT)is selected as the research object in this article,which is widely installed in substations of 110 kV and above.Researching its existing measurement methods-problems with direct measurement methods on the secondary side and the improved measurement methods based on the CVT.In terms of studying the existing measurement method of CVT's secondary side,the specific structure of the CVT has been considered,and the test of obtaining 110 kV CVT parameters also has been accomplished.According to the test parameters obtained,the corresponding non-linear model which was considered distributed capacitance has been established by using the electromagnetic transient simulation software ATP-EMTP.It was proved the accuracy of the simulation model by simulating the power frequency overvoltage and lightning overvoltage.When measuring the voltage signal on the actual secondary side,the waveform will undergo a certain degree of distortion.Subsequently,the influence of the relevant parameters in the CVT equivalent impedance model on the transmission characteristics of the lightning overvoltage was deduced.Through MATLAB simulation and analysis of the key parameters,it was determined that the electromagnetic unit of the intermediate transformer is the main factor affecting its frequency response characteristics.Finally,the measured data using frequency sweep-frequency response analysis shows that there are indeed certain flaws in the direct measurement of the lightning wave on the secondary side.On the basis of CVT proposed improved measurement methods.It shows that the improvement of the measurement technology can truly optimize the monitoring of the frequency characteristics of lightning waveforms which was combined with theoretical analysis and experiments.First of all,according to the electromagnetic unit of the intermediate transformer will cause some distortion in the measurement,it is proposed ameasurement method that used the series capacitor voltage dividing idea directly at the lower end of the low voltage arm capacitance of the CVT capacitive voltage divider.Then considering the elimination of oscillations and other factors,using the chip capacitors for CVT low-voltage arm series capacitor conversion.The experimental results show that the improved measurement technology can complete the lightning wave voltage waveform measurement accurately within the error range in the laboratory.However,due to the limitations of actual site safety,this law has certain limitations.Finally,according to the investigation on the site,the development direction of using the CVT to measure lightning overvoltage waveform technology is proposed.