Synchronous Measurement System For Multi-type Transient States Of Transformer Switching Impulse Test

Large power transformer is the key equipment of power grid.Insulation fault is one of the main faults of the transformer.It is of great significance to find out the potential insulation fault of transformer and prevent transformer accident in time for improving the safe operation of the power grid.Switching impulse test is an important means to assess the health of transformer insulation,and it can find multiple types of insulation faults.Complete and accurate measurement and recording of state information in the test is the foundation of accurately judging the transformer insulation state.Most of the current measurement systems for switching impulse test can only measure the voltage and current in the test.When it is necessary to measure the partial discharge signals simultaneously,a digital oscilloscope is generally used.However,the use of digital oscilloscopes has the following shortcomings:(1)It is difficult to completely record the test waveform data of each state by manual coordination.(2)The digital oscilloscope cannot complete automatic analysis and calculation of the collected data.In order to develop an automatic measurement and analysis system for transformer switching impulse test,this paper studies the key technologies of the synchronous measurement and storage of the multi-type transient states of transformer high-voltage winding voltage,low-voltage winding voltage,neutral point damage current and partial discharge signals in the test,and designs the main hardware such as signal conditioning circuit.First of all,according to the requirements of test data analysis and the characteristics of various types of transient state signals,and comprehensively considering the technologies of data acquisition and storage,the scheme of collaborative acquisition and analysis of dual devices is determined.On this basis,the focus is on the time-scale alignment of the state signal waveform data between the two devices,and an inversion time synchronization method based on automatic sensing of the test process and automatic hardware marking at the end of the test is proposed to realize the time scale alignment of multiple state signal waveform data for signal correlation analysis.And according to the error analysis in the process of data time scale alignment,the accuracy of data time scale alignment is obtained.Then,according to the input requirements of the acquisition card and the requirements of data time scale alignment,the conditioning circuits of various types of transient state signals are designed,including the signal conditioning amplifier circuit and the time mark generation circuit.The amplitude adjustment of each state signal and the formation of time mark are completed,which lays the foundation for the subsequent accurate acquisition and the time mark alignment of waveform data.In addition,according to the characteristics that the test measuring device is ready to use and needs to be transported between different sites,a portable measuring device box with convenient disassembly and assembly is designed.Finally,according to the principle of partial discharge of the transformer under the oscillating operating impulse voltage,the characteristics of the partial discharge signal in the test are analyzed.According to signal characteristics and data analysis requirements,the continuous and uninterrupted acquisition strategy of partial discharge signals and the storage strategy for storing data 20 ms before the end of the test are designed.In addition,according to the waveform characteristics of the partial discharge pulse,a method for extracting the partial discharge signal pulse by setting a threshold is designed,and the sampling data is used to complete the calculation of the characteristic parameters of each pulse,and then the measurement of the partial discharge signal is completed.