Design Of Partial Discharge Test Platform On Oil-paper Insulation In Transformers With Multi Samples And Wideband Measurement System

In Smart Grid,condition of intelligent transformer constantly needs to be monitored, insulation fault is a main threat to the safe and stable operation of transformer and partial discharge is the important signs and manifestations of oil-paper insulation.However,PD is an extremely complex,many factors affected and great dispersion-owned process, the information of the severity of defects and so on may be included in the PD's pulse current waveform and a large number of PD tests should be done to the research on the warning of transformer failure,it is necessary to establish a PD test platform with multi samples and wideband measurement system to extract the pulse current waveform and increase work efficiency.In this paper,a PD test platform with 5 samples was designed. Through theoretical calculation,the coupling capacitance was determined as 500pF,the protecting resistance was determined as 200kΩand crosstalk between simulated circuits was simulated.In order to establish wideband test platform,wideband measuringsystem, protect the Oscilloscope and simulate the working environment of transformer oil-paper insulation, 50kV high-frequency quartz glass and ceramic capacitors;wideband sampling resistor, wideband Rogowski coil; the oscilloscope input protection system; small size glass container and heating circulation system were designed.The results showed that ceramic capasitors has perfect high-frequency characteristics and high corona inception voltage,the wideband sampling resistor and the Rogowski coil has the cut-off frequency of 80MHz at least. The oscilloscope input protection system can limit 50kV impulse voltage to 1.4V.Finally,the experiment results proved that,(1)the initial discharge voltage of multi-loop test platform is above 45kV;(2)the branch test circuit has good wideband characteristics,pulse waveform of about 3ns can be measured; (3)crosstalk between loops can be limited to one thousandth,that means,when a 2000pC PD occurs in one loop,there is 2pC PD in another loop,2pC PD is negligible;(4)the test platfrom is immune to outside interference.