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Name of experiment：application of high voltage amplifiers to the analysis of surface electrotrace corrosion degree based on insulation resistance

Research direction：corrosion degree of electric mark

Content of experiment：on the basis of the electrical mark test, the insulation performance of each ethylene-propylene rubber sample was measured after the test, and the insulation resistance was analyzed based on the resistance, polarization-depolarization current and recovery voltage.Firstly, the volume resistance, polarization-depolarization current and recovery voltage of each sample were measured in the drying oven under different measuring voltages and temperatures. Secondly, the influences of different fault degrees on volume resistance, polarization-depolarization current and recovery voltage were analyzed in detail. Finally, the insulation resistance under different measurement methods was compared to verify the reliability of the method.

Purpose of experiment：according to the electric mark test standard, evaluate the electric mark resistance performance of ethylene propylene rubber, extract the electric mark fault characteristi, study the electric mark fault diagnosis method, and evaluate the surface electric mark state of ethylene propylene rubber.

Test equipment：Ethylene-propylene rubber treated with different degrees of electric marking, ATA-7020 high voltage amplifier, three electrode system, drying box, etc.

Experimental process：

（1）Polarization - depolarization current of ethylene propylene rubber

The following figure showed the polarization - depolarization current measurement circuit diagram. In the process of depolarization, the current flowing through the ethylene propylene rubber insulation was capacitive, and the order of magnitude of the capacitive current was pA level, so to accurately measure the depolarization current, there were high requirements for measuring equipment. In the measurement system, KEITHLEY-6517B was selected as the ammeter, and ATA-7020 high voltage amplifier was selected as the high voltage DC power supply. The DC power suppl has the advantage of low noise, which could ensure the reliability of measurement data. The electrode selected in the measurement had a three-electrode structure, in which the high voltage end and the measuring end were used for polarization-depolarizing current measurement. The host computer transmitted the data collected in real time by 6517B to the host computer through the serial port for storage.

（2）Recovery voltage of ethylene propylene rubber

The recovery voltage method was based on the dielectric response theory, and it was a way to characterize dielectric polarization in time domain. During the measurement process, the recovery voltage was not susceptible to external electromagnetic interference, and the measurement results were stable and easy to observe. 

The recovery voltage measurement circuit was shown in the figure. The DC voltage source used for measurement was ATA-7020 high voltage amplifier, and the voltage value selected during measurement was 400V. The voltage measurement range of the voltage measuring unit fully met the measurement requirements. After the measurement, the host computer transmitted the data collected in real time to the host computer through the serial port for storage.

Result of experiment：

（1）The influence of electric mark size 

At the initial stage of discharge, the initial current and the discharge speed in the process of depolarization increased gradually with the deepening of the corrosion degree of electric trace, and the more serious the corrosion degree of electric trace, the greater the current value at the stable decay of depolarization current. It could be seen from the test results that there were obvious differences in the depolarization current curves of each sample. The attenuation of depolarization current had a concave point in the whole depolarization process.

                      Depolarization currents at different              Depolarization currents at different stages

 of electric mark development             stages of electric mark development  in logarithmic     coordinate system

With the increase of the degree of electrical mark corrosion and insulation pollution, the bulk resistance of ethylene propylene rubber decreased gradually, and the polarization - depolarization current and recovery voltage increased gradually. That was, the magnitude and change of insulation resistance, polarization-depolarizing current and recovery voltage could reflect the insulation fault condition.

                                     Recovery voltage under different                 Recovery voltage under different

                                    corrosion degree of electric mark                  degree of toner pollution

Amplifier's role in this experiment：amplify the voltage as a DC current source

Parameters and appearance of ATA-7020：