Application Cases

Experiment Title: Polarization-Depolarization Current Measurement of Ethylene-Propylene Rubber

Research Direction: Electromagnetism

Experimental Content:
Apply high voltage across both ends of the ethylene-propylene rubber and measure the depolarization current.

Test Objective:
Investigate the changes in the depolarization current of ethylene-propylene rubber under different temperatures and humidity levels.

Test Equipment:
Signal generator, ATA-2081 high-voltage amplifier, ammeter, host computer, ethylene-propylene rubber material, protective electrodes.

Experimental Procedure:

Measurement System:
Since the current flowing through the ethylene-propylene rubber insulation during the depolarization process is capacitive and on the order of picoamperes (pA), accurate measurement of the depolarization current requires high-precision equipment. In this measurement system, the KEITHLEY 6517B is selected as the ammeter, with a DC current measurement range of 10 μA to 21 mA, fully meeting the measurement requirements. The ATA-2081 is chosen as the high-voltage DC power source for its low-noise characteristics, ensuring data reliability. The measurement uses a three-electrode configuration: the high-voltage terminal and measurement terminal are used for polarization and depolarization current measurements, while the protective electrode prevents surface leakage currents that could interfere with the results. The DC power source is set to positive polarity with a voltage of 400 V. The experimental environment is maintained at a temperature of 30°C and a relative humidity of 15%. During the measurement, the host computer saves the data collected in real-time by the 6517B via a serial port.

Experimental Method:
Before the experiment, the specimen to be measured is short-circuited at both ends to ensure complete discharge. The 6517B is then calibrated. During measurement, switch S is first closed to position S1 to charge the specimen. At the moment charging ends, S is switched to position S2 to discharge the specimen and measure the depolarization current. Throughout the process, the host computer displays the data collected in real-time by the 6517B via a serial port and saves the data after the measurement is complete. Typically, the measurement times for polarization and depolarization currents are the same. Due to the extremely small magnitude of the polarization-depolarization currents, the results are highly susceptible to external interference. To mitigate this, the specimen and electrodes are placed in a desiccator to shield against external disturbances. Additionally, the measurement temperature is kept constant, and humidity is controlled within a specific range to minimize environmental influences.

Experimental Results:

Figure 1: Polarization current of ETI at different temperatures

Figure 2: Polarization current of TOI at different temperatures

Figure 3: Polarization current of SOI at different temperatures

Figures 1, 2, and 3 show the polarization currents under a measurement voltage of 400 V at temperatures of 30°C, 50°C, 70°C, 90°C, and 110°C for different types of insulation faults. The results indicate that for the same insulation fault, the polarization current gradually increases with rising measurement temperature.

Figure 4: Depolarization current of SOI at different temperatures
Figure 5: Depolarization current of TOI at different temperatures

Figures 4 and 5 show the depolarization currents for two types of oil-contaminated specimens after the external voltage is removed, measured at temperatures of 30°C, 50°C, 70°C, 90°C, and 110°C. The results show that for the same insulation fault, the depolarization current gradually increases with rising measurement temperature. After the same decay time, the stabilized depolarization current tends to converge. Additionally, the decay rate of the depolarization current increases with higher measurement temperatures.

Theoretical analysis suggests that polarization and depolarization current measurements are interrelated processes. The initial state of the depolarization current is related to the stable state of the polarization current, and the depolarization current reflects the insulation resistance condition of the material. Therefore, the influence of temperature on polarization current follows the same principle as its effect on insulation resistance: as temperature increases, the movement of polar particles within the dielectric accelerates.

Figure: ATA-2081 High-Voltage Amplifier Specifications and Parameters