The advantages and disadvantages of DC withstand voltage test are analyzed as follows:
advantage
① Local defect detection sensitivity: DC withstand voltage test is more sensitive to local defects in insulation, making it easier to detect local discharge and insulation weaknesses.
② The equipment is simple and easy to operate: The testing equipment for DC withstand voltage test is relatively simple and easy to operate.
③ Not affected by frequency: Compared with AC withstand voltage test, DC withstand voltage test does not need to consider the influence of frequency on insulation during the test.
④ Low damage to insulation: Under DC voltage, insulation basically does not produce dielectric loss, so the damage to insulation caused by DC withstand voltage is relatively small.
⑤ Discovery of insulation defects at the root of the motor: DC withstand voltage test is more effective in detecting insulation defects at the root of the motor than AC withstand voltage test.
shortcoming
① Polarization effect impact: During DC withstand voltage testing, it may be affected by polarization effect, resulting in inaccurate evaluation of insulation condition.
② Unable to simulate actual electric field: The DC withstand voltage test cannot simulate the electric field situation of the equipment under actual working voltage, so its test results may differ from the actual operating conditions to some extent.
③ Significant damage to cables: The voltage of the DC withstand voltage test is relatively high and the test time is relatively long, which may cause significant damage to the tested equipment such as cables and affect the service life of the equipment. Especially for rubber cables, under direct current voltage, due to changes in temperature and electric field strength, the resistance coefficient will change, resulting in changes in the distribution of electric field strength throughout the insulation, which may cause a decrease in the breakdown voltage of the insulation layer.
④ Unable to detect mechanical damage: DC withstand voltage tests usually cannot detect defects such as mechanical damage.
⑤ Generating DC bias voltage: Due to the "memory" nature of the rubber cable structure, DC withstand voltage testing may cause the cable to generate DC bias voltage. This DC bias voltage may be superimposed on the peak AC voltage during cable operation, which may result in overvoltage and damage to the cable.
In summary, the DC withstand voltage test has its unique advantages and limitations. In practical applications, it is necessary to choose whether to use DC withstand voltage test or combine it with other testing methods based on the characteristics, testing requirements, and relevant standards of the tested equipment, in order to more comprehensively evaluate the insulation condition of the equipment.
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