Precautions in DC withstand voltage test and DC leakage test

DC withstand voltage test and DC leakage test
(1) Methods of DC withstand voltage test and DC leakage test DC withstand voltage test:
The test voltage is generally divided into 2 to 5 sections, with each section’s amplitude being as equal as possible. During the voltage increase process, the voltage and current should be observed section by section.
2) The speed of voltage increase should be uniform, at 1 to 2 kV per second. If the capacity of the test subject is large, the speed of voltage increase should be appropriately slowed down to allow the charge on the test subject to accumulate gradually. During the voltage increase, keep an eye on the voltmeter and ammeter at all times to monitor the situation and proceed with the voltage increase.
After the voltage is raised to a higher level, according to the regulations and standards, a stable voltage should be maintained on the test subject for a certain period of time. For the assessment of electrical equipment, the duration should not be arbitrarily extended or shortened.
DC leakage test:
Observe the conductance current at each voltage level during the test. Whenever the voltage reaches a certain level, stop increasing it and observe the leakage current at that voltage level after one minute of pause, then make a record.
When the voltage reaches the final section, observe the leakage current for one minute. Then, divide the withstand voltage time of the final voltage section into several equal time periods to test the leakage current. Record the leakage current value for each time period.

3) After the set time, quickly and evenly reduce the voltage, cut off the power supply, and discharge to end this test.
When discharging the test subject, safety must be ensured. An insulated rod should be used to discharge through the discharge resistor, and it is important to ensure that the discharge is thorough and the discharge time is long enough; otherwise, it may bring about unsafe factors.
(2) The equipment and wiring for DC withstand voltage tests and DC leakage tests are generally composed of a complete set of DC withstand voltage test equipment, which includes: a voltage regulator, a step-up transformer, a rectifier silicon stack, a control box, a current-limiting resistor, test instruments, and a discharge rod, among other components.
(3) Precautions in DC withstand voltage test and DC leakage test
The test must comply with the safety work regulations and high-voltage operation rules, clearly designate the operator and supervisor, and they must fulfill their respective duties.
2) Before the test, make sure to understand the leakage situation of the test equipment and the condition of the test sample. Conduct an empty-rising test on the test equipment. Only after there are no issues should the test sample be connected for the test. The true test result should be the measured leakage current minus the leakage current of the test equipment. When measuring DC high voltage, use a meter with no less than 1.5 grade and a voltage divider with no less than 2.5 grade for measurement.
3) Before voltage boosting, divide the voltage into sections. During the voltage boosting process, increase the voltage step by step. Read the corresponding leakage value for each section. The leakage value indicated by the microampere meter should be read after one minute when it stabilizes. Finally, draw the volt-ampere characteristic curve based on the test values.
Before the test, the placement and wiring of the test equipment should be checked to ensure that the operators maintain a safe distance under high voltage. The instrument observation should be reasonable and convenient. The test wiring should be firm, and the voltage regulator should be at zero position.
5) During the test, the voltage increase method was correct, the test readings were relatively accurate, and the time was well controlled. After the test, the voltage regulator was returned to zero, the power was cut off, and the test sample was discharged.
When recording, the temperature at that time should be noted for conversion and comparison with the results of the previous test.
If there are any abnormal conditions such as breakdown, flashover, large swings of the microampere meter or sudden changes in current during the test, immediately reduce the voltage and cut off the power supply. After identifying the cause and completing the handling, the test can be resumed.
(4) Judgement of test results in DC withstand voltage test and DC leakage test
1) Judging the situation based on the indication phenomenon of the microammeter: If the pointer swings back and forth, there may be an AC component passing through the microammeter. The average value can be read. If the value cannot be read, check the protection circuit of the microammeter, or increase the filter capacitor. If necessary, change the filtering method.
If the pointer swings periodically, it may be due to poor contact of the test sample, causing periodic discharge. The cause should be identified and eliminated. If the pointer suddenly jolts in the direction of lower values, it may be caused by the power supply circuit. If it jolts in the direction of higher values, it may be due to flashover in the test circuit or the test sample, or it may be caused by intermittent internal discharge. If the pointer value gradually decreases over time, it may be due to a reduction in the charging current or an increase in the surface insulation resistance of the test sample. If it gradually increases, it may be due to insulation aging of the test sample.
2) Judging from the leakage microampere meter reading: If the leakage current is too large, the conditions of each device in the test circuit and the shielding should be checked first. Only after eliminating external factors can a correct judgment be made on the test sample; if the leakage current is too small, check whether the wiring is correct and whether there is any shunt or short circuit in the microampere meter protection part.