Wire and cable products withstand voltage test

1 AC voltage test Finished voltage test is AC voltage test, also called power frequency withstand voltage test. The AC withstand voltage test is to apply a certain multiple voltage value higher than the working voltage (rated voltage) on the wire and cable finished insulation, and to maintain a certain time without insulation breakdown. For insulated power wires and cables for power transmission, each product must undergo this test before leaving the factory.

The purpose of withstand voltage test is to evaluate the reliability of the product under the operating voltage and find serious defects in the insulation, but the most important is to find the defects in the production process, such as: the external damage in the insulation, the electric field makes the electric field sharp Serious defects such as distortion.

The principle of selecting the withstand voltage test voltage is: it is necessary to be able to discover the serious defects in the insulation, and at the same time it will not damage the intact insulation, resulting in the dark injury of the insulation. General wire and cable withstand voltage for 5 minutes.

2 Requirements of test equipment The frequency of the test voltage shall be an alternating voltage of 40-60 Hz. The waveform of the voltage shall be close to a sine wave and the ratio of the peak value to the effective value shall be.

The test voltage value and withstand voltage time of the sample shall be in accordance with the relevant product standards.

3 Test methods 3.1 Preparation of test specimens The length of the terminal part of the test specimen and the method of handling the terminal shall be such that no flashover or internal breakdown occurs along the surface of the specimen under the specified test voltage.

When testing in the water tank, the length of the two ends of the specimen protruding from the water surface shall not be less than 200mm, and it shall be ensured that under the specified test voltage, no flashover discharge occurs along the surface of the specimen.

3.2 Test procedure The test procedure shall be conducted in accordance with the operating procedures of the factory pressure test. (On-site operation)

During the test, the difference between the test temperature and the ambient temperature should not exceed ±3°C.

During the test, the voltage shall be gradually and smoothly raised to the specified test voltage value from the beginning of the lower value (not exceeding 40% of the test voltage specified in the product standard), and the voltage shall be lowered after maintaining the specified withstand voltage time. Up to 40% of the specified test voltage value, and then cut off the power, it is not allowed to suddenly cut off the power under high voltage, so as to avoid overvoltage.

3.3 Evaluation of voltage test The test specimen is considered to pass the power frequency withstand voltage test without any breakdown phenomenon at the specified test voltage and duration.

If, during the test, an end or terminal of the test specimen has a flashover discharge or internal breakdown along its surface, it is permissible to make another end connection and repeat the test. In addition to special provisions in the product standard, it must be re-timed.

In the course of the test, if the test is continued after a power outage, it must be re-timed unless otherwise specified in the product standard.

3.4 AC withstand voltage test notes a) Test equipment should be regularly tested;

b) The test circuit shall have a quick overcurrent protection device to ensure that the test power supply can be quickly removed when the test breakdown or flashover or internal breakdown of the specimen end or terminal occurs along the surface.

c) There should be a metal grounding fence around the test area, and there are safety measures such as chain control, signal indicators and “high voltage hazard” warning signs at the entrance and exit.

d) There should be a grounding wire in the test area, and the grounding resistance should be less than 4 ohms. The grounding terminal of the step-up transformer and the grounding terminal or additional electrode of the tester should be connected to the grounding electrode very reliably.