I. Definition of Insulation Withstand Voltage Test
Insulation withstand test is a technical method used to inspect and evaluate the insulation voltage tolerance capability of electrical equipment. For some critical equipment in operation that lacks spare parts or has a long repair time, it is necessary to carefully consider whether to conduct an insulation withstand test.
It is a technical means for testing and evaluating the insulation withstand voltage capacity of electrical equipment. All the live parts of electrical equipment and the parts that are not at the same electrical potential need to be isolated by insulation structures to ensure the normal operation of the equipment. The dielectric strength of a single insulating material is expressed by the average breakdown electric field strength along its thickness (in units of kV/cm). The insulation structure of electrical equipment, such as the insulation of generators and transformers, is composed of various materials and has an extremely complex structure. Any damage in a local area of the insulation structure will cause the entire equipment to lose its insulation performance. Therefore, generally, only the withstand voltage (in units of kV) that the equipment can tolerate can be used to represent the overall insulation capacity of the equipment. The insulation withstand test voltage can indicate the voltage level that the equipment can withstand, but this is not equivalent to the actual insulation strength of the equipment. The specific requirements for insulation coordination in power systems are to coordinate and formulate the insulation withstand test voltages of various electrical equipment to indicate the insulation level requirements for the equipment. The insulation withstand test is a destructive test (see insulation test), therefore, for some running critical equipment that lacks spare parts or has a long repair time, it is necessary to carefully consider whether to conduct an insulation withstand test.
II. Types of Insulation Withstand Voltage Tests
During the operation of various electrical equipment in the power system, in addition to being subjected to the working voltage of alternating current or direct current, they will also encounter various overvoltages. These overvoltages not only have high amplitudes, but also have different waveforms and durations from the working voltage, and their effects on insulation and the mechanisms that may cause insulation breakdown are also different. Therefore, corresponding test voltages need to be used for the withstand voltage tests of electrical equipment. The Chinese national standards specify the insulation withstand voltage tests for the alternating current power system as follows: ① Short-term (1 minute) power frequency withstand voltage test; ② Long-term power frequency withstand voltage test; ③ DC withstand voltage test; ④ Operational impulse wave withstand voltage test; ⑤ Lightning impulse wave withstand voltage test. It is also stipulated that the insulation performance of 3-220kv electrical equipment under the power frequency operating voltage, temporary overvoltage and operational overvoltage should generally be tested using the short-term power frequency withstand voltage test, and the operational impulse test can be omitted. For 330-500kv electrical equipment, the operational impulse test is required to test the insulation performance under operational overvoltage. The long-term power frequency withstand voltage test is a type of test inspection carried out for the situations of insulation deterioration inside the equipment and contamination of the external insulation.
In the preventive insulation tests of power system equipment (see insulation tests), direct current high voltage is often used to measure the leakage current and insulation resistance of cables, capacitors, etc., and also to conduct insulation withstand tests. The tests show that when the frequency is within the range of 0.1 to 50 Hz, the voltage distribution within the multi-layer medium basically follows the capacitance distribution. Therefore, conducting withstand tests at 0.1 Hz ultra-low frequency can be equivalent to the industrial frequency withstand tests, which not only avoids the difficulties of using large-capacity alternating current withstand test equipment, but also can reflect the insulation condition of the tested equipment. Currently, ultra-low frequency withstand tests for the end insulation of motors are considered to be more effective than industrial frequency withstand tests.
Post time: Jun-23-2026