In the substation electrical equipment power supply and distribution system, high-voltage electrical equipment should be regularly tested for preventive stress, and the AC withstand voltage test is a critical test item.
In the substation electrical equipment power supply and distribution system, high-voltage electrical equipment should be regularly tested for preventive stress, and the AC withstand voltage test is a critical test item. In the preventive test, after insulation resistance test, absorption ratio test and leakage current measurement, DC withstand voltage test and other items are completed, although many insulation defects can be found, the test voltage is often lower than the working voltage of the test object. This is not enough to ensure safe operation. In order to further expose equipment defects, check the insulation level of the equipment, and determine whether it can be put into operation reliably, it is necessary to conduct AC withstand voltage test.
First, test safety operation and precautions
(1) The line connection of the test device must be correct and reliable, and the high-voltage part should maintain a sufficient safety distance. A thorough inspection should be done before power-on.
(2) The test object and test equipment should be properly grounded. All supported insulation must have sufficient insulation and mechanical strength.
(3) The AC withstand voltage test should be handled cautiously in the absence of insulation defects after other test items are completed; if other test items are completed and the equipment is found to have insulation defects, it is not possible to rashly decide to communicate. Withstand voltage test to prevent unnecessary damage to equipment. Before and after the AC withstand voltage test, the insulation resistance should be measured.
(4) The surface of the test object should be clean and dry. The resettlement condition should be in accordance with the actual use. For oil-filled equipment, the insulating oil should be basically in a static state before the voltage test can be applied.
(5) Check whether the voltage regulating transformer is at zero before closing. During the process of raising and lowering the voltage regulating transformer, it is necessary to monitor the relevant instruments; when adding voltage, the high voltage circuit should be closely monitored to monitor whether the tested product has sound.
(6) The boosting speed of the voltage regulating transformer may not be specified for porcelain insulation and switch equipment; however, for valuable equipment such as transformers and generators, before the test voltage is 40%, it may be arbitrary, and thereafter The boost must be uniform, with a test voltage of approximately 25%/s.
(7) The test circuit should have appropriate protection facilities. If abnormal conditions occur during the test, immediately step down, then disconnect the power supply, and hang the ground wire before checking.
(8) AC withstand voltage test time, generally 1 min; in the case of insulating rods, live working tools and separate organic insulating materials, it should be 5 min. After disconnecting the power, you must touch the part to check for heat.
Second, the test product
HYD series power frequency withstand voltage test device is used for insulation strength test under various voltages of various power products, electrical components, and insulating materials, and finds the insulation defect of the test article and the ability to measure overvoltage. Widely used in electrical manufacturing departments, power departments, research institutes and institutions of higher learning. Features: (1) small size, light weight, compact structure, no oil leakage, maintenance-free; (2) simple and intuitive wiring, easy to use; (3) good insulation reliability, beautiful appearance; (4) overvoltage protection;
Third, the test analysis (1) According to the test loop test conditions of the test article. If the setting value of the overcurrent relay is appropriate, the overcurrent relay should be operated when the test object breaks down, and the electromagnetic switch will follow. If the setting value is too small, it may be in the boosting process, not the breakdown of the test object, but the electromagnetic switch is tripped due to the large current of the test. If the setting value is too large, even if the test object discharges or the small current breaks down. It will not be reflected.
(2) Analyze according to the test conditions of the test article. During the test, if the test article emits a breakdown sound, emits intermittent sound, smoke, gas, burnt smell, fire, and burning, it must be checked whether the condition actually comes from the test object. The insulating part, if it is from the insulating part of the test piece, is considered to have a problem with the insulation of the test piece or has been broken down.
(3) For the equipment with integrated insulation, the insulation resistance before and after the withstand voltage should not drop by 30%, otherwise it will be unqualified. For pure porcelain insulation, or equipment with porcelain insulation on the surface, which is susceptible to the climatic conditions at the time, it can be disposed of as appropriate.
(4) In the test process, if the surface is flashed or discharged due to the influence of air humidity, temperature, or surface contamination, it should not be considered as unqualified. After cleaning, drying, etc., test again. If it is not caused by external factors, but due to insulation damage, aging, etc. of the glaze layer on the surface of porcelain, it should be considered unqualified if it is caused by localized redness on the surface after pressurization.
At the same time, in selecting the pressure test equipment of the transformer station, we must pay attention to the quality of the product and the long-term stability of the product. Only in this way can the substation electrical equipment be tested better.
Article source: Wuhan Huadian Hi-Tech ()
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