The dry-type transformer withstand voltage test is a method to detect the operation of the transformer.
Applied withstand voltage test
External withstand voltage test is a test in which a labor frequency high voltage is applied to the tested dry-type transformer for 1 minute, which is also called a labor frequency withstand voltage test. This is used to investigate the insulation performance between windings on different sides and between windings and ground. In other words, in order to investigate the main insulation level of dry-type transformers, it is only applicable to fully-insulated dry-type transformers.
Therefore, the test winding will be grounded on the other side of the dry-type transformer. When the external withstand voltage test is performed, switch the switch when the power supply voltage is low; when the test power supply voltage reaches below 40% of the test voltage, the boost speed is arbitrary; when the test power supply voltage is above 40%, it rises at a rate of 3% per second; After reaching the specified voltage and duration, the test voltage should be quickly and evenly reduced to less than 25% of the test voltage within 5S, and the power supply can be cut off.
Impulse voltage test
Impulse voltage test is divided into lightning impulse test (including full-wave impulse test and choba impulse test) and switching wave impulse test. In the newly specified iec76-3 standard, the usual tests for dry-type transformers with um≤40.5kV are full-wave impulse test and choba impulse test.
For dry-type transformers with UM≥72.5kV, the full-wave impulse test is a conventional test, and the chopper impulse test is a type test. The dry-type transformer, full-wave, choba, and working wave impulse tests for UM≥252kV are routine tests. Perform full-wave shock and cut-off shock tests alternately. Generally it is negative polarity. First, perform full wave shock, secondary shock wave, and second full wave shock. Therefore, a cutting device is required.
When the dry-type transformer has a large capacity, if the capacity is too large to meet the waveform requirements, please run the multi-level impulse voltage generator in parallel. When conducting an impulse test at the neutral point of a dry-type transformer, due to the waveform and large capacitance of the three-phase input line, the test voltage is generally not high. Please put several levels of impulse voltage generators in parallel.