The generation of the lightning impulse waveforms by the impulse voltage generator is quite simple. It only requires connecting an appropriate cutoff gap in parallel to the test specimen, allowing it to break down under the action of the full wave of the lightning impulse. Thus, the waveform acting on the test specimen becomes a cutoff wave.
Requirements for the cutoff device: low discharge dispersion; capable of accurately controlling the cutoff time.
The schematic diagram of the cutoff device based on the three-electrode pinhole spherical gap and the delay circuit shows that the self-discharge voltage of the main gap F of the spherical gap is slightly higher than the full wave voltage sent out by the generator. At the same time as the full wave voltage is applied to the cutoff gap, the starting voltage pulse from the voltage divider is sent through the delay circuit Y to the auxiliary triggering gap f of the lower sphere. After f breaks down, it immediately triggers the breakdown of the main gap F, thereby forming a cutoff wave.
The generation of the high voltage for the operational impulse of the impulse voltage generator. According to the standard, for ultra-high voltage electrical equipment with a rated voltage greater than 220 kV in factory tests and type tests (tests conducted to verify whether a new product can meet all the requirements of the technical specifications), it cannot be replaced by the equivalent power frequency withstand voltage test for 220 kV and below high-voltage electrical equipment. Therefore, an operational impulse voltage generation device is required.
Based on the non-periodic double-exponential impulse long wave simulation of the operational impulse voltage wave, the operational impulse voltage wave can be directly generated by the existing impulse voltage generator, which is exactly the same as the generation principle of the lightning impulse voltage wave. However, at this time, the front time and half-peak time have significantly increased. When choosing the circuit form and component parameters of the generator, the following issues need to be particularly considered:
1) To significantly extend the front time, or to series an external inductor L in the circuit, or to significantly increase the resistance value of R1 in the circuit, but doing so will significantly reduce the utilization coefficient of the generator. Therefore, a more efficient circuit (even so, its η is generally only 0.5 – 0.6) should be adopted. It can be seen that the maximum output voltage of a single impulse voltage generator for operational waves is much lower than that for lightning waves.
2) When calculating the parameters of the operational wave circuit, the approximate calculation method introduced for lightning waves cannot be used. Otherwise, it will bring a large error. The charging resistor R should also be considered for its influence on the waveform and the efficiency of the generator.
The insulation impulse high-voltage test of the electrical equipment’s lightning impulse withstand voltage test for internal insulation uses the three-impulse method, that is, applying three positive and three negative lightning impulse test voltages (1.2/50 μs full wave) to the test specimen. For the internal insulation of transformers and reactors, lightning impulse cutoff wave (1.2/2 – 5 μs) withstand tests should also be conducted. It is often more rigorous in testing the insulation of windings than the full wave lightning impulse voltage.
When conducting the operational impulse full wave withstand voltage test for internal insulation, a spherical gap should be connected in parallel to the test specimen, and its discharge voltage should be set 15% – 20% higher than the test voltage (for transformers and reactors) or 5% – 10% (for other specimens). The spherical gap serves as a protective function to prevent excessively high operational impulse voltages from being generated during the debugging of the impulse voltage generator, causing unnecessary damage to the test specimen.
The impulse voltage generator’s insulation impulse high-voltage test for external insulation of the power system can usually adopt the 15-impulse method: applying positive and negative impulse full wave test voltages to the tested specimen 15 times each, with the time interval between adjacent impulses not less than 1 minute. In each group of 15 impulse tests, if the number of breakdowns or flashovers does not exceed 2 times, it can be considered that the external insulation test is qualified. The methods of operational impulse high-voltage tests for internal and external insulation are exactly the same as the lightning impulse full wave tests.
Post time: Aug-14-2026