The charging method is one of the important determining factors of the performance of the impulse voltage generator. HZCJ-400kV adopts a constant current charging device, which is not a random choice, but a direct response to the accuracy requirements of the repeatability test.

The problem with ordinary charging methods

The charging current of traditional transformer charging method (RC charging) varies with the degree of capacitor charging - the current is high at the beginning of charging, and the closer it is to the target voltage, the smaller the current. Theoretically, it takes infinite time to charge to the target voltage (exponential curve approaching).

This brings two problems: firstly, it is difficult to accurately control the termination time of charging, as the charging to "99% or 101% of the target voltage" is determined by analog circuits, and the deviation is not fixed each time; Secondly, the charging time is not fixed, and there is a difference in the charging time between adjacent impacts, resulting in slight differences in the state of the generator (especially the temperature of the modulation resistor) each time, which affects the waveform repeatability.

The working principle of constant current charging

The constant current charging device maintains the charging current at a fixed value through feedback control, and the charging current remains constant (within the set range) regardless of the current voltage of the capacitor. This results in a linear increase in charging voltage over time, with precise and controllable timing of charging to the target voltage. Once the voltage reaches the set value, it immediately stops (with an accuracy of ≤± 1%).

Technical Implementation of HZCJ-400kV Constant Current Charging

Adopting a bilateral symmetrical constant current charging method: the secondary voltage of the charging transformer is 85kV, which is rectified by a high-voltage rectifier silicon stack (2DL-200kV/200mA), and then controlled by PID algorithm to achieve constant current charging within the range of 10% to 100% of the rated charging voltage.

Key indicators:

Deviation between charging voltage and set voltage: ≤± 1%

Instability of charging voltage: ≤± 1%

Non repeatability of charging voltage: ≤± 1%

Voltage adjustable accuracy: 1% (i.e. 0.1kV step size)

There are two selectable charging speeds, which can be flexibly adjusted according to experimental requirements

The actual value of constant current charging

For high-voltage insulation tests, the peak voltage of each impulse must fall precisely within the range required by the regulations (usually 100% ± 5% of the rated voltage). The ± 1% voltage accuracy of constant current charging ensures the comparability of test results and the authority of reports, and the determination of charging time greatly improves test efficiency - the preparation time for one impact is shortened, which is conducive to completing all impact cycles within the specified discharge interval.