Recently, while assisting a friend in reviewing his equipment procurement list, I discovered that the rated voltage of the ultra-low frequency high-voltage generator he selected was sufficient, but its load capacity did not match the tested cable, resulting in the inability to generate a normal waveform on site. Such issues could have been avoided with a bit of extra consideration during model selection. Below, let's discuss the key parameters to focus on when selecting ultra-low frequency equipment.

Firstly, allowance should be made for the rated voltage

The rated voltage must be higher than the test voltage of the tested object, and sufficient safety margin should be reserved. It is not allowed to choose the upper limit. Taking the 10kV power cable as an example, the ultra-low frequency test voltage is set at 3 times the rated phase voltage, which is about 17-18kV peak value. Choosing a 30kV model is sufficient; however, if it is a cable for a 35kV system, the test voltage will be close to 80kV peak value, and an 80kV model must be selected. It is not allowed to use a 50kV device to force the test.

Secondly, the load capacity must match the capacitance of the tested object

This is the parameter that is most easily overlooked. The load capacity of ultra-low frequency equipment is indicated by the maximum capacitance of the test sample, such as a maximum of 0.5µF at a frequency of 0.1Hz. If the capacitance of the tested cable exceeds this value, the output waveform of the equipment will be severely distorted, rendering the test data meaningless. It is recommended to estimate the capacitance of the test sample (calculated as cable length × unit capacitance) before purchasing, and then confirm whether it matches the equipment parameters. If the capacitance is too small (less than 0.05µF), it can also lead to abnormal output, in which case a parallel compensation capacitor is needed to assist the output.

Third: the more frequency levels, the more flexible it is

High-quality models typically offer three frequency settings: 0.1Hz, 0.05Hz, and 0.02Hz. The lower the frequency, the greater the capacitance that the same device can handle - at 0.02Hz, the load capacity is five times that of 0.1Hz. When the capacitance of the test sample on site is relatively large, switching to a lower frequency setting can expand the testing range, and this flexibility is valuable in practical work.

Fourth: whether the protection function is comprehensive

The on-site testing environment is complex, and overvoltage protection, overcurrent protection, and flashover protection are all indispensable. The protection action time of high-quality models should be within 10ms. Too slow a response will cause the tested product or equipment to bear unnecessary impact under abnormal conditions.

Fifth: Portability

The controller and booster are designed separately, allowing for more flexible on-site layout; the overall weight and shape of the machine determine whether it can enter a specific on-site environment, which also needs to be confirmed with the manufacturer in advance.