Very Low Frequency (VLF) generators are mainly used for insulation withstand voltage tests of power equipment such as cables, rotating motors, GIS, etc. Their frequency range is usually much lower than the power frequency (50Hz/60Hz) to reduce the size of the equipment and the capacitance current during testing. The common frequencies and corresponding applications are as follows:
Typical frequency range
0.1Hz (sine wave or cosine square wave)
The most widely used, suitable for withstand voltage testing of medium and high voltage cables (such as 10kV~35kV) and power capacitors.
Advantages: Good equivalence with power frequency, shorter testing time, and compliance with most international standards (such as IEC 60502, IEEE 400).
0.05Hz (commonly used cosine square wave)
Applicable scenarios: Insulation testing of ultra-high voltage cables (such as 110kV and above), large generators or transformers.
Features: Further reduce equipment load, suitable for long-distance cables or high capacitance load devices.
0.02Hz (ultra-low frequency, close to DC characteristics)
Special applications: Used for devices that require high DC withstand capability (such as certain DC cables), or for scenarios that require extremely low test power.
Other low frequencies (such as 0.01Hz or custom frequency)
Special requirements: Customized according to specific standards or equipment manufacturer requirements, commonly used in scientific research or special condition testing.
