Hipot test is an abbreviation of High Potential test, also known as a Dielectric Withstand Test.
Basically it is a test that applies high voltage to assets to determine the adequacy of the electrical insulation to withstand voltage transients and make sure the insulation is not marginal.
This sort of testing is most often used as part of commissioning tests along with Insulation Resistance (IR) testing. It is applied to identify significant defects within the insulation system, inadequate creepage or clearance distances that may have been introduced during manufacturing or installation.
Hipot testing will only detect major defects and issues. For the detection and location of smaller defects we use the same 50Hz power supply to carry out offline PD measurements on switchgear.
Offline Partial Discharge Measurement at 50Hz
Offline testing for PD is performed using a 50Hz external power supply, coupling capacitor and detecting equipment. We carry out this testing as part of commissioning acceptance or investigation tests in line with the Australian Standard AS 60270 (IEC 60270).
This testing is typically undertaken on busbars and circuit breakers or individual components when tracking down internal sources of PD detected using online techniques. It is a much more accurate and sensitive test than withstand testing.
Testing with a 50Hz power supply (high voltage but low power) means that cables and voltage transformers are generally disconnected during test due to their inherent capacitance. Testing long busbars or switchgear with cables connected will be done using a VLF power supply.
Very Low Frequency (VLF) Testing
The power required to energise an asset’s capacitance is proportional to the test frequency. Compared to 50Hz, energising using a VLF power supply will draw 500 to 5000 times less power (0.1 – 1Hz).
VLF testing is therefore a more practical approach for Hi-pot testing or offline PD testing of cables.
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