The insulation test (also called high resistance test) is always made DC. The insulation test is combined with a short-circuit test and high voltage test in DC.
The insulation test combines several functions.
The insulation test can perform:
- measurement of insulation resistances from 50 kΩ to 2000 MΩ at high voltage (20V to 2000V, depending on the switching matrix).
- measurement of dielectric strength and detection of short circuits.
The insulation test proceeds as follows:
- An initial test at low voltage (continuity measurement) to detect any short circuit(1). If a short circuit is found, the insulation test stops (the message SHORT CIRCUIT appears in the error list).
- If there is no short circuit, the high voltage is applied. During the programmable rise time(2), if breakdown occurs, the voltage is displayed and the test stops (the breakdown voltage is given in the error list).
- If no breakdown occurs and if the voltage does not reach the required value (±10%), the message U<Uprog appears in the error list.
- Next, the voltage is applied for the duration of the programmed application time(3). If breakdown occurs during this period, the moment when the fault appears is displayed in the error list and the test stops.
- Lastly, if all goes well, at the end of the application time(4), the insulation test is made and the insulation resistance measured. The tester will add a measurement time as a function of the range requested. The measurement time varies from 20ms to 240ms according to range.
- To end the sequence, the tester reduces the high voltage and then discharges the unit tested to an earth resistance (total time 20ms).
This procedure is identical at the end of every measurement of insulation.
The dielectric strength test detects any sudden variation in the increase of the test current outside the programmed limit.
The short circuit test or high voltage test can be programmed out of the test.