What are the results of IGBT transistor tests with/without motor when testing Altivar variable speed drive. Is there a difference?
The result can be: OK, open or short circuit.
The difference between IGBT diagnostic test with and without the motor is following:
During the test without the motor, there is not current flown from variable speed drive (VSD), because motor is not connected. So there is no information based on current measurement at VSD output. During this test the VSD switches on upper IGBT (between DC+ and phase U) and measures voltage on phase U. Then it continues to switch all other IGBTs. With this test it is possible to recognize if one or more IGBTS are permanently conductive which means in short circuit. During the test without the motor it is not possible to detect if one or more IGBTs are permanently open (not conductive).
To be able to detect also if IGBT is permanently open, the second test must be done - with the motor connected. If IGBT is permanently open and never go conductive, it will be recognized in the measured current. And it can be done only if the motor is connected.
So test without motor can bring OK/short circuit result and test with motor OK/open circuit/short circuit.