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 to the ATV output (because motor is not connected) so there is no information from current measured. During this test the ATV 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.
The difference between IGBT diagnostic test with and without the motor is following:
During the test without the motor, there is not current to the ATV output (because motor is not connected) so there is no information from current measured. During this test the ATV 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.
Released for: Schneider Electric Macedonia
