GE Industrial Solutions AF-600 FP High Power (460V_575V 150HP and above) - Manual (Page 80)

Disconnect motor leads when testing inverter section. With leads connected, a short circuit in one phase will read in all phases, making isolation
difficult.
Before starting tests, ensure that meter is set to diode scale. If removed previously, reinstall the soft charge card and power cards. Do not disconnect the cable
to connector MK105 on the power card since the path for continuity would be broken.
Inverter test part
1. Connect the positive (+) meter lead to the (+) positive DC bus connector MK105 (A) on the power card.
2. Connect the negative (–) meter lead to terminals U, V, and W in sequence.
Each reading should show infinity. The meter will start at a low value and slowly climb toward infinity due to capacitance within the frequency converter being
charged by the meter.
Inverter test part II
1. Reverse the meter leads by connecting the negative (–) meter lead to the positive (+) DC bus connector MK105 (A) on the power card.
2. Connect the positive (+) meter lead to U, V, and W in sequence. Each reading should show a diode drop.
Incorrect reading
An incorrect reading in any inverter test indicates a failed IGBT module. Replace the IGBT module according to the disassembly instructions in Section 7 or 8. It is
further recommended for units with two IGBT modules that both modules be replaced even if the second module tests correctly.
Inverter test part III
1. Connect the positive (+) meter lead to the negative (-) DC bus connector MK105 (B) on the power card.
2. Connect the negative (–) meter lead to terminals U, V, and W in sequence. Each reading should show a diode drop.
Inverter test part IV
1. Reverse the meter leads by connecting the negative (–) meter lead to the negative (-) DC bus connector MK105 (B) on the power card.
2. Connect the positive (+) meter lead to U, V, and W in sequence.
Each reading should show infinity. The meter will start at a low value and slowly climb toward infinity due to capacitance within the frequency converter being
charged by the meter.
Incorrect reading
An incorrect reading in any inverter test indicates a failed IGBT module. Replace the IGBT module according to the disassembly instructions in Section 7 or 8. It is
further recommended for units with two IGBT modules that both modules be replaced even if the second module tests correctly.
Indications of a failure in this circuit
IGBT failures may be caused by the frequency converter being exposed to repeated short circuits or earth faults, or by extended frequency converter operation
outside of its normal operating parameters. Following an IGBT failure, it is important to verify the gate frequency converter signals are present and of the correct
waveform. See the dynamic test section on checking IGBT gate drive signals.
Gate resistor test
Mounted to each IGBT module is an IGBT gate resistor board containing, among other components, the gate resistors for the IGBT transistors. Based on the nature
of the failure, a defective IGBT can produce good readings from the previous tests. In nearly all cases, the failure of an IGBT will result in the failure of the gate
resistors.
Located on the gate drive card near each of the gate signal leads is a 3 pin test connector (see Illustration 6-17). These are labelled MK 250, 350, 450, 550, 650,
750, and, if the frequency converter is equipped with a brake option, 850.
For the sake of clarity, refer to the 3 pins as one, two, and three, reading left to right. Pins 1 and 2 of each connector are in parallel with the gate drive signal sent
to the IGBTs. Pin 1 is the signal and Pin 2 is common.
1. With ohmmeter, measure pins 1 and 2 of each test connector. Reading should indicate 7.8K ohms for 41/43 Frames, 3.9K ohms for 42/44 Frames, and
2.6K ohms for 51/52 frames.
Incorrect reading
An incorrect reading indicates that either the gate signal wires are not connected from the gate drive card to the gate resistor board or the gate resistors are
defective. Connect the gate signal wires, or if the resistors are defective, the entire IGBT module assembly requires replacement. Replace the IGBT module according
to the disassembly procedures in Section 7 or 8.
AF-650 GP and AF-600 FP High Power Service Manual
79
6