GE Industrial Solutions AF-600 FP High Power (460V_575V 150HP and above) - Manual (Page 81)

6.2.6 Brake IGBT Test
This test can only be carried out on units equipped with a dynamic brake option. If a brake resistor is connected to terminals 81 and 82, disconnect it before
proceeding. Use an ohmmeter set on diode check or Rx100 scale.
Brake IGBT test part I
1. Connect the positive (+) meter lead to the brake resistor terminal R+ (82).
2. Connect the negative (-) meter lead to the brake resistor terminal R- (81).
The reading should indicate infinity. The meter may start out at a value and climb toward infinity as capacitance is charged within the frequency converter.
Brake IGBT test part II
1. Connect the positive (+) meter lead to the brake resistor terminal R- (81).
2. Connect the negative (-) meter lead to the brake resistor terminal R+ (82).
The reading should indicate a diode drop.
Brake IGBT test part III
1. Connect the positive (+) meter lead to the brake resistor terminal R- (81).
2. Connect the negative (-) meter lead to the negative (-) DC bus connector MK105 (B) on the power card.
The reading should indicate infinity. The meter may start out at a value and climb toward infinity as capacitance is charged within the frequency converter.
Incorrect reading
An incorrect reading on any of the above tests indicates that the brake IGBT is defective. Replace the brake IGBT in accordance with the disassembly procedures
in Section 7 or 8.
The failure of any IGBT may also lead to a failure of the gate drive circuit supplying that device. Following the replacement of an IGBT, always ensure the gate
drive signals are tested in accordance with the procedures in the dynamic test section.
6.2.7 Intermediate Section Tests
The intermediate section of the frequency converter is made up of the DC bus capacitors, the DC coils, and the balance circuit for the capacitors.
1. Test for short circuits with the ohmmeter set on Rx100 scale or, for a digital meter, select diode.
2. Measure across the positive (+) DC terminal (A) and the negative (–) DC terminal (B) on connector MK105 on the power card. Observe the meter polarity.
3. The meter will start out with low ohms and then move towards infinity as the meter charges the capacitors.
4. Reverse meter leads on connector MK105 on the power card.
5. The meter will peg at zero while the capacitors are discharged by the meter. The meter then begins moving slowly toward two diode drops as the meter
charges the capacitors in the reverse direction. Although the test does not ensure the capacitors are fully functional, it ensures that no short circuits
exist in the intermediate circuit.
Incorrect reading
A short circuit could be caused by a short in the soft charge, rectifier, or inverter section. Be sure that the tests for these circuits have already been performed
successfully. A failure in one of these sections could be read in the intermediate section since they are all routed via the DC bus.
If a short circuit is present, and the unit is equipped with a brake, perform the brake IGBT test next.
The only other likely cause would be a defective capacitor within the capacitor bank.
There is not an effective test of the capacitor bank when it is fully assembled. Although it is unlikely that a failure within the capacitor bank would not be indicated
by a physically damaged capacitor, if suspect, the entire capacitor bank must be replaced. Replace the capacitor bank in accordance with the disassembly
procedures in Section 7 or 8.
AF-650 GP and AF-600 FP High Power Service Manual
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