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 adjustable frequency drive.
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 accord-
ance with the procedures in the dynamic test section.
6.2.7 Intermediate Section Tests
The intermediate section of the adjustable frequency drive 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 func-
tional, 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.
6 Test Procedures
High Power Service Manual for VLT
®
FC Series
Adjustable Frequency Drives
6-14
MG.90.L1.22 - VLT
®
is a registered Danfoss trademark
6
Содержание VLT HVAC FC 100
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