6.2.1.3 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 LC
inductor secondary side terminals L1, L2, and L3
in sequence.
Each reading should show a diode drop.
6.2.1.4 Inverter Test Part IV
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 LC
inductor secondary side terminals L1, L2, and L3
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 filter 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
7 D-Frame Sizes Disassembly and
or
8 E-Frame Sizes Disassembly and
. It is further recommended for units
with two IGBT modules that both modules be replaced
even if the second module tests correctly.
6.2.2 Gate Resistor Test
Indications of a failure in this circuit
IGBT failures may be caused by the filter being exposed to
repeated ground fault faults or by extended filter
operation outside of its normal operating parameters.
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. These are labeled MK
250, 350, 450, 550, 650, 750, 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 7.8 K Ω
for D-frames and 3.9 K Ω for E-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
7 D-Frame Sizes Disassembly and
or
8 E-Frame Sizes Disassembly and
6.2.3 Intermediate Section Tests
The intermediate section of the filter is made up of the DC
bus capacitors, 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 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.
The only 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
Test Procedures
VLT Advanced Active Filter AAF006 D and E Frames Service Manual
MG90Z122 - VLT
®
is a registered Danfoss trademark
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