5.
The meter pegs at zero while the meter
discharges the capacitors. 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 that
the capacitors are fully functional, it ensures that
no short circuits exist in the intermediate circuit.
Incorrect reading
A short in the rectifier or inverter section could cause a
short circuit. 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 for failure would be a defective
capacitor.
There is not an effective test of the capacitor bank when it
is fully assembled. It is unlikely that a physically damaged
capacitor would indicate a failure within the capacitor
bank. If a failure is suspected, all the capacitors must be
replaced. Replace the capacitors in accordance with
chapter 7 Disassembly and Assembly Instructions
.
Further static tests could require some disassembly. See
chapter 7 Disassembly and Assembly Instructions
.
6.3.6 IGBT Temperature Sensor Test
The temperature sensor is an NTC (negative temperature
coefficient) device. As a result, high resistance means low
temperature. As the temperature increases, resistance
decreases. Each IGBT module has a temperature sensor
mounted internally. The sensor is wired from each IGBT
module to the gate drive card connector MK100.
On the gate drive card, the resistance signal is converted
to a frequency signal. The frequency signal is sent to the
power card for processing. The temperature data is used to
regulate fan speed and to monitor for over and under
temperature conditions. There are three sensors, one in
each IGBT module.
1.
Use ohmmeter set to read ohms.
2.
Unplug connector MK100 on the gate drive card
(see
) and measure the resistance across
each black and white pair.
The relationship between temperature and resistance is
nonlinear. At 77°F [25
°
C], the resistance is approximately 5
k Ohms. At 32°F [0
°
C], the resistance is approximately 13.7
k
Ω
. At 140°F [60
°
C], the resistance is approximately 1.5 k
Ω
.
The higher the temperature, the lower the resistance.
6.3.7 Gate Resistor Test
Mounted to each IGBT module is an IGBT gate resistor
board containing gate resistors for the IGBT transistors. In
some cases, a defective IGBT can still produce good
readings in the previous tests. In most cases, an IGBT
failure results in the failure of the gate resistors so the gate
resistor test can identify an IGBT failure.
Remove the AC input bus bars or RFI filter (depending on
options) if necessary to access the gate drive card. See
chapter 7 Disassembly and Assembly Instructions
for
disassembly instructions.
A 3-pin test connector is on the gate drive card near each
gate signal lead. These leads are labelled MK500, MK502,
MK600, MK602, MK700, MK702, and, if the adjustable
frequency drive is equipped with a brake option, MK200.
See
For the sake of clarity, refer to the three pins as 1, 2, and
3, reading bottom to top. 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.
With an ohmmeter, measure pins 1 and 2 of each test
connector. The reading should be the same for each test
connector.
Incorrect Reading
An incorrect reading indicates either that the gate signal
wires are not connected from the gate drive card to the
gate resistor board, or that the gate resistors are defective.
Connect the gate signal wires if needed. If the resistors are
defective, replace the entire IGBT module assembly. See
chapter 7 Disassembly and Assembly Instructions
for
disassembly and assembly information.
6.3.8 Electrical Fuse Test
Optional electrical fuses can be located in one of two
places. In most cases, they are in the main enclosure.
When an optional contactor and disconnect are both
present, the electrical fuses are located in the options
cabinet between these two components.
For the electrical fuse test:
1.
Use an ohmmeter set to measure the ohms.
2.
Measure the resistance across each fuse. A short
circuit indicates good continuity. An open circuit
means that the fuse needs to be replaced.
Perform the additional static checks before replacing the
fuse.
Test Procedures
Service Manual
MG94A222
Danfoss A/S © Rev. 2014-02-10 All rights reserved.
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Summary of Contents for VLT FC 103
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