6.3.2 Rectifier Circuits Test
Pay close attention to the polarity of the meter leads to
identify a faulty component if an incorrect reading
appears.
NOTICE!
If the unit has a circuit breaker, contactor, disconnect or
electrical fuse option, make test connections L1, L2, and
L3 to the output (drive) side of these devices.
Main rectifier circuit test part I
1.
Connect the positive (+) meter lead to the
positive (+) DC bus.
2.
Connect the negative (–) meter lead to terminals
L1, L2, and L3 in sequence.
The correct reading is infinity. The meter starts at a low
value and slowly climbs towards infinity due to the meter
charging capacitance within the adjustable frequency
drive.
Incorrect reading
With the Part I test connection, the SCRs in the SCR/diode
modules are reverse biased so they are blocking current
flow. If a short circuit exists, the SCRs are shorted. Replace
the shorted SCR/diode module.
Main rectifier circuit test part II
1.
Reverse meter leads by connecting the negative
(–) meter lead to the positive (+) DC bus.
2.
Connect the positive (+) meter lead to L1, L2, and
L3 in sequence.
The correct reading is infinity.
Incorrect reading
With the Part II test connection, even though the SCRs in
the SCR/diode modules are forward biased by the meter,
current does not flow through the SCRs without providing
a signal to their gates.
A short circuit reading indicates either one or more of the
SCRs are shorted in the SCR/diode module. Replace the
shorted SCR/diode module.
Main rectifier circuit test part III
1.
Connect the positive (+) meter lead to the
negative (-) DC bus.
2.
Connect the negative (-) meter lead to terminals
L1, L2, and L3 in sequence.
A diode drop indicates a correct reading.
Incorrect reading
With the Part III test connection, the diodes in the SCR/
diode modules are forward biased. The meter reads the
diode drops. If a short circuit exists, it would be possible
that the SCR/diode modules are shorted. Replace the
shorted SCR/diode module.
If an open reading occurs, replace the open SCR/diode
module.
Main rectifier circuit test part IV
1.
Reverse meter leads by connecting the negative
(–) meter lead to the negative (-) DC bus.
2.
Connect the positive (+) meter lead to L1, L2, and
L3 in sequence.
Infinity is the correct reading. The meter starts at a low
value and slowly climbs toward infinity due to the meter
charging capacitance within the adjustable frequency
drive.
Incorrect reading
With the Part IV test connection, the diodes in the SCR/
diode modules are reverse biased. If a short circuit exists,
the diodes in the SCR/diode modules are shorted. Replace
the shorted SCR/diode module.
6.3.3 Inverter Section Tests
The inverter section is primarily made up of the IGBTs used
for switching the DC bus voltage to create the output to
the motor. The IGBTs are grouped into modules. One
module is used for each output phase.
CAUTION
Disconnect motor leads when testing the inverter
section. With leads connected, a short circuit in one
phase reads in all phases, making isolation difficult.
Before starting tests, ensure that the meter is set to diode
scale.
Inverter test part I
1.
Connect the positive (+) meter lead to the (+)
positive DC bus.
2.
Connect the negative (–) meter lead to terminals
U, V, and W in sequence.
Infinity is the correct reading. The meter starts at a low
value and slowly climbs toward infinity due to the meter
charging capacitance within the adjustable frequency
drive.
Test Procedures
Service Manual
MG94A222
Danfoss A/S © Rev. 2014-02-10 All rights reserved.
73
6
6
Summary of Contents for VLT FC 103
Page 2: ......
