Danfoss VLT CDS 302, Troubleshooting Manual

Page: 12 / 18

Common drives and motor problems
Procedure to conduct the
dynamic test to check the
IGBT
Faults in the drive
Drive temperature sensor /
Over temperature fault
Current sensor fault
Dynamic tests have to be done without the
compressor connected to UVW connector, and
the Drive has to be programmed to a proxy 50Hz
at start.
The Dynamic test can indicate if one of the IGBT
doesn’t switch, and the output voltage will drop
on the fault terminal, UVW.
Program the multimeter to AC 1000V RM.
• Connect the positive terminal of the multimeter
lead to the U connector, and connect the
negative terminal to the V terminal.
• Connect the positive terminal of the multimeter
lead to the U connector, and connect the
negative terminal to the W terminal.
• Connect the positive terminal of the multimeter
lead to the V connector, and connect the
negative terminal to the W terminal.
The meter reading will be between 360V - 380V
when performing the dynamic test at 400V
mains and 50Hz/3000RPM output depending on
instrument used.
The reading should be within ±1.5 percent. When
the reading exceeds this, the IGBT is damaged.
• If the drive is stopped and cooled, the LCP
reading shall show the ambient temperature.
• If not, the temperature sensor or temperature
measurement circuit is defective.
When a current sensor fails, it is indicated
sometimes by an earth fault alarm that cannot be
reset, even with the motor leads disconnected.
• Disconnect the motor from the drive, and then
observe the current in the display of the drive.
• If the motor is disconnected from the unit, the
LCP shall read out 0.00A.
• If anything else is shown, this indicates a
defective current sensor.
Figure 11: Dynamic test
Note: Both faults above are non-reparable. Drive needs to be replaced
The motor or motor wiring can develop a phase
to phase or phase to ground short resulting in
alarm indication and a trip of the unit.
A motor with the unbalanced or non-
symmetrical impedances on all the three phases
can result in uneven or rough operation or
unbalanced output current.
• To determine whether the problem is internal
or external to the drive, disconnect the motor
from the drive output terminals.
• Perform the dynamic output test procedure on
all three phases with a digital voltmeter.
• If the three voltage measurements are
balanced, the drive is functioning correctly.
The problem is therefore external to the drive.
• If the voltage measurements are not
balanced, the drive is malfunctioning.
This typically means that one or more output
IGBT is not switching on and off correctly.
If one of the IGBT fails, the drive is damaged
and must be replaced.
IGBT, Motor or load
problems
12
FRCC.PC.036.A2.02
Check List