Main rectifier circuit test part IV
1.
Reverse meter leads by connecting negative (–)
meter lead to negative (-) DC bus.
2.
Connect positive (+) meter lead to L1, L2 and L3
in turn. Each reading should show infinity.
Each reading should show infinity. The meter will start at a
low value and slowly climb toward infinity due to
capacitance within the frequency converter being charged
by the meter.
Incorrect reading
With the Part IV test connection, the diodes in the SCR/
Diode modules are reversed biased as well as the lower
diodes in the soft charge rectifier. If a short circuit exists it
would be possible that either the diodes in the SCR/Diode
modules or the lower diodes in the soft charge rectifier are
shorted. To isolate between SCRs or the soft charge
rectifier, internal module testing must be performed.
6.2.2 Inverter Module Static Tests
The inverter module 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 three per
module. The frequency converter also has snubber
capacitors on each IGBT module.
WARNING
Before testing the inverter module, ohm check the top and
bottom of the DC fuses to ensure no voltage is present.
Dangerous and even fatal voltage levels can be present if
the capacitors are not fully discharged
Remove the safety covers to access the unit.
6.2.2.1 Test Point Access
To access test points in the module, remove the bus bars
as follows.
1.
If brake option is present, remove 2 brake option
jumpers bus bars from each module by removing
attaching nut on each end of bus bar.
2.
Remove 3 motor jumper bus bars from each
module by removing attaching nut on each end
of bus bar.
3.
Remove positive DC jumper bus bar from fuse by
removing attaching hardware on each end of bus
bar.
4.
Remove negative DC jumper bus bar from fuse
by removing attaching hardware on each end of
bus bar.
1
2
3
4
2
Illustration 6.5 F-frame inverter module test points
1
Brake option jumper bus bar (step 1)
2
Motor jumper bus bar (step 2)
3
Negative (-) DC link fuse block
4
Positive (+) DC link fuse block
Test Procedures
High Power Service Manual for Modular F Frame Drives
90
MG90K202 - VLT
®
is a registered Danfoss trademark
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