0.0 ms
5 ms/Div.
130BX142.10
Input A
Illustration 6.7 Normal AC Input Voltage Waveform
The waveform shown in the illustration below represents
the input current waveform for the same phase as in the
Illustration above while the frequency converter is running
at 40% load. The two positive and two negative jumps are
typical of any 6 diode bridge. It is the same for frequency
converters with SCR/diode modules.
0.0 ms
5 ms/Div.
130BX143.10
Input B
Illustration 6.8 AC Input Current Waveform with Diode Bridge
With a phase loss, the current waveform of the remaining
phases would take on the appearance shown below.
0.0 ms
5 ms/Div.
130BX144.10
Input B
Illustration 6.9 Input Current Waveform with Phase Loss.
Always verify the condition of the input voltage waveform
before forming a conclusion. The current waveform will
follow the voltage waveform. If the voltage waveform is
incorrect proceed to investigate the reason for the AC
supply problem. If the voltage waveform on all three
phases is correct but the current waveform is not then the
input rectifier circuit in the frequency converter is suspect.
Perform the static soft charge and rectifier tests.
6.3.9 Gate Signal Test
1.
Remove the output bus bars from all inverter
modules.
2.
Power drive in split bus mode. (See split bus
powering).
3.
Connect a 24VDC power supply to the (+) and (-)
DC bus bars.
4.
Connect the signal test board (p/n 176F8437) to
the 30 pin connector at the top of the inverter
module.
5.
Apply a run command and a speed command
above 0 RPM. (Hand Start mode is sufficient).
6.
Connect the common lead of an oscilloscope to
terminal 4 of the signal test board. Observe the
waveform on terminals 25 – 30 in turn. Each
reading should appear similar to the figure
shown.
7.
Repeat this procedure for each inverter module.
8.00
6.00
4.00
2.00
0.00 V
-2.00
-4.00
-6.00
-8.00
-4.0ms
50Us/Div
Input A
130BX153.10
Incorrect reading
If one or more of the IGBT gate signals is missing, this
indicates a faulty connection in the ribbon cable from the
control card to the MDCIC or from the MDCIC to the
inverter module. Check the cables and replaced if
necessary. If all six signals are missing, the control card is
likely defective and needs to be replaced.
Conduct the IGBT Switching Test with the frequency
converter powered as in this procedure.
6.3.10 IGBT Switching Test
1.
Power the unit in the split bus mode as described
in the gate signal test procedure.
2.
Observe the phase-to- phase output waveforms
on all three phases with the oscilloscope.
3.
All waveform readings should appear similar to
the below figure.
4.
Repeat this procedure for all inverter modules.
Test Procedures
High Power Service Manual for Modular F Frame Drives
MG90K202 - VLT
®
is a registered Danfoss trademark
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