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Test Procedures
2. Measure 10 V DC control voltage at terminal 50
with respect to terminal 55. Meter should read
between 9.2 and 11.2 VDC.
An incorrect reading here could indicate the supply is
being loaded down by a fault in the customer connections.
Unplug the terminal strip and repeat the test. If this test is
successful than continue. Remember to check out the
customer connections.
A correct reading of both control card voltages would
indicate the LCP or the control card is defective. Replace
the LCP with a known good one. If the problem persists
replace the control card.
6
6
6.3.6 DC Undervoltage Test
The initial charge of the DC bus is accomplished by the
soft charge circuit. If the DC bus voltage is below normal it
would indicate that either the line voltage is out of
tolerance or the soft charge circuit is restricting the DC bus
from charging. Conduct the input voltage test to ensure
the line voltage is correct.
If excessive input power cycling has occurred, the PTC
resistors on the soft charge card may be restricting the bus
from charging. If this is the case, expect to read a DC bus
voltage in the area of 50 VDC.
6.3.7 Input Imbalance of Supply Voltage
Test
Theoretically, the current drawn on all three input phases
should be equal. Some imbalance may be seen, however,
due to variations in the phase to phase input voltage and,
to some degree, single phase loads within the frequency
converter itself.
A current measurement of each phase will reveal the
balanced condition of the line. To obtain an accurate
reading, it will be necessary for the frequency converter to
run at its rated load or or at a load of not less than 40%.
1.
Perform the input voltage test prior to checking
the current, in accordance with procedure.
Voltage imbalances will automatically result in a
corresponding current imbalance.
2.
Apply power to the frequency converter and
place it in run.
3.
Using a clamp-on amp meter (analog preferred),
read the current on each of three input lines at
L1 (R), L2 (S), and L3 (T). NOTE: For 12-pulse units,
L11/L12 (R), L21/L22 (S), L31/L32 (T).
Typically, the current should not vary from phase
to phase by more than 5%. Should a greater
96
High Power Service Manual for Modular F Frame Drives
4.
5.
6.
7.
If the imbalance of supply voltage moves with swapping
the leads, then the mains supply is suspect. Otherwise, it
may indicate a problem with the gating of the SCR. This
may be due to a defective SCR or in the gate signals from
the power card to the module, including the possibility of
the wire harness from the power card to the SCR gates.
Further tests on the proper gating of the SCRs require an
oscilloscope equipped with current probes. Proceed to
testing the input waveform.
6.3.8 Input Waveform Test
Testing the current waveform on the input of the
frequency converter can assist in troubleshooting mains
phase loss conditions or suspected problems with the SCR/
diode modules. Phase loss caused by the mains supply can
be easily detected. In addition, the rectifier section is
controlled by SCR/diode modules. Should one of the SCR/
diode modules become defective or the gate signal to the
SCR lost, the frequency converter will respond the same as
loss of one of the phases.
The following measurements require an oscilloscope with
voltage and current probes.
Under normal operating conditions, the waveform of a
single phase of input AC voltage to the frequency
converter appears as in the illustration below.
®
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current variation exist, it would indicate a
possible problem with the mains supply to the
frequency converter or a problem within the
frequency converter itself.
One way to determine if the mains supply is at
fault is to swap two of the incoming phases. This
assumes that two phases read one current while
the third deviates by more than 5%. If all three
phases are different from one another, swap the
phase with the highest current with the phase
with the lowest current.
Remove power to frequency converter.
Swap the phase that appears to be incorrect with
one of other two phases.
Reapply power to the frequency converter and
place it in run.
Repeat the current measurements.
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