Input Imbalance Of Supply Voltage Test - GE AF-650 GP Operating Instructions Manual

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).
Typically, the current should not vary from phase to phase by more than 5%. Should a greater 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.
4. Remove power to frequency converter.
5. Swap the phase that appears to be incorrect with one of other two phases.
6. Reapply power to the frequency converter and place it in run.
7. Repeat the current measurements.
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.
High Power Service Manual for Unit Sizes 6x
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