Danfoss VLT series, Руководство по обслуживанию

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5-16
VLT is a registered Danfoss trademark
5.2.5 Input Phase Imbalance 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 drive 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 drive to run at its rated load or not less than
40% load.
1. Perform input voltage test prior to checking
current in accordance with procedure. Voltage
imbalances will automatically result in a
corresponding current imbalance.
2. Apply power to drive and place it in run.
3. Using a clamp-on amp meter (analog preferred),
read 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 main supply to the drive
or a problem within the drive 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 is more than 5% different. If all
three phases are different from one another, it would be difficult
to determine which leads to swap.
4. Remove power to drive.
5. Swap phase that appears to be incorrect with
one of other two phases.
6. Reapply power to drive and place it in run.
7. Repeat current measurements.
If the phase imbalance moves with swapping the leads, then
the main 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 requires an oscilloscope equipped with current
probes. Proceed to testing the input waveform and input SCR
in accordance with their procedures.
5.2.4 DC Under Voltage 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 (5.2.1.1) 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.
1. Check DC bus voltage by reading power card
connector MK105 (A) with respect to MK105
(B). If verified, remove power from drive and
allow it to cool for approximately 20 minutes.
2. Reapply power to drive after 20 minutes and
recheck DC bus voltage. If voltage remains, a
short circuit may exist within the intermediate
circuit preventing it from charging. Proceed to
static checks (5.1) earlier in this section.