Incorrect reading
CAUTION
Open (blown) input fuses or tripped circuit breakers
usually indicate a more serious problem. Before replacing
fuses or resetting breakers, perform static tests.
An incorrect reading here requires further investigation of
the main supply. Typical items to check would be:
•
Open (blown) input fuses or tripped circuit
breakers
•
Open disconnects or line side contactors
•
Problems with the power distribution system
If this test was successful, check for voltage to the control
card.
6.4.3 Basic Control Card Voltage Test
1. Measure the control voltage at terminal 12 with
reference to terminal 20.
The meter must read 21–27 V DC.
An incorrect reading here could indicate that a fault in the
customer connections loads down the supply. Disconnect
control wiring and repeat the test. If this test is successful,
then continue. Remember to check the customer
connections. If still unsuccessful, replace the unit.
2. Measure the 10 V DC control voltage at terminal
50 with reference to terminal 55. The meter must
read between 9.2 and 11.2 V DC.
An incorrect reading here could indicate that a fault in the
customer connections loads down the supply. Disconnect
control wiring and repeat the test. If this test is successful,
then continue. Remember to check the customer
connections. If still unsuccessful, replace the unit.
6.4.4 Input Imbalance of Supply Voltage
Test
Theoretically, the current drawn on all 3 input phases must
be equal. Some imbalance may be seen, however, due to
variations in the phase-to-phase input voltage, and single-
phase loads within the frequency converter.
A current measurement of each phase reveals the balanced
condition of the line. To obtain an accurate reading, the
frequency converter must run at its rated load, or at a load
of not less than 40%.
1. Perform the input voltage test before checking
the current, in accordance with procedure.
Voltage imbalances automatically result in a
corresponding current imbalance.
2. Apply power to the frequency converter and
place it in run.
3. Using a clamp-on ammeter (analog preferred),
read the current on each of 3 input lines at
L1 (R), L2 (S), and L3 (T).
Typically, the current should not vary from phase-
to-phase by more than 5%. If a greater current
variation exists, it indicates a possible problem
with the mains supply to the frequency converter,
or a problem within the frequency converter. One
way to determine if the mains supply is at fault is
to swap 2 of the incoming phases. This assumes
that 2 phases read 1 current while the 3
rd
deviates by more than 5%. If all 3-phases are
dierent from one another, swap the phase with
the highest current with the phase with the
lowest current:
3a Remove power to the frequency
converter.
3b Swap the phase that appears to be
incorrect with 1 of the other 2 phases.
3c Reapply power to the frequency
converter and place it in run.
3d Repeat the current measurements.
If the imbalance of supply voltage moves with swapping
the leads, the mains supply is suspect. Otherwise, it may
indicate a problem with the gating of the rectiers.
6.4.5 Input Waveform Test
Testing the current waveform on the input of the
frequency converter can help troubleshooting mains phase
loss conditions or suspected problems with the diode
modules. Phase loss caused by the mains supply can be
easily detected. In addition, the diode modules control the
rectier section. If 1 of the diode modules become
defective, the frequency converter provides a response
which is the same as loss of 1 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 Illustration 6.15.
Test Procedures TR150 and TR170 Service Manual
BAS-SVM04B-EN 02/2017 All rights reserved. 53
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