With a phase loss, the current waveform of the remaining phases would take on the appearance
shown in Figure 6-15.
Figure 6.15: 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 in-
vestigate 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 adjustable frequency
drive is suspect. Perform the static soft charge and rectifier tests and also the dynamic SCR/diode
module test.
6.3.9 Input SCR Test
The SCR can be disabled by the adjustable frequency drive for various reasons. Check the following
before making more complicated tests.
The SCRs can be disabled as a result of an input, or lack of input, at power card connector FK102,
the external brake temperature switch. Unless used as an input, a jumper must be placed between
terminals 104 and 106 of FK102
The SCRs are gated in sequence with the main supply. Verify that the voltage reference signal is
correct as follows.
1.
Using a voltmeter, measure phase to phase AC line voltage at Terminals R, S, and T of
power card connector MK106.
2.
Measurements should correspond with measurements called out in the Input Voltage
Test (6.3.2).
An incorrect reading at MK106 with a correct input voltage may indicate a problem in the soft
charge card or the connecting cable.
If the above tests reveal no abnormalities, it is further possible that the inrush signal has not been
enabled by the control card. Using the signal test card, verify the inrush signal is present and the
SCR disable signal is at the correct voltage level as follows.
High Power Service Manual for VLT
®
FC Series
Adjustable Frequency Drives
6 Test Procedures
MG.90.L1.22 - VLT
®
is a registered Danfoss trademark
6-27
6
Summary of Contents for VLT HVAC FC 100
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