Fault Indication; Dc Offset - Powertronix Quasar Service Manual

Service Manual

7.8.2 - DC offset

Fault indication

The output of the UPS is monitored by the Inverter Driver Feedback PCB for any DC component on the
output waveform. If the level of DC exceeds the limit of 400mV, a signal is generated and switched to
the control logic PCB. This signal is switched through the thermostat ST1 as shown below in
Figure 7-8 DC Offset Alarm Signal
The UPS will transfer to the bypass and the red LED LD 2 on the inverter driver/feedback PCB Part Nº
OSDE0071, will illuminate. The red LED D11 on the 3ph TL control logic PCB Part Nº OSDE0072 will
extinguish. The UPS will remain on bypass until the alarm condition is reset using the Reset push switch
S1 on the PCB, or the UPS is completely powered down and restarted.
Figure 7-9 Typical output current waveforms with DC offset.
0
Normal output current waveform
DC Offset
DC Offset Condition
The most likely cause of a
3x3 UPS
Issue 2 - November 2001
0
`DC OFFSET'
1. The UPS is supplying an unbalanced non linear load, this could be on any phase.
2. The load is drawing DC current.
A common reason for this is an input bridge rectifier on a computer power supply is
defective and only half wave rectifying its input power.
3. An inverter gate drive circuit is defective.
This could cause the inverter EIGHT's switching to be out of balance.
DC Offset
0
Output current waveform showing DC Offset
Effect on the Output current
waveform with unbalanced non linear
load
condition could be:
Test Procedures
Figure 7 8.
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