Danfoss VLT Series Service Manual page 28

Section Three
TESTING INPUT RECTIFIERS
3 - 10
Theoretically, the input current drawn on each of the three input phases should be
equal. These currents will vary, however, due to variations in phase-to-phase
input voltage and due to some single phase loads within the drive.
Given that the input phase voltages are equal, the input currents phase-to-phase
should not vary more than 5%. Current imbalances in excess of 5% may indicate
one of the diodes is not conducting properly. When the VLT is lightly loaded, it
may not be possible to detect a current imbalance. If suspect, the modules
should be statically tested. Refer to the Static Test procedures beginning on
page 3-1.