ABB TCC300, User Manual, Page: 593 / 716

22. Verify that the DVAR current on Transformer 1 is Leading and that the DVAR
current on Transformer 2 is Lagging with the same magnitude.
23. Raise or Lower either Transformer 1 or Transformer 2 so they are one tap apart to
generate some DVAR current.
The transformer with the higher voltage (typically the higher tap) will have the
Lagging DVAR current and the other transformer will have the same magnitude but
will Leading DVAR current.
Since Transformer 2 will be supplying all the load, its voltage may
decrease. Transformer 1 voltage may increase since it has no load (if
its PT is between the breaker and the transformer).
24. Open the Low Side Breaker for Transformer 1 and verify that the controls are not
calling for any tap change operations.
The load current on Transformer 2 should be doubled and Transformer 1 load should
be at or near zero.
25. Verify that the DVAR current is at or near zero.
26. If necessary, manually initiate tap change operations to bring the voltage back into
band.
27. Manually place the transformers to the same tap position (or the same difference as
noted above).
28. Close the Low Side Breaker for Transformer 1 and verify that the DVAR current in
all the transformers is at or near zero.
29. Raise or Lower either Transformer 1 or Transformer 2 by one tap to generate some
DVAR current.
The transformer with the higher voltage (typically the higher tap) will have the
Lagging DVAR current and the other transformer will have the same magnitude but
will Leading DVAR current. Since Transformer 1 will be supplying all the load, its
voltage may decrease. Transformer 2 voltage may increase since it has no load (if its
PT is between the breaker and the transformer).
30. Open the Low Side Breaker for Transformer 2 and verify that the controls are not
calling for any tap change operations.
The load current on Transformer 1 should be doubled and Transformer 2 load should
be zero.
31. Verify that the DVAR current is at or near zero.
32. If necessary, manually initiate tap change operations to bring the voltage back into
band.
33. Manually place the transformers to the same tap position (or the same difference as
noted above).
34. Close the Low Side Breaker for Transformer 2 and verify the DVAR current in all
the transformers is at or near zero.
—Test complete.—
1VAC388793-MB A
Section 9
Testing
TCC300 587
User Manual