NDB Technologies NDB-DOC-3 User Manual page 13

Tip: The secondary leads can stay connected to the transformers
while testing. The secondary leads and load do not alter test result.
8. The test sequence will start and normally last for a few seconds. In some
cases, the test will last up to 2 minutes.
9. Once the test is completed, the NDB-DOC-3 will display the result:
• SHORT: The NDB-DOC-3 detected a short circuit either on the primary
or secondary winding of the transformer. The SHORT red indicator will
turn on.
• OPEN: The NDB-DOC-3 detected an open circuit. The OPEN yellow in-
dicator will turn on. The test clamps may have poor electrical connec-
tions. For detection of open winding conditions in a 3 phase delta bank,
operator must use the single phase operation instructions and test all 3
transformers separately.
In cases where high DC resistance is measured, the test will last up to 2 minutes and
the transformer will be considered open.
• OK: The OK green indicator will turn on. The transformer's DC resistance
and AC impedance measured are within range. The transformer is con-
sidered in good condition.
Good condition
transformer
Always remove the NDB-DOC-3 before re-energizing the transformers.
N D B - D O C - 3
Short circuit
- U s e r M a n u a l
13
Open circuit