NDB Technologies NDB-DOC-3 User Manual page 11

Tip: The secondary leads can stay connected to the transformer
while testing. The secondary leads and load do not alter test result.
• Connect N/GND clamp to the transformer neutral or ground. In Del-
ta applications, simply connect the Neutral/ground clamp to a con-
ductive point on the transformer casing (example: chassis ground
wire) to enable the phase to chassis short-circuit detection.
7. Press the start button
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 indi-
cator will turn on. The transformer's primary winding may have an open
circuit, or the test clamps may have poor electrical connections. Import-
ant note: Detection of single winding open condition in a 3 phase delta
transformer is not possible with the NDB-DOC-3.
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 transformer.
N D B - D O C - 3
.
Short circuit
- U s e r M a n u a l
11
Open circuit