M
AVTMDELTA4000-EN Rev 6 April 2018
60
Exciting Current Tests
Measurements of the individual phase excitation current values are valuable in
determining defects in the transformer core and coils. Excitation current
measurements are generally performed on the high voltage winding only, to
minimize the amount of current required.
NOTE: All bushing shorting leads must be removed for exciting current
measurements. If the low voltage winding has a neutral, connect the
neutral bushing as it normally is in-service (grounded or ungrounded).
Measurements are usually made one phase at a time. Connections should be
documented in the fields provided at the top of the table. For initial or
commissioning tests, perform the measurements on each possible primary and
secondary tap setting. Unless conditions warrant, future tests may be reduced to
the tap settings as found.
For each test line on the form, document the DETC (De-Energized Tap
Changer) and LTC (Load Tap Changer) tap settings and perform three tests per
form line. On WYE / Y connected transformers, connections would be H1-H0
/ U-N /A-N, H2-H0 / V-N / B-N and H3-H0 / W-N /C-N. On DELTA D
(or WHYE / Y without accessible neutral) connected transformers, connections
would be H1-H2 / U-V /A-B, H2-H3 / V-W / B-C and H3-H1 / W-U /C-A
To perform the individual tests, connect the HV lead to one bushing and the
Red lead to the second bushing. The test mode will be automatically set on the
test form to UST-R.
To initiate the individual tests, right-click on the blue highlighted field of the
desired test line. The test sequence initiates and the results will be placed in the
proper fields automatically.
The number of test lines in the table is adjustable. Enter the number of lines
desired for the number of taps to be tested.
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