Download Single-Phase Test Circuit

10.6.5 Alternate circuit for high voltage delta-connected windings
For two-winding transformers with delta-connected high voltage windings, a single phase induced test executed three times may be used in lieu of the
applied test on the HV winding. Each phase is tested separately at the required applied voltage level. Each HV terminal is therefore tested twice at the full
level. The procedure is as follows:
Short and ground the low voltage winding of the tested phase.
Both HV terminals of the tested phase must remain open during the test. The third HV terminal must be grounded.
Apply a symmetrical (plus-minus) ac voltage to the ungrounded low voltage terminals. The voltage should be started at one quarter or less of the full value
and be brought up gradually to full value. After being held for the time specified in 10.6.1, it should be reduced gradually before the circuit is opened. The
test must be made at low frequency (< 500 Hz), but at a frequency high enough to avoid core saturation.
Figure xx below shows the circuit to be used.
Figure xx: Alternate induced test circuit used in lieu of applied voltage test for two-winding transformers with delta-connected HV winding.
This circuit is particularly recommended for cases where measurements of partial discharges are specified during the test. An applied test with pd-free supply
may be particularly difficult to achieve at very high voltages.