Vector Group For Step-Up Transformer - Deif GPC-3 Designers Reference Handbook

GPC-3 DRH 4189340587 UK
Typically the synchronising breaker is on the high voltage (HV) side, and there is no breaker (or only a man-
ually operated one) on the low voltage (LV) side. In some applications, the breaker could also be placed on
the LV side. But this does not influence on the setting in the ML-2, as long as the breaker and the step-up
transformer are both placed between the measuring points for the ML-2. The measuring points are shown as
black dots in the figures above and below.
The phase angle compensation would not be an issue if there was no phase angle shift across the step-up
transformer, but in many cases there is. In Europe, the phase angle shift is described using the vector group
description. Instead of vector group, this could also be called clock notation or phase shift.
When voltage measurement transformers are used, these must be included in the total phase
angle compensation.
When an ML-2 is used for synchronising, the device uses the ratio of the nominal voltages for the generator
and the busbar, to calculate a set point for the AVR and the voltage synchronising window (dU
Example:
A 10000 V/400 V step-up transformer is installed after a generator with the nominal voltage of 400 V. The
nominal voltage of the busbar is 10000 V. Now, the voltage of the busbar is 10500 V. The generator is running
400 V before synchronising starts, but when attempting to synchronise, the AVR set point will be changed to:
U * U
BUS-MEASURED GEN-NOM

4.20.2 Vector group for step-up transformer

Vector group definition
The vector group is defined by two letters and a number:
The first letter is an upper case D or Y, defining if the HV side windings are in delta or wye configuration.
The second letter is a lower case d, y or z, defining if the LV side windings are in delta, wye or zigzag configu-
ration.
The number is the vector group number, defining the phase angle shift between HV and LV side of the step-
up transformer. The number is an expression of the LV side lag compared to the HV side voltage. The num-
ber is an expression of the lag angle divided by 30 degrees.
Example:
Dy11 = HV side: Delta, LV side: Wye, vector group 11: Phase shift = 11 × (–30) = -330 degrees.
DEIF A/S
/U = 10500 * 400/10000 = 420 V
BUS-NOM
Additional functions
).
MAX
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