Figure. 5.4.29 - 162. Transformer earthing settings that compensates for external earth faults.
When the transformer settings are correct, the differential relay compensates the zero sequence
current and does not trip due to earth faults outside the differential zone.
Earthing (directly or via a resistor) forms a route outside the differential zone.
When an external earth fault happens, only the earthed side of the transformer is involved in the fault.
The "N" or "n" selection applies the correction and eliminates the zero sequence effect with the
following formulas:
No
Notte!
e! When you enable the zero sequence compensation by selecting the "N" or "n" in the transformer
vector group, the sensitivity to single-phase one end fault decreases by a third simultaneously. This is
why restricted earth fault protection (I0>, REF) should be enabled for the side where the zero sequence
is compensated. However, enabling the REF protection requires that both the phase
current measurements and the starpoint current are available and can be connected to the relay's
residual current channel on the corresponding (HV/LV) side measurement.
A
AQ
Q-M257
-M257
Instruction manual
Version: 2.07
306
© Arcteq Relays Ltd
IM00021
Summary of Contents for AQ-M257
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