ABB RELION 620 Series Technical Manual page 423

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1MRS757644 F

Technical Manual

shows that in case of outside faults, the measured admittance equals the

admittance of the protected feeder with a negative sign. The measured admittance is

dominantly reactive; the small resistive part of the measured admittance is due to the

leakage losses of the feeder. Theoretically, the measured admittance is located in the

third quadrant in the admittance plane close to the im(Yo) axis, see

The result of

method. In compensated networks the compensation degree does not

affect the result. This enables a straightforward setting principle for

the neutral admittance protection: admittance characteristic is set to

cover the value Yo = –Y

Due to inaccuracies in voltage and current measurement, the small

real part of the calculated neutral admittance may appear as positive,

which brings the measured admittance in the fourth quadrant in the

admittance plane. This should be considered when setting the

admittance characteristic.

is valid regardless of the neutral earthing

with a suitable margin.

Protection functions

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