ABB RELION REX640 Technical Manual page 496

Protection and control

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Protection functions

networks, the measured admittance equals the admittance of the background

network. The admittance is dominantly reactive; the small resistive part of the

measured admittance is due to the leakage losses of the background network.

Theoretically, the measured admittance is located in the first quadrant in the

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

compensated networks, the measured admittance equals the admittance of the

background network and the coil including the parallel resistor. Basically, the

compensation degree determines the imaginary part of the measured admittance

and the resistive part is due to the parallel resistor of the coil and the leakage

losses of the background network and the losses of the coil. Theoretically, the

measured admittance is located in the first or fourth quadrant in the admittance

plane, depending on the compensation degree, see

resistance earthed systems, the measured admittance equals the admittance of

the background network and the neutral earthing resistor. Basically, the imaginary

part of the measured admittance is due to the phase-to-earth capacitances of the

background network, and the resistive part is due to the neutral earthing resistor

and the leakage losses of the background network. Theoretically, the measured

admittance is located in the first quadrant in the admittance plane, see

Magnitude of the earth-fault current of the protected feeder when the fault resist-

ance is zero ohm

Magnitude of the uncompensated earth-fault current of the network when Rf is

Compensation degree, K = 1 full resonance, K<1 undercompensated, K>1 overcom-

Rated current of the neutral earthing resistor

shows that in case of a fault inside the protected feeder in unearthed

shows that in case of a fault inside the protected feeder in

Before the parallel resistor is connected, the resistive part of the

measured admittance is due to the leakage losses of the background

network and the losses of the coil. As they are typically small, the

resistive part may not be sufficiently large to secure the discrimination

of the fault and its direction based on the measured conductance. This

and the rating and the operation logic of the parallel resistor should be

considered when setting the admittance characteristic in compensated

shows that in case of a fault inside the protected feeder in high-

Technical Manual

1MRS759142 F