ABB RELION Series Technical Manual page 338

Section 4
Protection functions
332
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 Figure
Equation 18 shows that in case of a fault inside the protected feeder in 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
Figure 168.
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
networks.
Equation 20 shows that in case of a fault inside the protected feeder in high-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
168.
Figure
1MRS758755 A
168.
REC615 and RER615
Technical Manual