ABB RELION REX640 Technical Manual page 483

1MRS759142 C
REX640
Technical Manual
Directional mode = "Non-directional"
The admittance characteristic is set to cover the total admittance of the protected
feeder with a proper margin, see
allow adaptation of protection settings to different feeder and network configurations.
Conductance forward
This setting should be set based on the parallel resistor value of the coil. It must be set
to a lower value than the conductance of the parallel resistor, in order to enable
dependable operation. The selected value should move the boundary line from origin
to include some margin for the admittance operation point due to CT/VT-errors, when
fault is located outside the feeder.
Conductance forward: 15 A/(15 kV/sqrt(3)) * 0.2 = +0.35 mS corresponding to 3.0 A
(at 15 kV). The selected value provides margin considering also the effect of CT/VT-
errors in case of outside faults.
In case of smaller rated value of the parallel resistor, for example, 5 A (at 15 kV), the
recommended security margin should be larger, for example 0.7, so that sufficient
margin for CT/VT-errors can be achieved.
Susceptance forward
By default, this setting should be based on the minimum operate current of 1 A.
Susceptance forward: 1 A/(15 kV/sqrt(3)) = +0.1 mS
Susceptance reverse
This setting should be set based on the value of the maximum earth-fault current
produced by the feeder (considering possible feeder topology changes) with a security
margin. This ensures that the admittance operating point stays inside the "Box"-
characteristics during outside fault. The recommended security margin should not be
lower than 1.5.
Susceptance reverse: - (10 A * 1.5)/ (15 kV/sqrt(3)) = -1.73 mS
Conductance reverse
This setting is used to complete the non-directional characteristics by closing the
"Box"-characteristic. In order to keep the shape of the characteristic reasonable and to
allow sufficient margin for the admittance operating point during outside fault, it is
recommended to use the same value as for setting Susceptance reverse.
Conductance reverse = -1.73 mS
Protection functions
Figure 262. Different setting groups can be used to
Section 4
477