ABB RELION 620 Series Technical Manual page 215

1MAC504801-IB E
620 series ANSI
Technical Manual
accordingly. This is done with an auxiliary input in the protection relay which receives a
signal from an auxiliary switch of the disconnector of the Petersen coil in compensated
networks or of the grounding resistor in grounded networks. As a result, the characteristic
angle is set automatically to suit the grounding method used. The RCA_CTL input can be
used to change the Io characteristic:
Table 155: Relay characteristic angle control in Iosin(φ) and Iocos(φ) operation criteria
Operation mode setting:
Iosin
Iocos
Table 156: Characteristic angle control in phase angle operation mode
Characteristic RCA_CTL = FALSE
angle setting
-90° φ = -90°
RCA
0° φ = 0°
RCA
Use of the extended phase angle characteristic
In addition to the RCA_CTL input, the extended phase angle characteristic can be used
when the compensation coil is temporarily disconnected in compensated networks. When
the extended operation area is used, the operation area is wide enough to detect ground
faults selectively in compensated networks regardless of whether the compensation coil is
connected or not. Therefore, the RCA_CTL input is not required if the extended operation
area is used.
Sometimes the distance between the start point and the protection relay is long, which
makes it impractical to apply the scheme based on signal wiring between the protection
relay and the Petersen coil or the grounding resistor. This is the case when, for example,
a directional ground-fault protection relay is used in an MV-switching substation some
kilometers from the HV/MV-substation where the grounding facilities are located.
Another example is when HV/MV-substations are connected in parallel but located far
from each other.
It is easy to give the tripping sector such a width that all possible directions of the I
phasors of a faulty line are covered by one and the same sector. Thus, the problem of
setting the characteristic angle according to the grounding status of the network is easily
solved. There is no need to change any settings when a Petersen coil or a grounding
resistor is switched on or off. Auxiliary switches and other pieces of extra hardware are no
longer required for ensuring the selectivity of the directional ground-fault protection.
RCA_CTL = FALSE
Actual operation mode: Iosin
Actual operation mode: Iocos
RCA_CTL = TRUE
φ
RCA
φ
RCA
Section 4
Protection functions
RCA_CTL = TRUE
Actual operation mode: Iocos
Actual operation mode: Iosin
= 0°
= -90°
-
0
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