Figure 194: Earth-fault situation in a compensated network
The Petersen coil or the earthing resistor may be temporarily out of operation. To
keep the protection scheme selective, it is necessary to update the
Characteristic
angle setting accordingly. This can be 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. As a result the characteristic angle is set
automatically to suit the earthing method used. The RCA_CTL input can be used to
change the operation criteria as described in
Table 403: Relay characteristic angle control in Iosin(φ) and Iocos(φ) operation
criteria
Operation mode
setting:
RCA_CTL
= FALSE
RCA_CTL
= TRUE
Iosin
Actual operation mode: Iosin Actual operation mode: Iocos
Iocos
Actual operation mode: Iocos Actual operation mode: Iosin
Table 404:
Characteristic angle control in phase angle operation mode
Characteristic angle
setting
RCA_CTL
= FALSE
RCA_CTL
= TRUE
-90°
φ
RCA
= -90°
φ
RCA
= 0°
0°
φ
RCA
= 0°
φ
RCA
= -90°
Use of the extended phase angle characteristic
The traditional method of adapting the directional earth-fault protection function
to the prevailing neutral earthing conditions is done with the
Characteristic angle
setting. In an unearthed network,
Characteristic angle is set to -90 degrees and in a
compensated network
Characteristic angle is set to 0 degrees. In case the earthing
method of the network is temporarily changed from compensated to unearthed
due to the disconnection of the arc suppression coil, the
Characteristic angle
setting should be modified correspondingly. This can be done using the setting
Protection functions
1MRS757644 H
398
620 series
Technical Manual
