The Petersen coil or the grounding 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
grounding method used. The RCA_CTL input can be used to change the operation criteria
as described in
Table 346 and Table 347.
Table 346: 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 347: 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 ground-fault protection function to the
prevailing neutral grounding conditions is done with the Characteristic angle setting. In
an ungrounded network, Characteristic angle is set to -90 degrees and in a compensated
network Characteristic angle is set to 0 degrees. In case the grounding method of the
network is temporarily changed from compensated to ungrounded due to the
disconnection of the arc suppression coil, the Characteristic angle setting should be
modified correspondingly. This can be done using the setting groups or the RCA_CTL
input. Alternatively, the operating sector of the directional ground-fault protection
function can be extended to cover the operating sectors of both neutral grounding
principles. Such characteristic is valid for both ungrounded and compensated network and
does not require any modification in case the neutral grounding changes temporarily from
the ungrounded to compensated network or vice versa.
The extended phase angle characteristic is created by entering a value of over 90 degrees
for the Min forward angle setting; a typical value is 170 degrees (Min reverse angle in case
Directional mode is set to "Reverse"). The Max forward angle setting should be set to
cover the possible measurement inaccuracies of current and voltage transformers; a
typical value is 80 degrees (Max reverse angle in case Directional mode is set to
"Reverse").
1MAC059074-MB A Section 4
Protection functions
615 series ANSI 337
Technical Manual
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