formers. The residual current for the earth-
fault protection is derived from the phase
currents. When applicable, the core-balance
current transformers can be used for meas-
uring the residual current, especially when
sensitive earth-fault protection is required.
The standard configurations E and F offer
directional earth-fault protection with phase
voltage and residual voltage measurement.
Further, the two standard configurations
include current circuit supervision and fuse
Fig. 6 Substation O/C and E/F protection using the standard configuration C or D with
relevant options. In the incoming feeder bay the unemployed protection functions are
uncoloured and indicated with a dashed block outline. The busbar protection is based
on the interlocking principle, where the start of the O/C protection of the outgoing feeder
sends a blocking signal to the instantaneous O/C stage of the incoming feeder. In the
absence of the blocking signal, the O/C protection of the incoming feeder will clear the
internal switchgear (busbar) fault.
failure supervision for incoming feeders
with busbar voltage measurement. Standard
configuration F offers in addition to standard
configuration E directional overcurrent pro-
tection, overvoltage and undervoltage pro-
tection, positive-sequence undervoltage and
negative-sequence overvoltage protection and
residual voltage protection.
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