Toshiba GR200 Series Instruction Manual page 27

Remote backup protection (Retarded backup protection)
Due to practical problems such as the incidents of power supply and others, there is possibility
to fail to operate the main protection. Therefore, providing a backup protection from the remote
end is essential so that the main protection is backed up remotely. For the ZS/ZG protection,
the zone2 and zone3 for the relaying elements can be serviced as the remote backup protections.
Local backup protection (High-speed backup protection):
If the circuit breaker has failed to trip by the commands of the main protection, the CB could
be tripped by the commands of the backup protections located beside the main protection. For
the DIF function, the zone1 element of the ZS/ZG function and others are serviced as the local
backup protection.
Concepts of current differential protection (DIF) function
1.1.4
Current differential protection compares the currents flowing into and out of the protected line.
The difference of the currents, that is, the differential current, is almost zero when a fault is
external or there is no fault, and is equal to the fault current when the fault is internal. The
differential protection operates when the difference of the currents exceeds a set value.
The DIF function in the GR200 series relay located at the ends of the line can examines the
entering and outgoing currents in every 7.5 electrical degrees; they are transmitted to the other
terminals in every four samples using the telecommunication. As the DIF function can obtain
the current data at all remote-ends using the telecommunication, the DIF function at any
locations can perform as the master.
As synchronized sampling can be performed at all terminals, the current data are the
instantaneous values, which are sampled simultaneously at each terminal. Therefore, by using
the identical sampling address, the value of the differential currents can be obtained
straightforward by summing current data at the local and the remote. Thus, compensation of
transmission delay time is not required in the DIF function.
The GR200 series relay takes respective three-phase currents and a residual current in
so that performing segregated-phase and zero-phase current differential protection are
achieved.
Concepts of distance protection (ZS/ZG) function
1.1.5
In the distance protection function, the line protection is grouped into six zones; the zones are
protected with six measuring elements: zone1(Z1), zone1X(Z1X), zone2(Z2), zone3(Z3),
zone4(Z4) and zone5(Z5). Figure 1.1-4 illustrates the six elements in the Mho characteristic.
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6F2S1915 (0.46)
GRZ200 (Soft 031 & 032)