Toshiba GR200 Series Instruction Manual page 34

Figure 2.1-2 shows an example for a double-bus-bar system protected by DIF. Two
discriminating zone-protections (Zone A and Zone B) overlap the bus-coupler circuit breaker.
Discriminating-zone A
Figure 2.1-2 Check zone and discriminating zone protections in double bus-bar
Check-zone-protection (DIFCH)
(i)
The currents from all feeder bays and transformer bays are input to the check-zone protection
which protects the entire bus-bar system. Since check zone-protection does not need DS signals,
it is more secure against false operation during no-fault and through-fault conditions than
discriminating-zone-protection.
The user can also utilize the DIFCH element when applying the busbar protection in
unusual operational circumstances. The characteristic of the check-zone-protection (Figure
2.1-3(a)) can be modified to that of a non-restraint characteristic
and b) when a signal is applied to PLC connection point "DIFCH-CHARA
characteristic b., the DIFCH element can be used to accommodate the bus-bar configuration
shown in Figure 2.1-4. This configuration may result in a large restraining current flow and
as a consequence the DIF protection may be unable to operate with the normal DIFCH element
characteristic shown in (a). However, the characteristic of the DIFCH element can be modified
to that of the non-restraint characteristic shown in (b) thus enabling dependable operation of
DIFCH for internal faults despite the unusual operational busbar arrangement.
Check-zone
CB CB CB
CB
Discriminating-zone B
CB CB CB
- 20 -
CB CB CB
Busbar A
Zone A protected by DIFZA
Busbar B
CB CB CB
Zone B protected by DIFZB
Check-zone protected by DIFCH
(as shown in Figure 2.1-3 a
2
6F2S1931 (0.20)
". As a result using
3
Centralized GRB200
(Soft: 030, 031, 032, 033, 034)