Toshiba GR 200 Series, Instruction Manual

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6F2S1915 (0.46)
GRZ200 (Soft 031 & 032)
- 3 -
Figure 1.1-2(b) exemplifies that both the forward line and the busbar are protected using
a CT. Once a fault occurs between the CT and the CB
(N)
, the relay Ry
(S)
for the forward line can
operate, but the relay Ry
(X)
for the busbar may fail to operate to clear the fault. That is, we
should keep in mind that a blind spot never exits in the power system for designing the
protection.
: Circuit Breaker (which is located at M)
Busbar G
Ry (X) Ry (S) Ry (U)
M
N
Ry (V)
Busbar H
Ry (Q) Ry (P) Ry (O)
K
L
Ry (T)
Line
: Protection area by line protection scheme
: Protection area by busbar protection scheme
Ry
(V)
: Protection relay (which is located at V)
M
: Current transformer (which is connected with a relay)
Figure 1.1-1 Two protection schemes for line and busbar
(b)Line and Busbar protected relays with a CT
Ry (X) Ry (S)
N Line
Busbar G
Ry (X) Ry (S)
N Line
(a)Line and Busbar protected relays with two CTs isolated
Busbar G
Figure 1.1-2 Protection schemes and the location of the CB
(ii)
Speediness
As mentioned earlier, shortening the fault duration is realized by the speedy operation of the
relay; it is achieved by the high speed signal processing module. However, we have to note that
the operating time of the CB is slower comparted with the one of the processing module.
Additionally, the propagation delay of the communion should also be considered when the
carrier command protection function is considered for the protection.