Toshiba GR200 Series Instruction Manual page 25

GRL200 line differential protection has been designed to provide phase-segregated current
differential protection with digital telecommunications, together with control applications. The
GRL200—intelligent electronic device (IED)—provides the user with the flexibility to meet
their application and engineering requirements in addition to offering excellent performance,
the high quality and reliability.
Protection functions
The IED has a number of protection functions and these functions are being optimized for
transmission or distribution systems. The followings functions incorporated and programmed
with the user's settings using the menus on the IED or in the engineering tools can operate
well with mutual linkage between protection functions.
Purposes of the protection
1.1.1
In order to secure the stability in the power system, the protection function provides three
significant fundamentals for the protection in response to various faults:
(1) Prevention of power supply interruption is to clear the faults and recover the faulted power
transmission as soon as possible.
(2) Prevention of damage to equipment is serviced not to damage the primary device even if
faults occur successively. For example, destruction of insulators, rupture of lines, burning of
transformers, and others may result in severe damages in devices in the power system. The
protection function can serve the device not be vulnerable severely for such damages.
(3) Prevention of system instability is to clear faults in the power system speedy by the
operation in the protection functions. Otherwise, a generator will be in out-of-step if a fault
does not clear speedy.
Requirements in the protection functions
1.1.2
Several essences shall be considered for the operation within the relays:
Selectivity
(i)
If any fault occurs in the power system, it shall be cleared. At the same time, we should
consider that the unfaulted segments of the power system must be isolated from the faulted
segment in which the fault may clear. Figure 1.1-1 illustrates the protection areas constructed
with two different protection schemes; the two schemes are overlapped so that the entire areas
are protected.
Figure 1.1-2 illustrates the locations of a circuit breaker (CB) and a current transformer
(CT) connected with the relays. In Figure 1.1-2(a), for example, two CTs locates on the both
sides of the CB : a CT is connected with the relay Ry
(N)
connected with the relay Ry
overlapped.
seeing to the busbar; the zones protected by the two relays are
(X)
- 2 -
6F2S1914 (0.49)
seeing into the line and another CT is
(S)
GRL200 (Soft 033 & 037)