Table of Contents
Advertisement
3.2.2
Shunt Reactor Protection
Shunt reactors are frequently used on HV and
EHV lines. These line reactors are connected on
the line side of the circuit breakers (see
Figure 3–12). A remote trip channel is thus
required for a fault in the shunt reactor.
3.2.3
Remote Breaker-Failure
Protection
A remote breaker-failure system is necessary
where a multi-breaker bus, such as a breaker-and-
a-half or ring bus scheme, is applied at a transmis-
sion line terminal. A direct transfer-trip system
will be a part of the remote breaker-failure protec-
tion.
3.2.4
Direct Transfer Trip Channel
Considerations
The channel and its terminal equipment are major
factors in the proper operation of the direct trans-
fer-trip system. The DTT channel must neither fail
to provide a correct trip signal nor provide a false
signal.
While other types of modulation are possible, fre-
quency-shift keyed (FSK) equipment offers the
best compromise between noise rejection capabil-
ity and equipment complexity. Two frequencies
are usually transmitted in an FSK system: the
"guard" frequency is transmitted during non-trip
conditions and the "trip" frequency is transmitted
when a breaker trip is required. Because a signal
is always present, the FSK system will allow the
G
Transformer Bank
Transmission Line
87
Direct Transfer Trip Channel
Figure 3–13 Direct Transfer Trip for
Transformer Protection.
May 2012
+
DTT
52
TC
52a
–
Figure 3–14. Direct Transfer Trip for
channel to be continuously monitored. Continuous
channel monitoring is necessary in a direct trip
system, because breaker tripping is not supervised
by any local relays.
As noise in the channel increases, a point is
reached where there is a high probability of false
tripping. The level of noise at which the channel
becomes unreliable must be determined by tests.
Signal-to-noise ratio monitors must then be
included with any direct trip channel, to block
possible false tripping. It is important, however,
not to get the noise monitors any more sensitive
than required, since their operation will prevent
tripping.
There are three important aspects to the applica-
tion of FSK channels to direct trip systems: chan-
nel bandwidth, dual channel systems, and channel
protection.
H
Although faults should be cleared in the shortest
possible time, speed is not the only criterion for
selecting equipment. It is important to use the
narrowest bandwidth equipment possible. A wide
+
bandwidth channel may give the desired speed,
DTT
but more noise enters the system. Thus, the chan-
52
TC
nel will block tripping sooner than a narrower
bandwidth channel with the same received signal
52c
–
level. A wideband channel will consequently not
be as dependable as a narrower channel under
equal receive-level conditions.
Chapter 3. Applications
Shunt Reactor
Protection
87.50/51.63, etc.
Bi-Directional Direct
Transfer Trip Channel
Shunt Reactor Protection.
+
DTT
3
52
TC
52a
–
Page 3–15
Advertisement
Table of Contents
Troubleshooting
