Pulsar TCF-10B, System Manual, Page: 43 / 249

2.2.1 Transformer Protection
A typical transformer protection scheme is illus-
trated in Figure 2-10. A direct trip channel is
keyed to the trip state when the transformer
protective relays operate. The received trip signal
will then trip the remote end breaker and lock out
reclosing.
Although it is no longer widely used, you may use
a ground switch operated by the transformer
protective relays for transformer protection. In
this technique, a ground fault is initiated on the
transmission line at G, providing adequate fault
current for the ground relays at H to trip the
breaker at H. This system is slower but is widely
used on lower voltage systems and is fairly simple
and straightforward. It does not require any secure
communication medium between G and H. For
this type of application, the ground relays at H can
be set to operate for 100 percent of the line and not
overreach to bus G.
While a single switch on one phase is normally
applied, you may use a double switch on two
phases to initiate a double-phase-to-ground fault.
In the latter case, both phase and ground relays
can operate to ensure redundancy. Fault grounding
is not applicable to all systems because of high
short-circuit capacity.
2.2.2 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 2-11). A remote trip channel is thus
required for a fault in the shunt reactor.
2.2.3 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
transmission line terminal. A direct transfer-trip
system will be a part of the remote breaker-failure
protection.
2.2.4 Direct Trip Channel
Considerations
The channel and its terminal equipment are major
factors in the proper operation of the direct
transfer-trip system. The channel must neither fail
to provide a correct trip signal nor provide a false
signal.
While other types of modulation are possible,
frequency-shift keyed (FSK) equipment offers the
best compromise between noise rejection capa-
bility 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
channel to be continuously monitored. Continuous
channel monitoring is necessary in a direct trip
December 1996 Page 2–11
Chapter 2. Applications and Ordering Information
2
Direct Transfer Trip Channel
87
G H
Transformer Bank
Transmission Line
DTT
52c
52
TC
+
–
Figure 2–10. Direct Transfer Trip for
Transformer Protection.
Bi-Directional Direct
Transfer Trip Channel
– –
DTT DTT
52a 52a
52
TC
52
TC
+ +
Shunt Reactor
Protection
87.50/51.63, etc.
Figure 2–11. Direct Transfer Trip for
Shunt Reactor Protection.