Pulsar TC-10B, User Manual

Page: 23 / 190

2.1 Protective Relay
Applications Using
ON/OFF Carriers
The TC–10B carrier set is particularly suitable for
the following types of protective relay systems:
• Directional-Comparison Blocking
• Phase-Comparison Blocking
• Current Only
• Distance Supervised
2.1.1 Directional-Comparison
Blocking
The basic elements for directional-comparison
blocking systems are shown in Figure 2-1a and
Figure 2-1b. At each terminal, the phase and
ground trip units (P) must be directional and set to
overreach the remote terminal; that is, they must
be set to operate for all internal faults. Nominal
settings of the distance units are 120 to 150
percent of the line. The start units (S) must reach
farther, or be set more sensitively, than the remote
trip units. Thus S
1
must be set more sensitively
than P
2
or reach farther behind bus G. Likewise,
S
2
must be set more sensitively than P
1
or reach
farther behind bus H. In any case, the S and P
relays should be similar in type. If the trip unit (P)
is a directional overcurrent ground relay, the start
(S) ground relay should be a similar non-direc-
tional overcurrent unit. The same principle applies
for the phase relays.
When the TC–10B ON-OFF power line carrier is
used with these schemes, except for possible
auxiliary functions, no signal is normally trans-
mitted, since the S units operate only during fault
conditions.
Operation of the directional-comparison scheme
(shown in Figure 2-1a and Figure 2-1b) is internal
faults. Subscript 1 indicates relays at station G for
breaker 1; subscript 2, relays at
station H for breaker 2. (Figure 2-1c shows a
solid-state logic version of Figure 2-1b.)
The schemes shown are still widely used for their
flexibility and reliability. Since the communica-
tion channel is not required for tripping, internal
faults that might short and interrupt the channel
are not a problem. Over tripping will occur,
however, if the channel fails or is not established
for external faults within the reach of the trip fault
detectors. Since the carrier transmitter is normally
OFF, or non-transmitting, channel failure cannot
be detected until the system is tested or until an
external fault occurs. This limitation can be
overcome by using the optional TC–10B
checkback system with the TC–10B carrier.
2.1.2 Phase-Comparison Blocking
Basic elements of the phase-comparison systems
are shown in Figure 2-2. The system uses a
composite sequence current network to provide a
single-phase voltage output proportional to the
positive, negative, and zero sequence current
input. Sensitivity to different types of faults
depends on the weighting factors or constants
designed into the sequence current network.
Adjustments to the network are provided.
A squaring amplifier in the controlling relay
converts the single-phase voltage output to a
square wave. The positive voltage portion corre-
sponds to the positive half-cycle of the filter
voltage wave and the zero portion corresponds to
the negative half-cycle. The square wave is used
to key the TC–10B, transmitting to the remote
terminal. The square wave from the remote
terminal is compared to the local square wave,
which has been delayed by an amount equal to the
absolute channel delay time. This comparison of
the local and remote square waves at each
Copyright © 2003 Pulsar Technologies, Inc.
Chapter 2. Applications and Ordering Information
2