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3.1 ON/OFF Mode Protective
Relay Applications
The UPLC-II™ carrier set is particularly suitable
for the following types of protective relay sys-
tems:
• Directional-Comparison Blocking
• Phase-Comparison Blocking
• Phase-Comparison Blocking, Current Only
• Phase-Comparison Blocking, Distance
Supervised
3.1.1 Directional-Comparison
Blocking (DCB)
The basic elements for directional-comparison
blocking (DCB) systems are shown in Figure 3–
1a and Figure 3–1b. 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
must be set more sensi-
1
tively than P
or reach farther behind bus G.
2
Likewise, S
must be set more sensitively than P
2
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-
directional overcurrent unit. The same principle
applies for the phase relays.
When the UPLC-II™ is set for ON/OFF Power-
Line Carrier applications, except for possible aux-
iliary functions, no signal is normally transmit-
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3. Applications
ted, since the S units operate only during fault
conditions.
Operation of the directional-comparison scheme
in Figure 3–1a, Figure 3–1b & Table 3–1 is shown
for external and internal faults. Subscript 1 indi-
cates relays at station G for breaker 1; subscript 2,
relays at station H for breaker 2. (Figure 3–1c
shows a solid-state logic version of Figure 3–1b.)
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, how-
ever, 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 over-
come by using the optional checkback test system
with the UPLC-II™ carrier.
A sample schematic for the KA-4 relaying system
1
is shown in Figure 3–5a. A sample schematic for a
basic microprocessor relay system is shown in
Figure 3–6. Figures 3–7a & 3–7b illustrate some
GE EM relay schematics.
3.1.2 Phase-Comparison Blocking
Basic elements of the phase-comparison systems
are shown in Figure 3–2. The system uses a com-
posite sequence current network to provide a sin-
3
Page 3–1
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