Ametek UPLC CU44-VER04, Applications Manual

Page: 47 / 129

May 2012 Page 3–7
Chapter 3. Applications
3
Operation of the underreaching
transfer trip scheme shown in
Figure 3–5 is described in Table
3–2 for external and internal faults.
Because the trip fault detectors (P)
do not operate for external faults,
underreaching transfer trip systems
do not require external fault-clear-
ing coordination circuits (transient
blocking) and are, therefore, inher-
ently simpler than any of the other
schemes. You obtain maximum
security if you use additional per-
missive fault detectors. These
schemes also provide minimum
operating times for many faults that
are tripped directly, without using
the channel.
3.1.4 Dual Phase
Comparison
Unblocking
Systems
Dual comparison systems require a
duplex channel: one frequency for
each line terminal. The UPLC™
frequency-shift channel equipment
is available for this purpose; nor-
mally used in an unblocking sys-
tem. Continuous channel monitor-
ing is also provided, because either
a trip positive or trip negative carri-
er signal is always transmitted.
The transmitter is keyed to its trip
positive frequency when the square
wave from the filter goes positive,
and is keyed to its trip negative fre-
quency when the square wave is at
zero. There are two outputs at the receiver: the trip
positive output is a square wave that goes positive
when a trip positive frequency is received; the trip
negative output goes positive when a trip negative
frequency is received.
The basic operation of the Dual Phase Comparison
system is shown in Figure 3–6. For internal faults,
the single phase outputs of the sequence current
networks are essentially in phase, although such
Breaker 1 Trip Fault Detectors (P1) Breaker 1 Permissive Fault Detectors (FD1)
Breaker 2 Trip Fault Detectors (P2)
Breaker 2 Trip Fault Detectors (P2)
Protected Line
G H
F
I
F
E
1 2
Contact Logic (per Terminal)
P
FD Trip
Solid State Logic (per Terminal)
Channel
except Power Line Carrier
Audio Tone
Receiver f2
Audio Tone
Receiver f1
Audio Tone
Transmitter f1
Audio Tone
Transmitter f2
RR
Audio
Tone
Receiver
RR
Trip
Coil
52a
FD P
Key Audio Tone Transmitter
to Remote Station
Key Audio Tone Transmitter
to Remote Station
Key Audio Tone Transmitter
to Remote Station
Audio Tone
Receiver
Omit and Bypass
for Non-Permissive
Schemes
AND OR
Permissive Schemes
Non-Permissive Schemes
P
Trip
Audio Tone
Recovery
OR
Figure 3–5. Basic Logic Diagrams for
Underreaching Transfer Trip Systems.
output represents currents 180° apart in the power
system. The network output goes through a squar-
ing amplifier that keys the frequency shift transmit-
ter. An adjustable delay circuit delays the local
square wave by a time equal to the channel delay
time.
The network output is then used to develop two
complementary square waves. One wave, which
has a positive state during the positive half-cycle of
the sequence current network, is compared with the