Single-Phase, Distance-Supervised Comparison Blocking - Ametek UPLC CU44-VER04 Applications Manual

UPLC™ Application Manual
miles long, the FD pickup is set at
2
125 percent of FD . For lines longer
1
than 100 miles, the FD
2
set at 200 percent of FD
three-terminal line, FD
2
250% of FD , provided the line
1
length between any two breakers is
less than 100 miles. Phase-
Comparison cannot occur until FD
operates. The purpose of the two
fault detectors is to coordinate the
comparison of the local and remote
square waves with the keying of the
carrier square wave. The carrier
must be started before the com-
parison is allowed to ensure that
the remote square wave has been
received.
The basic operation of the system is
shown in Figure 3–28. FD 1 and
FD 2 at both terminals operate for
an internal fault (F I ). The square
wave inputs to the AND from the
local currents are essentially in
phase with those transmitted via the
channel from the remote terminal.
The local square wave turns the car-
rier "ON" and "OFF" to provide the
square wave receiver output for the
remote terminal.
A flip flop is energized if the inputs
to the AND continue for 4ms, pro-
viding a continuous trip output
supervised by FD operation. The
2
4ms correspond to a phase angle
difference of 90°, on a 60-Hz base,
between the currents at the two ter-
minals. The currents at the two ends
of the line may be out of phase by
up to 90° and still trip. This is a
blocking system, since the receipt of
a signal from the channel prevents
tripping. The carrier signal, there-
fore, does not have to be transmitted
through the internal fault. No
received signal puts a "1" on the
AND input. With the remote termi-
Page 3–34
pickup is
. On a
1
is set at
2
Receiver
Output
Local
Input
Arming
Internal Fault (F I )
(at Terminal G*)
Local Input
to AND
Receiver
Output
Receiver Input
to AND
AND Output
Trip Output
* Equivalent operation and same trip output at Station H.
Single Phase Comparison Blocking, Current Only Operation.
nals open, this system provides sensitive instantaneous overcur-
rent protection for the entire line. As is characteristic of block-
ing systems, the channel is not required for tripping on internal
faults.
For an external fault, such as F
essentially continuous, since the remote wave input to the AND
is out-of-phase with the local square wave. The secondary ct
currents are essentially out-of-phase for an external fault. The
currents can, however, be in-phase by up to 90
and still block.
3.5.4 Single-Phase, Distance-Supervised
Comparison Blocking
A distance-supervised scheme should be used if the minimum
internal three-phase fault current is less than twice the maximum
load current. Twice maximum load current allows FD
ate positively on the minimum internal three-phase fault, yet
G
F I & F E
Protected Line
1
Fault Detecting Logic
(Figure 2–2)
Transmitter
Channel
Receiver
Comparison Circuit Comparison Circuit
Basic Logic
4
0
AND
Trip Breaker 1 Trip Breaker 2
1
0
1
0
1
0
1
0
1
0
Figure 3–31.
in Figure 3–31, blocking is
E
H
F E
F E
F I
F I
2
Fault Detecting Logic
(Figure 2–2)
Transmitter
Receiver
Receiver
Output
Basic Logic
Local
Input
4
0
AND
Arming
External Fault (F E )
(at Terminal G*)
1
0
1
0
1
0
0 0
0 0
°
on a 60-Hz base
to oper-
l