Pulsar TC-10B, User Manual

Page: 27 / 190

2.1.4 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
l
to operate positively on the minimum
internal three-phase fault, yet reset when an
external fault is followed by a maximum load
current flowing through the line. The TC–10B
operates in the same manner as when used
with the current-only scheme, except for the
fault detection and arming techniques.
Two sequence current networks and two
distance relays supplement the two overcur-
rent fault detectors.
One sequence current network responds only
to negative and zero sequence currents,
detecting all phase-to-phase and ground faults
(but not three-phase faults). The output of this
adjustable network operates the conventional
overcurrent FD
l
and FD
2
fault detectors. The
two distance relays operate only for three-
phase faults. Thus, FD
2
provides the arming
function for all unbalanced phase and ground
faults, through the adjustable filter, and one of
the distance relays (21P) provides arming for
all three-phase faults.
The second and non-adjustable sequence
current network operates through the squaring
amplifier, providing the local square wave and
the carrier-keyed square wave required for
phase comparison. This signal is keyed by FD
1
and the second distance relay (21S) to provide
the carrier start functions. This second
network responds to positive, negative, and
zero sequence currents. Separate networks
provide greater sensitivity: with phase-to-
phase faults, for example, more than twice the
sensitivity is gained.
October 2003 Page 2–5
Chapter 2. Applications and Ordering Information
2
1
2
X
Bus H
Bus G
21 S at Breaker
21 P at Breaker
R
Z
C
Z
C
Z
A
Z
A
1
2
X
Bus H
Bus G
21 S at Breaker
21 P at Breaker
R
Z
C
Z
C
Z
A
Z
A
Figure 2–4. Single Phase-Comparison Blocking,
Distance-Supervised Operation.
The setting coordination of FD
l
and FD
2
overcurrent
units is the same as for the current-only system.
Settings for the two three-phase distance units are
shown in Figure 2-4. Both 21S and 21P distance relays
must be set to overreach both the local and remote
terminal buses; 21S must be set further than 21P, as
shown.