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1 PRODUCT DESCRIPTION
because of the blocking output maintained by the blocking function(s). TL24 never picks up on internal ground
faults. On internal phase faults, the tripping functions take priority over the blocking functions and prevent them
from operating, or cause them to reset if an internal fault occurs following an initial external fault.
In a typical application with ON-OFF carrier sets, only one receiver is used at each terminal of the line, regard-
less of the number of line terminals. The contact converter (RCVR 1 in Figure 1–14: BLOCKING SCHEME
LOGIC DIAGRAM on page 1–34) converts the receiver output into a blocking signal usable by the LPS-D.
Some blocking schemes use frequency-shift tone channels, such as the GE type NS40. For a three-terminal
application employing FSK tones, each terminal has two receivers and an additional contact converter must be
assigned. In the default settings, CC2 is used.
External contacts may be used to supervise the relay-channel interface. The EXTERNAL STOP CARRIER sig-
nal is assigned to contact converter CC3 in the default settings. EXTERNAL STOP CARRIER turns the local
transmitter OFF. This feature is typically used when the remote breaker must trip to clear a fault following a
breaker failure. An external contact closure, indicating a breaker failure, produces an output from CC3 that
turns the transmitter OFF, permitting the remote end to trip.
The BLOCK PILOT TRIPPING signal is assigned to contact converter CC4 in the default settings. BLOCK
PILOT TRIPPING disables the pilot scheme logic, while allowing the backup Zone 1, Zone 2, etc. to function.
Typically, an external contact wired to CC4 is closed when the associated carrier set is removed from service to
prevent overtripping on external faults.
C S 2 8 A
( R E C E I V E R
O U T P U T )
( S W I T C H E D P O S I T I V E B A T T E R Y )
( S T A R T )
U 1 1
( S T O P )
U 1 0
( R E D U C E D
U 1 3
P O W E R )
( S U P E R V I S O R Y )
U 1 2
( S W I T C H E D N E G A T I V E B A T T E R Y )
Figure 1–15: BLOCKING SCHEME INTERCONNECTION WITH CS28A
GE Power Management
T B 1
R A
4 0
3
( + ) B A T T E R Y
3 9
2
(-) BATTERY
1 3
1 4
1 4
1 3
3 8
9
1
7
2
6
4
1 7
3
1 8
5
1 0
3 7
8
LPS-D Line Protection System
1.8 PROTECTION SCHEME DESCRIPTIONS
L P S - D S E T F O R B L O C K I N G S C H E M E
PICKSCHEME = 4 (BLOCKING)
S H O W N F O R T H E D E F A U L T
L P S I / O A S S I G M E N T S
B 5
K T 1
S T A R T
B 2 3
B 2 1
K T 2
S T O P
B 6
N O T E : N C C O N T A C T S A R E
A L S O A V A I L A B L E F O R C A R R I E R
S T A R T / S T O P .
I N T E R C O N N E C T D I A G R A M
F O R P I L O T B L O C K I N G S C H E M E
U S I N G C S 2 8 A C A R R I E R S E T
A N D
L P S - D R E L A Y S Y S T E M
1
L P S - D
D 2
( R E C E I V E D
C C 1
C A R R I E R )
D 1 8
1-
35
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