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1.8 PROTECTION SCHEME DESCRIPTIONS
1.8 PROTECTION SCHEME DESCRIPTIONS
1
The six standard protection schemes are described in this section. Functional logic diagrams, (Figure 1–9:
STEP DISTANCE LOGIC DIAGRAM through Figure 1–17: HYBRID LOGIC DIAGRAM) show the scheme logic
for the protection schemes using conventional AND/OR combinational logic. The elementary diagram in Figure
1–23: ELEMENTARY DIAGRAM on page 1–48 shows the external connections to the LPS-D relay. Note that
all of the output relays and input contact converters included in the LPS-D are fully programmable by the user.
However, for ease of application, the LPS-D relay is shipped with the inputs and outputs assigned in Figure 1–
22: ELEMENTARY DIAGRAM WITH DEFAULT I/O ASSIGNMENTS on page 1–47. The programmability of the
LPS-D is discussed in Chapter 13: XPRESSION BUILDER. Figure 1–10: PUTT/POTT INTERCONNECTION
DIAGRAM WITH NS40A, Figure 1–15: BLOCKING SCHEME INTERCONNECTION WITH CS28A, and Figure
1–15: BLOCKING SCHEME INTERCONNECTION WITH CS28A show typical interconnections between the
LPS-D and appropriate carrier/tone equipment for three pilot schemes:
•
BLOCKING with CS28A
•
POTT with NS40A
•
HYBRID with Unblocking
Figure 1–9: STEP DISTANCE LOGIC DIAGRAM on page 1–27 is the logic diagram for the Step Distance
scheme. Since this non-pilot scheme overlays the other protection schemes in the LPS-D, it is in essence a
part of all of them. The Zone 1 distance functions are set to reach no greater than 90% of the positive-
sequence impedance of the protected line. All of the ground-distance functions are provided with self-compen-
sation so that they see only the positive-sequence impedance to a ground fault when the compensation setting
is properly selected to reflect the difference between the zero-sequence and positive-sequence impedance of
the line. This setting is explained in Section 2.3: PROTECTION SETTINGS on page 2–10.
There can be as many as three time-delayed zones. At a minimum, Zone 2 should be selected to provide pro-
tection for the last 10% of the protected line not covered by Zone 1. If the application permits, a forward-looking
third zone can be used to provide backup protection for adjacent line sections out of the remote bus. If a
reverse-looking zone is desired, the Zone 4 functions can be reversed. For some applications it may be desir-
able to implement both a forward-looking Zone 3 and a forward-looking Zone 4.
The phase-distance functions can be placed in or out of service by specifying a separate setting for each pro-
tection zone. The same is true for the ground-distance functions. Zone 2, Zone 3, and Zone 4 each have two
independently set zone timers. One timer is associated with the phase functions, the other with the ground
functions.
1-
26
LPS-D Line Protection System
1 PRODUCT DESCRIPTION
1.8.1 INTRODUCTION
1.8.2 STEP DISTANCE
GE Power Management
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