Date Code 20010731
Breaker Logic
3-19
SEL-352-1, -2 Instruction Manual
L
OAD OR
L
INE
-C
HARGING
C
URRENT
C
ONDITIONS
Application Description
Breaker failure protection during load conditions is completely independent from the fault
current protection. Use this protection in addition to the fault current protection as a second
level of breaker failure protection or by itself.
The output of the load current protection is the assertion of the LPF (pending failure) or LBF
(breaker failure) Relay Word bit. These bits must be used in control logic for energizing an
external alarm, retripping the breaker, or asserting a lockout relay. Refer to
Lockout Relay
Control
in
Section 4: Close Logic
.
The SEL-352 Relay provides two different protection schemes for failure of the breaker to
interrupt load or line-charging current. While the schemes share elements and timers, each is
independent. You may enable only one protection scheme at a time or customize the logic.
Both schemes require that the breaker is closed and that the relay receive a trip input. The two
schemes differ in how they determine a closed breaker condition. Refer to
Operating
Characteristic
for an operational description and logic diagram of each scheme. Setting
considerations for each scheme follow.
Scheme 1 and Scheme 2 are essentially the same, except Scheme 2 adds logic that determines if
a breaker has failed based on the 52A breaker status inputs. This scheme primarily is used when
load or line-charging current is not high enough to pick up 50LD.
Operating Characteristic
Scheme 1 (Load Current)
Scheme 1, shown in Figure 3.17, determines a closed breaker condition by comparing the phase
current with the 50LD setting. Because this logic is very sensitive, the trip input must be
asserted for two consecutive quarter-cycles before this logic acknowledges the input. This
feature provides the necessary security against incidental trip input assertions.
Figure 3.17: A-Phase Failure to Trip Load or Line-Charging Current Logic, Scheme 1
Содержание SEL-352-1
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