Schweitzer Engineering Laboratories SEL-421-4 - Figure 5.128 No Slip System Synchronism-Check Element Output Response

5.170
SEL-421 Relay Instruction Manual Date Code 20171021
Protection Functions
Synchronism Check
Slip Frequency and SFZBK1
Relay Word bit SFZBK1 (BK1 Slip Frequency less than 0.005 Hz) also asserts to
logical 1, indicating a “no slip” condition across Circuit Breaker BK1. In other
words, the slip frequency is less than 0.005 Hz (|f
S1
–f
P
| < 0.005 Hz).
Synchronism-Check Element Output Effects
Note that element outputs 25W1BK1 and 25A1BK1 operate identically in all of
the “no slip” cases in Figure 5.128 (both assert to logical 1 or deassert to logical
0).
“Slip—No Compensation” Synchronism Check
The four cases [(a), (b), (c), and (d)] shown in Figure 5.129 are “slip—no com-
pensation” cases for asynchronous systems (not paralleled). The cases progress
in time from top to bottom. The normalized synchronism-check voltage source
Figure 5.128 “No Slip” System Synchronism-Check Element Output Response
V
P
(a)
(b)
(c)
(d)
V
S1
V
P
V
S1
V
P
V
S1
V
P
V
S1
No slip (paralleled system)
Response of synchronism-check
element outputs (Relay Word Bits):
25W1BK1 = logical 1
25A1BK1 = logical 1
25W1BK1 = logical 1
25A1BK1 = logical 1
25W1BK1 = logical 0
25A1BK1 = logical 0
25W1BK1 = logical 0
25A1BK1 = logical 0
A
N
G
1
B
K
1
A
N
G
1
B
K
1
A
N
G
1
B
K
1
A
N
G
1
B
K
1
A
N
G
1
B
K
1
A
N
G
1
B
K
1
A
N
G
1
B
K
1
A
N
G
1
B
K
1