4.114
SEL-751 Relay Instruction Manual Date Code 20170927
Protection and Logic Functions
Group Settings (SET Command)
breaker closing does not have to wait for voltage VS* to slip
around again in phase with VP (Angle Difference = 0 degrees).
There might not be enough time to wait for this to happen.
Thus, the “Angle Difference = 0 degrees” restriction is eased
for this scenario.
3. Refer to Reclose Supervision Logic on page 4.131.
Refer to the bottom of Figure 4.81. If timer 79CLSD is set
greater than zero (e.g., 79CLSD := 100 ms) and it times out
without SEL
OGIC control equation setting 79CLS (Reclose
Supervision) asserting to logical 1, the relay goes to the
89lockout state (see top of Figure 4.82).
Refer to the top of Figure 4.81. If timer 79CLSD is set to zero
(79CLSD := 0.00), SEL
OGIC control equation setting 79CLS
(Reclose Supervision) is checked only once to see if it is
asserted to logical 1. If it is not asserted to logical 1, the relay
goes to the lockout state.
Refer to the top of Figure 4.69. Ideally, a circuit breaker closing
is initiated when VS* is in phase with VP (Angle Difference =
0 degrees). Then when the circuit breaker main contacts finally
close, VS is in phase with VP, minimizing system shock. But
with time limitations imposed by timer 79CLSD, this may not
be possible. To try to avoid going to the lockout state, the
following logic is employed.
If 79CLS has not asserted to logical 1 while timer 79CLSD is
timing (or timer 79CLSD is set to zero and only one check of
79CLS is made), the synchronism-check logic at the bottom of
Figure 4.68 becomes less restrictive at the “instant” timer
79CLSD is going to time out (or make the single check). It
drops the requirement of waiting until the decreasing Angle
Difference (VS* approaching VP) brings VS* in phase with VP
(Angle Difference = 0 degrees). Instead, it just checks to see
that the Angle Difference is less than angle settings 25ANG1 or
25ANG2.
If the Angle Difference is less than angle setting 25ANG1 or
25ANG2, then the corresponding Relay Word bit, 25A1 or 25A2,
asserts to logical 1 for that “instant” (asserts for 1/4 cycle).
For example, if SEL
OGIC control equation setting 79CLS
(Reclose Supervision) is set as follows:
79CLS := 25A1 OR …
and the angle difference is less than angle setting 25ANG1 at
that “instant,” setting 79CLS asserts to logical 1 for 1/4 cycle,
allowing the sealed-in open interval time-out to propagate on to the
close logic in Figure 4.80. Element 25A2 operates similarly.
Synchronism-Check
Applications for
Automatic Reclosing
and Manual Closing
Refer to Trip/Close Logic on page 4.128 and Reclose Supervision Logic on
page 4.131.
For example, set 25ANG1 = 15 degrees and use the resultant synchronism-
check element in the reclosing relay logic to supervise automatic reclosing,
e.g.,
79CLS := 25A1 OR … (see Figure 4.81)
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