3.53
Date Code 20060320 Instruction Manual SEL-311C Relay
Distance, Out-of-Step, Overcurrent, Voltage, Synchronism Check, and Frequency Elements
Synchronism Check Elements
Voltages V
P
and V
S
Are “Slipping”
Refer to bottom of Figure 3.31. If V
P
and V
S
are “slipping” with respect to
one another, the Angle Difference (compensated by breaker close time
TCLOSD) changes through time. Synchronism check element 25A1 or 25A2
asserts to logical 1 for any one of the following three scenarios.
1. The top of Figure 3.32 shows the Angle Difference
decreasing—V
S
* is approaching V
P
. When V
S
* is in phase
with V
P
(Angle Difference = 0 degrees), synchronism check
elements 25A1 and 25A2 assert to logical 1.
2. The bottom of Figure 3.32 shows the Angle Difference
increasing–V
S
* is moving away from V
P
. V
S
* was in phase
with V
P
(Angle Difference = 0 degrees), but has now moved
past V
P
. If the Angle Difference is increasing, but the Angle
Difference is still less than maximum angle settings 25ANG1
or 25ANG2, then corresponding synchronism check elements
25A1 or 25A2 assert to logical 1.
In this scenario of the Angle Difference increasing, but still
being less than maximum angle settings 25ANG1 or 25ANG2,
the operation of corresponding synchronism check elements
25A1 and 25A2 becomes less restrictive. Synchronism check
breaker closing does not have to wait for voltage V
S
* to slip
around again in phase with V
P
(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 6.5.
Refer to the bottom of Figure 6.2. If timer 79CLSD is set
greater than zero (e.g., 79CLSD = 60.00 cycles) and it times
out without SEL
OGIC control equation setting 79CLS (Reclose
Supervision) asserting to logical 1, the relay goes to the
Lockout State (see top of Figure 6.3).
Refer to the top of Figure 6.2. 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 3.32. Ideally, circuit breaker closing
is initiated when V
S
* is in phase with V
P
(Angle Difference = 0
degrees). Then when the circuit breaker main contacts finally
close, V
S
is in phase with V
P
, 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 3.31 becomes less
restrictive at the “instant” timer 79CLSD is going to
time out (or making the single check). It drops the
requirement of waiting until the decreasing Angle
Difference (V
S
* approaching V
P
) brings V
S
* in phase
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