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3-44 Overcurrent, Voltage, Synchronism Check, and Frequency Elements Date Code 990430
SEL-351P Manual Técnico
Synchronism Check Element Outputs
Synchronism check element outputs (Relay Word bits 25A1 and 25A2 in Figure SECTION 3:
.25) assert to logical 1 for the conditions explained in the following text.
Voltages V
P
and V
S
are “Static”
Refer to top of Figure SECTION 3: .25.
If V
P
and V
S
are “static” (not “slipping” with respect to one another), the Angle Difference
between them remains constant – it is not possible to close the circuit breaker at an ideal zero
degree phase angle difference. Thus, synchronism check elements 25A1 or 25A2 assert to
logical 1 if the Angle Difference is less than corresponding maximum angle setting 25ANG1 or
25ANG2.
Voltages V
P
and V
S
are “Slipping”
Refer to bottom of Figure SECTION 3: .25. 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 SECTION 3: .26 shows the Angle Difference decreasing – V
S
*
is
approaching V
P
. When V
S
*
is in-phase with V
P
(Angle Difference = 0
°
), synchronism check
elements 25A1 and 25A2 assert to logical 1.
2. The bottom of Figure SECTION 3: .26 shows the Angle Difference increasing – V
S
*
is
moving away from V
P
. V
S
*
was in-phase with V
P
(Angle Difference = 0
°
), 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
°
). There
might not be enough time to wait for this to happen. Thus, the “Angle Difference = 0
°
”
restriction is eased for this scenario.
3. Refer to Reclose Supervision Logic in Section 6: Close and Reclose Logic .
Refer to the bottom of Figure 6.2 in Section 6: Close and Reclose Logic . 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 in Section 6: Close and Reclose Logic . 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.