Schweitzer Engineering SEL-351P, Quick Start Manual

Page: 213 / 674

Date Code 990430 Overcurrent, Voltage, Synchronism Check, and Frequency Elements 3-45
SEL-351P Manual Técnico
Refer to the top of Figure SECTION 3: .26. Ideally, circuit breaker closing is initiated when
V
S
*
is in-phase with V
P
(Angle Difference = 0
°
). 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 SECTION 3: .25 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 (V
S
*
approaching V
P
) brings V
S
*
in-phase
with V
P
(Angle Difference = 0
°
). 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 + ...
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 6.1 in
Section 6: Close and Reclose Logic .
Element 25A2 operates similarly.
Synchronism Check Applications for Automatic Reclosing and Manual Closing
Refer to Close Logic and Reclose Supervision Logic in Section 6: Close and Reclose Logic .
For example, set 25ANG1 = 15
°
and use the resultant synchronism check element in the
reclosing relay logic to supervise automatic reclosing:
e.g., 79CLS = 25A1 + ... (see Figure 6.2)
Set 25ANG2 = 25
°
and use the resultant synchronism check element in manual close logic to
supervise manual closing (for example, assert IN106 to initiate manual close):
e.g., CL = IN106 * (25A2 + ... ) (see Figure 6.1)
In this example, the angular difference across the circuit breaker can be greater for a manual
close (25
º
) than for an automatic reclose (15
º
).
A single output contact (e.g., OUT102 = CLOSE) can provide the close function for both
automatic reclosing and manual closing (see Figure 6.1 logic output).