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3-84
Line Current Differential, Distance, Out-of-Step, Overcurrent,
Date Code 20011112
Voltage, Synchronism Check, and Frequency Elements
SEL-311L Instruction Manual
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 3.54 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 with V
P
(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 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 degrees 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 degrees) than for an automatic reclose (15 degrees).
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).
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