Sel 751A - Power Elements; Synchronism-Check Applications for Automatic Reclosing and Manual Closing

4.42
SEL-751A Relay Instruction Manual Date Code 20100129
Protection and Logic Functions
Voltage-Based Protection
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 4.30. Element 25A2
operates similarly.
Synchronism-Check
Applications for
Automatic Reclosing
and Manual Closing
Refer to Trip/Close Logic on page 4.50 and Reclose Supervision Logic on
page 4.54.
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 4.31)
Set 25ANG2 = 25° and use the resultant synchronism-check element in
manual close logic to supervise manual closing (for example, assert IN301 to
initiate manual close), e.g.,
CL := IN301 AND (25A2 OR ... ) (see Figure 4.30)
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 4.30
)
logic output).
Power Elements
You can enable up to two independent three-phase power elements in the
SEL-751A relay. Each enabled element can be set to detect real power or
reactive power. When voltage inputs to the relay are from delta connected PTs
or when single voltage input is used, the relay cannot account for unbalance in
the voltages in calculating the power. Take this into consideration in applying
the power elements.
With SEL
OGIC control equations, the power elements provide a wide variety
of protection and control applications. Typical applications are:
➤ Overpower and/or underpower protection/control
➤ Reverse power protection/control
➤ VAR control for capacitor banks