Schweitzer Engineering Laboratories SEL-700G Series, Instruction Manual

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4.171
Date Code 20170814 Instruction Manual SEL-700G Relay
Protection and Logic Functions
Group Settings (SET Command)
Angle Difference Example (Voltages VPY and VS Are “Slipping”).
Refer to the bottom of Figure 4.113. For example, if the breaker close time is
100 ms, set TCLOSDY := 100. Presume that the slip frequency is the example
slip frequency calculated previously. The angle difference calculator
calculates the angle difference between voltages VPY and VS, compensated
with the breaker close time:
Angle Difference = |(

VPY –

VS) + [(fPY – fS) • TCLOSDY
• (1 / 1000) • (360°/slip cycle)]|
Intermediate calculations:
(fPY – fS) = (59.95 Hz – 60.05 Hz) = –0.10 Hz = –0.10 slip cycles/second
TCLOSDY • (1 / 1000) = 0.1 second
Resulting in:
Angle Difference
= |(

VPY –

VS) + [(fPY – fS) • TCLOSDY • (1 / 1000)
• (360°/slip cycle)]|
= |(

VPY –

VS) + [–0.10 • 0.1 • 360°]|
= |(

VPY –

VS) – 3.6°|
During the breaker close time (TCLOSDY), the voltage angle difference
between voltages VPY and VS changes by 3.6 degrees. This angle
compensation is applied to voltage VS, resulting in derived voltage VS*, as
shown in Figure 4.114.
The top of Figure 4.114 shows the angle difference decreasing—VS* is
approaching VPY. Ideally, circuit breaker closing is initiated when VS* is in
phase with VPY (Angle Difference = 0 degrees). Then, when the circuit
breaker main contacts finally close, VS is in phase with VPY, minimizing
system shock.
The bottom of Figure 4.114 shows the angle difference increasing—VS* is
moving away from VPY. Ideally, circuit breaker closing is initiated when VS*
is in phase with VPY (Angle Difference = 0 degrees). Then, when the circuit
breaker main contacts finally close, VS is in phase with VPY. But in this case,
VS* has already moved past VPY. To initiate circuit breaker closing when
VS* is in phase with VPY (Angle Difference = 0 degrees), VS* has to slip
around another revolution, relative to VPY.
Synchronism-Check Element Outputs.
Synchronism-check element
outputs (Relay Word bits 25AY1 and 25AY2 in Figure 4.113) assert to logical
1 for the conditions explained in the following text.
Voltages VPY and VS Are “Static” or Setting TCLOSDY := OFF.
To
implement a simple fixed-angle synchronism-check scheme, set
TCLOSDY := OFF and 25SF = 0.50. With these settings, the synchronism
check is performed as described in the top of Figure 4.113.
If there is the possibility of a high slip frequency, exercise caution if
synchronism-check elements 25AY1 or 25AY2 are used to close a circuit
breaker. A high slip frequency and a slow breaker close could result in closing
the breaker outside the synchronism-check window. Max Slip Frequency
(25SF) should be set appropriately to avoid such an unwanted breaker closing.
Voltages VPY and VS Are “Slipping” and Setting TCLOSDY

OFF.
Refer to the bottom of Figure 4.113. If VPY and VS are “slipping” with
respect to one another and breaker close time setting TCLOSDY

OFF, the
angle difference (compensated by breaker close time TCLOSDY) changes
NOTE:
The angle compensation in
Figure 4.114 appears much greater
than 3.6 degrees. Figure 4.114 is for
general illustrative purposes only.