Schweitzer Engineering Laboratories SEL-700G Series, Instruction Manual

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4.169
Date Code 20170814 Instruction Manual SEL-700G Relay
Protection and Logic Functions
Group Settings (SET Command)
Block Synchronism-Check Conditions.
Refer to Figure 4.112. The
synchronism-check element slip frequency calculator runs if both voltages
VPY and VS are healthy (59VPY and 59VSY asserted to logical 1) and the
SEL
OGIC
control equation setting BSYNCHY (Block Synchronism Check) is
deasserted (= logical 0). Setting BSYNCHY is most commonly set to block
synchronism-check operation when the circuit breaker is closed (synchronism
check is only necessary when the circuit breaker is open):
BSYNCHY := NOT 3POY (see Figure 4.125)
In addition, synchronism-check operation can be blocked when the relay is tripping:
BSYNCHY :=
… OR TRIPY
Slip Frequency Calculator.
Refer to Figure 4.112. The synchronism-check
element Slip Frequency Calculator in Figure 4.112 runs if voltages VPY and
VS are healthy (59VPY and 59VSY asserted to logical 1) and the SEL
OGIC
control equation setting BSYNCHY (Block Synchronism Check) is
deasserted (= logical 0). The Slip Frequency Calculator output is:
Slip Frequency = fPY – fS (in units of Hz = slip cycles/second)
fPY = frequency of voltage VPY (in units of Hz = cycles/second)
fS = frequency of voltage VS (in units of Hz = cycles/second)
A complete slip cycle is one single 360-degree revolution of one voltage (for
example, VS) by another voltage (for example, VPY). Both voltages are
thought of as revolving phasor-wise, so the “slipping” of VS past VPY is the
relative revolving of VS past VPY.
For example, in Figure 4.112, if voltage VPY has a frequency of 59.95 Hz and
voltage VS has a frequency of 60.05 Hz, the difference between them is the
slip frequency:
Slip Frequency = 59.95 Hz – 60.05 Hz = –0.10 Hz = –0.10 slip cycles/second
The slip frequency in this example is negative, indicating that voltage VS is
not “slipping” behind voltage VPY, but in fact “slipping” ahead of voltage
VPY. In a period of one second, the angular distance between voltage VPY
and voltage VS changes by 0.10 slip cycles, which translates into:
0.10 slip cycles/second • (360°/slip cycle) • 1 second = 36°
Thus, in a period of one second, the angular distance between voltage VPY
and voltage VS changes by 36 degrees.
The SEL-700G runs the absolute value of the slip frequency output through a
comparator. If the slip frequency is less than the maximum slip frequency
setting, 25SF, Relay Word bit SFY asserts to logical 1.
Angle Difference Calculator.
The synchronism-check element angle
difference calculator in Figure 4.113 runs if the slip frequency is less than the
maximum slip frequency setting 25SF (Relay Word bit SFY is asserted).
Voltages VPY and VS Are “Static”.
Refer to the top of Figure 4.113. If the
slip frequency is less than or equal to 0.005 Hz, the angle difference calculator
does not take into account breaker close time—it presumes voltages VPY and VS
are “static” (not “slipping” with respect to one another). This would usually be the
case for an open breaker with voltages VPY and VS, which are paralleled via some
other electric path in the power system. The angle difference calculator calculates
the angle difference between voltages VPY and VS:
Angle Difference = |(

VPY –

VS)|