4.34
SEL-751A Relay Instruction Manual Date Code 20100129
Protection and Logic Functions
Voltage-Based Protection
q From Figure 4.20; w see Figure 4.31.
Figure 4.21 Synchronism-Check Elements
These synchronism-check elements are explained in detail in the following
text.
Angle
Difference
Calculator
Angle
Difference
Calculator
Slip Frequency Element
Maximum Angle 1
Maximum Angle 2
Maximum Angle 1
Breaker Close Time
Maximum Angle 2
Slip Frequency Element
SF
VP
VP
VS
VS
Relay
Word
Bits
SF
Slip
Frequency
q
0°
Relay
Word
Bits
25A1
25A2
25A1
25A2
Relay
Word
Bits
Angle
Difference
Angle
Difference
(absolute value)
(absolute value–
compensated by
setting TCLOSD)
Synchronism Check Element 1
Synchronism Check Element 2
Synchronize at
Angle Difference = 0°
Operation of Synchronism Check Elements if voltages VP
and VS are static (not slipping):
slip frequency 0.005 Hz or:
Setting TCLOSD = OFF
Operation of Synchronism Check Elements if voltages VP
and VS are slipping:
0.005 Hz < slip frequency setting 25 SF and:
Setting TCLOSD OFF
25ANG1
25ANG2
Settings
TCLOSD
25ANG1
25ANG2
Angle
Difference Increasing
Last Check of
SEL
OGIC Setting
79CLS (w)
Settings
Synchronism
Check
Element 1
Synchronism
Check
Element 2
VP = 25RCF*VPH
where VPH = VA, VB, VC,
VAB, VBC, or VCA,
depending on the
SYNCPH setting.
VP = 25RCF*VPH
where VPH = VA, VB, VC,
VAB, VBC, or VCA
depending on
the SYNCPH setting.
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