3.50
SEL-311C Relay Instruction Manual Date Code 20060320
Distance, Out-of-Step, Overcurrent, Voltage, Synchronism Check, and Frequency Elements
Synchronism Check Elements
Thus, in a time period of one second, the angular distance between voltage V
P
and voltage V
S
changes by 36 degrees.
The absolute value of the Slip Frequency output is run through a comparator
and if the slip frequency is less than the maximum slip frequency setting,
25SF, Relay Word bit SF asserts to logical 1.
Angle Difference Calculator
The synchronism check element Angle Difference Calculator in Figure 3.31
runs if the slip frequency is less than the maximum slip frequency setting
25SF (Relay Word bit SF is asserted).
Voltages V
P
and V
S
Are “Static”
Refer to top of Figure 3.31.
If the slip frequency is less than or equal to 0.005 Hz or TCLOSD = OFF, the
Angle Difference Calculator does not take into account breaker close time–it
presumes voltages V
P
and V
S
are “static” (not “slipping” with respect to one
another). This would usually be the case for an open breaker with voltages V
P
and V
S
that are paralleled via some other electric path in the power system.
The Angle Difference Calculator calculates the angle difference between
voltages V
P
and V
S
:
Angle Difference = |(∠V
P
– ∠V
S
)|
Voltages V
P
and V
S
Are “Slipping”
Refer to bottom of Figure 3.31.
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