Schweitzer Engineering SEL-351P, Quick Start Manual

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Date Code 990430 Overcurrent, Voltage, Synchronism Check, and Frequency Elements 3-41
SEL-351P Manual Técnico
0.10 slip cycles/second x (360
º
/slip cycle) x 1 second = 36
º
Thus, in a time period of one second, the angular distance between voltage V
P
and voltage V
S
changes by 36
º
.
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 SECTION 3: .25 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 SECTION 3: .25.
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 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 SECTION 3: .25.