3-44
Distance, Overcurrent, Voltage,
Date Code 20011205
and Synchronism Check Elements
SEL-311B Instruction Manual
If the slip frequency is greater than 0.005 Hz, the Angle Difference Calculator takes the breaker
close time into account with breaker close time setting TCLOSD (set in cycles; see Figure 3.26).
The Angle Difference Calculator calculates the Angle Difference between voltages V
P
and V
S
,
compensated with the breaker close time:
Angle Difference =
½
(
Ð
V
P
-
Ð
V
S
) + [(f
P
- f
S
) • TCLOSD • (1 second/60 cycles) •
(360
°
/slip cycle)]
½
Angle Difference Example (Voltages V
p
and V
s
are “Slipping”)
Refer to bottom of Figure 3.25 and Figure 3.26.
For example, if the breaker close time is 10 cycles, set TCLOSD = 10. Presume the slip
frequency is the example slip frequency calculated previously. The Angle Difference Calculator
calculates the angle difference between voltages V
P
and V
S
, compensated with the breaker close
time:
Angle Difference =
½
(
Ð
V
P
-
Ð
V
S
) + [(f
P
- f
S
) • TCLOSD • (1 second/60 cycles) •
(360
°
/slip cycle)]
½
Intermediate calculations:
(f
P
- f
S
) = (59.95 Hz - 60.05 Hz) = -0.10 Hz = -0.10 slip cycles/second
TCLOSD • (1 second/60 cycles) = 10 cycles • (1 second/60 cycles) = 0.167 second
Resulting in:
Angle Difference =
½
(
Ð
V
P
-
Ð
V
S
) + [(f
P
- f
S
) • TCLOSD • (1 second/60 cycles) •
(360
°
/slip cycle)]
½
=
½
(
Ð
V
P
-
Ð
V
S
) + [-0.10 • 0.167 • 360
°
]
½
=
½
(
Ð
V
P
-
Ð
V
S
) - 6
°½
During the breaker close time (TCLOSD), the voltage angle difference between voltages V
P
and
V
S
changes by 6 degrees. This 6 degree angle compensation is applied to voltage V
S
, resulting in
derived voltage V
S
*, as shown in Figure 3.26.
Note
: The angle compensation in Figure 3.26 appears much greater than 6 degrees. Figure 3.26
is for general illustrative purposes only.
The top of Figure 3.26 shows the Angle Difference decreasing; V
S
* is approaching V
P
. Ideally,
circuit breaker closing is initiated when V
S
* is in phase with V
P
(Angle Difference = 0 degrees).
When the circuit breaker main contacts finally close, V
S
is in phase with V
P
, minimizing system
shock.
The bottom of Figure 3.26 shows the Angle Difference increasing; V
S
* is moving away from V
P
.
Ideally, circuit breaker closing is initiated when V
S
* is in phase with V
P
(Angle Difference = 0
degrees). When the circuit breaker main contacts finally close, V
S
is in phase with V
P
. But in
this case, V
S
* has already moved past V
P
. In order to initiate circuit breaker closing when V
S
* is
in phase with V
P
(Angle Difference = 0 degrees), V
S
* has to slip around another revolution,
relative to V
P
.
Содержание SEL-311B
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