13.8.4.1
Introduction
Sudden change in current variation (SCCVPTOC, 51) function is a fast way of finding
any abnormality in line currents. When there is a fault in the system, the current
changes faster than the voltage. SCCVPTOC (51) finds abnormal condition based on
phase-to-phase current variation. The main application is as a local criterion to increase
security when transfer trips are used.
13.8.4.2
Principle of operation
Sudden change in current variation (SCCVPTOC, 51) function calculates the variation
in phase-to-phase current and gives the RI output when this variation crosses the sum
of start level and float threshold for a time of
tDelay
. The variation is calculated for all
the three phase-to-phase currents.
The variation in the current is calculated using the following equation:
( )
(
) (
)
2
2
i
i t
i t T
i t
T
D =
- ×
-
+
-
EQUATION2252 V1 EN
Where:
i(t)
Amplitude of the current at the present instant
i(t-T)
Amplitude of the current at the instant exactly one cycle time before
i(t-2T)
Amplitude of the current at the instant exactly two cycle time before
Criteria:
D
i > i
(
1.8
·
D
I
T
+
IPickup
)
EQUATION2253-ANSI V1 EN
(Equation 158)
IPickup: pickup level
It is the full-circle integral of the phase-to-phase current variation
(
)
2
1
1
T
T
n T
I
i t n
T
-
=
D
=
D
-
å
EQUATION2254 V1 EN
(Equation 159)
T: the count of the sampling value in one cycle
Section 13
1MRK505222-UUS C
Scheme communication
840
Technical reference manual
Содержание Relion 670 series
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