ABB Relion 670 Series Technical Reference Manual page 846

Section 13
Scheme communication
13.8.4.1
13.8.4.2
840
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.
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:
( ) ( ) (
D = - × -
i i t 2 i t T
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:
(
Di > i 1.8 · DI
+ IPickup
T
EQUATION2253-ANSI V1 EN
IPickup: pickup level
It is the full-circle integral of the phase-to-phase current variation
-
1 2 T 1
å
(
= D -
i t n
D
I
T
T
=
n T
EQUATION2254 V1 EN
T: the count of the sampling value in one cycle
)
+ -
i t 2 T
)
)
1MRK505222-UUS C
(Equation 158)
(Equation 159)
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