Phase-to-phase current variation
Phase-to-phase current variation one is main startup element. It covers most of the
abnormal status of the system. The phase-to-phase current variation fails in high
impedance faults, three-phase fault on weak side and switch onto fault on unloaded line
because of low sensitivity in these cases.
Phase-to-phase current variation takes the current samples as input and the signal is
evaluated using the sampling value based algorithm.
The phase-to-phase current variation criterion is shown below:
EQUATION2255 V1 EN
Where:
Δi
ФФ
sampling value of phase-to-phase current variation
ΔI
ZD
setting of fixed threshold, which corresponds to setting
ICV>
. The default value for the
setting is 0.2·
IBase
, where
IBase
is the base current.
ΔI
T
float threshold
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
-
FF
=
D = D -
å
EQUATION2256 V1 EN
Where:
T count of sample values in one cycle
Δi
ФФ
is calculated using the below formula:
( ) [ ( ) ( )] [ ( ) ( 2 )]
( ) 2 ( ) ( 2 )
i k i k i k N i k N i k N
i k i k N i k N
D = - - - - - -
= - - + -
EQUATION2257 V1 EN
N is the number of samples in one cycle.
Section 5 1MRK505222-UUS C
Differential protection
166
Technical reference manual
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