2.3 Restricted Earth Fault Protection
143
7UT613/63x Manual
C53000-G1176-C160-2
Figure 2-59
Principle of Restricted Earth Fault Protection
For auto-transformers 3
I
0
" is valid as the sum of all phase currents flowing to auto-con-
nected winding (full winding and tap(s)).
When an earth fault occurs outside the protected zone, another earth currents flows
through the phase current transformers. This is, on the primary side, in counter-phase
with the starpoint current and has equal magnitude. The maximum information of the
currents is evaluated for restraint: the magnitude of the currents and their phase posi-
tion. The following is defined:
a tripping effect current
I
from
= |3
I
0
'|
and the stabilisation or restraining current
I
stab
= k · ( |3
I
0
' – 3
I
0
"| – |3
I
0
' + 3
I
0
"| )
k is a stabilisation factor which will be explained below, at first we assume k = 1.
I
from
produces the tripping effect quantity,
I
stab
counteracts this effect.
To clarify the situation, three important operating conditions with ideal and matched
measurement quantities are considered:
Summary of Contents for SIPROTEC 7UT613 series
Page 16: ...Contents 16 7UT613 63x Manual C53000 G1176 C160 2 Literature 631 Glossary 623 Index 633 ...
Page 30: ...1 Introduction 30 7UT613 63x Manual C53000 G1176 C160 2 ...
Page 506: ...A Appendix 506 7UT613 63x Manual C53000 G1176 C160 2 7UT633 D E ...
Page 508: ...A Appendix 508 7UT613 63x Manual C53000 G1176 C160 2 7UT633 P Q ...
Page 510: ...A Appendix 510 7UT613 63x Manual C53000 G1176 C160 2 7UT635 D E ...
Page 512: ...A Appendix 512 7UT613 63x Manual C53000 G1176 C160 2 7UT635 P Q ...
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Page 632: ...Literature 632 7UT613 63x Manual C53000 G1176 C160 2 ...