-ETHOD OF OPERATION3*
6
#
' #
4HE HIGH VALUE STAGE IS DESIGNATED WITH )
%%
4HE LOW
VALUE STAGE OPERATES WITH A DEFINITE TIME
LAG CHARACTERISTIC !DDITIONALLY A USER SPECIFIED
CHARACTERISTIC IS POSSIBLE
4HE DEFINITE TIME EARTH OVERCURRENT STAGE IS OFTEN
USED AS THE LAST BACK
UP FOR HIGH OHMIC EARTH
FAULTS IN EFFECTIVELY EARTHED OR LOW
OHMIC EARTHED
SYSTEMS WHERE THE MAIN SHORT
CIRCUIT PROTECTION
MAY NOT PICK UP ON THESE FAULTS
4HE DIRECTION DETERMINATION IS PERFORMED WITH THE
ZERO SEQUENCES QUANTITIES )
%
| )
AND
5
%
o | 5
AS DESCRIBED IN 3ECTION
4HE LOGIC DIAGRAM OF THE CURRENT STAGES OF EARTH FAULT
PROTECTION IS SHOWN IN &IGURE
)%% BLOCK
)%% &AULT
!NNUNCIATION
4RIP
$IRECTIONAL
CHARACTER
ISTIC
)
%%
5
%
0ARAMETER
)%% $)2
%& -%!3
0() #/22
)%%
4RIP
0ARAMETER
)%% $)2
"LOCK )%%
ACC
&IG
5E
RELEASE
"LOCK )%%
%& UNDEFINED
42)34!"
&.O
&.O
&.O
%& REVERSE
%& FORWARDS
&/27!2$32%6%23%
)
%%
4 )%%
&.O
&.O
./. $)2%#4)/.!,
0ARAMETER
%2$&%(,%2+
"%) 5% /$%2 )%%
"%) 5% 5.$ )%%
)
%%
4 )%%
)%% 4RIP
)%% &AULT
0ARAMETER
)%% $)2
)%% BLOCK
&.O
&.O
!,!2- /.,9
ACC &IG
&.O
&.R
&UNCTION NUMBER
&/27!2$32%6%23%
./. $)2%#4)/.!,
4HE DEFINITE TIMER IS TO BE REPLACED BY THE
PROCESSING OF THE USER DEFINED CHARACTERIS
TIC IN CASE THIS IS USED
&IGURE ,OGIC DIAGRAM OF CURRENT STAGES OF DIRECTIONAL EARTH FAULT PROTECTION
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