Siemens SIPROTEC 7SJ531 - Page 56

-ETHOD OF OPERATION3*
6
#
' #

 $IRECTIONAL OVERCURRENT TIME PROTECTION OPTIONAL
 'ENERAL
3)02/4%# 3*PROVIDES DEPENDENT OF THE OR
DERED MODEL A DIRECTIONAL OVERCURRENT TIME PROTEC
TION 4HUS IT CAN BE USED IN SYSTEMS WHERE THE DI
RECTION OF ENERGY FLOW TO THE FAULT LOCATION IS REQUIRED
AS A FURTHER CRITERION BESIDES THE OVERCURRENT CRITERI
ON IN ORDER TO ACHIEVE SELECTIVITY
&OR PARALLEL LINES OR TRANSFORMERS WHICH ARE FED FROM
ONE SIDE REFER TO &IGURE  A FAULT ON ONE BRANCH
) CAN RESULT IN THE OTHER BRANCH )) BEING DISCON
NECTED UNLESS THE TRIPPING OF THE CIRCUIT BREAKER IN
THE PARALLEL HEALTHY BRANCH IS PREVENTED BY A DIREC
TIONAL MEASURING ELEMENT AT " 4HEREFORE A DIREC
TIONAL OVERCURRENT SCHEME MUST BE INSTALLED AT THE
POINTS INDICATED BY THE DIRECTIONAL ARROW IN &IGURE
 )T MUST BE NOTED THAT THE
FORWARDS DIRECTION OF
THE DIRECTIONAL RELAY IS THE DIRECTION TO THE PROTECTED
OBJECT 4HIS IS NOT NORMALLY IDENTICAL WITH THE DIREC
TION OF THE NORMAL LOAD FLOW AS CAN BE SEEN IN THE FIG
URE
!LSO IN NETWORKS WITH INFEED FROM BOTH SIDES OR IN
RING NETWORKS THE OVERCURRENT TIME PROTECTION MUST
HAVE A DIRECTIONAL CRITERION &IGURE  SHOWS A RING
NETWORK AS A DEVELOPMENT IN THE ACTUAL RING NET
WORK THE TWO INFEEDS SHOWN IN THE FIGURE MERGE INTO
A SINGLE INFEED
T
T
NORMAL LOAD
DIRECTION
!"
)
))
OVERCURRENT TIME PROTECTION
DIRECTIONAL OVERCURRENT TIME PRO
TECTION
&IGURE  /VERCURRENT TIME PROTECTION FOR PAR
ALLEL TRANSFORMERS
OVERCURRENT TIME PROTECTION
DIRECTIONAL OVERCURRENT TIME PROTECTION
T
T
&IGURE  $OUBLE END FED LINE OR RING FEEDER
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