-ETHOD OF OPERATION
3*
6
# ' #
^
^
^
^
^
M!
M!
M!
^
^
2EVERSE
&ORWARDS
&ORWARDS
2EVERSE
)
%
LAGGING
)
%
LEADING
)
%A
ACTIVE COMPONENT
&IGURE $IRECTIONAL EARTH FAULT MEASUREMENT CHARACTERISTIC
EXAMPLE )
|
COS
É
)N NETWORKS WITH ISOLATED STARPOINT THE EARTH FAULT
CURRENT FLOWS AS A CAPACITIVE CURRENT FROM THE HEALTHY
LINES VIA THE MEASURING POINT TO THE POINT OF FAULT 4HIS
CAPACITIVE CURRENT DETERMINES THE DIRECTION
)N NETWORKS WITH ARC SUPPRESSION COILS THE 0ETERSEN
COIL SUPERIMPOSES A CORRESPONDING INDUCTIVE CUR
RENT ON THE CAPACITIVE EARTH FAULT CURRENT WHEN AN
EARTH FAULT OCCURS SO THAT THE CAPACITIVE CURRENT AT
THE POINT OF FAULT IS COMPENSATED $EPENDENT UPON
THE POINT OF MEASUREMENT IN THE NETWORK THE RESUL
TANT MEASURED CURRENT CAN HOWEVER BE INDUCTIVE OR
CAPACITIVE AND THE REACTIVE CURRENT IS THEREFORE NOT
SUITABLE FOR THE DETERMINATION OF DIRECTION )N THIS
CASE ONLY THE OHMIC RESIDUAL CURRENT WHICH RESULTS
FROM THE LOSSES OF THE 0ETERSEN COIL CAN BE USED FOR
DIRECTIONAL DETERMINATION 4HIS EARTH FAULT OHMIC CUR
RENT IS ONLY A FEW PERCENT OF THE CAPACITIVE EARTH FAULT
CURRENT
)N THE LATTER CASE IT MUST BE NOTED THAT DEPENDENT
UPON THE LOCATION OF THE PROTECTIVE RELAY A CONSIDER
ABLE REACTIVE COMPONENT MAY BE SUPERIMPOSED
WHICH IN THE MOST UNFAVOURABLE CASES CAN ATTAIN
TIMES THE ACTIVE COMPONENT %VEN THE EXTREMELY
HIGH ACCURACY OF THE CALCULATION ALGORITHM IS THEN IN
ADEQUATE IF THE CURRENT TRANSFORMERS DO NOT EXACTLY
CONVERT THE PRIMARY VALUES
4HE MEASUREMENT INPUT CIRCUIT OF THE RELAY FOR HIGHLY
SENSITIVE EARTH FAULT DETECTION IS PARTICULARLY DE
SIGNED FOR THIS PURPOSE AND PERMITS AN EXTREMELY
HIGH SENSITIVITY FOR THE DIRECTIONAL DETERMINATION OF
THE WATTMETRIC RESIDUAL CURRENT )N ORDER TO UTILIZE THIS
SENSITIVITY IT IS RECOMMENDED THAT WINDOW TYPE CUR
RENT TRANSFORMERS BE USED FOR EARTH FAULT DETECTION IN
COMPENSATED NETWORKS !S EVEN THE CORE BALANCE
TRANSFORMERS HAVE AN ERROR OF ANGLE THE PROTECTION
SYSTEM ALLOWS THE SETTING OF FACTORS WHICH DEPEN
DENT UPON THE REACTIVE CURRENT WILL CORRECT THE ERROR
ANGLE
&URTHER EXPLANATION CONCERNING THE CHARACTERISTIC
AND SYMMETRY AXIS ARE GIVEN IN THE SETTING HINTS IN
3ECTION
www
. ElectricalPartManuals
. com