Siemens SIPROTEC 7SJ531 - Page 76

-ETHOD OF OPERATION3*
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' #
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 (IGHLY SENSITIVE DIRECTION DETER
MINATION


4HE HIGHLY SENSITIVE EARTH FAULT DIRECTIONAL DETERMI
NATION DOES NOT PROCESS THE MAGNITUDE OF THE EARTH
CURRENT BUT THE COMPONENT WHICH IS AT RIGHT ANGLE TO
A SETTABLE DIRECTIONAL SYMMETRY AXIS ! PRECONDITION
FOR DETERMINATION OF THE FAULT DIRECTION IS THAT THE RE
SIDUAL VOLTAGE EXCEEDS THE SET VALUE OF THE VOLTAGE
STAGE
&IGURE  SHOWS AN EXAMPLE IN THE COMPLEX PHA
SOR DIAGRAM IN WHICH 5
%
FORMS THE REAL AXIS )N THIS
EXAMPLE THE ACTIVE COMPONENT )
%A
OF THE EARTH CUR
RENT )
%
 RELATED TO THE DISPLACEMENT VOLTAGE 5
%
ISDE
CISIVE AND IS COMPARED WITH THE SET THRESHOLD VALUE
)
%% $)2%#
 4HUS THIS EXAMPLE IS VALID FOR DIRECTIONAL
EARTH FAULT DETERMINATION IN AN ARC COMPENSATED
SYSTEM WHERE THE QUANTITY )
%
| COS É IS THE DETERMIN
ING FACTOR 4HE SYMMETRY AXIS IS IDENTICAL WITH THE )
%A
AXIS
%& -%!3  #/3 0()
0() #/22  
5
%
)
%A
)
%R
CAPACITIVE INDUCTIVE
FORWARD DIRECTION
REVERSE DIRECTION
)
%
)EE $)2%#
&IGURE  $IRECTIONAL CHARACTERISTIC WITH COS É
MEASUREMENT
4HE SYMMETRY AXIS CAN BE SHIFTED BY UP TO q
SETTABLE 4HUS IT IS POSSIBLE FOR EXAMPLE TO
ACHIEVE MAXIMUM SENSITIVITY FOR OHMIC
INDUCTIVE
CURRENTS BY
 INDUCTIVE ANGLE DISPLACEMENT IN
EARTHED SYSTEMS OR FOR EXAMPLE TO ACHIEVE MAXI
MUM SENSITIVITY FOR OHMIC
CAPACITIVE CURRENTS BY

CAPACITIVE ANGLE DISPLACEMENT FOR USE ON
ELECTRICAL MACHINES WHICH ARE DIRECTLY CONNECTED TO
AN ISOLATED NETWORK )N ADDITION 
SHIFTING IS POS
SIBLE IN ORDER TO DETECT EARTH FAULTS IN ISOLATED SYS
TEMS
4HE EARTH FAULT DIRECTION AND THE MAGNITUDE OF THE
CURRENT IN THIS DIRECTION IS DETERMINED FROM A HIGHLY
ACCURATE CALCULATION OF ACTIVE AND REACTIVE POWER US
ING THE DEFINITIONS
!CTIVE POWER
0
%A


4
T  4
T
U
%

T

I
%

T

DT
2EACTIVE POWER
0
%R


4
T  4
T
U
%
T   I
%

T

DT
WHERE 4 EQUALS PERIOD OF INTEGRATION
4HE USE OF AN EFFICIENT CALCULATION ALGORITHM AND SI
MULTANEOUS NUMERICAL FILTERING ALLOWS THE DIRECTIONAL
DETERMINATION TO BE ACHIEVED WITH HIGH ACCURACY
AND SHARPLY DEFINED THRESHOLD LIMITS SEE &IGURE
 AND INSENSITIVITY TO HARMONIC INFLUENCES
PAR
TICULARLY THE FREQUENTLY STRONG THIRD AND FIFTH HARMON
ICS WHICH OCCUR PARTICULARLY IN OHMIC EARTH FAULT CUR
RENTS 4HE DIRECTIONAL DECISION RESULTS FROM THE SIGNS
OF ACTIVE AND REACTIVE POWER
3INCE THE ACTIVE AND REACTIVE COMPONENT OF THE CUR
RENT
NOT THE POWER DETERMINE PICK UP OF THE
EARTH FAULT DIRECTIONAL DECISION THESE CURRENT COM
PONENTS ARE CALCULATED FROM THE POWER COMPO
NENTS 4HUS FOR DETERMINATION OF THE DIRECTION OF THE
EARTH FAULT ACTIVE AND REACTIVE COMPONENTS OF THE
EARTH FAULT CURRENT AS WELL AS THE DIRECTION OF THE AC
TIVE AND REACTIVE POWER ARE EVALUATED
7ITH SIN É MEASUREMENT FOR ISOLATED SYSTEMS
EARTH FAULT FORWARDS WHEN 0
%R
  AND )
%R
 SET
VALUE
EARTH FAULT BACKWARDS WHEN 0
%R
  AND )
%R
 SET
VALUE
7ITH COS É MEASUREMENT FOR COMPENSATED SYS
TEMS
EARTH FAULT FORWARDS WHEN 0
%A
  AND )
%A
 SET
VALUE
EARTH FAULT BACKWARDS WHEN 0
%A
  AND )
%A
 SET
VALUE
)N ALL OTHER CASES THE SYMMETRY AXIS IS PRODUCED BY
PROCESSING THE SUM OF PARTS OF THE ACTIVE AND REAC
TIVE POWER

 ONLY FOR MODEL 3*J JJJJ JJJJ
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