-ETHOD OF OPERATION
3*
6
# ' #
(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
%
IS DE
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
T4
T
U
%
T I
%
T DT
2EACTIVE POWER
0
%R
4
T4
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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