-ETHOD OF OPERATION
3*
6
# ' #
3)02/4%# 3* PROVIDES AN ADDITIONAL DIRECTION
AL OVERCURRENT TIME STAGE FOR EACH OF THE PHASE CUR
RENTS AND FOR THE EARTH CURRENT 4HE NON DIRECTION
AL OVERCURRENT TIME STAGES AS DESCRIBED IN 3ECTION
CAN EITHER BE USED AS SUPERIMPOSED BACK UP
STAGES OR MADE INEFFECTIVE OR INDIVIDUAL NON DIREC
TIONAL STAGES CAN BE USED IN CONNECTION WITH THE DI
RECTIONAL OVERCURRENT TIME STAGES EG THE )
PHASE CURRENT STAGE ANDOR THE )
%
STAGE
4HE DIRECTIONAL OVERCURRENT TIME PROTECTION CAN BE
USED
AS THE NON DIRECTIONAL
AS DEFINITE TIME OR
INVERSE TIME OVERCURRENT PROTECTION &OR INVERSE TIME
MODE SELECTION CAN BE MADE FROM THE SAME CHAR
ACTERISTICS WHEREBY DIFFERENT CHARACTERISTICS CAN BE
CHOSEN FOR PHASE CURRENTS AS WELL AS FOR THE EARTH
CURRENT
$IRECTION DETERMINATION
4HE DIRECTION OF THE CURRENT FLOW IS DETERMINED IN FOUR
LOGICALLY INDEPENDENT MEASURING ELEMENTS ONE FOR
EACH OF THE PHASES AND ONE FOR EARTH FAULTS
4HE PHASE RELATED MEASURING ELEMENTS USE THE AS
SIGNED CURRENT AND A SOUND VOLTAGE 4HIS ENSURES
CORRECT AND RELIABLE DIRECTIONAL DECISION TO BE MADE
EVEN WHEN THE FAULT VOLTAGE HAS COMPLETELY COL
LAPSED CLOSE UP FAULT 3TORED VOLTAGES ARE USED IN
CASE OF A CLOSE UP THREE PHASE FAULT AS LONG AS THE
MEASURED VOLTAGES ARE NOT SUFFICIENT FOR RELIABLE DI
RECTIONAL DISCRIMINATION !FTER THE STORAGE TIME HAS
ELAPSED TWO AC PERIODS THE DETERMINED DIRECTION
IS MAINTAINED BUT ONLY AS FAR AND AS LONG AS NO SUFFI
CIENT MEASURED VOLTAGE IS AVAILABLE AND THE RELAY RE
MAINS PICKED UP
4HE EARTH RELATED MEASURING ELEMENT OPERATES WITH
THE ZERO SEQUENCES QUANTITIES )
%
|
)
AND
5
%
o
|
5
4HIS ENSURES HIGH SENSITIVITY IN CASE
OF EARTH FAULT EVEN WHEN THE ASSIGNED PHASE MEA
SURING ELEMENT DOES NOT PICK UP 4HE DISPLACEMENT
VOLTAGE 5
%
CAN BE CALCULATED WHEN THE RELAY IS CON
NECTED TO THREE STAR CONNECTED VOLTAGE TRANSFORM
ERS 7HEN ONLY PHASE TO PHASE VOLTAGES ARE FED
TO THE RELAY DISPLACEMENT VOLTAGE CALCULATION IS OF
COURSE NOT POSSIBLE )N THIS CASE THE DIRECTIONAL
EARTH OVERCURRENT TIME PROTECTION IS INOPERATIVE AND
NO SETTINGS ARE POSSIBLE
! SHORT CIRCUIT BETWEEN TWO PHASES IS PROCESSED
BY TWO PHASE MEASURING ELEMENTS NAMELY THOSE
WHICH ARE RELATED TO THE TWO AFFECTED PHASES !N
EARTH FAULT IS PROCESSED BY THE EARTH FAULT MEASURING
ELEMENT AND BY THE CONCERNED PHASE ELEMENT PRO
VIDED THE FAULT CURRENT IS SUFFICIENT FOR PICK UP OF THE
PHASE ELEMENT
&OR SINGLE PHASE FAULTS THE QUADRATURE VOLTAGES FOR
THE PHASE MEASURING ELEMENTS ARE AT RIGHT ANGLES TO
THE SHORT CIRCUIT VOLTAGES &IGURE 4HIS IS CON
SIDERED IN THE CALCULATION OF THE DIRECTIONAL VECTOR
&OR PHASE PHASE FAULTS THE SHAPE OF THE DIRECTIONAL
CHARACTERISTIC MAY BE DISPLACED DEPENDENT OF THE
MAGNITUDE OF THE FAULT VOLTAGE
4ABLE SHOWS THE ALLOCATION OF MEASURED VALUES
FOR THE DIRECTION TO THE DIFFERENT TYPES OF FAULT
5
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5
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5
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5
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5
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5
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5
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5
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5
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A
,OOP PHASE EARTH , %
B ,OOP PHASE PHASE , ,
&IGURE
2EFERENCE VOLTAGES FOR DIRECTIONAL DETERMINATION
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