Siemens SIPROTEC 7SJ531 - Page 57

-ETHOD OF OPERATION3*
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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 EG THE )
PHASE CURRENT STAGE ANDOR 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 AC 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
,
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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