-ETHOD OF OPERATION
3$
6
# ' #
-EASURED VALUE PROCESSING
4HE DIGITIZED CURRENTS ARE FIRST FILTERED BY NUMERICAL
FILTERS IN ORDER TO SUPPRESS DC COMPONENTS AND
HIGHER HARMONICS 4HE RMS VALUES OF THE FUNDA
MENTAL WAVE OF THE DIFFERENTIAL AND STABILIZING CUR
RENTS ARE USED FOR EVALUATION
4O CLARIFY THE SITUATION THREE IMPORTANT OPERATING
CONDITIONS SHOULD BE EXAMINED
A 4HROUGH FAULT CURRENT IN A HEALTHY LINE OR EXTERNAL
FAULT
)
REVERSES ITS DIRECTION IE THUS CHANGES ITS SIGN
IE
)
)
AND CONSEQUENTLY\
)
\ \
)
\
)
DIFF
\
)
)
\ \
)
)
\
)
STAB
\
)
\ \
)
\\
)
\ \
)
\
|
\
)
\
NO TRIPPING EFFECT )
DIFF
STABILIZATION )
STAB
COR
RESPONDS TO TWICE THE THROUGH FLOWING CURRENT
B )NTERNAL SHORTCIRCUIT EG FED WITH EQUAL CURRENTS
FROM EACH LINE END
)N THIS CASE
)
)
AND CONSEQUENTLY\
)
\ \
)
\
)
DIF
\
)
)
\ \
)
)
\
|
\
)
\
)
STAB
\
)
\ \
)
\ \
)
\ \
)
\
|
\
)
\
TRIPPING EFFECT )
DIFF
AND STABILIZING )
STAB
QUANTI
TIES ARE EQUAL AND CORRESPOND TO THE TOTAL FAULT
CURRENT
C )NTERNAL SHORTCIRCUIT FED FROM ONE LINE END ONLY
)N THIS CASE
)
)
DIFF
\
)
)
\ \
\ \
)
\
)
STAB
\
)
\ \
)
\ \
)
\ \
)
\
TRIPPING EFFECT )
DIFF
AND STABILIZING )
STAB
QUANTI
TIES ARE EQUAL AND CORRESPOND TO THE FAULT CURRENT
FED FROM ONE SIDE
4HIS RESULT SHOWS THAT FOR INTERNAL FAULT )
DIFF
)
STAB
4HUS THE CHARACTERISTIC OF INTERNAL FAULTS IS A STRAIGHT
LINE WITH THE SLOPE IN THE OPERATION DIAGRAM AS ILLUS
TRATED IN &IGURE 4HE FIGURE SHOWS THE COMPLETE
OPERATION CHARACTERISTIC OF THE RELAY 4HE BRANCH A
REPRESENTS THE SENSITIVITY THRESHOLD OF THE DIFFERENTIAL
PROTECTION "RANCH B TAKES INTO CONSIDERATION CUR
RENT PROPORTIONAL ERRORS WHICH MAY RESULT FROM TRANS
FORMATION ERRORS OF THE MAIN CTS THE SUMMATION
TRANSFORMERS AND THE INPUT TRANSFORMERS OF THE RELAY
)N THE RANGE OF HIGH CURRENTS WHICH MAY GIVE RISE TO
CURRENT TRANSFORMER SATURATION BRANCH C CAUSES
STRONGER STABILIZATION ! FURTHER EVALUATION IN CASE OF
SEVERE SATURATION ADDON STABILIZATION IS DESCRIBED
IN 3ECTION
4HE CURRENTS )
DIFF
AND )
STAB
WHICH ARE FORMED AS DE
SCRIBED IN 3ECTION ARE COMPARED BY THE DIFFER
ENTIAL PROTECTION WITH THE OPERATING CHARACTERISTIC AC
CORDING TO &IGURE )F THE QUANTITIES RESULT INTO A
LOCUS IN THE TRIPPING AREA TRIP SIGNAL IS GIVEN PRO
VIDED THE LOCAL CURRENT THRESHOLD IS EXCEEDED TOO
LOCAL CURRENT THRESHOLD SEE 3ECTION
&AULT CHAR
ACTERISTIC
4RIP AREA
"LOCK
AREA
!DDON STABILIZATION
)
DIFF
)
.LINE
)
STAB
)
.LINE
C
B
A
&IGURE /PERATING CHARACTERISTIC OF THE DIFFERENTIAL PROTECTION
Содержание 7SD502
Страница 148: ... PPENDIX 3 6 PPENDIX ENERAL DIAGRAMS ONNECTION DIAGRAMS 4ABLES ...
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