)NTRODUCTION3$ 6
# ' #
)NTRODUCTION
!PPLICATION
4HE NUMERICAL LINE DIFFERENTIAL PROTECTION IS A FAST AND
SELECTIVE SHORTCIRCUIT PROTECTION FOR CABLES AND OVER
HEAD LINES INDEPENDENT OF THE TREATMENT OF THE NET
WORK NEUTRAL
)T IS PARTICULARLY SUITED TO SHORT LINES WHERE FOR EX
AMPLE ZONE OF THE DISTANCE PROTECTION CANNOT BE
SET SUFFICIENTLY SHORT )T CAN BE USED WITH LINES DOWN
TO ANY LENGTH /NE SET OF CURRENT TRANSFORMERS IS RE
QUIRED AT EACH END OF THE LINE 6OLTAGE TRANSFORMERS
ARE NOT REQUIRED
!N ESSENTIAL ADVANTAGE OF THE DIFFERENTIAL PROTECTION
SYSTEM IS ITS ABILITY TO INITIATE THE IMMEDIATE DISCON
NECTION OF ANY SHORTCIRCUIT AT ANY LOCATION IN THE PRO
TECTED ZONE 4HE CURRENT TRANSFORMERS AT EACH END
SEPARATE THE PROTECTED ZONE FROM THE REST OF THE NET
WORK 4HIS PRECISE ZONE CUTOFF IS THE REASON FOR THE
ABSOLUTE SELECTIVITY OF THE DIFFERENTIAL PROTECTION PRIN
CIPLE 4HIS ELIMINATES THE NEED TO DELAY THE TRIP SIGNAL
WHICH IS NECESSARY WITH TIMEGRADED PROTECTION
4HE LINE DIFFERENTIAL PROTECTION SYSTEM REQUIRES THE
INSTALLATION OF ONE 3$ UNIT AT EACH END OF THE
PROTECTED LINE 4HE TWO RELAYS MUST BE INTERCON
NECTED BY TWO PILOT WIRES 4HESE PILOT WIRES MAY
HAVE A MAXIMUM LOOP RESISTANCE OF APPROXIMATELY
/HMS 4HEY MUST BE ADEQUATELY INSULATED
FROM ONE ANOTHER AND TO EARTH REFER TO 3ECTION
3$ IS PARTICULARLY DESIGNED TO OPERATE
WITH EXISTENT PILOT WIRE PAIRS )N CASE A BRANDNEW
COMPARISON LINK IS TO BE INSTALLED THE USE OF CURRENT
COMPARISON PROTECTION 3$ OR 3$ WITH OPTI
CAL FIBRE LINK IS ADVANTAGEOUS FOR TWOTERMINAL LINES
3INCE ANY FAULT ON THE TWO PILOT WIRES WILL CAUSE FAIL
URE OF THE PROTECTIVE DEVICES IT IS RECOMMENDED THAT
THE PILOT WIRE MONITORING SYSTEM BE INSTALLED )F A PILOT
WIRE FAULT IS DETECTED THE DIFFERENTIAL PROTECTION SYS
TEM MAY BE BLOCKED SELECTABLE AND AN ALARM IS IS
SUED
3INCE THE COMPARISON PROTECTION DOES NOT DISCON
NECT FAULTS OUTSIDE THE PROTECTED ZONE AN ADDITIONAL
TIMEGRADED PROTECTION MUST BE INSTALLED AT AT LEAST
ONE END OF THE LINE TO SERVE AS SUPERIMPOSED BACK
UP PROTECTION &OR THIS PURPOSE THE INCORPORATED
OVERCURRENT TIME PROTECTION MAY BE USED WHICH CAN
OPERATE OPTIONALLY AS DEFINITE TIME OR INVERSE TIME
PROTECTION
)N CASES WHERE A POWER TRANSFORMER IS DIRECTLY CON
NECTED IE WITHOUT A CIRCUITBREAKER TO A CABLE OR TO
AN OVERHEAD LINE CURRENT TRANSFORMERS SHOULD BE IN
STALLED AT THE CONNECTION POINT AND THE 3$ RELAY
SHOULD ONLY BE USED AS LINE PROTECTION "Y USE OF THE
INTEGRATED SECOND HARMONIC RESTRAINT FEATURE FROM
FIRMWARE VERSION 6 OR LATER 3$ IS IN PRINCI
PLE SUITABLE FOR THE INCLUSION OF A TRANSFORMER IN THE
PROTECTED ZONE BUT BECAUSE OF THE HIGH PARASITIC
CURRENTS ESPECIALLY ON CABLES THE ADVANTAGE OF HIGH
SENSITIVITY CANNOT BE EXPLOITED AS WITH A TRANSFORMER
DIFFERENTIAL PROTECTION EG 54 WHICH PROVIDES
ADDITIONALLY AN INTEGRATED MATCHING OF THE TRANS
FORMER VECTOR GROUP
! THERMAL OVERLOAD PROTECTION IS INTEGRATED FOR USE
ON CABLES
4HROUGHOUT A FAULT IN THE NETWORK THE MAGNITUDES OF
THE INSTANTANEOUS VALUES ARE STORED FOR A PERIOD OF
MAX SECONDS AT (Z AND ARE AVAILABLE FOR SUB
SEQUENT FAULT ANALYSIS &AULT INCEPTION IS TAGGED WITH
THE REAL TIME PROVIDED THE INTERNAL REAL TIME CLOCK IS
AVAILABLE
#ONTINUOUS PLAUSIBILITY MONITORING OF THE INTERNAL
MEASURED VALUE PROCESSING CIRCUITS AND MONITORING
OF THE AUXILIARY VOLTAGES TO ENSURE THAT THEY REMAIN
WITHIN TOLERANCE ARE OBVIOUSLY INHERENT FEATURES
3ERIAL INTERFACES ALLOW COMPREHENSIVE COMMUNICA
TION WITH OTHER DIGITAL CONTROL AND STORAGE DEVICES
OPTIONAL &OR DATA TRANSMISSION A STANDARDIZED
PROTOCOL IN ACCORDANCE WITH )%# AND
6$%7:6%) IS USED AS WELL AS ACCORDING $).
SELECTABLE 4HE DEVICE CAN THEREFORE BE INCORPO
RATED IN ,OCALIZED 3UBSTATION !UTOMATION NETWORKS
,3!
