Siemens 7SD502, Instruction Manual

Page: 60 / 178

)NSTALLATION INSTRUCTIONS 3$
6
# ' #
0ILOT WIRE REQUIREMENTS
4HE MEASURING TECHNIQUE OF THE 3$ REQUIRES
ONE PAIR OF SYMMETRICAL WIRES TO BE CONNECTED BE
TWEEN THE TWO STATIONS 4HE TEST VOLTAGES MUST EX
CEED THE MAX INDUCED LONGITUDINAL VOLTAGE CAUSED
BY EARTH FAULTS )T SHOULD BE AT LEAST 6 4HE PILOT
WIRES MUST MEET A SYMMETRY WIREWIRE AT (Z
TELEPHONE PAIR
)T IS ABSOLUTELY NECESSARY TO RECONSIDER THE INDUCED
LONGITUDINAL VOLTAGE DURING EARTH FAULTS 4HE PILOT
WIRES ARE NOT ONLY STRESSED BY THE HIGH CURRENTS
WHICH CAN BE TRANSMITTED DURING A SHORTCIRCUIT AND
HIGH SURGE VOLTAGES BUT ARE ALSO ENDANGERED ME
CHANICALLY TO THE SAME EXTENT AS THE POWER CABLES
THEMSELVES
4HE LARGEST ELECTRICAL DANGER FOR PILOT WIRE CABLES OC
CURS DURING A SHORTCIRCUIT WITH EARTH CONNECTION
4HE FAULT CURRENT INDUCES A LONGITUDINAL VOLTAGE INTO
THE PILOT WIRE CABLE WHICH IS OFTEN LED IN PARALLEL TO THE
POWER LINE OR CABLE
4HE INDUCED VOLTAGE IN THE PILOT WIRES CAN BE RE
DUCED BY USING GOOD CONDUCTIVE COVERS SMALL RE
DUCTION FACTOR FOR PILOT CABLE AS WELL AS POWER CABLE
!DDITIONALLY THE PILOT WIRES CAN BE ISOLATED BY BARRIER
TRANSFORMERS 4HUS A SUBDIVISION OF THE LONGITUDINAL
VOLTAGE IS ACHIEVED
4HE INDUCED VOLTAGE CAN BE CALCULATED ACCORDING TO
THE FOLLOWING EQUATION
5
I
à F | - | )
SC
| L | R | R
WHERE
5
I
INDUCED LONGITUDINAL VOLTAGE IN 6
F SYSTEM FREQUENCY IN (Z
- MUTUAL REACTANCE BETWEEN THE POWER LINE
AND THE PILOT WIRES IN M(KM
)
SC
MAXIMUM SINGLEPHASE EARTH FAULT CURRENT
IN K!
L LENGTH OF THE SECTION WHERE THE POWER LINE
AND THE PILOT WIRES ARE LED IN PARALLEL IN KM
R REDUCTION FACTOR OF THE POWER CABLE R
IN CASE OF OVERHEAD LINES
R REDUCTION FACTOR OF THE PILOT WIRE CABLE
4HE MUTUAL REACTANCE CAN BE INSERTED IN M(MILE IF
THE LINE LENGTH IS ALSO INSERTED IN MILES /NLY THE HALF
OF THE CALCULATED INDUCED VOLTAGE NEED BE RECOG
NIZED AS IT IS SHARED OUT AMONG THE TWO ENDS OF THE
PILOT WIRES
4HE 3$ IS INSULATED TO WITHSTAND K6 0ILOT
WIRES WITH A MAX K6 TEST VOLTAGE CAN BE DIRECTLY
CONNECTED UP
4HE INDUCED LONGITUDINAL VOLTAGE MUST NOT
EXCEED OF THE TEST VOLTAGE OF THE PILOT
WIRES
7ARNING
)F THE LONGITUDINAL VOLTAGE EXCEEDS OF THE RELAY
INSULATION LEVEL OF K6 IE K6 THE USE OF INSU
LATED EXTERNAL BARRIER TRANSFORMER 82 IS RE
QUIRED 4HE TEST VOLTAGE OF THE PILOT WIRES CAN REQUIRE
FURTHER SUBDIVISIONS %VEN IF BARRIER TRANSFORMERS ARE
USED NEITHER OF THE TEST VOLTAGE OF THE BARRIER
TRANSFORMERS NOR OF THE TEST VOLTAGE OF THE PI
LOT WIRES MUST BE EXCEEDED
4HE BARRIER TRANSFORMER SHOULD BE MOUNTED NEAR THE
CABLE SEALING END TO PREVENT THE INDUCED VOLTAGE TO
ENTER THE RELAY PANEL 4HE TYPE 82 &IGURE
IS RECOMMENDED WHICH HAS A K6 INSULATION
4HE CENTRE TAPPING OF THE BARRIER TRANSFORMER WIND
INGS ARE EARTHED AT THE RELAY SIDE FOR SAFETY REASONS
REFER TO &IGURE 4HE PILOT WIRE SIDED WINDINGS
ARE FLOATING AGAINST EARTH POTENTIAL
4HE PILOT WIRES MUST NOT BE EARTHED NOR
PROVIDED WITH SURGE ARRESTERS
#AUTION
3$ 3$
+
,
,
-
+ + ,
-
+ ,
- -
NO EARTH
CONNECTION
AT -
NO EARTH
CONNECTION
AT -
!
! !
!
&IGURE #ONNECTION OF BARRIER TRANSFORMERS 82