Post on 26-Feb-2018
transcript
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TransmissionSystemDesign
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SimplestepsforSagCalculation
1. Measurethehorizontaldistancebetweenthetowerattachment
points
(L).
2. Determinetheweightperunitlengthoftheconductor(w).
3. Findthetensionintheline(T).
4. Substitute
these
values
into
the
equation
T
x
y
=
(wx)(x/2)
where
yistheverticaldistancebetweentheattachmentpointandthe
lowestpointintheparabola,andwx istheweightthatactsata
horizontaldistancex/2fromtheattachmentpoint.
5. Solvetheequationfory.Thisyieldsy=wx/(2T).SubstituteL/2
forxsincethecenterbetweenthetowersisthelowspottoget
y=w/(2T)x(L/2),whichsimplifiestoy=wL/8T.
For
example,
the
sag
for
a
cable
with
a
weight
equal
to
1
kilogrampermetertensionedto10,000kgbetweentowers500
metersapartwouldhaveasagequalto(1)(500)/(8)(10,000)=
250,000/80,000=3.125meters.
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Bundle Conductors
2
4 S SSelfGMD D d D d
dDs
d d
d
d
d
dd
Ds
Ds Ds
Ds Ds
Ds Ds
3 29 3
4 3416 2 1.091
S S
S S
SelfGMD D d d D d
SelfGMD D d d d D d
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Inductance72 10 H/m
( )
a
GMDL In
SelfGMD GMR
Capacitance
2 //
anC F m
In GMD SelfGMD
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Insulators
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PotentialDistributioninStringInsulator
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M th d f I i St i Effi i
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Methods
of
Improving
String
Efficiency
1. By
using
longer
cross
arm2. Bygradinginsulators
3. ByusingGuardring
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