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No-Load Dielectric Losses 2

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sranwar

Electrical
Oct 1, 2008
7
Can anybody guide me or refer to any documentation which describes how to calculate the no-load dielectric losses for a 15 kV UD 750 mcm cable?

 
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Just a guess - perhaps you could do a Doble/power factor measurement for a given length of cable and calculate losses per unit length from there.
Losses = Irms * Vrms * powerfactor

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The cable manufacturer can provide data on dielectric losses for a particular type of insulation and cable construction. Some modeling programs also include this shunt resistance in their cable models.

EPR dielectric losses are much higher than XLPE.
 
Cable system is in design phase. There must be some theoretical/mathematical way of knowing this beforehand which helps in cable selection. Secondly, I need just the dielectric losses only
 
I would assume dielectric loss as beeing negliable vs. ohmic loss due to charging currents for lenght exceeding some 100 m.
 
You just need to get representative data from a couple of manufacturers. There is no way to calculate the dielectric loss unless you have the actual data for the type of insulation being used.

It is not insignificant for long runs of cable and is one of the reasons that many utilities use XLPE for long UG feeders.

 
I agree with dpc you do better ask the cable mfctr. But for your information you may use the follows:
IEC 60287 “Electric cables – Calculation of the current
rating” or from the old standard:
[According to IEC 287/1982 para 5]:
DIELECTRIC LOSSES:
Wd=2*pi()*frq*CAP*Uo^2*tandelta [w/m] Uo=ULL/sqrt(3)[V]
CAP=epsilonr/18/Ln(INS.DIA/CONDUCT.DIA)/10^9 [F/m]
EXTRAS FROM TABLE III&IV:
Insulation epsilonr tandelta
EPR (U=<36) 3 0.02
EPR(U>36) 3 0.005
PVC 8 0.1
PE(HD,LD) 2.3 0.001
XLPE(U=<36) 2.5 0.004
XLPE(U>36) 2.5 0.001

For 15 kV UD 750 MCM cable [shielded]
Diaoverinsulation=1.41 inches [220 mils ins.thick]
Conductordia=0.97 inches
XLPE insulation epsilonr=2.5 tandelta=0.004
Capacity=2.5/18*ln(1.41/.97)/10^9
CAP=3.71312E-07 F/km
Wd=2*pi()*60*3.71312E-07*(15000/sqrt(3))^2*.004= 42 w/km
WD=42*.3048= 12.8 w/1000ft
Regards
 
Thank you very much all. This will help. Also got some numbers from mfg.
 
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