power cable capacitance

[quality2011]

Q. In engineering books mostly capacitance and inductance of single core or 3 core belted cable given....I am interested to know the capacitance of 2 core, 3 core and 4 core cables armored and unarmored....is capacitance of 3 core belted is equal to 4 core armored or unarmored cable and 2core is equal to single core cable.....how can i calculate capacitance and inductance of 16 sq mm 2c and 4core cu/pvc/pvc 600/1000 v cable using ampere law and electric flux density dervied......q=cv and L=flux/current?????

 

[rbulsara]

I would ask the manufacturer of the cables.

Rafiq Bulsara

http://www.srengineersct.com

 

[quality2011]

engineer reply required??????

 

[rhatcher]

quality2011, you have received an Engineer's reply from rbulsara.

I agree with rbulsara's answer 100%. You can now consider that you have received a reply from two Engineers.

For a Design Engineer who is concerned with such things, the manufacturer is the correct source of information. This is because the values for capacitance and inductance may vary from one manufacturer to another.

This is an example of the type of information a Design Engineer would seek:

http://www.amercable.com/doc/catalogs/gexol/37-102-Four-Conductor.pdf

If you are asking for a mathematical method to calculate AC impedance and capacitance for different designs of cable, this sounds like a 'student' question. Student questions (homework help) are not allowed on this forum.

 

[davidbeach]

Besides (third engineer), many of the values needed to calculate it yourself are proprietary or otherwise generally unavailable.

 

[7anoter4]

The capacitance of a non-shielded pair of insulated conductor may be calculated using general equation:
integral(Dx*dS)=Q where Dx=eps*Ex and Q is the total electric charge[simplified].
From here eps.Ex=Q/(2*pi())/x/length and Ex=Q/eps/(2*pi())/x/length.
The static voltage drop from wire 1 to wire 2 is:
integral(Ex*dx)=V|x= from r=conductor radius to dist =distance between conductors
then V12=Q/(2*PI())/length*ln(dist/r)/eps
As C=Q/V C=2*pi()*eps*length/ln(dist/r)
This is a very simplified equation which does not take into consideration the electric field in the conductor itself. Also consider the field line from one conductor to another as straight line.
Using Maxwell rules in differential as div(D)=q and E= grad(V) E=ro*j j=current density [all these as vectors ] one would employ much sophisticated mathematics as Bessel function, for instance.
But from experience of a cable manufacturer, no theory is concluding. In order to fulfill the catalog a series of measurement was done-mainly for shielded or armored cables-with conductors short-circuited or grounded and recalculated the mutual capacity. But I have to declare: from cable to cable were differences.
Conclusion: I agree with rbulsara you'll better contact the manufacturer but don't take the answer as 100% accurate.