Grounding riddle no.2 – The best route for earth conductor running

A young electrical engineer who is recently graduated from university is in doubt about accepting that professional recommendation. He says that the reactance of cable is proportional to its inductance, and only mutual inductance is changed by cables cross distance. Also according to what he has learnt in classical electromagnetic, he knows that, cable mutual inductance increases when their cross distance is reduced. Therefore he says that standard recommendation is not correct!

Can you help to your friend for that misunderstanding?

#1
Thu, September 13, 2007 - 11:08
Finrod_Felagund
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Join Date: Jul 2007
Location: Arica - Chile
Posts: 2 #1
Re: The best route for earth conductor running
07/22/2007 1:07 AM
For the Fault Calculation you need to the zero sequence impedance, so in a trifasic line with neutral conductor the zero impedance is:

Z0=Z0A - (ZOAG)2/Z0G  Ω/m

with:

Z0A=three times the self impedance of an equivalent conductor of the three phase line (without the neutral conductor)

Z0G=three times the self impedance of the neutral conductor

Z0AG=three times the mutual impedancia between the equivalent phase conductor and the neutral conductor.

As you can see, for a lower zero impedance we required to maximized the mutual impedance between the phases and the neutral, and you can get this with closer neutral conductor to the phase conductors.