Is X1C = X0C for a shielded cable

[veritas]

When considering shielded three-phase or even 3 x singlephase cables, I've come to the conclusion that the positive sequence capacitive reactance (X1C) is the same as the zero sequence capacitive reactance (X0C). Conceptually, whether I excite the cable with a single or threephase source, the impedance the cable presents is the same, the way I see it.

In the attached I have thus concluded that X1C = X0C.

Of course the pps inductive reactance X1L is not equal to zps inductive reactance X0L with threephase excitation, there is no current in the shield. The flux linkage the phase conductors "see" are this different between threephase and singlephase excitation.

Is my understanding above correct?

Thanks.

 

[7anoter4]

In my opinion, if all three shields are connected together and with the ground directly then XC1=XCo. If it is not will be two capacities in series one from conductor to shield and one from shield to ground.

 

[veritas]

Interesting point - all 3 shields are always earthed at least at one end of the cable. Thus effectively tied together at the earthing location. When earthed at both ends, which is the case I'm considering, then yes, X1C = X0C.

However, if only earthed at one end, then yes, effectively there are two capacitances in series. The one between the shield and earth increases in C as one moves from the earthed end to the unearthed end. But how does one calculate or allow for this 2nd capacitance? Does this mean both X1C and X0C are different from the case where the shield is earthed both ends?

Need to do some more thinking.

 

[cuky2000]

I found the excerpt below. Not sure about the source.