Capacitive Charging On Ungrounded Systems

You should ask your friend why he thinks that the positive sequence currents seek a different route than the negative sequence currents; then look at a good book on Symmetrical Component Theory.

If this is a 3 phase AC circuit, I would think you would have 3 capacitors as an equivalent circuit for the parasitic capacitance, delta connected between the three phases.

Whatever you hope, this looks like a bad idea about to happen.

As a personal exercise why don't you calculate an example phase to phase or phase to ground fault current and compare it to the miniscule capacitive component current obtained from the lumped cable capacitive element (which will be lower in real life because the cable capacitance is distributed over the length of the line).

I would say many orders of magnitude difference in current.

Well......yes, but I wanted the original poster to come to that conclusion on their own.

I understand during single phase to ground faults, the fault current will be very low and for phase to phase faults the current will be high.

The discussion arose because of capacitive charge currents. To find the capacitive charging current theoretically, the capacitance of entire cable length from source to load should be considered, but he says the capacitance of the cable from the source till the ZCT should be considered. I fail to understand why?

Your colleague is looking at the quantity from the viewpoint of the protective equipment connected to the CT, the unmeasured offset.

The amount of heating provided by the capacitive coupling current is the total distributed current, heating that you would experience in your broken delta ground sensing equipment resistor, for instance, if you provide a circuit.

On (HV) shielded cables, the charging current is high enough to be sensed by typical zero sequence CTs, that is why you bring the shield drain wires back through the CT at the source end.

Er, there is no fault current illustrated.

Voltage. Cable type, Cable run length. 3 Cored or 1 Cores, Sheath type, collective screening, individual screening or both, are the 'many cables used in series' all the same cable type and configuration.

Might be of value to know.

Is this for an underground ungrounded system? Don't you think that is confusing? I think it should all be above board.

For a single core screen cable .

C = e _r / [18 * log e ( D / d )] ( m F/km)

where e_r = relative permittivity of insulation = dielectric constant

XLPE _ 2.5 e_r

F= Farads

D- Diameter over insulation

d = diameter of conductor

You really don't have much to worry about on these short lengths and if the screens are properly earthed.