Zero sequence impedance of the cable laid in the steel pipe
Zero sequence impedance of the cable laid in the steel pipe
(OP)
If it's possible I'd like to ask advice. We have three XLPE cables in trefoil formation laid in the steel pipe (the pipe was previously a part of high-pressure fluid-filled pipe-type cable system). The pipe and cable screens are directly earthed at both ends of the cable (see attached image).
I have several uncertainties:
1. How to calculate zero sequence impedance Z0 of a cable in this case?
2. Can I use Carson's equation? Assumption about equivalent earth conductor at a variable complex depth according to frequency and earth resistivity might not be valid here, as earth current most probably will flow in the steel pipe.
3. Is there a mutual coupling between cable conductor and steel pipe (it would influence the direction of the current induced in the pipe)?
4. Does anyone have similar cable layouts in their power systems?
Any help, links or suggestions appreciated.
I have several uncertainties:
1. How to calculate zero sequence impedance Z0 of a cable in this case?
2. Can I use Carson's equation? Assumption about equivalent earth conductor at a variable complex depth according to frequency and earth resistivity might not be valid here, as earth current most probably will flow in the steel pipe.
3. Is there a mutual coupling between cable conductor and steel pipe (it would influence the direction of the current induced in the pipe)?
4. Does anyone have similar cable layouts in their power systems?
Any help, links or suggestions appreciated.






RE: Zero sequence impedance of the cable laid in the steel pipe
RE: Zero sequence impedance of the cable laid in the steel pipe
There are some tables included for low voltage cables based on tests. You may have to get data from manufacturers based on tests. Maybe steel armoured cable test data could be used.
RE: Zero sequence impedance of the cable laid in the steel pipe
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But, as you remarked, the problem is more complicated. So Timesabroom proposal to see SEL paper "Protection of High-Voltage AC Cables." is still valuable.See:
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Also you may consult "Handbook of Electrical Power Calculation" by H. Wayne Beaty see:
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RE: Zero sequence impedance of the cable laid in the steel pipe
RE: Zero sequence impedance of the cable laid in the steel pipe
Thank you all for your answers and links. I was hoping there is some kind of established calculation methodology for this case, but it appears the things are quite difficult.
RE: Zero sequence impedance of the cable laid in the steel pipe