Sequence impedances of a power cable 1

[grounded7]

Hi all,

I am using a network distribution software and trying to create some new cables. For the creation of a cable, I have been given a number of parameters that I need to fill in.

I have a choice; either I can give the radius and GMR of the cable to calculate the positive and zero sequence impedances of the cable or I can simply put in the values of the positive and zero sequence impedances.

I do not have the data to get the software to calculate my impedances. However in the manufacturer data, I have been given the values for: Max AC resistance and reactance. I am using a waveform 4 core cable.

http://www.prysmian.co.uk/export/si...Cables/Low_Voltage_Utility/Waveform_Cable.pdf

The problem is that I have no idea if this is positive or zero sequence impedance or if its phase impedance.

Can anyone kindly help me out with it?

 

[davidbeach]

It would be the impedance of one cable. When three cables are used for a three phase circuit, that would also be the positive sequence impedance.

 

[jghrist]

The positive-sequence impedance, if direct buried or in PVC conduit, would be the table AC resistance and reactance. The manufacturer might be able to give some values for zero-sequence impedance or positive-sequence impedance if installed in metal conduit.

 

[grounded7]

Thanks guys. The cables will be laid in ducts, but from what you are saying I can take that:

Positive-seq Z = AC resistance and reactance in the datasheet
Zero-seq = unknown but could be found from the cable manufacturer.

This leads to another question. How essential is it to have the zero-sequence impedance if you are planning to run load-flow and fault analysis on your network?

 

[davidbeach]

Impossible to get a good ground fault value without the zero-sequence impedance. Load flow doesn't ever use zero-sequence impedance. If you are running a high impedance grounded system you probably don't need the zero-sequence impedance as the fault current will be determined by the grounding resistor, not the cable impedance.

 

[grounded7]

Thanks for that davidbeach!