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Active Contributor

Join Date: Jun 2011
Posts: 19

### Zero Sequence Suseptance = 0, Why?

10/11/2012 7:23 AM

Hey everyone,

I am trying to get some electrical data that describes the properties of an underground cable. The values I get are all sequence impedances, which i am fine with until it comes to the suseptance values, as I can only find the positive sequence quoted, why is this? Having only the positive sequence does not allow me to determine the mutual and series suseptances, as i understand it i need the zero sequence as well........

Pathfinder Tags: suseptance sequence impedance
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Guru

Join Date: Oct 2007
Location: India
Posts: 1272
#1

### Re: Zero Sequence Suseptance = 0, Why?

10/11/2012 2:09 PM
Guru

Join Date: May 2007
Location: NYC metropolitan area.
Posts: 808
#2

### Re: Zero Sequence Suseptance = 0, Why?

10/11/2012 6:24 PM

Typically the positive sequence value is supplied by the cable manufacturer, the reason you don't get the negative value is because it's the same as the positive value. Zero sequence is a totally different story and is highly dependent upon the cable shape, whether it's multi- or single cored, shielded or not, in conduit or trenched, how it's grounded, soil conditions, etc., etc.

Remember that zero sequence currents are the ones that result from phase imbalances caused by asymmetries in loading, cabling, grounding conditions, and faults; therefore the zero sequence impedance is going to be dependent upon your local conditions.

Your best bet is to contact some cable companies and describe your configuration and let them guide you, unless you want to learn such esoterica as GMD (Geometric Mean Distance) and GMR (GM Radius).

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Active Contributor

Join Date: Jun 2011
Posts: 19
#3

### Re: Zero Sequence Suseptance = 0, Why?

10/12/2012 3:41 AM

I understand sequential componants and i also appreciate that the positive and negative sequences are the same in passive componants such as cables..... my difficulty is that data supplied for the suseptance contains only a positive sequence value, meaning that the mutual and series actual values cannot be computed, unless i am missing something?????

Guru

Join Date: May 2007
Location: NYC metropolitan area.
Posts: 808
#4

### Re: Zero Sequence Suseptance = 0, Why?

10/12/2012 9:25 PM

Sounds like you're trying to program your own load-flow/short-circuit analysis program, so you're probably well versed in matrix math. Unfortunately this editing system makes it very difficult to engage in any meaningful discussion of matrices. I suggest that you examine your assumptions regarding the computability of, and/or the existence of, mutual coupling values, they may be infinitely small.

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