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Modelling SWER (Single Wire Earth Return) - Single Phase Conductor

Modelling SWER (Single Wire Earth Return) - Single Phase Conductor

Modelling SWER (Single Wire Earth Return) - Single Phase Conductor

(OP)
Hi

I'm trying find the correct way to model SWER. I'm aware some software's let you select the system type as SWER, but I'm stuck with just a 3-phase modelling software (PSS-ADEPT).

Can you represent SWER with sequence components in a 3-phase system? I've read that you can apply the Carson Equation to 1, 2, and 3 phase conductor systems, where I assume a 1 phase conductor system is identical to a SWER system?

So far I can produce the primitive impedance matrix as a 2x2 matrix: [[z_aa, z_ag],[z_ga, z_gg]], where z_aa is the self impedance of the conductor, z_ga = z_ag is the mutual impedance of the ground-conductor pair, and z_gg is the self impedance of the ground.

I have expressions for getting values for a z_aa, z_ag, z_gg from the physical parameters of the system. I can then use Kron Reduction to get rid of the neutral (is this step right, as Kron reduction requires 0 A current in the neutral and this technically isn't true because the neutral is the earth return path?) and produce a 1x1 matrix (scalar) that is the adjusted z_aa value (z_aa(new) = z_aa(old) - 2*z_ag/z_gg).

I then build the phase frame matrix [z_abc] = [[z_aa(new), 0, 0], [0, 0, 0], [0, 0, 0]]. Then proceed to do the typical thing: [z_012] = [A]^-1.[z_abc].[A]. Since the phase frame matrix is symmetrical we should expect to see 0 elements for the off-diagonal terms in the impedance matrix. This doesn't yield a meaningful result though.... so can someone explain where I might be going wrong, or what the correct approach is with SWER (and 2-phase/v-phase systems) and finding the zero, positive and negative sequence impedance.

RE: Modelling SWER (Single Wire Earth Return) - Single Phase Conductor

Symmetrical components were intended to simplify the calculations of unbalanced three phase systems. You're trying to go in an opposite direction. A SWER is just a single phase system with a phase conductor, transformers and using the earth for the return path.

I admire the fact that you've gone through a lot of work to look at the possibilities of being able to fool a three phase load flow so that it can accommodate a single phase model. I just don't think it's going to work.

I think you're better off just writing the single phase equations for a single phase system and developing your own software. You could probably make it work on a spreadsheet.

RE: Modelling SWER (Single Wire Earth Return) - Single Phase Conductor

(OP)
On page 87 (equation 4.58) shows a single phase line represented in the phase impedance/frame matrix, which makes me think it is possible to represent SWER in the 3 phase sequence component form. But like you say, the earth is the return path (so current does not equal 0), so I think that to represent SWER properly you would not do the Kron Reduction step to eliminate the neutral i.e. treat the earth return path as a separate phase conductor. Therefore, the phase frame matrix is [z_abc] = [[z_aa, z_ag, 0], [z_ga, z_gg, 0], [0, 0, 0]] - so that is just treating the ground return path as phase b (it could equally have been phase c). Do you see anything wrong with this approach?

RE: Modelling SWER (Single Wire Earth Return) - Single Phase Conductor

You can model a single wire in an three-phase network with the help of a double open-line fault (phases b and c open, or broken, for example), see the attached picture. In practice, this is very much the same as a single-line-to-earth fault.

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