Discussion Forum

Hi,

I am working on a design project where I'm looking to design a sensor that can detect defects (loss of cross-section, pitting, etc.) in the aluminum strands of an aluminum conductor steel reinforced (ACSR) power line cable while it is energized with about 900 A of alternating current at 50 or 60 Hz. The initial approach to this project has been to investigate whether it would be possible to design a sensor that can detect variations in the magnetic field produced from a typical ACSR cable (which has a ratio of 26 outer aluminum strands to 7 inner steel strands each spread across two layers) in the prescence of these defects.

In COMSOL, I have started with trying to model this cable in 2D using the Magnetic Fields Interface, and assuming a uniform constant DC current flowing through these aluminum strands. I have defined this condition using the External Current Density Domain with the 900 A over the total cross-sectional area of these aluminum strands specified as Jz. I have also been using a Stationary Study with a Parametric Sweep analysis to vary the radius of specific aluminum strands as well as the corresponding current density to examine their effect on the magnetic field.

Some issues and questions that I am having with COMSOL are:

1. The solution is not agreeing with the analytical solution for magnetic field produced from a straight current carrying wire as the COMSOL model is two times larger than what it should be. I'm not sure what's going on here as even when trying to model the magnetic field from current flowing through a single strand, this effect is still present.

2. I would like to expand this model to incorporate the effects of induced current in the steel core by the residual magnetic field produced from the aluminum strands, but I'm not sure how to go about doing this in COMSOL. When I do a surface integral over the cross-sectional area of the steel core to calculate external current density, the model is telling me that its zero despite a magnetic field being present. Is there a specific boundary condition that I should be applying to the steel core to allow for induced currents?

3. I would like to produce a plot of the difference in magnetic field produced from an unaltered ACSR cable, and a cable with the cross-sectional area of one of its aluminum strands varied. The Parametric Sweep Analysis that I have performed has given me individual plots of this, but I'm looking for a way to produce a plot of the difference between two parametric solutions in COMSOL. Is there any way to do this?

If anyone has any ideas that could help me solve these issues, that would be much appreciated. The version of COMSOL that I'm using is 5.6. and I have attached a couple of the graphs that I have been getting for reference.

Thank you,

Billy Thorpe