CT Magnetization Curve in MATLAB

Difficult, because without accuracy class or magnetization knee point, your parameters give nothing about the iron/air gap saturating circuit.

Also, magnetic materials of different types have different curves. There is a big difference between metering CT and protection CT.

High permeability core and low air gaps minimize magnetizing current error for metering but bring in saturation at lower primary current.

Protection CT need to work at typically 10 times normal rated current with reasonable accuracy so high saturation flux material and air gaps may be used.

Best approximation is to use magnetization data for a similar CT!

If you are talking about a real CT, you can do a secondary magnetization curve using a mains variac [+ step-down transfo, if needed] and voltmeter/ammeter.

@ 67model Thank you for replying.

I was referring to a protection CT only. Any other parameters at this point could be just assumed.

Basically I am just trying to be develop a logic/program to obtain magnetization curve of a CT from its parameters if at all its possible. I do not have actual CT presently.

You may find this helpful, hunt about in it.

http://sayedsaad.com/Protection/files/VT_CT/2_VT_CT.htm

@67model The link was very use full.

I am glad you found it useful.

For the "avoidance of doubt" in my mind, and wishing only to help, did you find the following...

http://sayedsaad.com/Protection/files/VT_CT/3_VT_CT.htm

which describes how to get the primary/secondary current curve from the secondary saturation test curve?

67model

@ 67model

Yes I did go through it and it was help full.

But in that, the secondary saturation test curve is given and we then find primary/secondary curve from it. But in my case, I need to find the secondary saturation test curve from given CT parameters but without doing any physical test.

Also refer to CR4 thread in Electrical Engineering...

Current Transformer Saturation 11/10/2011 7:05 AM

My suggestion would be to refer to the saturation graphs given on one of the websites you looked at. For a 5P10 protection CT the error at 10 times rated current would be 5%.

Assume the secondary saturation current at 10 times rated current is 10 x 0.05 = 0.5 x rated current (e.g. 2.5 amp for 5 amp secondary CT).

Compute the necessary saturation voltage from burden.

Use a specimen secondary saturation curve and match it to saturation voltage and 0.5 x rated excitation current.

You will note that the secondary saturation curve could be approximated by two intersecting straight lines on the graph. Note the scales are logarithmic. Make a suitable formula to approximate the curve. Compute the corresponding primary/secondary current graph.

I believe MATLAB has a curve approximating function - feed it with a table of values and it will find a near matching curve produced by a numeric series.

Do not forget that the less you know about the CT, the less reliable any "approximated" characteristic will be.