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Last Post 11/14/2011 9:27 AM by  dave forsythe
Phase angle error
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arun T
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11/14/2011 2:00 AM
    Hello Sir,
    I am Arun studying Bachelor of Engineering in India. For my project i have to calculate phase angle error for a CT.
    How to calculate phase angle error in theoretically for resistive burden (Non inductive).
    Example : 1:500 Turns ratio, 10A/0.02A, Burden = 50 ohms, DCR = 27 ohms. For this example how to calculate phase angle error for this CT. Pls help with formula...Advance thanks for ur help.
    dave forsythe
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    11/14/2011 9:27 AM
    To determine the phase angle error of a CT requires knowledge of multiple formulas and understanding of magnetic design. I am assuming this is the challenge your class has given you, and so I can only direct you to resources you can use to determine this the correct way.

    I suggest starting with http://www.crmagnetics.com/Portals/..._error.pdf and understand the thevinen equivalent model of a CT.

    The losses that are associated with the sources of error is a combination of the self inductance of the coil and the eddy current and heating losses of the magnetic material. You will need the size of the core and the type of material to determine these losses. You would then use the magnetism laws of Faraday, Gauss, and Maxwell to get the inductance and excitation losses in the material, and then apply these to the circuit above to get the exact phase relationship of the output.

    Fortunately, manufacturers of cores such as Magnetics, Inc. and Magnetic Materials, Inc. have available to the designer the multiple formulas that can be used to determine the above values, and calculate the phase error. Magnetics, Inc. has an excellent app note on CTs specifically.

    You will need to pick a core size, a material, and then you can use the canned formulas from the core manufacturers to come up with the corredct answer.

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