CT Parameter Calculations

[ohms]

Can anybody tell me, how to calculate the magnetising current for Class 'PS' or 'X' CTs. Required formulae are available for calculating the knee point voltage in the Relay catalogue. But none of the catalogue describes about the magnetising current requirement.

I feel the magnetising current plays major role in primary protections like Distance and differential. And this current will fix the operating parameter setting in those protections.

If the magnetising current of a CT is fixed by the CT manufacturer, what are all the factors they are considering?

 

[Marvie]

Ohms, I believe that once you have the value for the knee point voltage and you know your burden then from your ohm's law you should get your required minimum current before saturation.

 

[jghrist]

The magnetizing, or excitation, current is given by the CT excitation curve which plots secondary terminal voltage against excitation current and is available from the manufacturer.