Thread Starter


Joined Jan 6, 2009
Hi Guys, :)

I am grappling with a peculier (but somewhat common) problem with Current Transformer (CT) magnetic circuit. I will be very grateful if someone could help me out with my problem/s.
I will ennumerate my query in points for clarity as given below;

1) In an ideal Voltage Transformer (VT), the magnetic flux developed in the core is constant at all loads. But the magnetic flux in the core of a CT reduces as soon as a 'Burden' (load) is connected to the secondary winding of a CT! Hence, why is the magnetic flux in a CT not constant (with connected load, also) as is the case with a VT ? Why does this reduction in magnetic flux occur in case of a CT, since a CT basically resembles an ideal VT as far as the core magnetic circuit is concerned ?

2) I am looking for a phasor diagram for an UNLOADED CT (open circuited secondary) but i am unable to find one yet. I will be extremely grateful if someone could provide me with one or guide me to a suitable link.

3) The NO-LOAD primary current (excitation current) 'Io' in an ideal transformer (VT or CT) is the vector sum of Magnetizing current 'Im' and no-load Losses current ( iron + Cu) 'Iw'. But the no-load or on-load magnetic flux 'ψ' developed (visible) in an ideal transformer core is in phase with the Magnetizing current 'Im' only (which itself is in quadrature with the applied primary voltage 'Vp').
Hence my query is; What happens to the magnetic flux component of 'Iw' which is in phase with 'Vp' ? Why is it not 'visible' in the transformer magnetic core ? Where does it disappear ? Please explain.

For any additional information/discussions, please email me at

Thanks & Regards,