To evaluate a more complex construction sometimes it is necessary to take into account the physical construction. In the first place, a general equation of errors is developed, taking into account physical relations.

In order to maintain current I2 in the secondary circuit, we need an E (induced voltage) emf in the secondary winding, which is balancing the voltage drops: E = I2 (Z2 + Zc) (21) where Z2 is the internal impedance and Zc is the external impedance.

To maintain the flow, we need an excitation, which will be the difference of the primary excitation, θ1, and secondary, θ2. In some situations, it is more practical to do the calculations by the CT equivalent circuit.

Because of the shape of the power supply the impedance of the primary winding is not influencing the distribution of the currents, and therefore is not represented. Z2 is the internal impedance, defined by the secondary winding. boston

The next step proves that with these expressions based on the equivalent circuit, one can arrive at the same results based on the physical construction. The vacuum current I0 is expressed by the CT construction parameters. To maintain the flow, the vacuum current is needed, I0.