Deadweight current.

Recently people have spoken about deadweight current for high burden transformers having a current below 1/4 of nominal value.

For example, a transformer with 50 VA nominal value, is controlled, as regards ratio and phase errors, between 12,5 VA and 50 VA.

If current to which it is connected is lower than 12,5 VA it can show some errors (with positive sign) higher than allowed by prescriptions.

This can happen because modern electronic instruments have very low currents in respect of the past.
Obviously, it could be possible to solve the problem by increasing the length of the connecting cable or either by reducing the section or else by adding a resistance to achieve the required value.

However a doubt is left, why cosfi from a purely ohmmic resistance is 1, while prescriptions (for currents equal to or over 5 VA) mention 0,8 cosfi.

How can we resolve the question?

AE2 have solved the problem producing currents to be added in series, with 0,8 cosfi so that the transformer remains within its error range.