Correction factors of deflectional wattmeters

Abstract

The paper deals with the ordinary ironless wattmeter and the correction factors (due to the effect of mutual inductance between the current and voltage coil and the effect of the nature of the load) that should be applied to its indication. As the mutual inductance between the current and voltage coils changes its sign from negative to positive as it passes through zero, the correction factors differ in the first part of the scale from those in the second part. An attempt is also made to show that the device which consists of a coil in series with the voltage coil, and wound closely with but in opposition to the current coil and intended to compensate for the power loss in the voltage coil circuit, is of very limited value on alternating current. Correction factors which take into account all the relevant effects are calculated in the paper.