Abstract :
The two theories dealing with the operation of induction meters are reviewed. Their final expressions for the torque acting on the rotor, in terms of the power, voltage, load current and speeds of revolution, are found to be the same. However, despite this coincidence, the two theories are both considered to be admissible. The existing proofs of the erroneousness of the travelling-field theory tend to lead indirectly to the conclusion that only the transformer or eddy-current theory is valid. Furthermore, the measured distributions of the magnetic flux density along the air gaps of the electromagnets in the meter are analysed for agreement with the travelling-field theory. The conclusion reached is that, although the travelling-field theory fails to give a full description of the phenomena which determine the operation of the meter, it still deserves to be retained beside the transformer, or eddy-current, theory.
