Analysis and measurement of radial power flow in machine air gaps

The theory of radial power flow in a machine air gap is developed, with emphasis on the powers associated with individual harmonic effects and on the practical possibility of measuring these powers. The analysis is made in terms of travelling-wave modes in the air-gap annulus and leads to an alternative Poynting vector which is convenient for measurement. Some important analytical results relate to the simple measurement of axially nonuniform fields. The general construction of a measuring probe is described, and some experimental results on the measurement of synchronous power illustrate its effectiveness. The air gap offers a potential advantage for the direct measurement of individual harmonic loss, compared with either the stator or rotor region. More generally, the rigorous analysis in terms of wave modes and the discussion of their associated power flows forms an instructive and stimulating view of machine operation.