Some aspects of the theory of iron-testing by wattmeter and bridge methods

The paper, which is an attempt to survey the present position, opens with a discussion of the limitations of the dynamometer wattmeter. Compensation for voltage circuit phase angle and for eddy current and voltage circuit losses is discussed. The effect of the iron circuit is noted, the influence of leakage flux being pointed out. The effects of distortion are noted, and attention is drawn to some hitherto unformulated rules relating the distortion in the current and voltage waves. Null methods of using the wattmeter are briefly described, and a new circuit is proposed. The concept of complex permeability is introduced as an approach to bridge measurements, and an equivalent circuit for a test transformer is deduced. It is shown how this may be used in a novel circuit in such a way as to eliminate copper losses. The limitations of the bridge method are briefly discussed, and the relation between bridge and wattmeter methods is shown to lead to the concept of ¿distortion coefficient,¿ a new characteristic property of the iron, which can be determined experimentally and which may provide a succinct approach to distortion problems.