A theory of commutation and its application to interpole machines

In the usual theory of commutation it is considered that, when the current in a coil is commutated or reversed, the local magnetic flux due to the current reverses also, and in so doing sets up an e.m.f. in the coil which opposes the reversal. This is the so-called reactance voltage referred to in commutation problems. The fact that two or more coils may be undergoing commutation at the same time involves consideration of mutual as well as self-induction. The relation of the mutual to the self-induction, the probable value of each, etc., lead to such mathematical complication in the analysis of the problem, that empirical methods have become the usual practice in dealing with commutation. The usual analytical methods do not permit a ready or easy physical conception of what actually takes place. One must think in formulas rather than in the phenomena of the commutation itself.