. Electrical world. rcumference were used to judgecommutating ability. Railway work, with its suddenly varying loadsand calling for fixed position of commutation introduced the carbonbrush. High resistance commutator leads were tried and a greatnumber of special armature windings, such as the Sayers, and com-mutating lugs and pole face windings, as in the Thompson-Ryanmachine. A careful theoretical study of the very complicated phe-nomena of commutation was made by several men, among whommust be mentioned Prof. E. Arnold, and the various factors whichaffect this action were expressed matheinat
. Electrical world. rcumference were used to judgecommutating ability. Railway work, with its suddenly varying loadsand calling for fixed position of commutation introduced the carbonbrush. High resistance commutator leads were tried and a greatnumber of special armature windings, such as the Sayers, and com-mutating lugs and pole face windings, as in the Thompson-Ryanmachine. A careful theoretical study of the very complicated phe-nomena of commutation was made by several men, among whommust be mentioned Prof. E. Arnold, and the various factors whichaffect this action were expressed matheinatically. The inductance ofthe armature coil while passing through the period of discovered to be of vital importance and many experimentalresults and rules deduced therefrom have been published. The com-putation of what is termed the reactance voltage of the armaturecoil is now one of the important determinations in the present designof direct-current macliinery. Bj- making a few allowable assumptions. I.—F-\K-\U-\V S FIRST .\CHINE. and where we have but one turn per coil, the reactance voltage isconveniently expressed by the formula: £l = X I0-* X .Vb X S X Ic X le El = reactance voltage, .Vb = no of bars in commutator. !c = am-peres per conductor, Ic ^= length over armature iron in inches, and5 the revolutions per minute. A large number of generators andconverters have been designed using this rule, and it has been foundvery satisfactory. It must be remembered, however, that it considersbut one of the factors, and the limiting value will vary with suchquantities as percentage of pole arc, distortion of field from armaturereaction, kind of armature winding, number of conductors per of segments covered by brush, form of slot, ratio of lengthof idle to active conductor, kind of brush and resistance of armaturecoil, commutator leads, brush contact, etc. The subject of commutation is now one of great theoretical andpractical interest, espe
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Keywords: ., bookcentury1800, bookdecade1880, booksubjectelectri, bookyear1883
