CONTENTS

xxi

PACK
improving commutation—Demagnetizing armature reaction
and need of compounding by series field..........429
B. Variable ratio by change of the wave shape of the Y voltage. 429
234. Increase and decrease of d.-c. voltage by increase or decrease
of maximum a.-c. voltage by higher harmonic—Illustration
by third and fifth harmonic...............480
235. Use of the third harmonic in the three-phase system—Trans-
former connection required to limit it to the local converter
circuit—Calculation of converter wave as function of the pole
arc........................• . . 432
236. Calculation of converter wave resulting from reversal of
middle of pole arc...................435
237. Discussion......................436
238. Armature reaction and commutation—Proportionality of
resultant armature reaction to deviation of voltage ratio from
normal........................437
239. Commutating flux of armature reaction of high a.-c. voltage—
Combination of both converter types, the wave shape distor-
tion for raising, the flux shift for lowering the a.-c. voltage—
Use of two pole section, the main pole and the regulating pole . 437
240. Heating and rating—Relation of currents and voltages in
standard converter...................439
241. Calculation of the voltages and currents in the regulating pole
converter.......................440
242. Calculating of differential current, and of relative heating of
armature coil..................... 442
243. Average armature heating of n phase converter.......444
244. Armature heating and rating of three-phase and of six-phase
regulating pole converter................445
245. Calculation of phase angle giving minimum heating or maxi-
mum rating......................446
246. Discussion of conditions giving minimum heating—Design—
Numerical instance...................448
CHAPTER XXII. UNIPOLAR MACHINES.
Homopolar Machines—Acyclic Machines
247. Principle of unipolar, homopolar or acyclic machine—The
problem of high speed current collection—Fallacy of unipolar
induction in stationary conductor—Immaterial whether mag-
net standstill or revolves—The conception of lines of magnetic
force.........................450
248. Impossibility of the coil wound unipolar machine—All electro-
magnetic induction in turn must be alternating—Illustration
of unipolar induction by motion on circular track.....452
249. Discussion of unipolar machine design—Drum type and disc
type—Auxiliary air-gap—Double structure—Series connec-
tion of conductors with separate pairs of collector rings . . . 454