Hydro-Electric Power Stations

This historic book may have numerous typos and missing text. Purchasers can usually download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1917 edition. Excerpt: ...superior, but where the two-phase load predominates, the T connection is preferable. Three-phase to Six-phase. In transforming from three-to sixphase, there are four different connections, which may be used, namely: Diametrical. Double-delta. Double-Y. Double-T. Diametrical. The diametrical connection, as represented in Fig. 261, is the most commonly used of any three-phase to sixphase transformations, and there is very little reason for using any other connection for the operation of six-phase converters. It requires only one low-voltage coil on each transformer which are connected to diametrically opposite points on the armature windings. It furthermore gives the simplest arrangement of switches, transformer taps and connections for starting six-phase converters from the alternating current side, while on the other hand it is possible to operate a six-phase converter at reduced capacity with one transformer out of service, leaving the other two connected across their respective diameters. With diametrically connected low-voltage windings, the highvoltage windings should preferably be connected in delta so as to avoid the triple frequency harmonics of the e.m.f., as described under Y-Y connection on page 403. With regulating pole converters, however, the high-voltage windings must be connected Y on account of the fact that the third harmonic voltage is made use of to obtain the direct-current voltage regulation and in such a case the windings must be insulated for double line voltage to ground and 3.46 times normal Y-voltage across windings, due to the presence of the third harmonic e.m.f's. The middle points of the diametrical windings can readily be connected together and brought out for three-wire Edison service, the unbalanced...