Electrical news and engineering . wire three phase, 2,400 V. (delta) 75% 3 wire three phase, 2400 V. (star) 25%1 wire three phase, 2400 V. (star) ! (neutral wire one-half outer) 4 wire three phase, 2400 V. (star) (neutral wire same as outer)This clearly shows advantages in the choice of one ofthe 2400 volt Star connected systems. Again let us decide as to nature of secondary service tobe supplied. It is. desirable to supply mixed lighting andpower loads from the same primary lines to avoid duplica-tion of feeder equipment and lines, more so if the powerloads are moderate and do no
Electrical news and engineering . wire three phase, 2,400 V. (delta) 75% 3 wire three phase, 2400 V. (star) 25%1 wire three phase, 2400 V. (star) ! (neutral wire one-half outer) 4 wire three phase, 2400 V. (star) (neutral wire same as outer)This clearly shows advantages in the choice of one ofthe 2400 volt Star connected systems. Again let us decide as to nature of secondary service tobe supplied. It is. desirable to supply mixed lighting andpower loads from the same primary lines to avoid duplica-tion of feeder equipment and lines, more so if the powerloads are moderate and do not overlap the lighting loads toany great extent. This condition allows the feeder regulat-ing equipment to care exclusively for lighting loads whenoperating at maximum load, without interference from pow-er load surges so detrimental to good regulation. Whereconsiderable power load only has to be taken care of un-regulated three phase feeders should be run as motor loadsdo not require closely regulated service. A choice of feeder. Feeder and main curves supplying exclusive power or mixed loads will, therefore,eliminate the choice of the single phase feeder leaving usthe three phase systems. Where three phase power load- arc to be supplied it isoften desirable to connect two transformers in open deltaon secondary side, thus making it possible at any time toclose the delta with a third transformer should a largeipower demand occur. The reverse, of course, is desirablealso and it should be possible to continue service if onetransformer (wdiere three are used) become- defective. Thiscondition can be handled by the three wire three phase 34 THE ELECTRICAL NEWS July 1, 1919 delta system and by the four wire three phase star sjThis cannot, however, be supplied from the three wire starconnected system. Referring to the matter of regulating equipment requiredFor lighting loads the three phase 4 wire system has decidedadvantages. With a single phase regulator on each phasewire this can b
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