[Electric engineering.] . in the voltageresults in a large decrease in the amount of copper lighting was first carried out at a pressure of110 volts, but this pressure rendered the use of large con-ductors necessary, and systems w,ere, therefore, broughtout that would permit the use of a higher pressure. Instreet-railway work, a pressure of about 500 volts soonbecame the standard, because this appeared to be the limitto which the voltage could be pushed for this class of workwithout danger to life. The Edison three-wire system allows current to be sup-plied at 110 volts,
[Electric engineering.] . in the voltageresults in a large decrease in the amount of copper lighting was first carried out at a pressure of110 volts, but this pressure rendered the use of large con-ductors necessary, and systems w,ere, therefore, broughtout that would permit the use of a higher pressure. Instreet-railway work, a pressure of about 500 volts soonbecame the standard, because this appeared to be the limitto which the voltage could be pushed for this class of workwithout danger to life. The Edison three-wire system allows current to be sup-plied at 110 volts, although the transmission itself is reallycarried out at 220 volts, and, therefore., results in a large 42 ELECTRIC TRANSMISSION. 14 saving in copper over the old 110-volt system. The three-wire system is shown in Fig. 13. Two compound-wounddynamos A and B are connected in series across the twolines de and h k. Each dynamo generates 110 volts, so thatthe pressure between the two outside wires is 220 volts, F/ because the two machines are connected in series, and theirpressures will be added. A third wire, called the neutralzaire, is connected to the point f between the machines, sothat between the lines de and fg we have a pressure of110 volts, and between fg and // k a pressure of 110 voltsalso. 53. In order to illustrate the action of such a system,we will suppose that we have six 32-candlepower lamps on § 14 ELECTRIC TRANSMISSION. 43 one side and four on the other, each lamp taking, say,1 ampere. A current of 4 amperes will flow from the posi-tive side of B through the line h k and through the lamps tothe neutral wire. At the same time, a current of 6 ampereswill tend to flow out from the positive pole of A over the\\\\& fg through the left-hand set of lamps and back throughe d, as shown by the arrows. In the neutral wire we have acurrent of 6 amperes tending to flow in one direction and acurrent of 4 amperes tending to flow in the other direc-tion, the result
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