Fig. 135
In our transformer the number of turns in the coil between the binding posts a and b is 400 and the number of turns between c and d is 1200. If now we connect a 112-volt alternating current with the binding posts a and b, a volt meter connected across between c and d will show 336 volts, and if b and c be connected by a short wire, bringing in 1600 turns into the secondary circuit, a volt meter connected across between a and d will show a voltage of 448. Or if, leaving b and c still connected by a short wire, we connect the 112-volt alternating current to a and d a volt meter connected across between a and b will show 28 volts, or if connected between c and d it will show 84 volts, and if finally the 112-volt current is connected to c and d the pressure between a and b will be 37⅓.
Fig. 136
The story, then, of the central station which we have chosen as a type is briefly this: Falling water makes dynamos revolve, generating a 4000-volt alternating current. This current is sent through the primary windings of transformers. The secondary windings of these transformers have twenty-five times as many turns as the primary coils. This steps up the voltage from 4000 to 100,000, making it necessary to send only one twenty-fifth as many amperes over the lines as would be required at 4000 volts, and reduces the loss in transmission to nearly one twenty-fifth. At the other end of the line the current traverses the secondary windings of transformers, and the consumer receives his current from primary coils which may step the e. m. f. down to any required volts of pressure, generally 110.
Now I shall be glad to have you consider whether this suggests any practicable problems for us here in Millville.
The sun is nearly setting and I suppose the family is expecting me home.
