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Extract from http://www.ebooksread.com/authors-eng/national-school-of-electricity/electricity-and-magnetism--lessons-of-the-national-school-of-electricity--gene-hci/page-24-electricity-and-magnetism--lessons-of-the-national-school-of-electricity--gene-hci.shtml

Copyrighted, 1895, The National School of Electricity.

We will suppose, for an example, a large continuous current

station in which one or two engines with their dynamos have been

running all day to supply the demand for current in the daytime,

and, as evening approaches, additional engines and dynamos must

be put into service to provide for the greater demand for current dur-

ing the hours of dusk. A short time before additional machines

are likely to be needed one or more engines with their dynamos are

made ready for running, and are then started at a slow speed to warm

them up. After a time one of the sets is brought to full speed and

the dynamo attendant at the switchboard changes the resistance in

the field circuit by means of the dynamo regulator, which is placed

on the board, until the lamps mounted on top of the dynamo burn

with approximately normal candle-power. The dynamo is then

ready to be put into circuit whenever it is needed. When this time

comes, the dynamo attendant connects the free terminal of the

dynamo to the dynamo galvanometer (Fig. 322) and moves the dynamo

regulator until the galvanometer needle comes to zero. The pressure

developed by the fresh dynamo is then exactly equal to the bus bar

pressure. The dynamo attendant now closes the dynamo switch, thus putting

the machine into circuit, and then moves the regulator until the

amperemeter shows that the dynamo is taking its proper proportion

of the load. While this is being done, another generating set is

brought to speed and made ready to go into circuit whenever it is

required. The operation is repeated until all the dynamo capacity

that is required during the period of heavy load is in service. Some

cities are subject to sudden periods of darkness caused by clouds

or smoke, and at such times it often requires very prompt action on

the part of station attendants to get the dynamos into circuit as

quickly as they are needed.

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