ay he
wishes to transmit 26 amperes with a loss of 10 volts. What size wire
will be necessary?

2640 x 22 x 26
Thus: -------------- = 151,000 circular mills.
10

A No. 000 wire is nearest this size, and 5,280 feet of it would cost
over $650.00. This cost would be prohibitive. If, however, he
installed a 220-volt dynamo--at no increase in cost--then he would
have to transmit only a half of 26 amperes, or 13 amperes, and he
could allow 22 volts loss, counting 10 per cent. In this case, the
problem would work out as follows:

2640 x 22 x 13
-------------- = 34,320 circular mills,
22

or approximately a No. 5 wire which, at 19 cents a pound, would cost
$120.65.

Install a 550-volt generator, instead of a 220-volt machine and the
amperes necessary would be cut to 5.2, and the volts lost would be
raised to 55. In this case a No. 12 wire would carry the current; but
since it would not be strong enough for stringing on poles, a No. 8
wire would be used, costing about $63.

It will be readily seen from these examples how voltage influences the
efficiency of transmission. Current generated at a pressure in excess
of 550 volts is not to be recommended for farm plants unless an expert
is in charge. A safer rule is not to exceed 220 volts, for while 550
volts is not necessarily deadly, it is dangerous. When one goes into
higher voltages, it is necessary to change the type of dynamo to
_alternating current_, so that the current can be transformed to safe
voltages at the point where it is used. Since only the occasional farm
plant requires a high-tension system, the details of such a plant will
not be gone into here.

In transmitting the electric current over miles of territory,
engineers are accustomed to figure 1,000 volts for each mile. Since
this is a deadly pressure, it should not be handled by any one not an
expert, which, in this case, the farmer is not.

_Over-Compounding the Generator_

One can absorb the loss in transmission frequently, by
over-compounding the machine. In describing the compound machine, in
Chapter Five, it is shown that the usual compound dynamo on the market
is the so-called flat-compounded type. In such a dynamo, the voltage
remains constant at the switchboard, from no load to full load,
allowing for a slight curve which need not be taken into account.

Now, by adding a few more turns to the series wires on the field coils
of such a dynamo, a machine