10 ALTERNATING GENERATORS AND SYNCHRONOUS MOTORS. 
is also in accordance with a certain specification, any de- 
parture from the above mentioned conditions in one or 
the other way has the following effects: 
21. Increase of Efficiency.—A higher efficiency than that 
stated in Tables 1 and 2 offers to the station engineer 
a generator which is more economical in working, but 
it necessitates the manufacturer producing a more expen- 
sive machine. Taking into consideration a perfect design, 
an inexpensive inerease in efficiency can only be obtained 
by the choice of good material for the iron core and 
copper winding. For the different items of efficiency eal- 
culation see Par. 78. 
22. Decreased Voltage Drop.—aA smaller voltage drop than 
that given in Par. 14 seems a desirable feature to the 
station engineer, as it insures better regulation on the 
light and power circuit and reduces the attendant’s work, 
but on the other hand a lower voltage drop may cause 
trouble when alternators are running in parallel, or when 
a short cireuit accidentally oeceurs. The manufacturer, 
in order to produce any decrease of the voltage drop, has 
to increase the weight of material in the machine, which 
of course increases the cost of the generator. 
23. Increase of Slots.—Tie experience of the station engineer 
has generally proved, that it is most advantageous to 
have a generator with an EK. M.F. of a nearly sinusoidal 
wave form. It helps the parallel running of alternators, 
the switching of same on the cireuit and improves the 
running of motors from a ecireuit so supplied. The more 
armature slots a generator has, the nearer will be the 
wave form of the E. M. F. to the sine curve, but this ad- 
vantage can be obtained only at an increase in manu- 
facturing cost. 
A generator with many slots will be larger than one with 
