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THE THEORY OF AUTOMATIC EEGULATOES. 
By H. Bohle. 
General Eemarks. — The regulation of electrical generators is usually 
expressed by the percentage voltage rise from full load to no load, or by the 
percentage drop of pressure from no load to full load, assuming that in the 
case of a separately excited machine the excitation and speed, in self-excited 
machines, the speed and resistance of the field circuit, are constant. 
In practice it is mostly asked to keep the pressure of a generator con- 
stant at the terminals for all loads, or to keep the pressure constant at the 
feeding points. In the latter case the pressure of the generator must rise 
with an increase in the load, to account for the drop in the feeders. 
Various methods have been devised for obtaining these results. One of 
the first arrangements consisted of compound windings, which are simple 
enough for direct current machines, but which require complicated trans- 
formers or special windings in the case of alternators. In both cases the 
machines are no longer of standard design, and therefore expensive. More- 
over, the compound windings are sluggish in their action on account of 
magnetic lag. 
To reduce the voltage drop of a generator as much as possible, the 
machine itself used to be built with good inherent regulation, /. e. the 
machine was worked beyond the knee of the magnetisation curve and given 
a low resistance. This again adds to the expense of the generator and 
possesses the disadvantage that during a sudden short-circuit currents 
twenty to thirty times larger than full-load currents might temporarily 
flow, pulling the windings to pieces unless they are very carefully stayed, 
and causing abnormal heating. This is especially dangerous with large 
machines, which to-day are built in sizes up to 30,000 kilowatts. 
Most of these disadvantages are overcome with automatic regulators, 
especially with those of the fast type. 
It is not intended here to describe automatic regulators, but simply to 
explain their theory. 
Automatic Eegulatoes. — They may be divided into sluggish and fast 
regulators. The former can be used only where the load varies very gradu- 
ally, so that the regulator has time to move into the correct position before 
a further load variation occurs. 
