tors, armature windings are placed in slots of iron core.)
Let us change subjects on technical terms used in
electrical machinery, that is, iron machines and copper
ones. Output power of electrical machine is determined
by magnetic flux in air-gap and current through armature
winding as shown above. Which is major, flux or
current? If flux is major, the machine is called iron
machine. If current is major, that is called copper machine.
The characteristics of iron machine are smaller
voltage regulation due to lower synchronous impedance,
higher efficiency but larger volume, which leads to be
more expensive. Those of copper machine are smaller
volume but larger voltage regulation. In the history of
developing larger conventional generators, copper machines,
which are of smaller size, have been adopted
because larger machines are restricted by mechanical
problems. By applying copper machines in power systems,
which are becoming larger and more complex,
subjects on power system stability had been actualized.
To solve the above problems, many kinds of control
methods and control equipments have been developed
and be developing, for examples, automatic voltage
regulator (AVR which controls terminal voltage of
generator), power system stabilizer (PSS), reactive
power compensator and its control, and so on. The
controls are not so easy due to non-linearity of power
systems, then they are under developing