The generators need the direct current for the purpose of energizing the magnetic field it has got. The DC field current that it has is acquired from a completely separate source which is known as an exciter. Either of the both, static-type or rotating exciters are mostly used in the AC power generation process. There are commonly two different types of these rotating exciters and they are the brush exciter and the brushless exciter. The basic difference between the brush exciter and the brushless exciter is that the process that is used for transferring of the DC current to generators. The Static excitation due to these generator fields are offered in various forms including the field-flash voltage that is from the storage voltage and batteries from a large system of the solid-state components that are there. The DC generators which are available are either self-excited or separately excited. The excitation process in the use of the current includes the directly connected or may be gear- connected shaft driven DC generators.
The special thing about the Wound Rotor Motors has got three phase induction motor which has got high starting torque and it makes that ideal for the applications in which the standard NEMA design motors lag behind. The wound rotor motor is specifically effective and efficient for the purpose of application in which the use of a squirrel cage motor might be resulting in an initial current that is too high in comparison to the potential of the power system. The Wound rotor motor is good for the high inertia loads for a long accelerating time. This is the reason why you are able to control the torque, speed and also the resulting heating of the motor. This particular control over the motor could be manual or automatic. It is also quite effective and efficient with the high slip loads along with the adjustable speed that can be installed and not needing any precise speed regulation or control. The construction and the configuration of the wound rotor motor is quite different from the above mentioned squirrel caged motors, particularly in the design of the rotor. They also put the slip rings and the brushes. The stationary brushes are made to ride on each and every slip ring that is forming an external circuit and in that you can insert any desired amount of resistance. These work very good that way.