subject: Special Purpose Motors Fitting into Individuals Need [print this page] Special Purpose Motors Fitting into Individuals Need
If seen into the times of invention Dc motor was accidently invented by Zenobe Gramme when he connected spinning dynamo to a second similar unit and he had a driving motor. The process is the conversion of electrical energy into kinetic energy. The reverse motion is adopted generally in generator or dynamo.
There are many universal motors available to fit into individual needs. One can use either AC or DC supply current as when he needs. The basic rules say that wound field DC motor current will alternate in both field and the armature. Thus the mechanical force generated is always in the same direction. Generally special purpose motors are designed to cope with the AC current keeping the resultant motor less efficient being equivalent to DC motor. Some special purpose motors form the basis of traditional railway traction motor. While operating for this the motors are operated from a very low frequency to keep electrical efficiency high. These are very much capable of operating from a third rail permanent magnet dc motor.
The advantages of using special purpose motors include supplies to be used on motors which have the typical standards of DC motors like high stating torque and a very compact design. The darker side is such motors are usually used in AC devices like food mixers and power tools. To control any speed AC motor is easy to use with thyristor circuit and also stepped speed control can be accomplished with multiple taps on the field coil.
The special purpose motors can easily exceed one revolution per cycle of the mains current so are used where high speed operations are required. But today scenario is changing with changing times, with very low cost of semi conductor rectifiers previously used universal motor now use only a pure permanent magnet DC motor. It works even when semi conductor circuit is also used for a variable speed control.
The use of special purpose motors is accepted due to the fact that installation of the low frequency traction current distribution system is very much economical even for railway installations. During the times of low frequencies the performance is almost same as permanent magnet DC motor.
