Motors & Energy Saving (2)

3. Key Components

3.1 DC Motor
• Field pole – The purpose of this component is to create a steady magnetic field in the motor. or the case of a small DC motor, a permanent magnet, field magnet, composes the field structure. However, for larger or more complex motors, one or more electromagnets, which receive electricity from an outside power source, is/are the field structure.

• Armature – When current goes through the armature, it becomes an electromagnet. The armature, cylindrical in shape, is linked to a drive shaft in order to drive the load. For the case of a small DC motor, the armature rotates in the magnetic field established by the poles, until the north and south poles of the magnets change location with respect to the armature. Once this happens, the current is reversed to switch the south and north poles of the armature.
• Commutator – This component is found mainly in DC motors. Its purpose is to overturn the direction of the electric current in the armature. The commutator also aids in the transmission of current between the armature and the power source.

3.2 AC Motor
• Rotor
– Induction motor – Two types of rotors are used in induction motors: squirrelcage rotor and wound rotor. A squirrel-cage rotor consists of thick conducting bars embedded in parallel slots. These bars are short-circuited at both ends by means of short-circuiting rings. A wound rotor has three-phase, double-layer, distributed winding. It is wound for as many poles as the stator. The three phases are wyed internally and the other ends are connected to slip-rings mounted on a shaft with brushes resting on them.
– Synchronous motor – The main difference between the synchronous motor and the induction motor is that the rotor of the synchronous motor travels at the same speed as the rotating magnetic field. This is possible because the magnetic field of the rotor is no longer induced. The rotor either has permanent magnets or DC-excited currents, which are forced to lock into a certain position when confronted with another magnetic field.
• Stator
– Induction motor – The stator is made up of a number of stampings with slots to carry threephase windings. It is wound for a definite number of poles. The windings are geometrically spaced 120 degrees apart.
– Synchronous motor – The stator produces a rotating magnetic field that is proportional to the frequency supplied.

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