Electric motors Essay Example | Topics and Well Written Essays - 1250 words

Electric push backs - Essay Example(i) DC tug This move uses a DC current. An armature is placed between magnetic celestial poles, cognize as field poles. Field poles remain stationary and provide the static magnetic field which runs from North Pole to South Pole. The armature is mounted on air and there is winding of conduction wire on it. When a DC current is made to pass by the windings on the armature, it becomes an electromagnet and the interaction between the pole magnet and the armature electromagnet forces the armature to turn until North and South poles of the two magnets align. Once this happens direction of the current in the armature windings is reversed to switch the North and South poles using a Commutator and thus the armature keeps on rotating 2. (ii) AC Motor It consists of a stator and a Rotor as shown in Fig. 1 3. As implies by the name Stator is the stationary component. It consists of number of magnetic poles arranged in a cylindrical symmetry around the r otating component or the Rotor. As an AC current passes through the Rotor, it experiences a torque which rotates it and this rotation is coupled to external load through a suitable drive mechanism. Fig. 1 Schematic Diagram Showing split of an AC Motor 3 (iii) servomechanism Motor It is primarily a DC motor, but is much more refined one. It consists of a sensor to sense spotlight of the shaft and used this as feedback to control hurry of the DC motor 4. Q1. (b) (i) Applications of Motors DC motor It is much easier to control amphetamine in case of DC motors and therefore, these motors are preferred for applications where speed control is very important. Computer disc drive is one very important application of DC motor. AC motor It is inexpensive however, the speed control is not good. One typical application of an AC motor is to drive fans where speed control is not so critical. Servo Motor It is feedback controlled system and hence it is used for applications which need precise position and speed control. One such application is drive for CNC stage, where control of position and speed is very critical. Q1. (b) (ii) Speed mesh DC Motor In a DC motor the back electromagnetic force and torque is given by the following equations. Back electromagnetic force E = K?N Torque T = K?Ia Where E = electromagnetic force developed at armature terminal (volt) ? = field flux which is directly proportional to field current N = speed in RPM (revolutions per minute) T = electromagnetic torque Ia = armature current K = an equation constan Therefore, speed of DC motors commode be controlled by controlling either armature voltage or field current. AC Motor Control of speed is difficult for AC motors. Speed of a synchronous AC motor is given by the following equation 5. Ns = 120 f / P Where f = frequency of the supply frequency P= number of poles It can however, be controlled by using variable frequency drive, because speed of an AC motor can be controlled by controlling freq uency of AC supply only. Servo Motor It is a DC motor only so speed can be controlled in the same manner as in case of a DC motor. It uses a feedback system to control its speed. Q1. (b) (iii) Two Limitations DC Motor Power is limited due to difficulty in commutation at high size. This limits application of DC motors for high power applications. Besides, there can be sparks from the commutator especially at higher powers. Therefore, a DC motor cannot be used in hazardous and fire prone areas. AC Motor Speed control is more difficult. Cannot be