Permanent DC Motor working in tamil скачать в хорошем качестве

Permanent DC Motor working in tamil

Permanent Magnet DC Motor Working principle of operation. Permanent Magnet D.C. Motor A permanent-magnet d.c. (PMDC) motor is similar to an ordinary d.c. shunt motor except that its field is provided by permanent magnets instead of salient-pole wound-field structure. shows 2-pole. Construction: The permanent magnets of the PMDC motor are supported by a cylindrical steel stator which also serves as a return path for the magnetic flux. The rotor (i.e. armature) has winding slots, commutator segments and brushes as in conventional d.c. machines. There are three types of permanent magnets used for such motors. The materials used have residual flux density and high coercivity. (i) Alnico magnets – They are used in motors having ratings in the range of 1kW to 150 kW. (ii) Ceramic (ferrite) magnets – They are much economical in fractional kilowatt motors. (iii) Rare-earth magnets – Made of samarium cobalt and neodymium iron cobalt which have the highest energy product. Such magnetic materials are costly but are best economic choice for small as well as large motors. Another form of the stator construction is the one in which permanent-magnet material is cast in the form of a continuous ring instead of in two pieces. Working: Most of these motors usually run on 6V, 12 V or 24 V dc supply obtained either from batteries or rectified alternating current. In such motors, torque is produced by interaction between the axial currentcarrying rotor conductors and the magnetic flux produced by the permanent magnets. Advantages: (i) In very small ratings, use of permanent-magnet excitation results in lower manufacturing cost. (ii) In many cases a PMDC motor is smaller in size than a wound-field d.c. motor of equal power rating. iii) Since field excitation current is not required, the efficiency of these motors is generally higher than that of the wound-field motors. (iv) Low-voltage PMDC motors produce less air noise. (v) When designed for low-voltage (12 V or less) these motors produced very little radio and TV interference. Disadvantages (i) Since their magnetic field is active at all times even when motor is not being used, these motors are made totally enclosed to prevent their magnets from collecting magnetic junk from neighbourhood. Hence, as compared to wound-field motors, their temperature tends to be higher. However, it may not be much of a disadvantage in situations where motor is used for short intervals. (ii) A more serious disadvantage is that the permanent magnets can be demagnetized by armature reaction mmf causing the motor to become inoperative. Demagnetization can result from (a) improper design (b) excessive armature current caused by a fault or transient or improper connection in the armature circuit (c) improper brush shift and (d) temperature effects. Applications (i) Small, 12-V PMDC motors are used for driving automobile heater and air conditioner blowers, windshield wipers, windows, fans and radio antennas etc. They are also used for electric fuel pumps, marine engine starters, wheelchairs and cordless power tools. (ii) Toy industry uses millions of such motors which are also used in other appliances such as the toothbrush, food mixer, ice crusher, portable vacuum cleaner and shoe polisher and also in portable electric tools such as drills, saber saws and hedge trimmers etc. Thank You for watching