DC MOTOR WORKING PRINCIPLE PDF
A machine that converts dc power into mechanical energy is known as dc motor. Its operation is based on the principle that when a. The Working Principle of DC Motor, is based on the principle that in a magnetic field, when a current carrying conductor is placed, a mechanical. Principles and Working of DC and AC A magnetic field is produced when a direct current is applied to . This is the principle on which the dc motor works.
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working principle of dc motor - Free download as Powerpoint Presentation .ppt), PDF File .pdf), Text File .txt) or view presentation slides online. speed/torque characteristics of d.c. motors are much more superior to that of a.c. motor. Its operation is based on the principle that when a current carrying. Principle of operation By its very nature, the D.C. motor is a motor with a reversible This motor follows linear laws of operation and because of this it is.
Now in the above expression for speed, voltage V is constant and the armature drop Ia Ra is negligible compared to supply voltage V.
Therefore, the speed of the motor is inversely proportional to the flux per pole i. Therefore percentage speed regulation. The motor capable of maintaining a nearly constant speed for varying loads is said to have a good speed regulation. TORQUE The measure of causing rotation of the wheel or the turning or twisting moment of a force about an axis is called the torque.
Torque continues….. Consider a wheel of radius r meters acted by circumferential force F newtons, as shown in the fig. Ia watt …. Comparing expressions 1 and 2 , we get. A since Z, P and A are constant for a particular machine. Armature torque continues…….
The important characteristics of dc motors are:.
Torque — Armature Current Characteristic. This characteristic curve gives relation between torque developed in armature, T and armature current, Ia. This is also known as electrical characteristic. Speed - Armature Current Characteristic. This characteristic curve gives relation between speed, N and armature current, Ia. This is also known as speed characteristic.
Speed - Torque Characteristic. This characteristic curve gives relation between speed, N and torque, T. This is also known as mechanical characteristic The important relations to be kept in mind while discussing motor characteristics are: Magnetic characteristic.
Working Principle of a DC Motor
The flux first saturation FLUX increases following in linear. FLUX IN Wb point law with the increase in load current, becomes maximum at saturation point and finally becomes constant.
If the applied voltage remains constant, speed is inversely proportional to flux. So if a curve is drawn between reciprocal of the flux and current I, the speed — current characteristic is obtained, which is a rectangular hyperbola in shape as shown in fig.
Since on no load the speed is dangerously high, As obvious from speed current characteristic curve, which will result in heavy centrifugal Force which in turn will ] damage the motor. That is why, series.
Torque — Current Characteristic of dc series motor: After saturation point flux is almost independent of excitation current and so torque is directly proportional to the armature current i. Hence the characteristic becomes a straight line. Speed — Torque Characteristic of dc series Motor: Fig below shows the speed — torque characteristic of a dc series motor.
It is obvious from the fig below that as the torque increases speed decreases. Hence series motors are best suited for the services where the. Speed — Current characteristic of dc Shunt motor: If the voltage V is kept constant the field current will remain constant hence flux will have maximum value on no-load but will decrease slightly due to armature reaction as the load increases.
Since flux is considered to be constant as mentioned above, so with the increase in load current the speed slightly falls due to increase in voltage drop in armature. Torque — Current Characteristic of a dc Shunt Motor: Since in case of shunt motor the flux is considered to be constant,.
Speed - Torque Characteristic of a dc Shunt Motor: This characteristic curve can be drawn from the two other curves i. The characteristics of a the cumulative compound wound motor are the combination of shunt and series characteristics. As the load is increased, flux due to series field winding increases, and cause the torque greater than it would have with shunt field winding alone for a given machine and for a given current. The increase in flux due to series field winding on account of increase in load causes the speed to fall more rapidly than it would have done in shunt motor.
Characteristic of a dc Differential Compound Wound Motor: In differential compound wound motors, the series field winding is connected in such away that the series field opposes the shunt field while in cumulative compound wound motor series field helps the shunt field. Since the flux decreases with the increase in load so the speed remains nearly the constant as the load is increased and in some cases the speed will increase even.
The decrease in flux with the increase in load causes the torque to be less than that of shunt motor. The characteristics are similar to those of a shunt motor. Since the shunt motor develops a good torque and almost constant speed, therefore, differential motor is seldom used.
Speed control means intentional change of the drive speed to a value required for performing the specific work process. The concept of speed control or adjustment should not be taken to include the natural change in speed which occurs due to change in load on the drive shaft. Speed can be controlled manually by operator or by some automatic control device.
Speed can be adjusted mechanically by means of stepped pulleys, sets of change gears, variable speed friction clutch mechanism and other mechanical devices. But the electrical speed control has many economical as well as engineering advantages over mechanical speed control. In this method speed variation is accomplished by means of a variable resistance inserted in the series with the shunt field. Since in this method of speed control the flux can only be reduced not increased so the speed only above the normal one can be obtained.
This method consists of a variable resistance connected in series with the armature as shown in the fig in next slide. The speed at the full load may be reduced any desired value depending on the amount of resistance. With this method the voltage across the armature is lower than the line voltage.
Speed of dc series motor may be obtained through either armature or field control. Whole of the input energy is not converted into useful output energy but a part of the input energy is converted into heat and the same is lost. The power losses in a dc motor consist of input power that is converted into heat.
These losses are divided into. Copper or Electrical Losses: Iron or Magnetic Losses: B max. These losses consist of power loss due to friction of bearings, air friction or windage and are caused by the motion of the moving parts.
The armature magnetic field has two effects:. Use of High Brush-Contact Resistance 2. Shifting of Brushes to the New mna 3.
Basic construction and working of a DC Generator.
Use of Commutating Poles or Interpoles 4. Use of Compensating Winding. As observed from the different characteristics for dc series motor, these motors are suitable where high starting torque is required such as , electric traction, Hoists, trolleys, cranes, gears drives.
DC Series motors have dangerously high speed at no-loads. So these motors are not suitable for the services where the load may be entirely removed and also these motors are not suitable for belts drives. Applications of dc motors continues…….. Application of DC Shunt Motors: As observed from the different characteristics for dc shunt motors, these motors have almost constant speed and due to this feature these motors are suitable where constant speed is required in wide range of load such as, lathe machines, milling machines, conveyors line shafts etc.
These are also useful where medium starting torque is required such as boring machines, blowers, fans, conveyors centrifugal pumps, shapers, spinning and weaving machines, machine tools, printing presses DC shunt motors are not suitable for use with flywheel or with fluctuating loads services. Application of DC cumulative Compound Motors: As observed from the different characteristics for dc cumulative compound motors, these motors are used in driving machines which are subjected to sudden applications of heavy loads such as occur in rolling mills, punching and shearing machines, lifts, mine- hoist.
These motors are also used where high starting torque is required but series motors cannot be employed conveniently such as cranes and elevators. These motors are not suitable for applications requiring adjustable speed for field control Applications of dc motors continues…….
In differential compound wound motors, since series field opposes the shunt field, the resultant flux decreases with the increase in load; thus the machine runs at a higher speed than it would do as a shunt motor. The decrease in flux with the increase in load causes the torque to be less than that of a shunt motor.
So such motors are rarely used in practice as the differential arrangement causes difficulties during overloads and starting. Specifications of dc motors are shown on the specification plate of the motors. The meaning of different specifications of Kirloskar make dc motor as:.
Screen protected ii IP Screen protected drip proof iii IP Screen protected splash proof iv IP Totally enclosed duct ventilated. Motor mounted blower and free outlet ii IC Cooling air inlet via duct, free outlet iii IC Flag for inappropriate content. Related titles. Jump to Page. Search inside document. Field system The function of the field system is to create a uniform magnetic field within which the armature rotates.
Figure a shows the uniform magnetic field between the two opposite poles N S Fig. Compound wound dc motors: The important characteristics of dc motors are: If the voltage V is kept constant the field current will remain constant hence flux will have maximum value on no-load but will decrease slightly due to armature reaction as the load increases SPEED IN RPM but for most purpose the flux is considered to be constant, neglecting the effect of armature reaction.
Since in case of shunt motor the flux is considered to be constant, TORQUE IN N- m therefore, torque increases with the increase in load current following linear law i.
These losses are divided into i Copper losses or electrical losses ii Iron or magnetic losses iii Mechanical losses 99 Power losses of dc motor continues…….. Mechanical Losses in a DC Motor: Power losses of dc motor continues…….. The armature magnetic field has two effects: Application of DC Series Motors: The meaning of different specifications of Kirloskar make dc motor as: Specification of DC Motors continues….
Documents Similar To working principle of dc motor. Vatsal J Patel. Nisar Ahmed Rana. Pulkit Kumar Chauhan.
Saad Memon. Izhar Jiskani. The same DC machine can be used as a motor or generator. Therefore, theoretically, construction of a DC motor is same as that of a DC generator.
Working principle of a DC motor An electric motor is an electrical machine which converts electrical energy into mechanical energy. The basic working principle of a DC motor is: "whenever a current carrying conductor is placed in a magnetic field, it experiences a mechanical force".
Fleming's left hand rule : If we stretch the first finger, second finger and thumb of our left hand to be perpendicular to each other, and the direction of magnetic field is represented by the first finger, direction of the current is represented by the second finger, then the thumb represents direction of the force experienced by the current carrying conductor.
How a DC motor works?
When armature windings are connected to a DC supply, an electric current sets up in the winding. Magnetic field may be provided by field winding electromagnetism or by using permanent magnets. In this case, current carrying armature conductors experience a force due to the magnetic field, according to the principle stated above.
Commutator is made segmented to achieve unidirectional torque. Otherwise, the direction of force would have reversed every time when the direction of movement of conductor is reversed in the magnetic field. This is how a DC motor works! Back EMF According to fundamental laws of nature, no energy conversion is possible until there is something to oppose the conversion. In case of generators this opposition is provided by magnetic drag, but in case of dc motors there is back emf.
When the armature of a motor is rotating, the conductors are also cutting the magnetic flux lines and hence according to the Faraday's law of electromagnetic induction , an emf induces in the armature conductors.However, three-phase BLDC motors with permanent magnet rotor are most commonly used.
Magnetic field may be provided by field winding electromagnetism or by using permanent magnets. Hence it is observed that when a current carrying conductor is placed at right angle to the direction of magnetic field, a mechanical force is Experienced on the conductor in a direction perpendicular to both the direction of magnetic field and flow of current. Specification of DC Motors continues…. BLDC motors are also referred as trapezoidal permanent magnet motors. The magnets are mounted in the inner periphery of this cylinder.