DC MOTER IT'S WORK AND PRINCIPLE ETC.
DC MOTER:A DC motor is any of a class of rotary electrical machines that converts direct current electrical energy into mechanical energy.
PRINCIPLES: It is based on the principle that when a current-carrying conductor is placed in a magnetic field, it experiences a mechanical force whose direction is given by Fleming's Left-hand rule and whose magnitude is given by
Force, F = B I l newton
Where B is the magnetic field in weber/m2.
I is the current in amperes and
l is the length of the coil in meter.
The force, current and the magnetic field are all in different directions.
If an Electric current flows through two copper wires that are between the poles of a magnet, an upward force will move one wire up and a downward force will move the other wire down.
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Figure 1: Force in DC Motor
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Figure 2 : Magnetic Field in DC Motor
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Figure 3 : Torque in DC Motor
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Figure 4 : Current Flow in DC Motor
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The loop can be made to spin by fixing a half circle of copper which is known as commutator, to each end of the loop. Current is passed into and out of the loop by brushes that press onto the strips. The brushes do not go round so the wire do not get twisted. This arrangement also makes sure that the current always passes down on the right and back on the left so that the rotation continues. This is how a simple Electric motor is made.
The dc generators and dc motors have the same general construction. In fact, when the machine is being assembled, the workmen usually do not know whether it is a dc generator or motor. Any dc generator can be run as a dc motor and vice-versa.
- Magnetic frame or Yoke
- Pole Cores and Pole Shoes
- Pole Coils or Field Coils
- Armature core
- Armature winding
- Commutator
- Brushes and Bearings
The diagram given below represents the various parts of a DC machine.
Yoke
The outer frame or yoke serves double purpose :
- It provides mechanical support for the poles and acts as a protecting cover for the whole machine
- It carries the magnetic flux produced by the poles
In small generators where cheapness rather than weight is the main consideration, yokes are made of cast iron.
But for large machines usually cast steel or rolled steel is employed.
The modern process of forming the yoke consists of rolling a steel slab round a cylindrical mandrel and then welding it at the bottom.
The feet and the terminal box etc. are welded to the frame afterwards. Such yokes possess sufficient mechanical strength and have high permeability.
But for large machines usually cast steel or rolled steel is employed.
The modern process of forming the yoke consists of rolling a steel slab round a cylindrical mandrel and then welding it at the bottom. The feet and the terminal box etc. are welded to the frame afterwards. Such yokes possess sufficient mechanical strength and have high permeability.
Pole Cores and Pole Shoes
The field magnets consist of pole cores and pole shoes. The pole shoes serve two purposes:
- they spread out the flux in the air gap and also, being of larger cross-section, reduce the reluctance of the magnetic path
- they support the exciting coils (or field coils)
There are two main types of pole construction.
- The pole core itself may be a solid piece made out of either cast iron or cast steel but the pole shoe is laminated and is fastened to the pole face by means of counter sunk screws
- In modern design, the complete pole cores and pole shoes are built of thin laminations of annealed steel which are rivetted together under hydraulic pressure. The thickness of laminations varies from 1 mm to 0.25 mm.
There are two main types of pole construction.
- The pole core itself may be a solid piece made out of either cast iron or cast steel but the pole shoe is laminated and is fastened to the pole face by means of counter sunk screws
- In modern design, the complete pole cores and pole shoes are built of thin laminations of annealed steel which are rivetted together under hydraulic pressure. The thickness of laminations varies from 1 mm to 0.25 mm.
Field system
The function of the field system is to produce uniform magnetic field within which the armature rotates.
Field coils are mounted on the poles and carry the dc exciting current. The field coils are connected in such a way that adjacent poles have opposite polarity.
The m.m.f. developed by the field coils produces a magnetic flux that passes through the pole pieces, the air gap, the armature and the frame.
Practical d.c. machines have air gaps ranging from 0.5 mm to 1.5 mm.
Since armature and field systems are composed of materials that have high permeability, most of the m.m.f. of field coils is required to set up flux in the air gap.
By reducing the length of air gap, we can reduce the size of field coils (i.e. number of turns).
The function of the field system is to produce uniform magnetic field within which the armature rotates.
The m.m.f. developed by the field coils produces a magnetic flux that passes through the pole pieces, the air gap, the armature and the frame.
Since armature and field systems are composed of materials that have high permeability, most of the m.m.f. of field coils is required to set up flux in the air gap.
By reducing the length of air gap, we can reduce the size of field coils (i.e. number of turns).
●Armature core and Laminations
The armature core is keyed to the machine shaft and rotates between the field poles.
It consists of slotted soft-iron laminations (about 0.4 to 0.6 mm thick) that are stacked
to form a cylindrical core as shown in figure.
The laminations are individually coated with a thin insulating film so that they do not come in electrical contact with each other.
The purpose of laminating the core is to reduce the eddy current loss. Thinner the lamination, greater is the resistance offered to the induced e.m.f., smaller the current and hence lesser the I²R loss in the core.
The laminations are slotted to accommodate and provide mechanical security to the armature winding and to give shorter air gap for the flux to cross between the pole face and the armature “teeth”.
It consists of slotted soft-iron laminations (about 0.4 to 0.6 mm thick) that are stacked
to form a cylindrical core as shown in figure.
The laminations are individually coated with a thin insulating film so that they do not come in electrical contact with each other.
The purpose of laminating the core is to reduce the eddy current loss. Thinner the lamination, greater is the resistance offered to the induced e.m.f., smaller the current and hence lesser the I²R loss in the core.
The laminations are slotted to accommodate and provide mechanical security to the armature winding and to give shorter air gap for the flux to cross between the pole face and the armature “teeth”.
Armature winding
The slots of the armature core hold insulated conductors that are connected in a suitable manner. This is known as armature winding.
This is the winding in which “working” e.m.f. is induced. The armature conductors are connected in series-parallel; the conductors being connected in series so as to increase the voltage and in parallel paths so as to increase the current.
This is the winding in which “working” e.m.f. is induced. The armature conductors are connected in series-parallel; the conductors being connected in series so as to increase the voltage and in parallel paths so as to increase the current.
Construction of DC Machine (Generator & Motor)
All dc machines have five principal components
Yoke
The outer frame or yoke serves double purpose :
Pole Cores and Pole Shoes
The field magnets consist of pole cores and pole shoes. The pole shoes serve two purposes:
Field system
The function of the field system is to produce uniform magnetic field within which the armature rotates.
Armature core and Laminations
The armature core is keyed to the machine shaft and rotates between the field poles.
It consists of slotted soft-iron laminations (about 0.4 to 0.6 mm thick) that are stacked
to form a cylindrical core as shown in figure.
It consists of slotted soft-iron laminations (about 0.4 to 0.6 mm thick) that are stacked
to form a cylindrical core as shown in figure.
Armature winding
The slots of the armature core hold insulated conductors that are connected in a suitable manner. This is known as armature winding.
This is the winding in which “working” e.m.f. is induced. The armature conductors are connected in series-parallel; the conductors being connected in series so as to increase the voltage and in parallel paths so as to increase the current.
This is the winding in which “working” e.m.f. is induced. The armature conductors are connected in series-parallel; the conductors being connected in series so as to increase the voltage and in parallel paths so as to increase the current.
Commutator
A commutator is a mechanical rectifier which converts the alternating voltage generated in the armature winding into direct voltage across the brushes.
A commutator is a mechanical rectifier which converts the alternating voltage generated in the armature winding into direct voltage across the brushes.
DC Generator, DC Motor, Electrical Machines
Construction of DC Machine (Generator & Motor)
All dc machines have five principal components
Yoke
The outer frame or yoke serves double purpose :
Pole Cores and Pole Shoes
The field magnets consist of pole cores and pole shoes. The pole shoes serve two purposes:
Field system
The function of the field system is to produce uniform magnetic field within which the armature rotates.
Armature core and Laminations
The armature core is keyed to the machine shaft and rotates between the field poles.
It consists of slotted soft-iron laminations (about 0.4 to 0.6 mm thick) that are stacked
to form a cylindrical core as shown in figure.
It consists of slotted soft-iron laminations (about 0.4 to 0.6 mm thick) that are stacked
to form a cylindrical core as shown in figure.
Armature winding
The slots of the armature core hold insulated conductors that are connected in a suitable manner. This is known as armature winding.
This is the winding in which “working” e.m.f. is induced. The armature conductors are connected in series-parallel; the conductors being connected in series so as to increase the voltage and in parallel paths so as to increase the current.
This is the winding in which “working” e.m.f. is induced. The armature conductors are connected in series-parallel; the conductors being connected in series so as to increase the voltage and in parallel paths so as to increase the current.
Commutator
A commutator is a mechanical rectifier which converts the alternating voltage generated in the armature winding into direct voltage across the brushes.
Brushes
DC motors are of two types : one is brushed dc motor and the other one is brushless dc motor. Brushless dc motors are mainly used in high speed applications such as multicopters (eg:- quadcopters).
If the brush pressure is very large, the friction produces heating of the commutator and the brushes. On the other hand, if it is too weak, the imperfect contact with the commutator may produce sparking.
Multipole machines have as many brushes as they have poles. For example, a 4-pole machine has 4 brushes. As we go round the commutator, the successive brushes have positive and negative polarities. Brushes having the same polarity are connected together so that we have two terminals viz., the +ve terminal and the -ve terminal
●WORKING PRINCIPLES :
The very basic construction of a DC motor contains a current carrying armature which is connected to the supply end through commutator segments and brushes. The armature is placed in between north south poles of a permanent or an electromagnet as shown in the diagram above.
As soon as we supply direct current in the armature, a mechanical force acts on it due to the electromagnetic effect of the magnet. Now to go into the details of the operating principle of DC motor it's important that we have a clear understanding of Fleming’s left-hand rule to determine the direction of the force acting on the armature conductors of DC motor.
If a current carrying conductor is placed in a magnetic field perpendicularly, then the conductor experiences a force in the direction mutually perpendicular to both the direction of field and the current carrying conductor. Fleming’s Left-Hand Rule can determine the direction of rotation of the motor. We extend the index finger, middle finger and thumb of our left-hand perpendicular to each other. The middle finger is in the direction of current in the conductor, and index finger is along the direction of magnetic field, i.e., north to south pole, then thumb indicates the direction of the created mechanical force.
DC motors are of two types : one is brushed dc motor and the other one is brushless dc motor. Brushless dc motors are mainly used in high speed applications such as multicopters (eg:- quadcopters).
Multipole machines have as many brushes as they have poles. For example, a 4-pole machine has 4 brushes. As we go round the commutator, the successive brushes have positive and negative polarities. Brushes having the same polarity are connected together so that we have two terminals viz., the +ve terminal and the -ve terminal
●WORKING PRINCIPLES :
The very basic construction of a DC motor contains a current carrying armature which is connected to the supply end through commutator segments and brushes. The armature is placed in between north south poles of a permanent or an electromagnet as shown in the diagram above.
If the brush pressure is very large, the friction produces heating of the commutator and the brushes. On the other hand, if it is too weak, the imperfect contact with the commutator may produce sparking.
Multipole machines have as many brushes as they have poles. For example, a 4-pole machine has 4 brushes. As we go round the commutator, the successive brushes have positive and negative polarities. Brushes having the same polarity are connected together so that we have two terminals viz., the +ve terminal and the -ve terminal
●WORKING PRINCIPLES :
The very basic construction of a DC motor contains a current carrying armature which is connected to the supply end through commutator segments and brushes. The armature is placed in between north south poles of a permanent or an electromagnet as shown in the diagram above.
As soon as we supply direct current in the armature, a mechanical force acts on it due to the electromagnetic effect of the magnet. Now to go into the details of the operating principle of DC motor it's important that we have a clear understanding of Fleming’s left-hand rule to determine the direction of the force acting on the armature conductors of DC motor.
If a current carrying conductor is placed in a magnetic field perpendicularly, then the conductor experiences a force in the direction mutually perpendicular to both the direction of field and the current carrying conductor. Fleming’s Left-Hand Rule can determine the direction of rotation of the motor. We extend the index finger, middle finger and thumb of our left-hand perpendicular to each other. The middle finger is in the direction of current in the conductor, and index finger is along the direction of magnetic field, i.e., north to south pole, then thumb indicates the direction of the created mechanical force.
If a current carrying conductor is placed in a magnetic field perpendicularly, then the conductor experiences a force in the direction mutually perpendicular to both the direction of field and the current carrying conductor. Fleming’s Left-Hand Rule can determine the direction of rotation of the motor. We extend the index finger, middle finger and thumb of our left-hand perpendicular to each other. The middle finger is in the direction of current in the conductor, and index finger is along the direction of magnetic field, i.e., north to south pole, then thumb indicates the direction of the created mechanical force.The commercial motor uses
1)Electromagnet in place of permanent magnet.
2)A soft iron core on which coil is wound.
Uses of D.C. motor
It is used in electric cars,rolling mills,electric cranes,lifts,drilling machine,fan,hair dryers,blowers,tape recorder,refrigerators,washing machine,mixers,blenders.
Hi friends if you wants basic information about dc motor and eles please comment.
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