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Sunday, 29 December 2019

How AC MOTOR Works? Its Construction, Types, Applications

AC MOTOR

  • An AC motor is an electric motor driven by an alternating current (AC).
  • The AC motor commonly consists of two basic parts, an outside stator having coils supplied with alternating current to produce a rotating magnetic field 
  • An inside rotor attached to the output shaft producing a second rotating magnetic field.

Construction of AC Motor

It consists of a Frame or Yoke, stator, rotor, bearings, fan, shaft, and slip rings. The parts of an AC machine is explained below.

Yoke

  • Yoke is outer part of body which is made up of cast steel or iron.
  • It provides mechanical strength to the inner parts of body

Rotor

  • The rotor in an electric motor is the moving part, and the main function of this is to rotate the shaft for generating the mechanical power. 
  • Generally, the rotor includes conductors which are laid to carry currents, and communicate with the magnetic field in the stator.

Bearings

  • The bearings provide proper friction for the rotor to run smoothly. 
Fan
  • A fan is employed to remove the unwanted heat that gained during the running of the rotor. 
  • It is expelled out through the ventilation that is provided behind the machine. 

Shaft

  • A shaft is provided to deliver the mechanical output as the rotor rotates. 

Slip rings 

  • The slips rings are employed for a normal Ac machine where rotating armature stationary field winding is employed. 
  • In this situation, the slip rings allow the input alternating current to change continuously in the coils.



Construction of AC Motor
Construction of AC Motor

Working principle

whenever a current-carrying conductor is placed in the magnetic field it exhibits some force in it. When alternating current supply is fed to the coil of the rotor, it experiences some force due to the law of the Lorentz force equation. Due to this force, torque will be developed in the clockwise direction that enables the rotor to rotate.

Types of AC Motors

  • Synchronous motor 
  • Asynchronous motor - 1) Single phase induction motor                                      2) Three phase induction motor

Applications of AC Motors

  • It is used in mixer grinders, pumps, and household appliances.
  • Used in industries.




Saturday, 28 December 2019

How DC MOTOR Works? and Its Construction, Types, Applications.

ELECTRIC  MOTORS


  • An electric motor is an electrical machine that converts electrical energy into mechanical energy.
  • Most electric motors operate through the interaction between the motors magnetic field and electric current in a wire winding to generate force in the form of rotation of a shaft. 
  • Electric motors can be powered by direct current (DC) such as from batteries, motor vehicles or rectifiers.
  • And powered by an alternating current (AC) called ac motors.

DC MOTORS

DC MOTOR
DC MOTOR
=
DC motor is  electrical machines that converts direct current electrical energy into mechanical energy.

Construction of DC Motor

A DC motor or a DC machine consists of two windings namely field winding and armature winding. The field winding is stationary and armature winding can rotate.
 
The field winding produces a magnetic flux in the air gap between the armature and field windings and the armature is placed in this magnetic field.


 The construction of DC motor or machine is shown in Figure.





construction of dc motor
Yoke
  • The yoke acts as the outer cover of a DC motor and it is also known as the frame. 
  • The yoke is an iron body, made up of low reluctance magnetic material such as cast iron, silicon steel, rolled steel etc
  • It provides mechanical protection to the outer parts of the machine
  •  It provides low reluctance path for the magnetic flux. 
 Pole and pole shoe
  • The pole and pole shoe are fixed on the yoke by bolts. 
  • These are made of thin cast steel or wrought iron lamination which are riveted together. Poles produce the magnetic flux when the field winding is excited. 
  • Pole shoe is an extended part of a pole. Due to its shape, the pole area is enlarged and more flux can pass through the air gap to the armature.
Field Winding 
  • The coils around the poles are known as field (or exciting) coils and are connected in series to form the field winding. 
  • Copper wire is used for the construction of field coils. 
  • When the DC current is passed through the field winding, it magnetizes poles which produce magnetic flux. 
Armature Core
dc motor construction
  • It is a cylindrical drum and keyed to the rotating shaft. A large number of slots are made all over its periphery, which accommodates the armature winding. 
  • Low reluctance, high permeability material such as cast iron and cast steel are used for armature core. 
  • The laminated construction is used to produce the armature core to minimize the eddy current losses.

Armature Winding
  • The armature winding plays very important role in the construction of a DC motor because the conversion of power takes place in armature winding. 
  • On the basis of connections, there are two types of armature winding named:                                               Lap winding                                                                                                                                     Wave Winding
 Commutator
  • It is a mounted on the shaft. It is made up of a large number of wedge-shaped segments of hard drawn copper, insulated from each other by a thin layer of mica. 
  • The commutator connects the rotating armature conductor to the stationary external circuit through carbon brushes. 
  • It converts alternating torque into unidirectional torque produced in the armature.
Brushes

  • The current is conducted from voltage source to armature by the carbon brushes which are held against the surface of commutator by springs. 
  • They are made of high-grade carbon steel and are rectangular in shape.
Bearings
  • The ball or roller bearings are fitted in the end housings. 
  • The friction between stationary and rotating parts of the motor is reduced by bearing. 
  • Mostly high carbon steel is used for making the bearings as it is very hard material.
Working principle of DC Motor 
  • "Whenever a current carrying conductor is placed in a magnetic field, it experiences a mechanical force". 
  • The direction of this force is given by Fleming's left-hand rule and its magnitude is given by 
  • F = BIL. 
                 Where,   B = magnetic flux density, 
                                I = current and 
                                L = length of the conductor within the magnetic field.
Fleming's Left Hand Rule: If we stretch the first finger, second finger and thumb of ur 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.
DC Motors working
DC Motors working
Types of DC Motor

DC motors are usually classified on the basis of their excitation configuration, as follows -
  • Separately excited (field winding is fed by external source)
  • Self-excited -
    • Series wound (field winding is connected in series with the armature)
    • Shunt wound (field winding is connected in parallel with the armature)
    • Compound wound -
      • Long shunt
      • Short shunt
Applications 
  • Blowers and fans
  • Centrifugal and reciprocating pumps
  • Cranes 
  • Hoists, elevators 
  • Rolling mills
  • Drilling machines



Friday, 27 December 2019

Basic In Electrical Engineering- Electric Voltage,Current, Power, Resistor, Capacitor, Inductor, Ohm's law

ELECTRICAL BASICS




Electric Engineering

      It is the branch of engineering that deals with the technology of electricity, applications of equipment,devices and system which use electricity, electronics and electromagnetism.

Electric voltage
  • Electrical potential energy per unit charge. 
  • Potential difference between two points in electrical circuit.
  • Voltage is a pressure which pushes the charged electrons means current. 
  • Measured in joules/coulomb
  • SI unit volt (V)
  • V = I . R

Electric Current
  • Rate at which charge is flow from one terminal (positive) to the another terminal (negative).
  • Measured in ampere (A)
  • SI unit ampere
  •  I = V/R
Alternating Current (AC)
  • The current that changes its magnitude and polarity at regular intervals of time is called an alternating current.
  • The major advantage of using the alternating current instead of direct current is that the alternating current is easily transformed from higher voltage level to lower voltage level.
  • When the resistive load R is connected across the alternating source shown in the figure below, the current flows through it. The alternating current flows in one direction and then in the opposite direction when the polarity is reversed.
Alternating Current Circuit
Alternating Current Circuit

Advantages of AC

  • The alternating current produces low iron and copper losses in AC rotating machine and transformer because it improves the efficiency of AC machines.
  • The alternating current offer less interference to the nearby communication system (telephone lines etc.).
  • They produce the least disturbance in the electrical circuits.

Direct Current (DC)
  • Direct Current, which is electrical current that flows in one direction. 
  • In dc circuits, the current is in one direction unlike the alternating current (AC) where the current reverses direction 50 or 60 times a second depending on the frequency of the supply.
Sources of Direct Current
  • DC generators
  • Batteries
  • DC power converters that rectify the AC
  • Solar panels
  • Thermocouples
Advantages of DC
  • Most equipment are more efficient when directly powered from DC.
  • More efficient especially when the power leads are less than 100 feet.
  • Less risks of shock hazard for voltages below 48 Volts.
Applications of Dc

DC is used in almost all electronics equipment, electric vehicles, automation, control of electrical equipment, and more. 
Most office and domestic equipment such as TVs, audio systems, amplifiers, flash lights, computers, tablets and smartphones use DC power to function. However, since the universally available power is AC, the equipment uses an external or internal power supply to convert the utility mains AC into the desired DC for the equipment.


Resister

  • Materials tendency to resist the flow of charge.
  • The effect of resistor is known as resistance.
  • Measured in ohm (R)
  • SI  unit ohm
  • R = V/I
Capacitor
  • Capacitor stores energy in electrical field.
  • Passive electronic component with two terminals.
  • The effect of capacitor is known as capacitance.
  • Its SI unit is Farads 
  • Denoted as E.
Inductor

  • An inductor, also called a coil, choke, or reactor. 
  • is a passive two-terminal electrical component that stores energy in a magnetic field when electric current flows through it. 
  • An inductor typically consists of an insulated wire wound into a coil around a core.
  • Its SI unit is Henries (H). 
Electric Power
  • Electric power is the rate, per unit time, at which electrical energy is transferred by an electric circuit. 
  • The SI unit of power is the watt, one joule per second. 
Power Efficiency
  • Ratio of the output power into the input power is called power efficiency.
  • Measured in watt (P).
  • P=E/t
Power Factor
  • The power factor is equal to the real or true power P in watts (W) divided by the apparent power |S| in volt-ampere (VA)
Ohm's Law
  • Ohm's law states that the current through a conductor between two points is directly proportional to the voltage across the two points  inversely proportional to the resistance, at the constant temperature.
  • I= V/R
Kirchoff's current law
  • Total current entering into the junction is equal to the total current leaving the junction.
Kirchoff's voltage law
  • Algebraic sum of the voltage drop in closed loop is zero. 

                                             


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