C.V. Raman Global University, Bhubaneswar

Topic: 1ɸ & Special Machines

Prepared By: Smitarani Sahoo, Assistant Professor, Dept. of Electrical Engineering Contents . Construction . Double field revolving theory . Starting methods . Capacitor-start & Capacitor run Induction motor . Shaded pole induction Motor . . . AC series motor . Servo motors . Stepper motors . Equivalent Circuit . No load and blocked test

Smitarani Sahoo, CGU, BBSR 1ɸ Induction Motor

• It operates with single phase AC supply. • It is cheap in cost and robust in construction. • These motors are not self starting.

Smitarani Sahoo, CGU, BBSR Washing Vacuum Centrifugal Blowers

Machines Cleaners Pumps APPLICATIONS APPLICATIONS

Fans Mixer Grinder Hair Dryer Trimmer

Smitarani Sahoo, CGU, BBSR Ferrari’s Principle The produced by a single phase is an alternating magnetic field that can be resolved into two rotating fields of half of its amplitude rotating in opposite direction with the same speed.

Y

X component: 퐴1 푂퐴1퐶표푠 θ + 푂퐴2퐶표푠 θ 푂퐴1푆푖푛 θ 푂퐴 퐶표푠 θ 1 =H퐶표푠 θ+H퐶표푠 θ=2H퐶표푠 θ θ 퐴1(H) O X Y component: θ 퐴2(H) 푂퐴 푆푖푛 θ − 푂퐴 푆푖푛 θ 푂퐴 퐶표푠 θ 1 2 푂퐴 푆푖푛 θ 2 2 = H 푆푖푛 θ-H 푆푖푛 θ = 0 퐴2 Resultant field= 2H퐶표푠 θ

-Y Smitarani Sahoo, CGU, BBSR Double revolving field Theory

• According to Ferrari’s Principle, an alternating single phase current produces two magnetic fields of half of its amplitude rotating in opposite direction at the same angular velocity.

• Under static condition, these two field induce equal currents on the rotor.

• This produces two equal and opposite torques in the rotor.

• So, Single phase induction motors are not self starting

Stator

ɸ AC Supply AC ɸ -

1 Rotor

Smitarani Sahoo, CGU, BBSR Suppose the rotor is given a rotation of N RPM in clockwise direction. • Slip with respect to forward (clockwise) rotating field, 푁푠−푁 푠푓 = = s 푁푠 • Slip with respect to backward (anti clockwise) rotating field, 푁푠−(−푁) 푠푏 = 푁푠 푁 +푁 = 푠 푁푠 푁 +푁 −푁 +푁 = 푠 푠 푠 푁푠 2푁 −(푁 −푁) = 푠 푠 푁푠 2푁 −푠푁 = 푠 푠 푁푠 푁 (2−푠) = 푠 = 2 − 푠 푁푠 • Hence, if these motors are given an external movement, they will have starting torque and continue rotating thereafter.

Smitarani Sahoo, CGU, BBSR Construction

• They have essentially two parts, and rotor. • Rotor is squirrel cage type. • Stator is cylindrical types and contains two windings i.e main and auxiliary. • Main winding (Running winding) is highly inductive and less resistive. • It consists of less no. of turns of a thick wire. • Auxiliary winding (starting winding) is highly resistive and has more no. of turns of a thin wire. • This stator construction is common to all the 1- ɸ induction motors except shaded pole motors.

Smitarani Sahoo, CGU, BBSR Starting Methods of Single Phase Induction Motors

• When two windings are placed 90 degrees apart, a rotating magnetic field is produced.

• By proper selection of impedance, currents may be made to differ by 90 degrees.

• This is method of phase split.

Smitarani Sahoo, CGU, BBSR Capacitor Start Capacitor Run Induction Motor

• The two stator windings are displaced 90 degrees in space.

• There are two capacitors, starting capacitor and running capacitor.

• There are two capacitors in this motor represented by CS and CR. During starting, the two capacitors are connected in parallel.

• The motor starts off as a two phase motor.

• After the motor picks up speed, starting capacitor is disconnected.

Smitarani Sahoo, CGU, BBSR Smitarani Sahoo, CGU, BBSR Smitarani Sahoo, CGU, BBSR Features:

. It produces a constant torque.

. They can be used with heavy loads.

. Quiet in operation.

. Efficiency if 55-65%.

. Power factor 0.8-0.9.

. They can work with around 25% overload.

. They are used in compressors, refrigerators, pumps etc.

. These are costly.

Smitarani Sahoo, CGU, BBSR Shaded Pole Motor

• Stator has salient poles with exciting coils.

• A part of each pole is wrapped by a copper strap known as .

• Air-gap length is 0.25mm- 0.5mm.

Smitarani Sahoo, CGU, BBSR Working Principle

ɸ푚

푇 4 푇 2

I I

ɸ푅 ɸ푅 ɸ푅 Smitarani Sahoo, CGU, BBSR Features:

. Efficiency is around 20-50%.

. Power factor is 0.5-0.6.

. Low overload capacity.

. Speed can be controlled by varying supply .

. Direction of rotation depends on the position of shading coil.

. Applications: hair dryers, vending machines, photo-copying machines, projectors etc.

Smitarani Sahoo, CGU, BBSR Repulsion Motors

Repulsion start Repulsion Motors Repulsion Induction Induction Run Motors Motors

Smitarani Sahoo, CGU, BBSR Repulsion Motors Construction: • The main components of repulsion motor are stator, rotor, and . • The stator carries a single phase exciting winding. • The rotor has distributed winding as in DC motor. • Brushes are short circuited by jumpers.

Smitarani Sahoo, CGU, BBSR Working Principle:

• The stator winding produces the working MMF in the air gap.

• EMF is induced in the by mutual induction.

• Brushes on rotor are shorted, so current starts flowing in the armature by action.

• The rotor receives power from stator by transformer action.

• Magnetic poles will be induced in the rotor and by repulsion action, the motor will rotate.

Smitarani Sahoo, CGU, BBSR Smitarani Sahoo, CGU, BBSR Repulsion start Induction Run Motors :

A centrifugal switch short circuits the commutator and lifts up the brushes after motor attains 75-80% of rated speed.

Repulsion Induction Motors :

Rotor contains two windings. One squirrel cage and one DC armature winding.

Smitarani Sahoo, CGU, BBSR Advantages:

• They have high starting torque.

• Can withstand longer starting periods.

• Provide constant speed characteristics.

Disadvantages:

• Require more maintainance.

• Noisier in operation.

• Might cause radio interference and expensive.

Application: Traction, house-hold refrigerators, air pumps, compressors etc.

Smitarani Sahoo, CGU, BBSR AC Series Motor

A DC series motor is given a single phase AC supply

Smitarani Sahoo, CGU, BBSR DC series Motor with AC supply

Pulsating torque

Excessive heating and low efficiency

Large Reactance

Extensive Sparking

Lower speed of operation

Low starting torque

Smitarani Sahoo, CGU, BBSR Modifications in Design

Whole magnetic circuit is laminated. Inter-poles are used.

Series field winding has fewer turns. More no. of poles are present in the field.

More no. of armature conductors are High permeability core with small used. air-gap is used.

More commutator segments are Operating voltage is kept low. present.

Compensating winding is provided. Low frequency operation is generally preferred.

Smitarani Sahoo, CGU, BBSR Characteristics of AC series motor

DC operation

AC operation

Torque Speed

Armature Current Armature Current Torque

Smitarani Sahoo, CGU, BBSR AC Series Motors

Conductively Inductively Compensated Compensated

Compensating winding Compensating winding

Smitarani Sahoo, CGU, BBSR Hysteresis Motor It is a with uniform air-gap and no DC excitation. Construction: • Stator is CSCR type. • Rotor is cylindrical made of a high retentivity magnetic material. • Rotor does not have any winding placed on a non-magnetic arbor.

Smitarani Sahoo, CGU, BBSR Working Principle

• When stator is energized a rotating magnetic field is produced.

• This magnetizes the rotor, but due to hysteresis, the axis of magnetization of rotor lags behind the stator by some angle δ.

• Rotor gets attracted towards the stator poles and experiences a hysteresis torque.

• The motor initially experiences hysteresis and eddy current torques and finally rotates at synchronous speed.

Smitarani Sahoo, CGU, BBSR Advantages: Quieter in operation, gives a constant speed characteristic, can drive high inertia loads.

Applications: Electric Clocks, Audio Equipments

Smitarani Sahoo, CGU, BBSR Stepper Motors

Permanent Variable Reluctance Hybrid Stepper Motors

Smitarani Sahoo, CGU, BBSR Construction

• Stepper motors work with an external drive that supplies a train of pulses.

• could be salient or non-salient types.

• The stator terminals are brought out for DC excitation.

• Rotor could be a permanent magnet or a variable reluctance type.

Smitarani Sahoo, CGU, BBSR Working Principle

• When a particular pole is energized, the rotor aligns itself along its direction.

• As the sequence of pulses progress, the rotor moves in steps.

Smitarani Sahoo, CGU, BBSR Step Angle: the angle through which the shaft moves in each pulse.

3600 3600 α= = 푛표.표푓 푝ℎ푎푠푒푠 ∗푛표.표푓 푟표푡표푟 푡푒푒푡ℎ 푚푁푟 Where, m= no. of stator phases

푁푟 = no. of rotor teeth

푁 −푁 Or, α= 푠 푟 * 3600 푁푠푁푟

Applications: scanners, disk drives, camera lenses, 3D printers etc.

Smitarani Sahoo, CGU, BBSR Linear Induction Motor

It is a special purpose motor that produces recti-linear motion.

Construction:

• The stator is laid in form a track of flat coils. The rotor is like a moving platform and is known as secondary.

• Field system has a 3 phase distributed winding. It can have single primary system or double primary system.

• Secondary is a conducting plate made of aluminium or copper.

Smitarani Sahoo, CGU, BBSR Smitarani Sahoo, CGU, BBSR Working Principle

• When the primary gets excited by a balanced three-phase power supply, a flux starts traveling along the entire length of the primary. • This linearly traveling magnetic field is equivalent to the rotating magnetic field of 3 phase induction motor • Currents is induced in the secondary due to the relative motion. • The induced current interacts with the traveling flux wave to produce linear force or thrust. • If the primary is fixed and the secondary is free to move, the force will pull the secondary in the direction of the force.

Smitarani Sahoo, CGU, BBSR Advantages: • Low maintenance • No limitation on maximum speed due to centrifugal force. • No over heating

Disadvantages: • Poor utilization of motor • More magnetizing current requirement. • High cost

Applications: Maglev , Conveyers, Travelling Cranes, High Speed Traction Etc.

Smitarani Sahoo, CGU, BBSR Servo Motors

• Motors which respond to error signal abruptly and accelerate the load quickly are called servo motors.

• Servo mechanism: The automatic control of a physical quantity i.e. angular displacement or speed of a motor is called servo mechanism. Disturbance Measurement Error of Reference Signal Error Error Corrector or Detector Amplifier Controller

Amplifier Error Applied Output Corrector Control Output

Measurement of Regulated Quantity Smitarani Sahoo, CGU, BBSR Special features of servo-motors:

. They can develop high torque at all speeds and hold a static position.

. They have low inertia so, can accelerate quickly.

. They don’t overheat at standstill or lower speeds.

. They can return to a position without any drift.

Desirable characteristics:

. Output torque should be proportional to the voltage applied to it.

. The direction of torque developed should depend upon the instantaneous polarity of control voltage.

Smitarani Sahoo, CGU, BBSR Servo-Motor

AC Servo-Motor DC Servo-Motor

Field Controlled DC Armature Controlled DC Servomotor

Smitarani Sahoo, CGU, BBSR AC servo-motors • The stator has two distributed windings displaced from each other by 900electrical.

• One winding is known as a main winding, supplied from a constant voltage source.

• The other one is Control winding, and it is provided with a variable voltage.

• The speed and torque of the rotor are controlled by the phase difference between the control voltage and the reference phase voltage.

• By reversing the phase difference from leading to lagging or vice versa, the direction of the rotation of the rotor can be reversed.

Smitarani Sahoo, CGU, BBSR Advantages: . Rugged construction. . Less maintainace as brush commutator is absent. . Better heat dissipation. . Less inertia of armature.

Smitarani Sahoo, CGU, BBSR DC Servo-Motors

• The rotors of this kind of motor are designed with long rotor length and smaller diameters.

• Armature is designed to have large resistance to have a linear torque speed characteristics.

• It could be series motor, split series motor, shunt control motor or permanent magnet shunt motor.

Smitarani Sahoo, CGU, BBSR Field Controlled Armature Controlled

• Field is excited by the amplified • Armature is energized by amplified error signal and armature winding is error signal and field is excited by a energized by a constant source. constant current source.

• Field is controlled below the knee • Field is operated at well beyond the knee point of O.C.C. point of O.C.C.

Smitarani Sahoo, CGU, BBSR Equivalent Circuit of A Single Phase Induction Motor

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V Em

Equivalent Circuit under stand-still condition

Smitarani Sahoo, CGU, BBSR Equivalent Circuit of A Single Phase Induction Motor Under Normal Operating Conditions

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V

Smitarani Sahoo, CGU, BBSR A 220V, 1ɸ induction motor gave the following test results: : 120V, 9.6A, 460W No-load test: 220V, 4.6A, 125W The stator winding resistance is 1.5Ω and during blocked rotor test, starting winding is open. Determine the equivalent circuit parameters, core, friction and windage losses.

Smitarani Sahoo, CGU, BBSR