CLIL experience Content and Language Integrated Learning

CLIL experience Content and Language Integrated Learning

2nd Second lesson

Induction Motor(Asyncronous motor)

Induction Motor(Asyncronous motor)

Why induction motor (IM)? –Robust; No brushes. No contacts on rotor shaft –High Power/Weight ratio compared to Dc motor –Lower Cost/Power –Easy to manufacture –Almost maintenance-free, except for bearing and other

mechanical parts

Disadvantages –Essentially a “fixed-speed” machine –Speed is determined by the supply frequency –To vary its speed need a variable frequency supply

Why induction motor (IM)? –Robust; No brushes. No contacts on rotor shaft –High Power/Weight ratio compared to Dc motor –Lower Cost/Power –Easy to manufacture –Almost maintenance-free, except for bearing and other

mechanical parts

Disadvantages –Essentially a “fixed-speed” machine –Speed is determined by the supply frequency –To vary its speed need a variable frequency supply

Cutaway of a three-phase induction motorCutaway of a three-phase induction motor

Three-phase induction motorThree-phase induction motor

Squirrel cage rotor

Stator windings

The stator consists of wound 'poles' that carry the supply current to induce a magnetic field that penetrates the rotor. In a very simple motor, there would be a single projecting piece of the stator (a salient pole) for each pole, with windings around it; in fact, to optimize the distribution of the magnetic field, the windings are distributed in many slots located around the stator, but the magnetic field still has the same number of north-south alternations. The number of 'poles' can vary between motor types but the poles are always in pairs (i.e. 2, 4, 6, etc.).

The stator consists of wound 'poles' that carry the supply current to induce a magnetic field that penetrates the rotor. In a very simple motor, there would be a single projecting piece of the stator (a salient pole) for each pole, with windings around it; in fact, to optimize the distribution of the magnetic field, the windings are distributed in many slots located around the stator, but the magnetic field still has the same number of north-south alternations. The number of 'poles' can vary between motor types but the poles are always in pairs (i.e. 2, 4, 6, etc.).

Three-phase induction motorThree-phase induction motor

• 2P; 50Hz• n0= 60f/2P• P=coppia polare• 1500 rpm

Squirrel cage rotor

Stator windings

Laminated Stator

Construction statorConstruction stator

stator

Construction squirrel cage rotorConstruction squirrel cage rotor

The most common rotor is a squirrel-cage rotor. It is made up of bars of either solid copper (most common) or aluminum that span the length of the rotor, and are connected through a ring at each end.

The most common rotor is a squirrel-cage rotor. It is made up of bars of either solid copper (most common) or aluminum that span the length of the rotor, and are connected through a ring at each end.

Construction stator & rotorConstruction stator & rotor

ConnectionsConnections

Star Delta

E

V

A

+

V

A

+E

V

A

+

V

A

+

Star connection RL=2 Rph Delta connection RL=2/3 Rph

How does it work?How does it work?

P

fn

600 P

fn

600

The relationship between the supply frequency, f, the number of poles, p, and the synchronous speed (speed of rotating field), ns is:

The relationship between the supply frequency, f, the number of poles, p, and the synchronous speed (speed of rotating field), ns is:

wheren = Revolutions per minute (rpm)f = AC power frequency (hertz)p = Number of poles per phase (an even number)

wheren = Revolutions per minute (rpm)f = AC power frequency (hertz)p = Number of poles per phase (an even number)

min]/[120

revp

fnS min]/[

120rev

p

fnS

Rotating Magnetic Field Rotating Magnetic Field

Look at magnetic field component.Blu, yellow and red vector rappresente the fields generated by trhee windings.Black vector is rotating field as result in every moment.

Look at magnetic field component.Blu, yellow and red vector rappresente the fields generated by trhee windings.Black vector is rotating field as result in every moment.

Tesla polyphase induction motorsTesla polyphase induction motors

• A polyphase induction motor consists of a polyphase winding embedded in a laminated stator and a conductive squirrel cage embedded in a laminated rotor.

• Three phase currents flowing within the stator create a rotating magnetic field which induces a current, and consequent magnetic field in the rotor. Rotor torque is developed as the rotor slips a little behind the rotating stator field.

• Unlike single phase motors, polyphase induction motors are self-starting.

• Motor starters minimize loading of the power line while providing a larger starting torque than required during running. Line current reducing starters are only required for large motors.

• Three phase motors will run on single phase, if started. • A static phase converter is three phase motor running on single

phase having no shaft load, generating a 3-phase output.

• A polyphase induction motor consists of a polyphase winding embedded in a laminated stator and a conductive squirrel cage embedded in a laminated rotor.

• Three phase currents flowing within the stator create a rotating magnetic field which induces a current, and consequent magnetic field in the rotor. Rotor torque is developed as the rotor slips a little behind the rotating stator field.

• Unlike single phase motors, polyphase induction motors are self-starting.

• Motor starters minimize loading of the power line while providing a larger starting torque than required during running. Line current reducing starters are only required for large motors.

• Three phase motors will run on single phase, if started. • A static phase converter is three phase motor running on single

phase having no shaft load, generating a 3-phase output.

Power flow diagramPower flow diagram

Determination of machine parametersDetermination of machine parameters

The following tests are usually carried out to determine the parameters of an asyncronous machine.

•Ohmic resistance measurement •No-Load Test•Locked-Rotor Test

The aims of the no–load test are to determine: •Stator ohmic/copper losses Pcu(s)•Stator core losses due to hysteresis and eddy current•Rotational losses due to friction and windage •Magnetizing reactance.

The blocked–Rotor Test provide information necessary to determine:•The winding resistances•The leakage (dispersion) reactances

The following tests are usually carried out to determine the parameters of an asyncronous machine.

•Ohmic resistance measurement •No-Load Test•Locked-Rotor Test

The aims of the no–load test are to determine: •Stator ohmic/copper losses Pcu(s)•Stator core losses due to hysteresis and eddy current•Rotational losses due to friction and windage •Magnetizing reactance.

The blocked–Rotor Test provide information necessary to determine:•The winding resistances•The leakage (dispersion) reactances

Translate the following words:Translate the following words:

1. No brusches ………………………….2. Rotor shaft …………………………………3. Squirrel cage rotor………………………4. Bearing ……………………………5. Stator windings……………………………….6. Delta connection ………………………………….7. Air-gap………………………………..8. Rotor torque ……………………………..9. Rotor slips ……………………………..10. Terminals ………………………………11. hysteresis and eddy current ………………………………..12. winding embedded in a laminated stator ……..................

.........................................................................

1. No brusches ………………………….2. Rotor shaft …………………………………3. Squirrel cage rotor………………………4. Bearing ……………………………5. Stator windings……………………………….6. Delta connection ………………………………….7. Air-gap………………………………..8. Rotor torque ……………………………..9. Rotor slips ……………………………..10. Terminals ………………………………11. hysteresis and eddy current ………………………………..12. winding embedded in a laminated stator ……..................

.........................................................................

Answer to the following questionsAnswer to the following questions

1. Which are the advantages of the induction motor?

2. Which are the disadvantages?

3. What are the main parts of the induction motor?

4. How can the connecting terminals of the IM be connected?

5. How does the IM work?

6. What are the main tests that have to be carried out in order to determine the parameters?

1. Which are the advantages of the induction motor?

2. Which are the disadvantages?

3. What are the main parts of the induction motor?

4. How can the connecting terminals of the IM be connected?

5. How does the IM work?

6. What are the main tests that have to be carried out in order to determine the parameters?

Fill the gapsFill the gaps

1. Speed is determined by …………………………………

2. Stator core losses due to ………….…. and ……..…. current

3. Rotational losses due to ……..…….. and ……….…….

4. Stator core losses due to …………………. and eddy current

5. Rotational losses due to friction and ……….………

1. Speed is determined by …………………………………

2. Stator core losses due to ………….…. and ……..…. current

3. Rotational losses due to ……..…….. and ……….…….

4. Stator core losses due to …………………. and eddy current

5. Rotational losses due to friction and ……….………

Complete the power flow diagramComplete the power flow diagram