AC Machines6077 SANUE 046

1 Phase Induction Motors

• Identify the basic components of a 1Ø induction motor

• List the types of rotors used• Test motor windings for suitability to connect

to the supply• Connect in both Clockwise and counter

clockwise rotation• List the steps for dismantling it

At the end of this section you will be able to:

TypesSquirrel Cage • Split phase

• Capacitor start

• Capacitor start Capacitor run

• Permanent split phase capacitor run

• Shaded Pole

Wound Rotor • Series universal

• Repulsion

Construction

Construction1. Low resistance

2. High XL

3. Set deeper in laminations to increase XL

Run or Main Windings

Start or Auxiliary Windings1. High resistance (thinner wire)

2. Low XL (fewer turns)

3. Set shallower in laminations to limit XL

Electrical Characteristics

Run Winding

IR

IS

Start Winding

Large phase Angle due to high Inductance

Phase Angle less, as Inductance is less than run winding

IRef

Split Phase Motor Construction

High resistance

Low XL

Low resistance

High XL

Switch opens ≈ 70 – 80% full load speed

Split Phase Motor Construction

Low resistance

High resistance

Split Phase Motor Construction

Capacitor Start Motor

Electrical Characteristics

IR

IS

IRef

Split Phase

Capacitor Start

Torque = K IR IS sinα

α = Angle between IR and IS

K = constant

Construction

Construction

Shaded Pole

Shaded Pole

Shaded Pole

Shaded Pole

Shaded Pole

Reluctance Motor

• Low efficiency

• Low torque

• Constant Speed

• Fractional sizes

1Φ Synchronous Machine

Reluctance Motor

Same as: Split phase

or

Capacitor Start Motor

Stator

Reluctance Motor

Same as: Squirrel cage motor

Rotor

Uneven slots cut into laminations to form Salient poles

BUT, with

Uneven slots assist in starting

Rotor Slots generally ≠ Stator Slots

Reluctance MotorStarting

Motor becomes Synchronous

• As per induction motor with squirrel cage providing torque

• Centrifugal switch operating as per normal(75%)

• As motor is lightly loaded slip speed is small

• Rotor salient poles become magnetised and lock with RMF

Reluctance MotorIf rotor poles are a multiple of the stator poles

Motor will operate at sub-multiples of synchronous speed

Hysteresis MotorRotor

• Outer section made up of hardened steel

Hysteresis MotorRotor

• Outer section made up of hardened steel

• This outer section supported on the shaft by a NON-MAGNETIC “Arbour”

Hysteresis Motor• Rotor has a very high Hysteresis loss

• The rotor tends to become magnetised

• A synchronous motor is born

PROBLEMSynchronous motors have ZERO START TOURQUE!

A Shaded pole stator is used

Universal Motor

Not the same as a series DC Motor

Fields are laminated for AC current

Universal Motor

Universal Motor