AC Machines 6077 SA NUE 046
1 Phase Induction Motors At the end of this section you will be able to: 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
Types Squirrel Cage Wound Rotor Split phase Capacitor start Capacitor start Capacitor run Permanent split phase capacitor run Shaded Pole Wound Rotor Series universal Repulsion
Construction
Construction Run or Main Windings Start or Auxiliary Windings Low resistance High XL Set deeper in laminations to increase XL Start or Auxiliary Windings High resistance (thinner wire) Low XL (fewer turns) Set shallower in laminations to limit XL
Electrical Characteristics IRef IS Run Winding Large phase Angle due to high Inductance IR Start Winding Phase Angle less, as Inductance is less than run winding
Split Phase Motor Construction Switch opens ≈ 70 – 80% full load speed Low resistance High XL High resistance Low XL
Split Phase Motor Construction Low resistance High resistance
Split Phase Motor Capacitor Start Motor Construction
Electrical Characteristics Capacitor Start Torque = K IR IS sinα K = constant α = Angle between IR and IS IRef IS Split Phase IR
Construction
Construction
Shaded Pole
Shaded Pole
Shaded Pole
Shaded Pole
Shaded Pole
Reluctance Motor 1Φ Synchronous Machine Low efficiency Low torque Constant Speed Fractional sizes
Reluctance Motor Stator Same as: Split phase or Capacitor Start Motor
Reluctance Motor Rotor Same as: Squirrel cage motor BUT, with Uneven slots cut into laminations to form Salient poles Uneven slots assist in starting Rotor Slots generally ≠ Stator Slots
Reluctance Motor Starting 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 Motor becomes Synchronous
Reluctance Motor If rotor poles are a multiple of the stator poles Motor will operate at sub-multiples of synchronous speed
Hysteresis Motor Rotor Outer section made up of hardened steel
Hysteresis Motor Rotor Outer section made up of hardened steel This outer section supported on the shaft by a NON-MAGNETIC “Arbour”
Hysteresis Motor PROBLEM Rotor has a very high Hysteresis loss The rotor tends to become magnetised A synchronous motor is born PROBLEM Synchronous 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