2 3 Phase Induction Motor Principles At the end of this section you will be able to:List the characteristics of the magnetic fields produced by a 3Ø windingsCalculate the speed of rotation of a rotating magnetic fieldDescribe the basic principles of operation of an induction motorReverse the direction of rotation of a 3 phase induction motor
10 Rotating Magnetic Field Synchronous SpeedThe speed of the RMF is dependant on two factors:-minutesFrequency of the supplyNumber of poles in the statorsecondsThere are always a multiple of 2 poles (North & South) per phase
11 Rotating Magnetic Field Converts Seconds to minutesDivides the poles by 2Nsync = f= P=Synchronous Speed (RPM)Frequency of supplyNumber of poles per phase
12 Rotating Magnetic Field What happens if we increase the frequency of supply?NsyncWhat happens if we increase the number of poles?Nsync
18 Magnetic field cuts conductor Current is induced in conductorA force acts on conductorConductor moves
19 What happens if the conductor is the same speed as the RMF? SlipWhat happens if the conductor is the same speed as the RMF?
20 Magnetic field does not cut conductor No current is induced in conductorFriction slows conductorMagnetic field then cuts the conductor
21 DIFFERENCE between SYNCHRONOUS speed and ROTOR speed SlipSlip SpeedDIFFERENCE between SYNCHRONOUS speed and ROTOR speedNormally expressed as a percentages% =n=nsync=Slip in %Rotor speed (RPM)Synchronous Speed (RPM)