DO PHYSICS ONLINE MOTORS AND GENERATORS AC MOTORS PRINCIPLE OF AN AC INDUCTION MOTOR AC induction motors - avoid problems with wear, electrical arcing (sparking) across split ring commutators of DC motors. AC induction motors - simple & rugged construction; low cost and minimum maintenance; high reliability; efficient; no extra starting motor. AC induction motors torque on wire loops on a rotating armature (rotor) due to – induced currents in an ac magnetic field produced in stationary coils (stator). Stator groups of coils together with a steel core form an electromagnet – Rotor most common type squirrel cage stacks of steel laminations with – – evenly spaced conductor bars around the circumference - induced current from alternating magnetic field produced by stator torque on rotor produces rotation – from induced currents in rotor interacting with magnetic field of stator. Figure (1) shows a schematic diagram of an ac induction motor which shows the operational principles but it is a long way from a practical motor. The stator (stationary electromagnet) is shown with its field windings at an instant when the current is increasing. This produces a magnetic field of increasing Ifield Bfield strength pointing towards the right (right hand screw rule). The changing magnetic flux through the coil of the rotor induces an emf in the coil. By Lenz’s law, the induced emf induces an induced current in the coil of the rotor in a Icoil direction to produce an induced magnetic field which points to the left Binduced (right hand screw rule to give current direction for from Icoil Binduced). Therefore, the magnetic force from the on the induced current in F Bfield Icoil the coil of the rotor produces a clockwise torque on the rotor. Fig. 1. Schematic diagram of an ac induction motor. Real practical ac induction motors are much more complex than shown in figure (1). An ac induction motor must achieve a rotating magnetic field to continue to exert a torque on the rotor (armature) coils. This is achieved by having extra coils for the stator to produce the rotating magnetic field Bfield.
DO PHYSICS ONLINE MOTORS AND GENERATORS AC MOTORS PRINCIPLE OF AN AC INDUCTION MOTOR AC induction motors - avoid problems with wear, electrical arcing (sparking) across split ring commutators of DC motors. AC induction motors - simple & rugged construction; low cost and minimum maintenance; high reliability; efficient; no extra starting motor. AC induction motors – torque on wire loops on a rotating armature (rotor) due to induced currents in an ac magnetic field produced in stationary coils (stator). Stator – groups of coils together with a steel core form an electromagnet Rotor – most common type squirrel cage – stacks of steel laminations with evenly spaced conductor bars around the circumference - induced current from alternating magnetic field produced by stator – torque on rotor produces rotation from induced currents in rotor interacting with magnetic field of stator. Figure (1) shows a schematic diagram of an ac induction motor which shows the operational principles but it is a long way from a practical motor. The stator (stationary electromagnet) is shown with its field windings at an instant when the current Ifield is increasing. This produces a magnetic field Bfield of increasing strength pointing towards the right (right hand screw rule). The changing magnetic flux through the coil of the rotor induces an emf in the coil. By Lenz’s law, the induced emf induces an induced current Icoil in the coil of the rotor in a direction to produce an induced magnetic field Binduced which points to the left (right hand screw rule to give current direction for Icoil from Binduced). Therefore, the magnetic force F from the Bfield on the induced current Icoil in the coil of the rotor produces a clockwise torque on the rotor. Fig. 1. Schematic diagram of an ac induction motor. Real practical ac induction motors are much more complex than shown in figure (1). An ac induction motor must achieve a rotating magnetic field to continue to exert a torque on the rotor (armature) coils. This is achieved by having extra coils for the stator to produce the rotating magnetic field Bfield.
t6_acmotors.docx