Alternating Current Machines 6

Single phase induction motorsJenneson chpt 10.6 p 232

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Single phase motorsSplit phaseShaded poleCapacitor motorsUniversal motors

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Single phase motors usually have and external starting capacitor.Appliance motorTEFC motor on a resilent mount.

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www.angelfire.com/moStator winding for 1 phase cage motor.Separate start and run windings.

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www.emerson-ept.comSinglephase motor driving a gearbox.

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Cap start cap run motor

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Standard split phase motorwww.delviesplastics.comNo capacitor. These rely on inductance between the main and axillary (run/start) windings for the phase shift.

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Cap. Start motor driving a fan in a gas fired burner.CapacitorFan drumGas & burner controls.

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To obtain a starting torque there needs to be some angle between the fluxes. This is achieved by a physical (spacial) displacement plus an electrical angle caused by the phase shift due to the added inductance between the windings.

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These fluxes are NOT happening at the same instant in time due to the difference in inductance between the start and run windings.

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The start winding is normally made of finer wire and with fewer turns compared to the run winding. To increase the inductance of the run winding, the run winding is deeper in the core.The run winding has less resistance than the start winding. More current flows in the run winding.Most standard split phase motors have a centrifugal switch to remove the start winding from the circuit after it has run up to about 75% speed.

Not all motors have switches, some are designed to leave both windings in the circuit.

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The number of poles of the motor is the number of poles of the run winding.A 4 pole single phase motor has 4 run winding poles and 4 start winding poles. 120 f

pn =P 233

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Permanently Split capacitor motorJenneson p 237Both windings have the same R The phase shift is due to the C.

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Capacitor motors are the most popular type of single phase motor we find in industry.Cap. Start motors have high starting torque and good speed regulation.Cap. Start cap run motors have very high starting torque and very good running torque due to both windings being in circuit while the motor is running.Read carefully Jenneson p235 & 236 & 237.

This is important !!

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Universal motorhttp/csd.ijs.si

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BearingBrushCommutatorArmatureField coilMagnetic circuitSlot insulationUniversal motor

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Shaded pole motor from a washing machine driving the main pump.

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Series MotorThis motor is also known as a universal motor as it will run on both AC and DC.Read carefully Jenneson section 10.7The motor uses distinct field coils to produce the main fields and a wound armature which produces another field. The 2 fields interact to produce rotation. A commutator is used for switching the armature polarity (field).

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http;//img.aibabaShaded pole motor.

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Flux is growing Flux is decayingP 237 & 238

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A shaded pole motor has very poor starting torque and a large slip.P 238

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Check page 240 table 10.2 for a comparison of 1 phase motors.

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Power, torque and efficiency of 1 phase motors.P = V x I x pfP = 2 x x N x T / 601 HP = 746WEfficiency = power out / power in x 100

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