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Why a single phase motor is not a self starting motor

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3 Answers

+1 vote
Because single phase motor don't get required flux to revolve. That's why an auxiliary winding is required to produce required flux. That means at first you need to make it a two phase motor. Once it starts to revolve you can remove the auxiliary winding.
0 votes
For any machine or rotating electrical equipment, we require atleast two fluxes so that they could interact. But as the motor bears only one phase, two fluxes are not possible. Thus in order to obtain a second flux to be cut, we introduce phase shift (usually through condensers) of 90 degree(ideal). This new flux thus obtained interacts with the actual flux and then the motor starts to rotate.

If we need we could keep the capacitor connected for pf improvement or else the auxiliary winding could be removed by using centrifugal switches.
0 votes

For a motor to self start,there should exist phase shift between windings but now in single phase motors, flux produced oscillates on the same axis.This means that when you introduce another winding there will be an alternating flux.There will exist a rotation in the fluxes that will cause rotation of the rotor.The whole process is achieved by introduction of capacitors or auxillary winding or other methods.

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