Why is a 3 phase synchronous motors not self starting?

Answer 1

A single phase induction motor is not self starting; thus, it is necessary to provide a starting circuit and associated start windings to give the initial rotation in a single phase induction motor. The normal running windings within such a motor motor can cause the rotor to turn in either direction, so the starting circuit determines the operating direction.

Answer 2

Hi! As per the operating principle of the Synchronous motor, due to continuous & rapid rotation of stator poles,the rotor is subjected to a torque which is rapidly reversing i.e. in quick succession,the rotor is subjected to torque which tends to move it first in one direction & then in the opposite direction.Owing to its large inertia,the rotor cannot instataneously respond to such quickly-reversing torque,with the result that it remains stationary or in other words it is not self starting.

Answer 3

in single phase induction motor ,there is no self starting....initially torque is zero.

but you can make it self stating by adding extra winding known as starting or auxiliary winding

and spaced the two by 90 degrees due to this two currents will produced

the two currents will produce revolving flux what will make the induction motor self starting .

Answer 4

Induction motors turn due to two opposing fields, just like any motor. This is similar to two magnets put in close proximity. The magnets both generate a field, and will push or pull on each other depending on the closest polarity. In a three phase motor, there are three phases that can be used to create three distinct fields that push/pull on each other. A single phase induction motor requires an auxilliary winding that causing a phase shift to create the second field.

Answer 5

small high impedance Three phase synchronous motors are self starting.

large low impedance synchronous motors must go fro 0 to 3600 rpm in 1/60th of a second ... requires a great deal of power or something to limit the power until synchronous speed is achieved

Answer 6

Induction motors are not necessarily self-starting.

To be self-starting, there must be a rotating magnetic field. This can be provided by three-phase power, single-phase power with a capacitor phase shifted start winding, or a shaded-pole induction motor.

Once the motor is started, it can continue on single-phase power because the rotor is generating a magnetic field that is out-of-phase with respect to the winding relative to rotor position. The rotor actually contains a winding, although it is usually a one-turn winding. This is why induction motors are called induction, and it explains why they are not necessarily synchronized with the AC power source. (Their speed is a function of power, not phase.)

Answer 7

Induction generator is nothing but a induction motor(IM).When the slip of IM is negative, it's working as generator. 3-phase IM is seft starting dur to rotating magnetic field.But 1-phase IM is not self starting due to induced e.m.f in rotor coil is opposite to each other hence net torque is zero.

Answer 8

Without a special starting circuit a single phase induction motor builds up speed in whichever direction it is spun. To make it start in one direction it needs a starting winding fed by a capacitor to simulate a 2-phase rotating magnectic field to cause it to start one way. After it has started the capacitor can be disconnected.

Answer 9

Single-phase motors are all inherently not self-starting because the magnetic field pulsates intead of rotating. The motor will pick up speed in either direction depending on which way it is spun initally.

To overcome this problem a secondary winding is included in the motor which is fed by a capacitor from the supply, to give a phase shift and thereby create a small component of rotation in the magnetic field, to bias the motor to start in the required direction. Once it is up to speed the capacitor is no longer needed and can be switched out if necessary.

The pulsating magnetic field can be thought of as two fields rotating in opposite directions, and when the motor has reached its operating speed the field that is rotating with it - in the same direction as the rotor - controls the torque and power.

Answer 10

the induction motor is not self start in 3phase because it have a phase difference