Answer / glenn20sal

IN INDUCTION MOTOR LOAD HAS EFFECT ON SPEED
HENCE IF LOAD INCREASES SPEED DECREASE
BUT IN SYNCRONOUS MOTOR THE ROTOR NS=NR
THUS IF LOAD INCREASE ROTOR FALL BACK BY CERTAIN ANGLE
W.R.T STATOR FIELD
IF LOAD IS STILL INCREASED THERE WILL BE A POINT WHERE THE
MAGNETIC LOCK BETWEEN STATOR AND ROTOR WILL BE BROKEN AND
THE ROTOR WILL BE OUT OF SYCRONISM AND ULTIMATELY STOP

Answer / bhavin

simple yaar, in i.m. speed is inversely proportional to
load , and in synchronous motor speed is always constant u
cant change it ,if want to do that motor will be trip.

Answer / mayank sharma

induction motor is singly excited,the rotor's field is due
to trasformar induction action,hence eith increase load the
torque generated due to lenge current decreases.on the
other hand synchronous motor is doubly excited and works on
the interlocking of stator and rotor generated poles..the
synchronous matchine can only work on its synchronous speep
else it will not run.

Answer / manas ghosh

To produce a stable torque relative speed between rotor and stator field should be zero.
In sync. motor rotor is dc excited and the field itself doesn't rotate and stator is ac excited and stator field always rotate at Ns. So, to make the relative speed between rotor and stator zero the rotor should always physical rotate at Ns.
In IM to at any speed relative speed between stator and rotor is always zero. When load increase means torque should increase which means rotor current should increase and for that rotor induced emf should also increase. Now rotor induced emf is directly proportional to slip(s) (considering fixed input voltage). So, to increase torque in IM slip(s) should increase which means physical rotational speed of rotor should decrease.

Answer / apeksha tarle

we all know that “Like poles repel each other". So, the North Pole in the stator repels the north pole of the rotor. Also the south pole of the stator repels the south of the rotor. This makes the rotor to rotate in anti-clockwise direction thus, half a period later, the stator poles interchange themselves, thus making them get aligned with “unlike poles" which attracts each other. I.e. the South Pole of the stator & the North Pole of the rotor gets attracted and get magnetically interlocked.
At this position the poles Ns attracts S and poles Ss attracts N. These opposite unlike poles of the rotor & stator start rotating in the same direction as the stator poles. This makes the rotor to rotate unidirectional and at a synchronous speed which is the same speed of rotation of the stator poles. Thus as the position of the stator poles keep changing with a rapid speed and reversal, the rotor poles also rotate and reverse as same as the stator thus causing the rotor to rotate at a constant

Recently we had experienced following problem All RCCB breakers (connected to the load as well as spares) connected to various UPS systems at various floors at a high rise building tripped during a power break down and upon starting up of generator.This Generator is recently inducted into the installation. Can any one explain the reason behind this tripping. Regards Viswanathan

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