shobhit bansal

 Profile Answers by shobhit bansal Questions by shobhit bansal

• Apr 3rd, 2009

 

When we increase the mechanical load on the motor, it starts drawing more active power from the source and as the frequency is constant becoz usually appliances are connected with the infinite bus bar(constant voltage and frequency), speed of rotating magnetic field will not change so the speed of the motor will also remain synchronous.
Ns= 120*f/p

muralykrishna

 Profile Answers by muralykrishna 

• Jun 2nd, 2009

 

Synchronous machines cannot self start, it can start only by separate excitation for field windings (Rotor) , by using DC Supply/AC motor/Grid or DAMPER Winding on Poles.

R.K parvathaneni

 Profile Answers by R.K parvathaneni 

• Mar 29th, 2010

 

The main point for power generation in synchronous generator by saliency is
- only in sailent pole construction sine wave can be obtained.
- If we use cylindical pole construction we will get approximatly Trapezoidal wave as out put.

shatakshi

• Sep 2nd, 2011

 

Synchronous motors have damper windings in its poles. They provide additional torque (like in induction motors) whenever the speed falls below the synchronous speed. Thus even after loading, the speed is maintained constant.

amol khandagale

• Sep 6th, 2011

 

Synchronous machine running with syn. speed either load increase or decrease. because the magnetic locking take place in the machine

bittu123

 Profile Answers by bittu123 Questions by bittu123

• Nov 10th, 2011

 

Even if you increase the load on synchronous motor upto specified limit, SPEED will NEVER fall down(unlike dc or induction motor), while maintains synchronous speed.

BUT why???
It takes more current from supply as load gets increased by increasing its load angle, not by falling in speed(while dc motor takes more current by decreasing own speed).

Angle between -V and E is called load angle, say angle A(real notation for load angle is delta, but assume A, since no keyboard button for delta)

1. When rotor is moved by external agent for synchronising it, and achieved synchronous speed, at that time load angle is 0, means V is opposite to E.

2. When external agent is removed, still rotor is in synchronising mode. Small load angle can be seen. Now V and E is not in exact opposition. so, resulting emf can be seen, say Er and it will result in extracting Isy current from source.

So, motor is receiving active power=V.Isy.cos(angle bet V and Isy). This power is just enough to make motor running at syn speed in no load condition.

3. Let Load applied on motor, so load angle will increase again, resulting increase in Er and finally in Isy.
Now, active power extracted from source is increased as Isy gets increased.

In this way syn motor extract more current(result in more power) from source by increasing load angle not by decrasing speed and maintained sync speed at any load.

But, you can't increase the load beyond limit, since load angle is also having its stability limit

maverick

• Mar 28th, 2015

 

In synchronous machine speed always remains constant even when load on it changes.

For increased load motor develops increased torque because of rotor falling out of phase by large angle delta; which is angle bet axes of stator n rotor poles magnetically locked.

On no load sufficient torque is developed to overcome mechanical losses only.