Question

A 3 phase 11 kv,25 mva, 60 Hz salient pole synchronous motor is running from a 11 Kv, 60 Hz balanced three phase supply the meachince reactances are Xd=1.2 pu and Xq=0.6 pu ,neglect the meachanicalloss and armature copper loss the maximum power input is obtained with no field excitation determine the power factor of motor

Answer 1

Ans:

Recall the equation of active power in salient pole syncronous motor.

Here,

is excitation emf.

is terminal voltage per phase.

is d-axis reactance.

is q-reactance.

is power angle.

It is given that field excitation is zero.

Power is maximum , therefore value of should be maximum.

i.e.

Now recall the equation of reactive power of a syncronous motor working at lagging power factor.

Put

  

  

   

Put

  

  

Let    is power factor angle.

power factor   lagging