Synchronous Generators

Synchronous Generators

Generators are the active elements in the network.

They are connected by a shaft to turbines - in any type of power plants - to have the same speed and the same torque.

Its speed must be constant and not to vary with load variation. It can be determined by the law:

W=(120 f / P) where:

W (r.p.m) : revolution per minute.

P (poles) : number of generator poles.

f (Hz) : frequency .

· Modeling of Synchronous Generator :

The model of synchronous generator is shown in the following figure:

where :

V_t : Terminal voltage.

d : Power angle (rotor angle)

Ra : Armature resistance.

Xs : Synchronous reactance 

Xa : Armature reactance

XL : Leakage reactance.

I_a : Armature current

Cos j : Power factor.

Noting that:

1 - X_s >> R_a , (X_s / R_a > 10)

2 - X_s = X_a + X_L

3 - Emf. is always constant (neglecting any change in I_f).

4 - In some times, (R_a) is neglected w.r.t (X_s).

● Mathematical model:

The mathematical model of synchronous generator is indicated in the following equation :

 

 - Where f is the angle between the voltage and the current (the power factor angle).

reference :
http://en.wikipedia.org/wiki/Synchronous_generator