3 situation of synchronous machine

Three ways operation of synchronous machine

 

1. One machine feeds one load

: If you change the prime mover, the machine goes faster or slower.

In other words, the frequency changes.

: If you change the excitation dc current on the rotor and magnetic field stronger or weaker, and that makes output voltage up and down.

 

2. Two machines feed a load in parallel

When two machines feeding a load they always share the load very firmly.

: If you change the prime mover, it changes the real power-sharing.

: If you change the excitation dc current on the rotor and magnetic field stronger or weaker, only reactive power changes.

 

 

* Between the two machines: P=E1E2sin(angle)/x

If E1 of machine 1 is bigger and E2 of machine 2, the power flow to machine 2.

Since the voltage is fixed for the machines, the angle is the one that can change power flow to each other.

If the angle is big (for example 89 degrees), the power flow will be big, and vice versa.

 

* From the load bus bar: P=E1E2cos(angle)/x

This means if the difference phase angle of two machines is small (for example 1 degree), the power is big, and vice versa.

 

 

3. One machine feeds a grid.

When a synchronous machine feeds a national grid, the machine can't change the voltage or frequency of the grid.

A national grid is called infinite bus because of the enormous.

NZ has a fairly small national grid around 7 to 9 GW but it is also an infinite bus.

No matter what you do to the prime mover or excitation which are only two ways that you can change, it won't change the terminal of the machine another word infinite bus bar.