Generator Theory

Faraday Law
Any change in the magnetic environment of a coil of wire will cause a voltage (emf) to be "induced" in the coil. No matter how the change is produced, the voltage will be generated. The change could be produced by changing the magnetic field strength, moving a magnet toward or away from the coil, moving the coil into or out of the magnetic field, rotating the coil relative to the magnet, etc.




Faraday's law is a fundamental relationship which comes from Maxwell's equations. It serves as a succinct summary of the ways a voltage (or emf) may be generated by a changing magnetic environment. The induced emf in a coil is equal to the negative of the rate of change of magnetic flux times the number of turns in the coil. It involves the interaction of charge with magnetic field.

From http://hyperphysics.phy-astr.gsu.edu/hbase/electric/farlaw.html


































Lenz Law
When an emf (electromotive force) is generated by a change in magnetic flux according to Faraday's Law, the polarity of the induced emf is such that it produces a current whose magnetic field opposes the change which produces it. The induced magnetic field inside any loop of wire always acts to keep the magnetic flux in the loop constant. In the examples below, if the B field is increasing, the induced field acts in opposition to it. If it is decreasing, the induced field acts in the direction of the applied field to try to keep it constant.


















Coil and Magnetic
When a magnet is moved into a coil of wire, changing the magnetic field and magnetic flux through the coil, a voltage will be generated in the coil according to Faraday's Law.

In the animation picture at the top page show, when the magnet is moved into the coil the galvanometer deflects to the left in response to the increasing field. When the magnet is pulled back out, the galvanometer deflects to the right in response to the decreasing field.

The polarity of the induced emf is such that it produces a current whose magnetic field opposes the change that produces it. The induced magnetic field inside any loop of wire always acts to keep the magnetic flux in the loop constant. This inherent behavior of generated magnetic fields is summarized in Lenz's Law.


Generator 3 Phase



From http://anto-hendarto.blogspot.com/2011/04/turbine-blade-design.html we can found that the torque to rotating the generator which power produce 710MW is 730MW, where the equation Power is equal to torque multiply with the speed. Because in Indonesia electric frequency is 50Hz or 50 1/s so the Generator torque needed is 14.6 MJ.

P = torque x speed
730MW = torque x [3000 rpm 2phi/60s]
torque = 232 MJ

But there are 3 phase, R S and T so the torque should divided by 3 too, that is 77.3 MJ.

So how much magnetic field should be created to get 710MW electric generated (output current 18.5 kA; output voltage 22.0 kV; cos phi 1.73 and power factor 0,98) if the excitation data 374V and 4044A.






































If I have the generator with length 10 m and height 1 m, the calculation for the magnetic field strength B is E = B.v.l
22 kV = B 3000 rot/min 2phi/60s 0.5m 10m
B = 14 Weber/m^2

The magnetic field strength ang torque between stator and the rotor I think is same.

Rotor Side:
Torque = Coil Turns (N) . Current (I) . B . Area (A)
77.3 MJ = N . 4045A. 14W/m^2. 1m . 10m
N = 136 turns

Stator Side:
Torque = Coil Turns (N) . Current (I) . B . Area (A)
77.3 MJ = N . 18.5kA. 14W/m^2 . 1m . 10m
N = 29 turns.

Let's check it out....

Next http://idpowerstation.blogspot.com/2009/02/generator-auxiliary-system.html