After all, each frame is a full bitmap image. The disadvantage is that you have to keep the animation pretty simple to keep the file size down. You then post the file and code the tag for the image, just as you would with an ordinary static GIF. With a shareware program, such as GIF construction set for Windows or GifBuilder for Macintosh, all you have to do is provide the individual bitmap images that make up the frames of your animation. For our simple little generator it will be the voltage at the terminals of the machine.Ī couple more important things to recall, the voltage drop across X (V x) will lead the current by 90°and V t and V x will add to give E g,so long as we remember that when we add AC stuff we have to use phasors.The main advantages of GIF animation are that it is incredibly simple to work with and it is automatically recognizable to most Web browsers. A single generator in a large system has little effect on the frequency and the voltage or the system. The terminal voltage V t is a voltage that is determined by the rest of the system. The resistance of the windings is small compared to the inductive reactance and can be ignored in a circuit designed to give one a feel for machine operation rather than a look into the minute detail. The inductive reactance X represents the impedance of the windings on the machine.
Increasing the load angle will advance the phase angle of E g. The phase of E g will be determined by the load angle. If the excitation current is increased E g will increase. The generated voltage E g is directly proportional to the strength of the magnetic field of the rotor. The generator represents a theoretical generator. It consists of a generator and inductor and a load with a voltage fixed across it by the system. And the rotor takes an extra revolution it will undergo severe mechanical stresses as the horrendous magnet force put torques on the shaft first trying to brake the machine and then trying to accelerate it. However, lets not forget the millions of Newtons force that the magnetic fields can produce. It will start to travel faster than the rotating magnetic field of the armature. If the power input to the machine pushes the rotor past the 90°position the retarding forces on the shaft start to decrease not increase. There is a limit to this phenomenon. If the load angle of the machine reaches 90°it has reached its maximum power output for the strength of the magnetic fields. Most large steam turbines in CANDU plants have the capability of motoring at least of a time period. Motoring is a condition that may or may not be allowed in a generator. The machine is driven as a synchronous motor. The magnetic fields will go out of alignment and a force will be generated to pull the rotor in the direction ofrotation. If the steam valves are closed to allow less energy in than that required overcoming the friction losses the rotor will tend to slow down. Increasing the steam flow increases the load angle and the power output of the machine increases. Increasing the field strength decreases the load angle but the load stays the same. In the operation of an individual synchronized machine there are two things that can be altered the governor valve and the rotor field strength, both affect the load angle.
The power output cannot change the steam flow into the machine determines the power alone.
If a three-phase supply is connected to three windings displacedaround the core of the generator, the winding will generate a rotating magnetic field. The second magnetic field is the one set up by the current flow in the three-phase stator winding. The magnitude is directly proportional to the field current (as long as we do not saturate the magnetic circuit). It is field that is constant in strength and rotates around the machine at the speed of rotation of the rotor. The first magnetic field is the one set up in the rotor by the excitation system. The same arguments hold for generators with more poles however, the pictures and words to describe the interactions get more complicated. One of the keys to understanding the strange behavior of the generator is develop a mental image of the magnetic field in the generator. Although there is only one magnetic field, for the most part we can consider it to be two and a lot of the behavior of the machine can be explained by the interaction of the two magnetic fields.įor simplicity a two-pole generator is considered. This technical article of the course will, hopefully, explain some of these phenomena. It has nowhere near the effect that changing the excitation would have on the machine when it is not synchronized or connected to the system. Reactive power flows are not supposed to be taking any energy and yet they change as the steam valves open and close.Ĭhanging the excitation on the generator will change the voltage at the terminals but just a little. Then there is the strange concept of reactive power.