AC synchronous generator are the one of the major item in power generation industry. Using alternators AC power supply can generate under predetermine frequency. Another name for alternators are synchronous generator.In here we are plan to discuss main features of this ac synchronous machines.
Working Principal of AC Synchronous Generator
The theory behind the power generation using alternators are the electromagnetic induction.
To generate power in the coil should rotate with respect magnetic field or magnetic field should rotate with the respect to the coil.
Alternators the power is generate by the magnetic field rotate respect to the coil principal.
Windings of Synchronous Generator
Two main part of the alternator are armature coil and rotor coil. In here rotor produce rotating magnetic flux (rmf). Armature coils are stationary inside the alternator.
The rotating magnetic flux which connect with rotor are used to induce electricity in the armature coil.There are several type of rotors available in this synchronous generator .
Rotor coils of the alternators are excited with DC power supply and after providing DC power magnetic field is produce around it. According to the electrical action rotor made to rotate by prime mover.
This make the rotor flux to rotate along with it at the same speed. So revolving magnetic flux intersects with armature coils which connect to the rotor.
How EMF generate
This process will generate an alternating EMF across the winding. It can easily establish that the frequency of the induced electromagnetic field are connect Number of polar and speed of the rotor.
f = PN/120
So the frequency electricity produced is also synchronize with mechanical rotational speed.
Normally salient pole rotors have 10 to 20 number of poles which demands lower RPM. Salient pole rotor are work when the prime mover rotates at relatively lower RPM. Core of the pole in alternators are used to transfer magnetic flux effective way. This core is also made with fairly thick steel lamina. This insulate lamina the eddy current effect get low and so the losses of the motor get reduce.
In armature windings the stator core is use to enhance the magnetic flux transfer. Direct Current (DC) supply into the rotor of the alternator through pair of slip rings.DC current are supplied from external source or by using small DC generator which is fitted onto the same prime mover. These kind of alternators are call self excited generator.
With variation of the load the generator terminal output voltage will get very. So it’s also better to keep the terminal voltage in predetermine limit.
So the Automatic voltage regulator can use to keep the terminal voltage under specific limit.
Voltage regulations can be easily achieved by controlling the field current. When the terminal voltage of the alternator is below the specified limit, the AVR increased the field current , so the field strengthen.
The above phenomena will result the increase of the terminal voltage. When the terminal voltage is high the reverse is done. Hope that you have get some good understanding on AC synchronous generator.