[attachment=10839]
Synchronous generator
One of the most important types of electrical rotating machines is the synchronous generator, this machine is capable of converting mechanical energy into electricity when operated as a generator and power mechanics when operated as a motor.
Synchronous generators are used in the majority of hydroelectric and thermoelectric plants.
The name Sync is because of this machine to operate with a constant speed synchronized with the frequency of the alternating voltage applied to the terminals of the same.
Constituent parts of the Synchronous Generator
Rotor (Field)
Part of the spinning machine, consisting of a ferromagnetic material wrapped in a coil called the field winding, which is designed to produce a constant magnetic field as well as in the case of direct current generator to interact with the field produced by stator winding.
The voltage in this winding is continuous and the current supported by the winding is much smaller than the stator winding, the rotor also can contain two or more windings, where an even number and all connected in series with each winding will be responsible the production of one of the poles of the electromagnet.
Stator (armature)
Fixed part of the machine, mounted around the rotor so that it can rotate inside, also made of a ferromagnetic material wrapped in a set of coils distributed along its circumference. The stator windings are fed by a system of three-phase AC voltages.
For the stator runs all the electricity generated, and both the voltage and electric current is moving quite high in relation to the field (rotor), whose function is only to produce a magnetic field to excite the machine so it was possible to induce voltages at the terminals of the stator windings.
Compare, for example, a large generator in which circulating 18kV and 6556A against the stator 350V and 1464A rotor.
Working principle
Operating as a synchronous generator
When operating as a generator, mechanical energy is supplied to the machine by applying a torque and the rotation axis thereof, a source of mechanical energy can be, for example, a turbine, gas or steam. Once the generator being connected to the grid, its rotation is dictated by the frequency of the network, because the frequency of the phase voltage depends directly on the speed of the machine.
For the synchronous machine is able to effectively convert mechanical energy applied to its axis, it is necessary that the field winding located in the rotor of the machine is powered by a voltage source so that by rotating the magnetic field generated by the rotor poles can move on to the drivers of the stator windings.
Because of this relative motion between the magnetic field of rotor poles, the intensity of the magnetic field through the stator windings will vary over time, and so will the law of Faraday induction of strain on the terminals of the stator windings. Because the distribution and spatial arrangement of the set of stator windings, the voltages induced at its terminals will be three-phase alternating sinusoidal.
The electric current used to power the field is called the excitation current. When the generator is operating in isolation from an electrical system (ie, is an island of power), the excitement of the field will control the voltage generated. When the generator is connected to an electrical system that has several generators connected, the excitement of the field will control tHe reactive power generated.
Operating as a synchronous motor
When operating as a synchronous motor, the power is supplied to the machine by applying three-phase AC voltages at the terminals of the stator windings, in addition to the field windings of the rotor is fed by a voltage source.
Since the voltages applied to the stator windings are switched on and three-phase, will be circulated in the same alternating current of same frequency as the voltage, this current will produce alternating magnetic fields that also vary over time.
Furthermore, because the spatial arrangement of the stator windings, magnetic fields with time-varying will also move in the stator, so that the magnetic field will rotate around the circumference of the stator with angular velocity proportional to the frequency of the alternating voltage applied to the windings .
So when one of the poles of the magnetic field generated by the field winding of the rotor interact with the rotating field resulting from the stator, will attempt to align with the pole of opposite sign, and as the pole of the rotating stator field is rotating, the rotor will come a torque of forces that will generate a torque so that the rotor turns and keep the fields in the field winding of the rotor and the stator rotating field line.
With the rise of torque, the rotor will rotate following the direction and speed of the rotating field of the stator, so the angular velocity of the synchronous motor is synchronized with the frequency of the alternating voltage applied to the stator windings.