The structure of large generators

The structure of large generators
In fact, the rotor is not a permanent magnet(ordinary magnet), to make it easier to obtain and can control the magnetic field strength, in fact, the rotor is the electromagnet.
Large generators are 3-phase alternator, and in order to increase power generation capacity, generatorsoutput voltage is usually a few thousand volts, and this according to P = UI can make the current drop to reduce the conductor loss.
The stator has three windings, respectively, placed in 120-degree angle, so that three windings of the two endpoints of one, tied together, is the neutral line (zero line) while the other three windings of the other endpoint line, compared to phase (FireWire)
And the rotor is usually 2-6 pole rotor, the rotor poles directly determines the power frequency, but the Chinese power is 50HZ, which cut 50 times per second the magnetic induction lines, or 3,000 times per minute, cutting said magnetic induction lines. At this time, if it is a unipolar (only one magnet rotor) would need 3000 rpm spin speed, then if you use 2 pole, only to switch to 1500. 6-pole only need to switch to 500 (the formula of 3000 rev / min ÷ poles = speed)
Each of these poles and, in fact, a winding, brush them through and by the ring (not a commutator, is a ring, let the power flow into the rotor to play but does not affect the operation of the function of the rotor) will send the stator out of the power of a small part, rectified to the rotor excitation. As long as the control excitation current, you can control the magnetic field strength, the control power voltage and current.
As the rotor even if no current flows through the coil, he also has a small amount of remanence (residual magnetism, which is a small amount of magnetic steel) and then just up and running, even if given a little bit of the stator electric voltage can also be slow to establish, then build current to operate the new unit or if it is a little residual magnetism did not, and can take an external power supply for excitation, so the voltage built up and then become self-excitation.
Large generators so power.
Laboratory generators, often used as a permanent magnet stators (ie, ordinary magnets), so that the rotor operation, the rotor conductors cut the magnetic induction lines and power generation, the electricity passed by the ring (ring generator is used by He has 2 of each winding ring, usually the laboratory on a winding, so to achieve power generation) of course, plenty of two windings, in order to get the DC you need to use a commutator. Otherwise, if the direct use by the ring, the electricity is alternating current.
Obviously, the efficiency of large units is certainly higher than the laboratory.
To put it simply, if your generator power of up to several megawatts (millions of watts) (now the large units are basically a few megawatts to hundreds of MW capacity) of capacity, so if you use the ring to be output power, this equipment will be heavily loaded, while good may be due to poor contact caused by the unstable voltage and current, while the spark is a loss, the reason why there are sparks, electrical energy is lost through heat loss.
Therefore, large-scale power generation mode of the stator unit, more economic, more stable, and the capacity to do much, and high stability, power generation more efficient. This unit is the current power plant, including small gasoline generator  (banks, Internet cafes that use) is.