The generator is mainly composed of stator, rotor, frame, thrust bearing and upper and lower guide bearings, air cooling system, brake and jacking system, fire extinguishing system, automation system and other components.
The basic principle of the generator is that the rotating magnetic field sweeps the winding and generates electromotive force in the winding to emit power. And the rotating magnetic field is generated by the excitation current through the rotor, Generators so the excitation is very important for the generator, for the general generator, no excitation can not send electricity, whether excitation is permanent magnet or electromagnetic.
Therefore, the generator excitation mainly has the following three roles:
1, to maintain the generator terminal voltage at the given value, when the generator load changes, by adjusting the strength of the magnetic field to constant machine terminal voltage.
2, the rational distribution of parallel operation between the reactive power unit.
3, to improve the stability of the power system, including static stability and transient stability and dynamic stability.
The operating characteristics of the generator include no-load characteristics, Generators short circuit characteristics, load characteristics, external characteristics and adjustment characteristics of five. Outer characteristics and adjustment characteristics are the main operating characteristics, according to these characteristics, Generators you can determine the normal operation of the generator in order to timely adjustment to ensure high-quality safe power generation. The no-load characteristic, short-circuit characteristic and load characteristic are the characteristics of the basic performance of the generator. It is used to measure and calculate the basic parameters of the generator
First, the generator no-load characteristics
The so-called generator no-load operation is the generator to run at rated speed, the stator without load when the operation. At this time, the relationship between the no-load potential Eo and the excitation current IL is called the no-load characteristic. When the generator is in the no-load operation state, Generators the terminal voltage U is equal to the potential Eo, therefore, the terminal voltage U and the excitation current curve is the no-load characteristic.
No load characteristic curve E0 = f (I), do no load test, should keep the generator speed unchanged, and gradually increase the excitation current, until the terminal voltage is equal to 130% of the rated voltage so far. In the process of increasing the excitation current, read the excitation current value and its corresponding terminal voltage value, we can get the no-load characteristics of the rising branch. Generators Then reduce the excitation current, according to the above method to read the value; then get the descending branch, as shown in Figure 2-1-2 (a) below. Generators Due to the average of the two curves, as indicated by the dotted line in the figure. The no-load characteristic curve is one of the most basic special curves of the generator. Can be used to make the generator voltage change rate, Generators unsaturated synchronous reactance and other parameters.
Second, the short-circuit characteristics of the generator
The so-called short-circuit characteristics of the generator, refers to the generator at rated speed, the stator winding short circuit, the stator winding steady current I and the excitation current Ii curve.
Short-circuit test measured short-circuit characteristic curve, not only can be used to obtain the important parameters of synchronous generator saturation synchronous reactance and short circuit ratio, in the power plant, Generators it is used to determine whether the excitation winding orifice short circuit fault. Obviously, there is a turn-to-turn short circuit in the field winding, and the short-circuit characteristic curve is reduced due to the decrease in ampere turns.
Third, the external characteristics of the generator
The so-called generator external characteristics, that is, excitation current, speed, power factor is constant under the conditions of changing the stator load current, the terminal voltage U curve, that is, U = f (I) curve.
In the case of lagged power factor cos (θ), Generators when the stator current increases, the voltage drop is large, because the armature reaction is demagnetized at this time. In the case of advanced power factor [cos (-θ)], when the stator current increases, the voltage rises, which is due to the armature reaction being magnetized. At cos (θ) = 1, the voltage drop is small. The external characteristics can be used to analyze the voltage fluctuation in the generator operation, and to propose the adjustment range of the automatic adjustment excitation device.
Generators are divided into two kinds of DC generators and alternators, as the name suggests, the alternator generated by the energy is generated in the form of AC waves, with our home 220V50Hz power supply, are alternating current (frequency is not necessarily the same) The