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No-load Characteristics Of Generators
Sep 26, 2017

The generator has many forms, but its working principle is based on the law of electromagnetic induction and electromagnetic force. Therefore, the general principle of its construction is: using the appropriate magnetic conductivity and conductive materials to form each other electromagnetic induction magnetic circuit and circuits, in order to generate electromagnetic power, to achieve the purpose of energy conversion.

Generators are usually composed of stator, rotor, end cover, base and bearing and other components.

The stator is composed of a stator core, a coil winding, Generators and other structural parts fixing these parts.

The rotor is made of a rotor iron core (magnetic choke.) Slip ring, (also known as copper ring).

The stator and the rotor connection of the generator are assembled by the bearing and the end cover, so that the rotor can rotate in the stator, do the movement of the cutting magnetic field, thus generate the inductive potential, lead through the terminal terminals, and then generate the current in the loop.

The operation characteristics of the generator are five kinds, such as no-load characteristic, short-circuit characteristic, load characteristic, outer characteristic and adjustment characteristic. External characteristics and adjustment characteristics are the main operating characteristics, Generators according to these characteristics, can determine whether the operation of the generator is normal, in order to adjust in time to ensure high-quality and safe power generation. No-load characteristics, short-circuit characteristics and load characteristics are the characteristics of testing the basic performance of generators for measuring and calculating the basic parameters of generators.

No-load characteristic of generator

The so-called generator no-load operation refers to the generator operating at rated speed, the stator without load when the operation. At this time, the relationship between the no-load EMF EO and the excitation current IL is called no-load property. When the generator is in no-load operation state, Generators the terminal voltage U equals EMF eo, so the relation curve between the terminal voltage U and the excitation current is the no-load characteristic.

The no-load characteristic curve e0=f (I), when the short load characteristic test, should maintain the generator speed invariable, gradually increases the excitation current, until the end voltage equals the rated voltage 130%. In the process of increasing excitation current, reading the excitation current value and its corresponding end voltage value, we can get the ascending branch of the no-load characteristic. Generators Then reduce the excitation current, read the value according to the above method, then get the descending branch. Because of the average of the two curves, as shown by dashed lines in the figure. The no-load characteristic curve is a basic special curve of the generator. It can be used to calculate the voltage variation rate of generator and the parameters of the synchronous reactance of unsaturated.

Second, the short circuit characteristics of the generator

The short circuit characteristic of the generator refers to the relation curve between the steady current of the stator winding and the excitation current II when the stator winding is shorted at the rated speed.

The short-circuit characteristic curve measured by short-circuit test can not only be used to calculate the synchronous reactance and short-circuit ratio of the important parameter saturation of synchronous generator, Generators but it is commonly used in the power plant to judge the faults such as the short-circuit of the excitation windings. Obviously, the short circuit characteristic curve of the excitation winding is reduced because of the decrease of the number of turns.

Third, the external characteristics of generators

The so-called generator's exterior characteristic, is refers to the excitation current, the rotational speed, the power factor is the constant condition, changes the stator load current, the terminal voltage U curve, namely u=f (I) curve.

In the case of the hysteresis of the Power factor cos (θ), Generators when the stator current increases, the voltage drop is larger, because this time the armature reaction is demagnetization. In the case of Advanced Power factor [cos (-θ)], when the stator current increases, the voltage increases, which is due to the armature reaction is to help the magnetic. In cos (θ) = 1, the voltage drop is small. The external characteristic can be used to analyze the voltage fluctuation in the operation of the generator, Generators so as to put forward the requirement of adjusting range of the excitation device automatically.

Generator is divided into DC generators and alternator two kinds, as the name implies, the power generated by the alternator is in the form of alternating waves, and the $unit power supply of our household is the same as the alternating current (not necessarily the same frequency).