Functional characteristics of the generator

Working characteristics:
The main characteristics of synchronous generator performance are no-load characteristics and load operation characteristics. These characteristics are an important basis for users to choose generators.

No-load characteristics:

When the generator is not connected to the load, the armature current is zero, which is called no-load operation. At this time, the three-phase winding of the motor stator only has the no-load electromotive force E0 (three-phase symmetry) induced by the excitation current If, and its size increases with the increase of If. However, due to the magnetic circuit of the motor core saturation phenomenon, so the two are not proportional. The curve reflecting the relationship between the no-load electromotive force E0 and the excitation current If is called the no-load characteristic of the synchronous generator.

Armature reaction:

When the generator is connected to a symmetrical load, the three-phase current in the armature winding will generate another rotating magnetic field, called the armature reaction magnetic field. Its speed is exactly equal to the speed of the rotor, and the two rotate synchronously.

The armature reaction magnetic field and the rotor excitation magnetic field of the synchronous generator can be approximately considered to be distributed according to the sine law. The spatial phase difference between them depends on the time phase difference between the no-load electromotive force E0 and the armature current I. The armature reaction magnetic field is also related to the load situation. When the load of the generator is inductive, the armature reaction magnetic field plays a demagnetizing role, which will cause the voltage of the generator to decrease; when the load is capacitive, the armature reaction magnetic field plays a role of assisting the magnetic field, which will increase the output voltage of the generator. rise.

Load operating characteristics:

Mainly refers to the external characteristics and adjustment characteristics. The external characteristic is the relationship between the generator terminal voltage U and the load current I when the speed is rated and the excitation current and the load power factor are constant. The adjustment characteristic is the relationship between the excitation current If and the load current I when the speed and terminal voltage are rated and the load power factor is constant.

The voltage change rate of the synchronous generator is about 20-40%. General industrial and household loads require that the voltage remain essentially constant. For this reason, as the load current increases, the excitation current must be adjusted accordingly. Although the trend of the adjustment characteristics is the opposite of the external characteristics, it rises for inductive and purely resistive loads, and generally decreases under capacitive loads.