Main characteristics of the generator

Working characteristics:

The main characteristics of the synchronous generator are the no-load characteristics and load operation characteristics. These characteristics are an important basis for users to choose a generator.

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 has only the no-load electromotive force E0 (three-phase symmetry) induced by the excitation current If, and its magnitude increases as the If increases. However, since the motor magnetic circuit core is saturated, 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 generates another rotating magnetic field, which is called the armature reaction magnetic field. The rotation speed is exactly equal to the rotation 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 approximated to be distributed in a sinusoidal manner. 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 condition. When the load of the generator is inductive, the armature reaction magnetic field demagnetizes, which will cause the voltage of the generator to decrease. When the load is capacitive, the armature reaction magnetic field acts as a magnetic flux, which will cause the output voltage of the generator. Raise.

Load operation characteristics:

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

The voltage change rate of the synchronous generator is about 20 to 40%. Both industrial and household loads require a constant voltage. For this reason, as the load current increases, the field current must be adjusted accordingly. Although the trend of the adjustment characteristics is opposite to the external characteristics, it is rising for inductive and purely resistive loads, and generally decreases under capacitive loads.