When the generator set experiences abnormal voltage fluctuations during operation, the possible fault points include the following aspects:

1、 Internal factors of the generator

Excitation system malfunction

Short circuits or open circuits in the excitation winding can affect the magnetic field strength, resulting in voltage fluctuations. For example, if the insulation layer of the excitation winding is damaged, it may cause a short circuit in some windings. In this way, the path of the excitation current changes, and the magnetic field strength cannot be stably maintained, resulting in fluctuations in the output voltage of the generator.

The problem with the automatic voltage regulator (AVR) is also an important factor. The function of AVR is to automatically adjust the excitation current based on changes in the generator output voltage to maintain voltage stability. If the control circuit of AVR malfunctions, such as component damage, parameter drift, etc., it may not be able to adjust the excitation current correctly, resulting in voltage fluctuations.

Generator winding fault

A turn to turn short circuit in the stator winding or rotor winding can alter the electromagnetic characteristics of the motor. Taking the stator winding as an example, when a turn to turn short circuit occurs in a certain phase winding, the inductance and resistance of that phase winding change, and the symmetry of the three-phase output voltage is disrupted, resulting in voltage fluctuations. Moreover, as the degree of short circuit worsens, the amplitude of voltage fluctuations may increase.

2、 External load factors

Load mutation

When the load connected to the generator set suddenly increases or decreases significantly, the output voltage of the generator will be affected. For example, in a factory, if multiple large equipment are started simultaneously (with a sudden increase in load), the generator needs to provide a larger current. Due to the internal resistance of the generator, according to Ohm's law (where is terminal voltage, is electromotive force, is current, is internal resistance), when the current increases, the voltage drop across the internal resistance increases, and the terminal voltage will decrease, resulting in voltage fluctuations.

On the contrary, when a large number of loads suddenly stop working (load suddenly decreases), the output current of the generator instantly decreases, and the terminal voltage will increase due to the decrease in internal resistance voltage drop, which will also cause voltage fluctuations.

Load imbalance

If the three-phase load is severely unbalanced, such as in a three-phase four wire system, if one phase load is too heavy or too light, it will cause three-phase voltage asymmetry. This asymmetry will result in uneven current distribution in the three-phase windings of the generator, affecting the balance of the magnetic field and causing voltage fluctuations. Moreover, unbalanced loads may also lead to increased losses in the generator, further affecting voltage stability.

3、 Other factors

The speed of the prime mover is unstable

For generator sets with diesel engines, gasoline engines, etc. as prime movers, the unstable speed of the prime mover will affect the output voltage frequency and voltage amplitude of the generator. Because the output voltage of the generator is related to the speed and magnetic field strength (where is the induced electromotive force, is the frequency, is the number of winding turns, and is the magnetic flux). If the speed of the prime mover fluctuates rapidly, it will cause frequency and voltage fluctuations.

Transmission line issues

Poor contact, short circuit, or aging of transmission lines may also cause voltage fluctuations. For example, if the connection point of the line is loose, it will increase the contact resistance and generate a large voltage drop when the current passes through, resulting in a voltage drop from the generator output terminal to the load terminal, and this voltage drop may fluctuate with the change of current. A short circuit in the circuit can cause a sharp drop in voltage and may even damage the generator. Aging of power lines can cause changes in parameters such as resistance and capacitance, affecting the stability of power transmission and leading to voltage fluctuations.