The Function of the Voltage Regulator Panel (AVR Automatic Voltage Regulator) of Diesel Generator Sets (Practical Insights, Suitable for Beginners)

1. Core Voltage Regulation (Primary Function)

 

It collects the generator's output three-phase voltage for feedback and internally compares it with the standard rated voltage (commonly 400V three-phase, 230V single-phase):

 

1. If the voltage is too low → the AVR increases the excitation current, the rotor's magnetic field strengthens, and the output voltage rises;

 

2. If the voltage is too high → the AVR reduces the excitation current, the magnetic field weakens, and the voltage drops;

Regardless of no load, sudden load addition, or sudden load removal, it always keeps the voltage within the allowable range, preventing damage to lamps, motors, and control cabinets caused by voltage spikes or drops.

 

2. Excitation Start and Voltage Build-up

When the unit is first started and the speed has not yet reached the rated value, the residual magnetism is weak, and the generator itself cannot produce voltage. The voltage regulator panel has a self-excitation circuit that uses a small amount of residual magnetism or battery-assisted power to provide initial current to the excitation winding, allowing the generator to quickly reach the rated voltage.

 

Without an AVR or if the AVR is damaged, the unit will rotate but no voltage will be output.

 

3. Adapting to Load for Dynamic Voltage Regulation

When high-power equipment starts (motors, air compressors), there is a large instantaneous voltage drop. The AVR will instantly increase the excitation compensation voltage so that the voltage does not collapse immediately when the load is applied.

 

When a large load is removed, it prevents voltage from spiking and damaging electrical devices.

4. Supporting Protection Functions (Standard on Different AVR Models)

 

1. Low-Frequency Protection: When the unit speed is too low (insufficient frequency), excitation is limited to prevent equipment damage caused by low-voltage load;

2. Overvoltage Limitation: Suppresses the highest voltage during faults to prevent breakdown of the generator winding and downstream electrical equipment;

3. Soft Start Excitation: Gradually increases voltage during startup, avoiding instantaneous load impact.

 

5. Parallel/Grid Connection Function (AVR for Paralleling Use)

When multiple units operate in parallel, the AVR can adjust reactive power distribution, ensuring that the voltage of multiple units is consistent, preventing circulating currents and not competing for reactive power.

 

6. Distinguishing Between Brushless and Brushed Generator AVR

1. Brushless Generator AVR: Supplies power to the stator of the exciter, indirectly controlling the magnetic field of the main generator;

 

2. Brushed Generator AVR: Directly delivers excitation current to the rotor slip rings.

 

Typical Symptoms of AVR Damage

 

1. No voltage output at startup;

 

2. Normal voltage when unloaded, but voltage drops sharply when loaded;

 

3. Voltage fluctuates unpredictably and cannot stabilize;

 

4. Voltage remains excessively high, frequently burning out light bulbs and switches.