Why Frequency Is Unstable After Starting Cummins Generator

by Generator D. Diesel Generator

After the diesel generator generates electricity, the faults of unstable voltage and frequency are usually caused by unstable excitation current or low residual excitation voltage of the exciter. When the excitation current of the diesel power generator is unstable or the residual magnetic voltage of the exciter is low, the AC voltage produced by the cutting force line of the stator will be unstable and the frequency will fluctuate. What shall I do? Starlight manufacturer answers for you.

The reason for unstable frequency after starting diesel generator:

1.Air enters the fuel line of fuel supply system, which makes the speed of the diesel engine unstable.

2.Blockage in oil pipeline.

3.The uneven fuel supply of high-pressure oil pumps leads to different deflagration power of diesel fuel in combustion chamber.

4.Poor atomization of fuel injector in cylinder results in different deflagration power of diesel fuel in combustion chamber.

5.Damage of stable regulating components in AVR control board.

6.Contact part of each circuit has bad contact or short circuit fault.

The solutions for unstable frequency faults:

1.After starting the diesel engine, the speed is increased to observe whether the voltage and frequency are stable. With the increase of speed, the fluctuation range of voltage and frequency is larger, but the diesel engine has become stable and the smoke exhaust is light gray. This indicates that the diesel engine works normally and the fault may occur in the control box and exciter.

2.The exciter and related circuits are measured by multimeter, and abnormal results are found.

3.Adjust the stability of AVR control board, failures can not be solved.

4.After the diesel generator shuts down, the exciter is charged with 6V battery, and then the diesel engine is started until the speed reaches about 750r/min. The generator starts to build up voltage, and the fluctuation range of voltage and frequency meets the technical requirements of the generator set.

5.Start the diesel engine again after shutdown. Observe how the frequency and voltage of the generator react, and find that the frequency and voltage are unstable.

6.After shutdown, increase the starting speed of diesel engine (increase the fuel supply of governor) and restart the diesel engine until the speed reaches about 800 r/min. At this time, the frequency and voltage of the generator are stable. However, the frequency and voltage of the generator are unstable when the diesel engine is started by lowering the control handle. After several repetitions, it is concluded that the starting speed of the diesel engine of this diesel generator set must be 750-800 r/min before the generator can generate electricity and the range of voltage and frequency fluctuations meets the requirements.

Hope above information can help you to solve unstable frequency of diesel generating set.