Common Diesel Generator Failures and Maintenance Suggestions

Diesel generators are widely used in locations where connection to the regular power grid is not possible. They are an essential power source for many critical facilities, especially during emergency power outages or as backup power. Therefore, regular protection, inspection, and maintenance of diesel generators are crucial. By understanding common causes of failure and the parts that may be damaged, we can detect and repair issues promptly to avoid serious breakdowns during operation, ensuring long-term stable performance.

Overheating Failures

Overheating is one of the most common failures in diesel generators. It can cause severe damage to various parts of the generator, shortening its lifespan. The main causes of overheating are:

Generator Overload: When the load on the generator exceeds its rated capacity, the current increases, causing internal heating. Prolonged overload operation exacerbates thermal damage to the generator.
Overspeed Operation: If the generator's speed exceeds its design limits, the system's temperature may rise, resulting in overheating.
Winding Insulation Breakdown: Damage to the generator's winding insulation can lead to current leakage, causing heat accumulation and further damage to the generator's performance.
Insufficient Bearing Lubrication: Poor lubrication of bearings increases friction, raising temperatures and eventually damaging both the bearings and the generator.
When a generator overheats, it not only affects its operation but also impacts the performance of the alternating current parts, decreasing the insulation of the windings and potentially leading to other failures. To prevent overheating, regular checks of the cooling system, ensuring sufficient lubrication, avoiding prolonged overload operation, and ensuring proper ventilation are essential preventive measures.

Fault Current

A fault current refers to an abnormally high current in an electrical system, usually caused by a low-impedance short circuit. If the generator's windings experience a short circuit, the fault current can cause overheating and damage to the windings. Fault currents can also lead to electrical fires and other severe consequences.
If a fault current occurs, especially in the case of a winding short circuit, the generator should be shut down immediately for inspection and repair. Regular checks of the electrical system's grounding, insulation, and short circuit protection equipment can effectively prevent such failures.

Motor Drive

Diesel generators typically rely on engines to provide power. However, in some special cases, when the engine cannot provide sufficient power, the generator may operate like an electric motor. In this scenario, the generator system is forced to provide active power to the engine to compensate for the power shortage. Although this motor drive may not immediately damage the generator, prolonged neglect could lead to engine overheating or other mechanical damage.
To avoid damage from motor drive, ensure the generator and engine are properly power-matched. Limiting switches or exhaust temperature detectors can be used to protect the engine if necessary. Additionally, regularly checking the engine's load and power output ensures it operates within the appropriate range.

Residual Magnetism Loss

Residual magnetism refers to the magnetic flux remaining in the circuit after the external magnetic field is removed. Diesel generators and engines often have residual magnetism, which is vital for starting and maintaining voltage. However, if a generator is not used for an extended period, the residual magnetism may dissipate due to aging of the excitation winding or improper connections, leading to the generator being unable to produce sufficient voltage, thus affecting startup and operation.
This issue typically occurs in generators that have been idle for a long time, especially when the excitation circuits or windings are problematic. To prevent the loss of residual magnetism, it is recommended to start the generator regularly and inspect the excitation system and windings for aging or damage.

Under-voltage Faults

Under-voltage faults are common issues in diesel generators, especially when the generator has not been used for an extended period or when there is an electrical fault. Under-voltage is typically caused by:

Blown Voltage Sensing Fuses: When the voltage exceeds safe limits, the fuse blows, preventing the voltage from being properly regulated.
Excitation Circuit Damage: Damage to the excitation circuit can prevent proper excitation of the generator, resulting in low voltage.
Long-Term Inactivity: If the generator is not used for a long period, the capacitor may fail to charge properly, leading to insufficient capacity and consequently low voltage.
To prevent under-voltage faults, the generator should be regularly activated and the electrical system checked to ensure that the voltage sensing and excitation circuits are in good working order. If the generator has been unused for a long time, the excitation system should be reactivated to prevent under-voltage due to uncharged capacitors.

Conclusion

Diesel generators provide critical power support for many key facilities, especially in areas without access to the regular power grid. However, due to prolonged use and environmental factors, various failures may occur, significantly affecting efficiency and safety. By understanding common failure types such as overheating, fault currents, motor drive issues, residual magnetism loss, and under-voltage faults, we can identify problems early and take effective repair measures to ensure the generator operates smoothly. Regular maintenance and timely inspections are vital to ensuring the reliability and longevity of diesel generators.