The Dangers of a Load Too Small for a Diesel Power Generator
The generator starts up, and not long after, white smoke and oil are seen coming out of the exhaust. It is new, and tested, good quality diesel... I wonder what happened? This is the classic symptom of a diesel generator operating at a load far below its specification. And it's a more common mistake than you might think. When connecting a 100 kVA generator to power a load that consumes 10 kVA, it will not work “quietly” as one could deduce from a layman. On the contrary, she will be making a greater effort than if she were fully loaded. Why does it happen?
First, it is important to understand that generator sets are designed to run on load. This may sound trivial, but properly sizing and running a generator set is critical to engine availability and long life. Manufacturer's maintenance intervals and component life projections are based on statistical data from operations with proper workload.
Incorrect operation of the generator set can result in reduced power, component damage, reduced life and unscheduled downtime.
In general, diesel generator sets, standby and prime, are designed to operate between 50 and 85 percent load, while continuous diesel generator sets operate best between 70 and 100 percent load. Operating diesel generator sets at loads below 30 percent for extended periods can impact engine life. This is because it needs to reach a minimum temperature to function properly, which is not achieved with a load below the specified.
The most common consequence of underloading is exhaust manifold lubricant leakage, or carbonization, which is a black, oily liquid that can leak from the exhaust gaskets when the engine does not reach the minimum temperatures and pressures. Visible leaks in the engine do not necessarily indicate a problem, but they do signal possible underload, low ambient temperature or very low temperature of the cooling ducts. In addition, long periods of operation at lower loads can cause deposits of material behind the piston rings, on the spark plugs or inside the cylinders, which can lead to loss of power, poor performance, accelerated wear and in extreme cases, damage. to the cylinder lining.
But if in certain situations, it is absolutely necessary to operate with low loads, there are some procedures to minimize its impact, in particular a specific maintenance for this type of situation. After underloading, the generator sets must be run at higher loads (you can use a load bank, for example) to increase the pressure and temperature in the cylinders, which will clear the combustion chamber of deposits. Continuous operations at low loads require a more aggressive maintenance plan to reduce excessive component wear and may require engine modifications.
Power system underload impacts both individual components and overall performance, so it should not be overlooked. While the simple
solution is to run generator sets at loads according to design requirements, the truth is that system needs change at times. This makes
underloading common in the field of power generation — especially in standby applications. However, the effects of underloading can be
minimized with a meticulous operation and maintenance plan to preserve system health and avoid extra costs down the road.
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