The situation that diesel generator sets provide power to the city grid is called reverse power transmission. There are two serious consequences
1) If the power supply of the city network is not cut off, the power supply of the city network and the power supply of the self provided generator will generate asynchronous parallel operation, which will destroy the unit. If the capacity of the self provided generator is large, the city network will be shaken.
2) The city power grid has been cut off and is being inspected, and its self provided generator is back to power. The power supply inspection staff will be electrocuted. If the diesel generator set shutdown with load is an emergency shutdown, the impact on the unit is greater. Start up with load is illegal operation, which will cause damage to power generation equipment and electrical equipment.
When the diesel generator set is under high load, the exhaust will easily emit black smoke. At present, the natural process of black smoke is not completely clear. It is generally believed that when the diesel engine load is high, the fuel injected into the combustion chamber will increase, and the temperature in the combustion chamber will be higher. In addition, the diesel engine mixture will form uneven characteristics, which will cause the combustion of insufficient air in local areas of the combustion chamber, and the fuel will decompose and polymerize to form soot (carbon black) under the condition of high temperature and hypoxia. Soot is not pure carbon, but a polymer, the main component is carbon (more than 85%), but also contains a small amount of oxygen, hydrogen and ash, and its composition varies with the load of diesel engine. After collecting the soot through the filter and observing under the electron microscope, we can see that the diameter of the large soot particles is 0. About 05mm. High temperature cracking reaction in diesel engine is inevitable, especially in the space mixed combustion diesel engine, the high temperature gas surrounds the liquid oil droplets, resulting in the most favorable conditions for cracking reaction. The high-speed photography of combustion process confirmed that there will be a lot of black smoke around the top dead center, but in general, the soot can be found in the subsequent combustion Gas and complete combustion, so that no black smoke exhaust. However, if the air in the cylinder is insufficient and the mixing process is slow, then the negative cylinder temperature drops due to expansion, and the carbon cannot be burned and polymerized into soot. The formation of soot makes the combustion incomplete, the economy of diesel engine decreases, the exhaust temperature rises, the exhaust emits black smoke, the surface area of combustion chamber is carbon, and the load can not be further improved. Carbon deposit can also cause piston ring or piston stuck, valve seizure and other faults. Therefore, the diesel engine is not allowed to work under the condition of overload for a long time.
