The parallel connection of generator sets shall first meet the requirements of uniform power distribution. Uniform power distribution includes active power and reactive power. The so-called uniform distribution means that the active power and reactive power borne by each generator unit should be proportional to their rated power. There are clear requirements for power distribution of parallel operation generator sets in China. When the AC generator sets are operating in parallel.
When the load changes within 20%~100% of the total rated power, it shall be able to operate stably, and its power distribution error shall meet the following requirements:
(1) The difference between the actual active power borne by each generator unit and the calculated value distributed according to the rated power proportion shall not exceed+10% of the rated active power of the generator unit when the rated power of the generator unit is the same; When the rated power of the generator set is different, it shall not exceed 110% of the rated active power of the maximum generator set and+20% of the rated active power of the minimum generator set.
(2) The difference between the reactive power actually borne by each generator unit and the calculated value distributed according to the rated power proportion of the generator unit shall not exceed+10% of the rated reactive power of the maximum generator unit.
If there is a large imbalance in power distribution, both active power and reactive power will not only affect the efficiency and economy of unit operation, but also cause the failure of the whole power plant.
If the active power distribution of parallel generator units is seriously unbalanced, when the total load power is large, one generator unit is usually full load or overloaded, while the other generator unit is still under light load, so the capacity of the unit cannot be fully utilized to give play to the efficiency of the whole power station. The overload of the unit will not only bring harm to the diesel engine or generator set, but also cause the action of protective equipment, affecting the operation of the whole power station. On the contrary, when the total load power is very small, the imbalance of active power will often cause active circulation among generator sets, making some units turn to motor state, which is also not allowed for diesel engines. When the unit has reverse power protection, the reverse power phenomenon will cause reverse power trip, resulting in fault. For diesel electromechanical stations with frequent and large load changes, the above situations should be paid more attention.
The unbalance of reactive load can also be regarded as a circulating current between two generator sets, which sometimes exceeds the load current of generator sets, Produced in the generator set "It may cause additional losses. It may even overload the generator set. The overload current of reactive power will also trip the main switch of the generator set, causing a fault. In addition, the reactive current of the generator set is consistent with its excitation current. The imbalance of reactive current often occurs at the same time with the imbalance of excitation current, causing overload of the excitation system and even generating a fault, such as the rotor winding of the generator set being burnt, and the rectifier diode of the phase compound excitation device being damaged, The consequences of such failures are often quite serious. It can be seen that the uniform distribution of reactive load and active load has the same meaning. The factors and adjustment methods that affect the uniform load distribution will be discussed in detail in the future.
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