一．The capacity of generator set
The capacity that the user ultimately needs is calculated according to the long-term continuous operation output power of the unit to meet the maximum calculation load of the whole project. Among them, the type of load is usually the primary consideration for unit capacity selection. The load is generally divided into the linear load of resistive and inductive, and non-linear loads containing rectifier bridge circuits (also known as rectifier loads).
The characteristic of the resistive load is that the resistance remains basically unchanged, and the current decreases proportionally with the voltage. In application with such a load, the capacity of the generator set can be only slightly larger than the load power.
When the load is inductive (such as three-phase squirrel cage induction motor), there is a large current (which is 5-7 times that of normal operation) and the power factor is far below the normal operation value during starting. If to start directly, it requires that the rated power of unit has to be enlarged to give sufficient capacity to meet the start-up demands and results that the power need in normal operation will be far less than the rated power of the unit, which is obviously not economical. Therefore it is an awkward situation that if the capacity of the unit is selected smaller, it will not be able to drive the entire load or cause a sudden shutdown when starting the high-power load; if the unit capacity selection is too large, the investment and maintenance costs will be higher, which results in waste of resources. According to the characteristics of internal combustion engine, when it works at low load for a long time, it will cause problems such as serious carbon deposition in piston rings & spark plugs, worn cylinders, oil leakage and so on. In this case, decompression startup or frequency conversion startup are commonly used.
There are some disturbances such as impulse current, harmonic feedback and sudden change of current when starting a non-linear load, and often has high requirements for the unit's voltage drop. In this case, it is better to choose a generator with AREP or PMG.
二．The number of generator sets to be selected
The number of diesel generator sets in parallel use should be at least two units or more. Such configuration requirement is to ensure that the gensets can be used in turn in the maintenance and repair state, and to ensure the continuity of the power supply and adapt to changes in the load curve. This method also determines the need for parallel operation between generator set and generator set. In addition to Not only AOSIF's Power Station series can meet the total power requirements, but can determine the number of genset to be put into operation according to the change of the load so as to keep the diesel engine running under economic load to reduce the fuel consumption rate and reduce the power generation cost. The optimal economic operation state of diesel engine is between 75% and 90% of the rated power. For some places with high power supply requirements, a backup control system will be designed for each control system, and the backup control system and the main system have seamless switching function to ensure that the power generation system will not be cut off. Usually the system diagram is as follows:
Two unit parallel operation