The capacity estimation of diesel generator set is a very important and complicated problem. The capacity is too small to carry the full load or cause sudden shutdown when the high-power load is started. Large capacity, high investment and maintenance costs, resulting in economic waste. And according to the characteristics of the diesel engine, if it works for a long time under a small load, it will cause serious carbon accumulation in the piston ring, the nozzle, the cylinder wear and other adverse consequences of damaging the unit. Therefore, it is necessary to consider various factors in capacity estimation, including the usage environment, the type of load and the reserve margin.
(1) Use environment
Different working environment will affect the output power of the unit. The operating environment mainly includes ambient temperature, altitude, and relative humidity. When the ambient temperature and altitude are too high, the air density will decrease, and the oxygen supply required for combustion of the unit will be reduced during operation. The output power of the unit should be lowered accordingly. In other words, the power of the selected unit is higher than the absolute power of the load. The rated power of the diesel generator set is measured at full load operation in a standard state environment, that is, the intake temperature is 27℃, the altitude is 152.4m and the relative humidity is 60%. When the standard is exceeded, the calibration power will be discounted. See the specific discount calculation method in this chapter.
It is worth noting that the electronically controlled diesel engine uses the electronic injection control technology, through the electronic control unit installed on the generator on the intake manifold of the intake pressure, fuel temperature accurate measurement, control each injector injection timing and injection amount of fuel, so that the unit in the non-standard environment has a small power drop.
(2) Type of load
Different types of loads have very different requirements on the capacity of the generator set. The load types are generally divided into linear loads such as resistive and inductive loads and nonlinear loads including rectifier circuits (also known as rectified loads). Resistive load such as light bulbs, electric stoves, ovens, etc., inductive load such as air conditioning, machine tools, water pumps, etc., nonlinear load such as UPS, electronic computers, program-controlled switches, PLC equipment, etc. With resistive loads, the capacity of the generator set only needs to be slightly greater than the load power. However, in the case of charged inductive load and nonlinear load, capacity needs to be recalculated.