Selection of diesel generator capacity

a. Calculate the capacity of the generator set according to the stable load. The design shall take the larger value of power supply capacity of important load and emergency power supply capacity under fire-fighting state when the power supply is cut off. The calculation of fire emergency power supply capacity is controversial in the actual design. The author thinks that the capacity of generator set can be calculated according to the maximum fire-fighting state at a fire point, and the design of water supply and drainage and air conditioning professional fire-fighting is based on a fire point. The fire emergency power supply capacity can be calculated by referring to article 4.1.13 of code for design of electrical fire protection of civil buildings (DGJ 08-2048-2016): the normal power supply of all emergency lighting, fire elevator, fire pump, smoke exhaust fan and positive pressure fan of the two largest adjacent fire zones in the building shall be ensured in case of fire.

b. The capacity of generator set shall be calculated according to the starting demand of the largest single motor or group motor. In the actual design, if the capacity of a single motor is large, the fire-fighting equipment can be started by star delta or autotransformer, and the non fire-fighting important equipment can also be started by soft starter and frequency converter; the equipment with large starting current should be started in time to reduce the capacity of diesel oil generator set.

c. The capacity of generator set is calculated according to the allowable voltage drop of generator bus when starting the generator. In the actual design, the measures in B above can be used to reduce the capacity of diesel generator set.

d. When selecting the capacity of diesel generator set, the common power / standby power of the set shall be indicated. The common power refers to the maximum power continuously used by the generator set within 24 hours, while the standby power refers to that the generator set can be overloaded by 10% on the basis of the common power every 12 hours, for example, the common power / standby power is 1000 kW / 1100 kW. Generally, the power given by domestic units is the common power, while the power given by imported units is the standby power.

e. When selecting the capacity of diesel generator set, the difference of external air pressure (altitude), temperature and other conditions shall be considered, and the power of generator set shall be corrected.

f. When selecting the capacity of diesel generator set, the cost, voltage level, reliability of power supply and other factors of the set shall be considered comprehensively. The capacity of a single low-voltage diesel generator set shall not be more than 2000 kW, and multiple sets of diesel generator set shall be used for parallel operation, and the total capacity of parallel operation shall not be more than 4000 kVA.