Discussion on the selection of diesel generator sets for civil buildings (two)

2. capacity selection

The power unit capacity selection, calculation formula of the current state is no uniform, so the method adopted by designers in practical work is not the same, some simply press 10%-20% power transformer capacity; some by adding capacity of fire fighting equipment; others according to the wishes of investors, resulting in no self generating capacity choose the correct choice, if the capacity is too large resulting in a waste of investment, it is too small in the accident can not be used to meet the requirements. Then, how to choose the capacity of the own generator set? After consulting the materials and referring to various experiences and practices, the author sums up the following points:

(a) programme or preliminary design phase;

The capacity of the self-contained generator shall be calculated according to the 10%-20% of the total capacity of the power transformer.

(two) stage of construction drawings;

(1) according to the calculation load selection of generator capacity we know that the building of the electricity load can be divided into three categories: the first category is the security type load, which is to ensure the building of persons and equipment safe and reliable operation of the load, such as fire pumps, fire elevator, smoke control equipment, emergency lighting, communication equipment, computer major and related equipment; the second category is to protect the load, is to protect the basic equipment building load operation, the main work area is part of lighting, elevator, channel lighting; third is the general load, which in addition to the above load than the load, such as: air conditioning, water pumps and other general lighting and power equipment. Calculation of power generator capacity, the first load must be taken into account, second kinds of load according to the building function and the network circumstances, if the building functional requirements are higher or the power supply of city power grid is not stable, it should be second kinds of load into account, but if the first and second class load to select the sum of generator capacity then, the selected volume is too large, because the fire in the state, only to ensure the operation of fire fighting equipment, second kinds of load is not used; while in power grid, non fire condition, without the use of fire fighting equipment. Therefore, I think we can choose the larger of them as the capacity of the generating set.

The equipment capacity statistics, according to the actual situation to choose the coefficient Kx (normally 0.85-0.95), to calculate the capacity of Pj=KxP sigma, power generator set of the calculated P=kPj / ETA type:

P power of self generating set kw;

Pj computing capacity of load equipment kw;

P Sigma - total load kw;

ETA - generator parallel operation uneven coefficient is 0.9, single 1;

K - coefficient of reliability, usually 1.1.

(2) according to the biggest single motor or group of motor starting, calculate the generator capacity of P= (P -Pm) / ETA sigma PSI + PmKCcos m (KW)

Pm - the capacity of the motor or group motors with the largest starting capacity (kW);

The calculation efficiency of sigma total load, generally 0.85;

Cos m - the motor starting power factor is 0.4;

K - starting times of motors;

C - Y - C=l.0 full voltage starting, the starting C=0.67 autotransformer starting 50% tap tap C==0.42 C=0.25, 65%, 80% tap C=0.64.

(3) according to the starting motor bus allowable voltage drop calculation of generator capacity P=PnKCXd (1 / E-1) (kw)

Pn the capacity of a motor or group starting motor set that causes the maximum bus pressure drop (kw)

K - starting current multiples of an electric motor;

"Xd" - generator transient reactance, usually take 0.25;

Instantaneous voltage Delta E - bus allows the elevator down, take 0.20, no elevator to take 0.25. in the practical work, also available coefficient method to estimate the starting ability of diesel generator.