In recent years, with the continuous improvement of people's living standards and the rapid growth of housing construction, a large number of residential quarters have appeared, and with the increase of a large number of private enterprises, the selection of transformer capacity can not be only a few percent of the total load, so load forecasting is more important.
1 power load forecast of residential buildings
Demand coefficient method: according to people's living habits, the electrical equipment that may be used are: lamps 300W, stereos 600W, televisions 400W, refrigerators 200W, microwave ovens or rice cookers 1800W, water dispensers 100W, range hoods 200W, washing machines 200W, and water heaters1500 W. Residents in some big houses will also add air conditioners, televisions, or double bathrooms, which will greatly increase the electricity consumption. The maximum load of residents' electricity consumption appears in the summer of 19~22, when the electricity load is about 3800W, which is 45% of the capacity of electrical equipment, so the demand coefficient is 0.45. The calculation load of general residence is 3800W, and that of large residence is 9500W W. ..
Pjs = kXPS PJS- calculation load Ps-equipment capacity
Unit area method: According to the relevant provisions of the Electricity Law of People's Republic of China (PRC) and the Regulation on Electricity Supply and Consumption, the project of one meter per household should reach the goal of increasing the electricity consumption of residents to medium electrification within 30-50 years. The medium electrification level of residential electricity is based on the popularity of household appliances such as TV sets, washing machines, refrigerators and rice cookers. Considering that air conditioners or electric heaters enter residents' homes, the cookers are initially electrified, and the average daily electricity consumption level of each household reaches 7~20kwh. According to different levels of economic development and residential electricity consumption structure, the renovation of one meter for one household and indoor wiring should be ensured in the next 30-50 years, the power supply capacity should reach 4~ 10KW, and the minimum design standard for electricity consumption in residential areas should not be less than 50W/m2.
Pjs =ρ×sρ- Load density of building area, i.e. 50W/m2.
2 Selection of transformer
Simultaneous coefficient method: pjs = k∑kxps k∑- simultaneous coefficient.
Because the working hours of residents in residential quarters are different and the coefficient is small, it is generally 0.55 for less than 50 households, 0.45 for 50 ~ 100 households, 0.40 for 100 households and 0.35 for more than 200 households.
Because there is basically no reactive power compensation for residential electricity consumption, the load power factor is 0.7.
For example, there are 490 households in a residential area. What is the capacity of the transformer?
Using the demand coefficient method to calculate the community load is:
Pjs=KxPs=3.8×490= 1862KW
Use the unit area method to calculate the residential load, and each household is calculated at 5KW, then
Pjs=490×5=2 450KW
Because kx of 490 & gt200 households is 0.35.
Pjs=2450×0.35=857.5KW
sjs = Pjs/cosφ= 857.5/0.7 = 1 225 kva
According to the specification, the capacity of a single transformer in a residential area should not be greater than 630KVA, and two 630KVA transformers are acceptable.
3 private small factory transformer capacity selection
For a user's private small factory, the choice of transformer will be simpler. Electrical equipment is composed of some equipment with the same technological properties and similar demand coefficients, and is divided into several groups according to specific conditions. Because all electrical equipment works at the same time, but the maximum load of each electrical equipment group does not appear at the same time, it is included in a simultaneous coefficient K∑ when calculating the total load.
For example, a cotton processing factory has 1 1 fine sand machine, each 15, 10 carding machine, each with 3.5KW, three cleaning machines, each with 10KW, two dust collectors, each with 20KW, and four in parallel. 2 grit machines, each 13KW. 2 grooved drum machines, 5KW each. Slotting machine is used occasionally. Occasionally, balers and electric welding machines are used. Capacitor 10 group12kVA. Choose a transformer according to the above, first.
Load calculation, equipment grouping, consult the demand coefficient, power factor and tangent value of electrical equipment in the specification.
1 1 fine sand unit
Look-up table kx1= 0.75cosφ = 0.8tgφ = 0.75.
pjs 1 = kx 1ps 1 = 0.75× 1 1× 15 = 123.75 kva
qjs 1 = pjs 1tgφ= 123.75×0.75 = 92.8 kvar
Carding unit 10 units
Look-up table kx2 = 0.7cosφ = 0.8tgφ = 0.75.
pjs 2 = kx2ps 2 = 0.7× 10×3.5 = 24.5 kw
qjs 2 = pjs 2 TGφ= 24.5×0.75 = 18.38 kvar
Four drawing units
Look up table kx3 = 0.75cosφ = 0.5tgφ =1.73.
Pjs3=kx3Ps3=0.75×4×2.5=7.5KW
qjs 3 = pjs 3 TGφ= 7.5× 1.73 = 12.98 kvar
2 sets of coarse sand units
Look-up table kx4 = 0.6cosφ = 0.8tgφ = 0.75.
pjs 4 = kx4ps 4 = 0.6×2× 13 = 15.6 kw
qjs 4 = pjs 4 TGφ= 15.6×0.75 = 1 1.7 kvar
Three sets of cleaning units
Look up table kx5 = 0.15cosφ = 0.8tgφ = 0.75.
pj S5 = kx5ps 5 = 0. 15×3× 10 = 4.5 kw
qjs 5 = pjs 5 TGφ= 4.5×0.75 = 3.38 kvar
Two sets of dust removal devices
Look-up table kx6 = 0.15cosφ = 0.8tgφ = 0.75.
pjs 6 = kx6ps 6 = 0. 15×2×20 = 6KW
qjs 6 = pjs 6 TGφ= 6×0.75 = 4.5 kvar
Slotting machines, electric welding machines and baling machines rarely start, and they only start for half an hour, which can be ignored. Let k∑=0.9.
pjs = k∑kxi psi = 0.9×( 123.75+24.5+7.5+ 15.6+4.5+6)= 163。
67 kw
qjs = k∑Qjsi-Qc = 0.9×(92.8+ 18.38+ 12.98+ 1 1.7+3.38+4.5)
-120 = 9.37kVA.
Sjs = √ pjs2+qjs2 = √163.672+9.372 =163.94 KVA transformer can be selected.
4 conclusion
As can be seen from the above, the transformer selection in residential quarters is more complicated than that in small factories, and there are more factors to consider. Load calculation is an important basis for transformer selection. When selecting a transformer, firstly, the load should be collected and sorted, and the calculation method should be determined to make it conform to the actual situation on site, so as to avoid light load or overload operation of the transformer, which can make the user's transformer in an economic operation state and reduce the line loss of the power grid system.