Load Forecasting of Central Urban Area Power Grid Based on Saturated Load Density Index

In the current society, coordination between urban power grid development and city development has become more and more prominent. Electricity saturated load forecasting plays an important role in the planning and development of power grids. Electricity saturated load forecasting is a new concept put forward by China in recent years in the field of grid planning. Urban saturation load forecast is different from the traditional load forecasting method for specific years, the time span of it often relatively large, and involves a wide range of aspects. This study takes a county in eastern Jiangxi as an example, this paper chooses a variety of load forecasting methods to carry on the recent load forecasting calculation to central urban area. At the same time, this paper uses load density index method to predict the Longterm load forecasting of electric saturation load of central urban area lasted until 2030. And further study shows the general distribution of the urban saturation load in space.


Introduction
Urban electricity saturation load is a new concept put forward by power load forecasting and power network planning in recent years.Power load forecasting is one of the important work of the power sector. Accurate load forecasting can reasonably arrange the start and stop of the generator set inside the grid, keep the safety and stability of the grid operation, reduce the unnecessary reserve capacity and arrange the unit maintenance Plan to protect the normal production and life of society, effectively reduce power generation costs, improve economic efficiency and social benefits.The power load density is closely related to per capita GDP, population density, land use nature and regional economic planning layout. The trend of power load density increases with the growth of social and economic indicators.But load density can not grow indefinitely, regional electricity demand will become saturated after full development.

Common methods of load forecasting
Commonly used power load forecasting methods are broadly divided into two categories: The first method starts from the predicted power and is converted to the electricity load,such as integrated electricity level method, single consumption method, growth rate method and power elastic coefficient method; another type of method predicts the electricity load directly, such as regression analysis, gray system method and load density method. To forecast electrical load in the Central Urban Area, we mainly use the growth rate method, the regression method, the gray method, the per capita electricity consumption method, the average load method for calculating and Load density method. At the same time, we check with the number of hours of using the maximum load.

Load Forecasting
In this study, we selected a county in Jiangxi Province as an example to load forecast, the county is located in the eastern part of Jiangxi Province, it has a good industrial base. In the 12th five-year plan period, the economic and social development achievements of the central urban area are very significant. So it needs to further increase the demand for power network construction. This load forecast is a recent load forecast for the central urban area from the future to 2020, and the long-term load forecast from the future to 2030.

Electricity forecast.
According to central urban area historical load development level，a variety of methods are calculated by programming, we selected five of these methods for analysis.At the same time,we made a horizontal comparison of the development trend of meeting the maximum load utilization hours. The five methods are the growth rate method, the regression method, the gray method, the per capita electricity consumption method and the elastic coefficient method. Year 2015 Year 2016 Year 2018 Year 2019 Year 2020  Unit: 100 million kWh We choose high, medium and low three programs as the electricity forecast alternative,and recommend the program as the final plan for this power forecast,we can see from the table below, to 2020,Dongxiang County, the whole society electricity consumption is 13.2789 billion kwh. Table 3 Year 2014 Year 2015 Year 2016 Year 2017 Year 2018 Year 2019 Year 2020 According to load history data,combining with electricity consumption forecast results,we choose the appropriate forecasting method is used to forecast the power load. The five methods are the growth rate method, the gray method, the average load method and the maximum load utilization method. After a comprehensive analysis, we recommend a basic forecasting scheme.  Year 2015 Year 2016 Year 2017 Year 2018 Year 2019 Year 2020 Gray method Growth rate method Average load method Maximum load typical day of this central urban area appears in the summer, summer temperatures are higher, residents living electricity consumption was affected by temperatures and increased. We combine the maximum load utilization hours in central urban area in recent years. Annual maximum load utilization hours of central urban area as shown in the table below.

Load density index method.
Load Forecasting in this central urban area determine the load density indicator by investigating the load density of some of the same land properties in the case of saturation, considering plots development timing and strength. We use the cell load density index method to predict, and compare with other regions of the domestic load density and analysis, verify the rationality of the forecast results.According to the basic data collected in this plan, we determine load classification of load distribution prediction take the planning department classification method which according to land properties.Finally, we determine divide planning area load and land properties into eight categories. We divide Public management and public service facilities into administrative office land, cultural facilities land, educational research sites, sports land, medical and health land and so on. According to city planning results,the demand for electricity is different for different land properties, and therefore must be divided into blocks for analysis. Year 2015 Year 2016 Year 2017 Year 2018 Year 2019 Year 2020 The whole society electricity consumption(Billion kWh) 6

Selection of Load Density Index
Through the study of load density indicators, referring to a large number of similar types of urban load density indicators,and according to central urban area regional development, finally, we get the central urban area load density indicators of various types of land. As shown in the following table.

Spatial load forecasting.
According to the selected results of the load density index for different types of land, combined with the actual situation of planning of planning area land, using the space load density index method, We get the load distribution prediction results of planning area land. Considering simultaneous rate of 0.85 331.0649 As can be seen from the table above, to target year, central urban area total load is 331.0649MW, the city area is 31.45km² , the load density is 10.53 MW / km² . Growth rate method is a more accurate way to predict long-term data, in this maximum load forecast of the whole society, we use the growth rate method. 331.0649 From the table can be seen, to the vision of the whole society, the maximum load of 483.4458MW, central urban area load of 331.0649MW.Combined with urban positioning and development planning of this central urban area, the electricity consumption of central urban area is mainly composed with residential electricity and industrial electricity, to the maximum annual use of the number of hours to consider the number of hours 5700h, the total electricity consumption of 27.5564 billion kWh.

Load forecast results
From the short-term forecast results, we can see that by 2020, the total electricity consumption of Dongxiang County is 1.327 billion kWh, the maximum load of the whole society is 227.09MW, and the average annual growth rate of the "13th Five-Year Plan" period is 15.17% and 12%.From the long-term forecast calculation results, by 2030, Dongxiang County, the total electricity consumption of 2.756 billion kWh, the whole society, the maximum load of 483.45MW, the average annual growth rate of 18.54% and 16.83%.

Conclusion and analysis
Combined with the results and process of the load forecasting in this study，it can be found that the growth rate method, the gray system method and the regression analysis method in the load forecasting method have the advantages of accurately reflecting the overall level of the urban electricity load, but the disadvantage of these methods is that it can not reflect the spatial distribution of the load. In the construction of power grids, in order to more accurately promote the grid substation distribution and power grid construction, the total load and load growth position is the amount that we must know. The load density method is based on the acquired basic data and the predicted path, and it is more accurate than other prediction methods,the load density method satisfies our demand for the total load and the spatial load distribution. Therefore, the load density method is the better algorithm in our research process.