Science and Technology Daily: How Power Grids Cope with Record-breaking Peak Load in 20

Influenced by the summer heat, China saw rapid increase in power generation since July. The latest data of State Grid shows that by midnight 26th July, daily power generation peak in China has reached 21.122 TW, breaking historic record for the 7th time. 20 provinces including Beijing, Shandong, Shanghai, Jiangsu, Anhui, Hunan, Liaoning and Xinjiang saw the power load of provincial grid reaching new highs. On 24th July, 2017, Jiangsu Grid became the first provincial grid of State Grid to realize a load dispatch of 100 GW. In the night of 24th July, the peak load of Jiangsu Grid increased to 102.18 GW, becoming the largest provincial grid in China in terms of power load.

A Provincial Grid with the Power Load of a Country

What does a power load of 100 GW mean? It means as a provincial Grid, Jiangsu Grid has a power load equivalent to that of a country.

As the world¡¯s fourth largest economy and the largest economy in Europe, Germany has the largest power consumption in the EU. However, the peak load of the German Grid is only 82 GW, far less than that of Jiangsu Grid. In addition, Jiangsu Grid has also surpassed the grid in South Korea and Australia in terms of power load.

To be more specifically, 100 GW of power load is equivalent to the power consumption of 130 million 1P air conditioners working at the same time, or lighting 1 billion 100W bulbs, or the power generation of 4.5 Three-Gorge Hydropower Stations operating at full load.

What kind of grid can support such a huge power load?

According to Mr. Wang Xu, Director of the Department of Development of State Grid Jiangsu Electric Power Company, Jiangsu Grid is the largest provincial grid in China in terms of load intensity and scale. Now, Jiangsu has built one AC and two DC UHV power transmission lines and upgraded the 500 KV grid network from four horizontal and four vertical lines to six vertical and five horizontal lines. The voltage-grading and district-dividing of 220 KV grids is also being constantly improved with 3,086 35KV converter stations and a power transmission line of 92,000 kilometers. As a provincial grid, the size of Jiangsu Grid has surpassed that of the Great Britain and France, equivalent to that of Germany.

Power Consumption by Air Conditioners Accounts for Half of the Total National Power Consumption

Similar to the Spring Festival and summer vocation travel rush, the summer peak load of grids also came every year as an ¡°unexpected¡± event. But this also means that there are certain laws to follow to cope with the situation.

Wang Yuling, Deputy Director of State Grid Power Dispatching and Control Center pointed out that summer represents ¡°the greatest challenge for State Grid staff¡±, because ¡°with huge demand for power, power transmission lines and transformers run at nearly full load next to their extreme status¡±, which is a big challenge for the safe operation of grids.

The second feature of the summer peak load is that the power consumption of cooling appliances represented by air conditioners keeps increasing. During peak hours, power consumption by air conditioners accounts for nearly half of the power load on urban grids, especially large grids. For example, Beijing grid reached the peak load of 22.54 GW in the noon of 13th July with the load of cooling appliances accounting for 52% of the total. Actually, in big cities, this phenomenon would last for more than ten days every year. The extremely hot and humid weather this year makes the challenge greater.

The influence of the power load of air conditioners on grid changes from time to time. When the heat wave comes, air conditioners would run at full load, causing rapid increase in power consumption in certain areas and then, with the coming of rain, power consumption by air conditioners would quickly fall down. This requires grid utilities to make quick adjustments in power supply according to the weather forecast. Of course, the adjustments should be made within a certain range.

Making Full Use of ¡°Geographical Differences¡±

It is interesting to note that the changes in power load also have distinct geographic features.

In State Grid¡¯s service area, the change in grid load usually has ¡°three peaks¡± and ¡°two valleys¡±. To be more specifically, apart from the nighttime valley load, there are two ¡°waist loads¡± (11:30-14:00 and 17:00-19:30) in between the three peak loads (9:30-11:30; 14:00-17:00 and 19:30-23:30). They are called waist loads as the load curve goes down a little bit but doesn¡¯t reach the bottom. However, it is different in Beijing as power load stays stable the whole day, especially that there is no obvious decrease in the noon. This is because Beijing relies on the development of the tertiary industry and a lot of people can¡¯t go back home at noon as the city is too big. But in many Southern cities like Chengdu and Changsha where people enjoy going out at night to entertain themselves after a whole day of work, the night peak load is obvious, while in industrial and commercial developed places like Shanghai and Zhejiang, the day peak load is more obvious. The hot weather this summer drives power load even higher.

Making adjustments according to these geographical features is an importantly way to fully unleash the potential of large grids and use regional and interprovincial power transmission channels to dispatch power resources.

According to meteorological authorities, the extreme hot weather will last until early August in East China and Central China with the peak temperature breaking historic records in some places. Against such background, Wang Yuling pointed out that currently inter-regional and interprovincial power transmission channels of State Grid are working at full load or overload. Fufeng, Jinsu and Binjin UHV DC projects for hydropower transmission from Southwest China are working at full load or overload. Channels for power transmission from West Inner Mongolia, Shanxi, Northwest China and Northeast China to Beijing, Tianjin, Hebei and Shandong are working at maximum capacity and regional grids of NorthChin and East China are basically working at full load. In response, State Grid will further strengthen load forecast and analysis and the control of the operation of major grids, keep a close eye on the changes of temperatures and continue to strengthen inter-regional and interprovincial power transmission to ensure stable power supply.

Source: Science and Technology Daily

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