The continuous expansion of the interconnected power grid is an objective law for the development of the world power grid

Regarding some developments in the power grid, the issue had an exclusive interview with Zhang Yunzhou, dean of the State Grid Energy Research Institute:

The continuous expansion of the interconnected power grid is caused by objective laws

Reporter: What are the developments of power grids in major foreign countries and regions? What are the characteristics of China's power grid?

Zhang Yunzhou: Most power grids in developed countries and regions completed their rapid expansion in the 1980s. Among them, the Russian power grid is synchronized with the Eastern European, Central Asian, and Baltic countries, and is the world’s largest synchronous power grid. The North American interconnected power grid is the largest interconnected power grid in the world. After entering the 21st century, the rapid development of new energy has put forward new requirements for the optimal allocation of resources for large power grids. The interconnection of large power grids in developed countries and regions has also ushered in a new period of development. For example, U.S. experts estimate that in the next 20 years, the average length of construction of US transmission lines will reach 1,500-2,000 miles, an average increase of 50%-100% compared to the past decade.

Throughout history and reality, it is not difficult to find that the continuous expansion of the grid interconnection scale is an objective law for the development of the world power grid, and the interconnection of multinational power grids has become an important direction, which is driven by gaining greater economic, environmental, and social benefits. For example, the European power grid has been connected to the Eastern European power grids in Romania, Bulgaria, and other countries in the east; taking into account the rich oil and gas resources of the Mediterranean coastal countries, the South connects with the national grid of the Mediterranean Sea, including Morocco, Algeria, and Tunisia in the southern Mediterranean. The exchange of 400 kV submarine cable is linked to Turkey's 400 kV AC line.

In contrast, China's large-scale power grid interconnection started about 20 years later than that of developed countries. With the rapid development of social economy and continuous increase in power demand, the power grid is still in a period of rapid development. In order to meet the basic requirements of large-scale power transmission and efficient deployment, China needs to build a safe, reliable, cost-effective and powerful power grid. According to relevant plans, in the future, China’s power grid will form a nationwide interconnected power grid consisting of four synchronous grids (“Three China Power Grid”, Northeast China Power Grid, Northwest Power Grid, and China Southern Power Grid) that are connected asynchronously and connected to an integrated energy base based on UHV AC and DC. The main load center. At the same time, distributed energy systems and microgrids have also been rapidly developed, and the level of grid intelligence continues to increase.

The use of AC interconnection between power grids is the dominant method

Reporter: How are the grids of major countries and regions in the world interconnected?

Zhang Yunzhou: From an international point of view, the development of power grids in the United States, Europe, and Russia is based on exchanges, supplemented by direct-current power transmission technology, and a large-scale interconnected synchronous power grid with coordinated development of AC and DC has been constructed, which has achieved tremendous overall benefits.

Comprehensive analysis, in the absence of insurmountable geographical, political, technical barriers, exchange is often the dominant networking method. There are mainly three ways to use DC to interconnect: First, once the submarine cable exceeds 40 kilometers, due to technical restrictions can only use the DC mode, so the long-distance submarine cable must use DC networking; Second, the connection between adjacent power grids is weak, or because Operational regulations cannot be combined. To ensure the stable operation of the interconnection system, back-to-back interconnection should be adopted. For example, the western and eastern power grids in the United States are separated by the Rocky Mountains, and it is more reasonable to use back-to-back; third, the long-distance transmission over land uses direct current. This kind of project is a scenario with more application of DC technology and has obvious economic advantages.

Overall, it is common to use the highest AC voltage level connection between adjacent power grids. This is based on the results of a comprehensive demonstration of safety, technology, and economy. The continuous development of the synchronous power grid has ensured the development and utilization of large-capacity generating units, large hydropower, nuclear power, and renewable energy, reduced the system's reserve capacity, realized a large-scale optimized allocation of energy resources, and improved grid efficiency, safety, and reliability.

Adhere to the “Three Lines of Defense” of the Power Grid and Unified Planning, Unified Dispatch, and Unified Management

Reporter: What are the main causes of the major power grid accidents? Is the size of the synchronous grid related to the grid accident? What are the implications for the development of China's power grid?

Zhang Yunzhou: We analyzed the 140 international power outage accidents since 1965. North America is a frequent area for blackouts, and Brazil, India, and other developing countries have also experienced many blackouts. The reason is that, in addition to equipment failures and natural disasters are the main causes of power grid accidents, improper or inadequate technical measures such as system protection is the direct cause of the accident expansion.

At the same time, the “congenital deficiency” of the power grid structure is an important reason for the frequent occurrence of certain grid accidents. For example, the North American power grid spontaneously forms spontaneously by the states and regions, and lacks unified planning, causing voltage levels to be more confusing. The Brazilian power grid lacks a reasonable partition structure, and the receiving end main grid is not strong, and the voltage support capability is poor. Looking through the phenomenon to see the essence, many of the deep-seated reasons for blackouts are caused by the decentralized dispatch management system of the power grid and poor coordination and data sharing mechanisms.

The results of the analysis indicate that in the past 20 years, 22 major power outages (loss of load exceeds 5 million kilowatts) have occurred in the world, Brazil-Southeast-Central Western Power Grid, North India-East-Northeast-Western Grid, and East Japan Power Grid The power outages occurred in both the Nordic power grid and the Nordic power grid. The scale of these synchronous power grids is smaller than the scale of synchronous power grids in North China, Central China, East China, or South China. Geographically, Russia, which has the largest area of ​​synchronous grid coverage, has never experienced a blackout with a loss of more than 5 million kilowatts. Therefore, there is no inevitable link between the large-scale power grid accidents and the size and scope of the synchronous power grid.

There are two main experiences in the absence of blackouts in China for more than 30 years: First, we have established a reliable “three lines of defense” for power grids, and second, we have always insisted on unified planning, unified scheduling, and unified management of the grid. It can be seen from this that ensuring the safe operation of large power grids depends on whether the grid structure is reasonable, whether safety prevention and control measures are in place, and whether information sharing and efficient coordination mechanisms are established between different power grid dispatches. Looking into the future, China should accelerate the establishment of a comprehensive defense system for large power grids, give full play to the institutional advantages of unified planning, unified dispatch, and unified management of large power grids, and effectively ensure the safe and efficient operation of China's power grids.

In summary, the development of the interconnected power grid has made the development of the world's power grids inevitable.