On June 17, the Ejina wide area large grid with high penetrated renewable energy power system of Inner Mongolia Power Grid was formally formed when the 220 kV Tai'e line zero power flow was disconnected. The off grid system was connected to the main grid, on June 19 after 49 hours of safe and stable operation. This experiment fully verified that NR grid-forming energy storage technology can play the role of traditional synchronous generator voltage source support, and has the ability to build a 100% renewable energy regional power grid.
In the first phase of the test on May 26th, the Ejina regional power grid successfully conducted the first 100% renewable energy black start test in a wide area grid environment across three voltage levels of 110 kV, 35 kV, and 10 kV. During the black start process, 30 grid supported energy storage PCSs operated in parallel and stably, enduring harsh operating conditions such as single circuit 110 kV line energizing and 20 MVA main transformer energizing without load.
Ejina is a vast territory and a total area of 114,600 square kilometers. The power supply scope covers about 490 kilometers from east to west and 324 kilometers from north to south in Ejina. The total length of transmission lines in the region is 950 kilometers, and the largest load scale in history is 75 MW. The installed capacity of wind and solar power reaches 110MW. The regional power grid is only connected to the main grid through a 440 kilometer single circuit long chain 220 kV line, without conventional synchronous voltage source support. Once the 220 kV transmission line is repaired or trips due to faults, it will cause the entire regional power grid to lose power.
NR provided Ejina grid with the innovating grid-forming technology as the core, proposing an integrated solution for source, grid, load, and storage. It provides 30 sets of equipment with a total capacity of 25 MW/25 MWh grid-forming energy storage, stability control, coordination control, and energy management system, fully realizing the flexible and optimal control of regional grid source, grid, load, and storage integration.
The Ejina regional power grid has experienced a high proportion of 94.94% of renewable energy operation tests for 49 consecutive hours, with 100% of renewable energy and 100% of power electronic equipment operating for 22 consecutive hours. During this period, it also experienced severe tests such as 10 kV line grounding faults, large load bidirectional large range fluctuations with a range exceeding 30% of the total load power, and wind power high wind speed shutdown. The grid keeps continuous and stable, and the user's power supply is completely normal.
This experiment has proven the high feasibility of the integrated solution of source, grid, load, and storage based on grid-forming technology by NR. It can meet the requirements of adverse operating conditions such as bidirectional random fluctuations of renewable energy and load, high load power supply of renewable energy, extreme heat and no wind, and no light at night peak. It can achieve rapid recovery of frequency and voltage in transient situations and precise control of frequency and voltage in steady-state situations. At the same time, the strong adaptability of grid supported energy storage to multiple operating modes and complex operating conditions under wide coverage and large renewable energy startup conditions was verified.
The integrated solution of source, grid, load, and storage adopted in this project can be effectively promoted and applied to application scenarios such as 100% off grid operation of renewable energy, green power development and utilization of enterprise power grids, and load guarantee of terminal power grids. The core grid-forming technology, NR has already applied for energy storage, flexible DC transmission, and static synchronous condenser. These applications can better support the construction of multiple application scenarios such as 100% renewable energy with energy storage through ultra-high voltage DC transmission. The successful practice of this project provides an innovative model for the construction of a new type of power system.
NR will continue to focus on new demands and problems in the development of the power system, continue to carry out technological innovation, and contribute new ideas and solutions to the construction of the new generation power system.
