On May 20, 2017, the Chinese Society of Electrical Engineering held an appraisal meeting in Changzhou for the "High-voltage and Large-capacity Flexible DC Grid Key Equipment" completed by Nanjing NARI Relay Protection Electric Co., Ltd. and Changzhou Borui Electric Automation Equipment Co., Ltd. Secretary-General Xie Mingliang presided over the meeting. The appraisal committee consisted of nearly 60 experts, including 9 academicians, including Zhou Xiaoxin, Zheng Jianchao, Han Yingduo, Pan Yuan, Cheng Shijie, Li Lixuan, Wang Xifan, Chen Weijiang, and Luo An.
The appraisal committee appraised the key equipment of the high-voltage and large-capacity flexible DC transmission system in groups. Key equipment including high-voltage DC circuit breakers, high-voltage and large-capacity flexible DC converter valves, flexible DC grid control and protection systems, and high-voltage DC current and voltage high-speed measurement devices passed the appraisal and reached the international leading level as a whole, marking a new height of "cross-border cooperation" between power electronics technology and power system technology, paving the way for the realization of global high-voltage and large-capacity flexible DC transmission projects!
Energy transformation is a major trend in global energy development today. All countries in the world have made the development of renewable energy a key focus of promoting future energy transformation, and the proportion of renewable energy power generation in my country is increasing. Large-scale renewable energy grid connection requires the support of a strong power grid, and it is imperative to carry out core technology research and key equipment development of DC grids. NARI Relay Protection keenly grasps the trend of technological development and takes the lead in carrying out key technology research work on related complete sets of equipment.
High voltage DC circuit breaker:
NARI Relay Protection has innovatively proposed a bridge rectifier hybrid DC circuit breaker topology, mastered key technologies such as IGBT valve group high-current shutdown, mechanical switch ultra-high-speed disconnection, and high-potential energy supply, and successfully developed the world's first 535kV high-voltage DC circuit breaker, achieving a breaking current of up to 25kA, a breaking time of less than 3ms, and a reclosing function, with extremely fast and reliable disconnection to gain a wider stability margin for the entire power grid.
High-voltage and large-capacity flexible DC converter valve:
NARI Relay Protection has realized the ±535kV/3000MW converter valve and ±800kV/5000MW converter valve section for the first time. During the development process, it innovatively proposed a converter valve design scheme with partition shielding and multi-level separation. According to the characteristics of modular multi-level topology (MMC), a charging balancing and loss balancing control method with mixed arrangement of full-bridge and half-bridge sub-modules with different topology was proposed to achieve a win-win situation of converter valve reliability and economy. It proposed a coordinated control technology for multiple key equipment such as converter valves, bridge arm damping and DC circuit breakers, which can achieve fault crossing and rapid recovery without locking the converter valve, thereby improving system reliability and availability.
Flexible DC grid control and protection:
NARI relay protection continues to take advantage of its technology to achieve comprehensive coordinated control of multiple power electronic devices such as flexible direct current, UPFC, SVG, etc. in complex power grids. The upper-layer coordinated control and lower-layer slope control technologies are used to achieve high-power and voltage optimization control of DC power grids under multiple time scales; an ultra-high-speed detection method for DC line faults is proposed, which meets the dual requirements of protection rapidity and selectivity at a speed of 3ms; a fast failure and small disturbance reclosing scheme for DC circuit breakers is proposed to effectively reduce the impact on the system.
High-speed measurement of high-voltage DC current and voltage:
NARI Relay Protection has achieved ultra-high-speed response of DC measurement, and the overall performance has reached a new level. It has innovatively proposed patented demodulation technology to achieve 100kHz high-speed sampling, improving the response speed, measurement accuracy and dynamic range of DC optical current measurement devices; it has proposed a new shunt design, which improves the frequency response and anti-interference ability of the shunt, and improves the response speed and stability of the DC electronic current measurement device; it has proposed and implemented a new DC voltage divider winding process and low-power design, which effectively reduces the partial discharge and heating of the DC voltage divider, and improves the temperature stability and long-term operation reliability of the DC voltage divider.
From a global perspective, high-voltage and large-capacity flexible DC transmission technology has entered an accelerated channel. NARI Relay Protection has carried forward the innovative spirit of "perseverance and perseverance" and continues to lead the world in this field. In addition, NARI Relay Protection has spent several years upgrading and building a modern, intelligent high-end equipment production line, as well as the leading test conditions in China, and using a complete production test system to ensure the excellent quality of products.
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