low-voltage dc power supplies are low-voltage basic professional equipment for the normal and safe operation of power plants, substations and their protection facilities, as well as basic equipment for the normal and safe operation of national machinery, chemical, information and other industrial enterprises. in the tide of national reform and opening up, the low-voltage dc power supply system of china's electric power industry has undergone major innovations and development. a careful review and summary have a lot of inspiration.

in the 1980s and 1990s, the department of health and safety of the former ministry of electric power, while advancing the safe and civilized production of power plants and power supply enterprises to achieve the first-class work, listened to the opinions and suggestions of a group of scientific and technological experts. joint design team" organizes research, summary, and design to promote the innovation of dc power supply. after more than 20 years of persistent hard work by scientific and technological personnel from all parties, tracking the application of new technologies, several times of updating, optimizing design and testing, fundamentally innovating the functions of dc power equipment, forming a new series of standardized production, consolidation and improve the basic level of safe operation of the power industry, adapt to and promote the needs of intelligent development. for example, a simple manual operation device (commonly known as a knife switch fuse) that is commonly used in low-voltage dc systems (commonly known as a knife switch insurance) is designed to be updated to an intelligent computer-controlled, superior-performance dc power system; a magnetic amplifier with inferior technical parameters and phase-controlled rectifiers, design innovations as high-frequency switching rectifiers with high technical parameters (as shown in figure 1), and successfully independently developed dc air circuit breakers with protective characteristics; updated the design of highly polluting liquid lead-acid batteries to valve-controlled sealed lead-acid batteries and high-energy lithium batteries; the design of activating and discharging the battery pack with resistance wire is updated to a high-frequency active inverter (see figure 2), which can convert the chemical energy of the battery pack into electric energy as needed, and is safe reliably return to the power grid, and realize automatic meter reading and data storage during the discharge process (figure 3); the design of backward insulation monitoring is updated to high-precision microcomputer-controlled insulation monitoring (figure 4), support road positioning method, etc.; the previous backward method of detecting the terminal voltage of a single battery is designed and updated to a computer-controlled automatic scanning measurement of the battery and the entire group, and data storage (figure 5). this significantly improves the reliability of the new dc power supply system and the efficiency of operation and maintenance, laying a good foundation for the development of modern smart grids.

01 brief review of the innovative development of dc power supply devices in power systems as we all know, in the 1970s and 1980s, low-voltage dc control and operating power supply failures or accidents frequently occurred. from time to time, the switchgear of distribution substations (intermediate) was burnt, causing regional power outages; even low-voltage dc power supply systems caught fire and power failures. the protection voltage is lost, causing large equipment such as switch cabinets and transformers to burn out. at that time, the dc power supply facilities were very backward: the performance of components was extremely poor; the charger had low voltage stabilization accuracy and large ripple coefficient, unable to control the charging and floating charge currents, resulting in serious overcharge or undercharge; battery packs often had internal short circuits when one or two batteries fail, the entire battery pack will be quickly damaged; the electrical circuits of the charger are varied and there is no unified standard; the dc fuse and the control and protection switch are poorly matched, often skipping trips or abnormal fuse fusing, etc. . there are many problems, and there is a lack of professional and technical personnel or standardized management. in 1991, the "ministry of electric power dc power supply joint design group" was established to organize research and develop typical design and prototype development of cadmium-nickel dc screens. led by china electric power research institute, sichuan electric power research institute, beijing power supply bureau, heilongjiang electric power bureau, shanghai electric power bureau, qingdao electric power bureau, xuzhou electric power bureau, xuchang relay factory, xi'an electric power rectifier factory, beijing changhe electromechanical co., ltd., guangdong electric control equipment factory, sichuan electric appliance factory, beijing electrical appliance research institute, xinxiang donghai power distribution equipment factory, xuzhou electric power repair factory and other 15 units. in response to the problems raised by the operation department, the main components of the dc power supply, the technical indicators of the battery and the rectifier were redesigned and trial-produced. in 1992, a review meeting for the design of the dc power supply cabinet of the power system was held. 51 design, scientific research, operation, use, and manufacturing units participated and put forward the requirements of "five unification". in march 1993, it completed the prototype manufacturing and type test of the gzd dc power supply cabinet, and passed the product technical appraisal. subsequently, the general office of the ministry of electric power issued a document to transfer technology through longyuan electric company to promote the use of gzd dc power cabinets in the power grid. in 1994, the gzd series dc power supply cabinet was granted a utility model patent (patent number: zl93 2 23344.9). there are nearly 100 domestic enterprises manufacturing and producing, and thousands of sets of products are put into operation in the power system every year, bringing the dc power supply device of the power system to a new level. in 1995, the technical conditions and design plan of the gzdw microcomputer-controlled dc power supply cabinet were reviewed twice in shanghai and chengdu in 1995, and the automatic operation process curve chart was innovatively proposed, and the microcomputer monitoring device (figure 3) was developed and a series of the purpose of setting technical parameters is to meet the requirements of unattended. in 1998, the high-frequency switching rectifier was designed and developed. the gzdw type high-frequency switching dc power supply cabinet began to be popularized and used. this high-efficiency, small-sized, high-precision steady current and stable voltage and complete function of the high-frequency switching dc power supply cabinet has jumped into more advanced level. in 1999, a summary meeting of the gzd and gzdw joint design work was held in beihai, guangxi. the work of the dc power supply in the past 10 years was summarized and the gzd and gzdw series dc power cabinets were mainly undertook in the research, development, testing and promotion of the application. the unity and cooperation of the unit and the supporting component factory and the spirit of quality assurance. since then, the gzd and gzdw (see figure 6) series of dc power supply cabinets have entered the transformation of urban and rural power grids and have been included in the third batch of products from the state economic and trade commission. in 2000, a joint design group for rectifier and inverter devices for battery packs was established, and a technical committee for dc power supplies for power systems was established. it forms a closed cycle with design and development ® research ® type test ® product review ® promotion and application ® operation opinion return ® standard compilation and revision, etc., so that operation, design, research, development, testing, standards, etc. become integrated management. in 2004, the "rectification and inverter equipment for batteries in power plant substations" passed the power industry power equipment and instrument quality inspection and testing center in accordance with dl/t 857-2004 national industry standards for all type tests and trial operation. the federation of electric power enterprises invited experts from the national electric power system to conduct conference review and passed the product appraisal. at the same time, the newly developed high-frequency switch active inverter module, battery inspection instrument, ammeter and other supporting components have also passed the product appraisal. in 2005, the third generation of high-frequency switching rectifier and inverter dc power supply cabinets (gcfw (figure 7) and kcfw) began to be promoted and used. it fills the gap of active inverter activation battery pack in my country.

02 compile and revise low-voltage dc power supply standards following the guidance of national standards, a series of low-voltage dc power supply standards were drafted, reviewed, submitted for approval, published and distributed nationwide from 1991 to 2019. starting from the joint design of the gzd series of dc power supply cabinets, the corresponding power industry standards have also been produced. in 1991, the first dc power supply standard dl/t 459-1991 "technical conditions for ordering dc panels of cadmium nickel battery" was released; accompanied by dc power supply devices with continuous technological innovation and advancement, corresponding standards have been continuously compiled and revised. now there is a series of power industry standards in the low-voltage dc power supply system of china's power grid. series standards dl/t 637-2019 ordering technical conditions for valve-regulated sealed lead-acid batteries dl/t 459-2017 power system dc power supply cabinet ordering technical conditions dl/t 724-2000 technical specification for operation and maintenance of battery dc power supply device for power system dl/t 781-2001 high frequency switch rectifier module for power dl/t 856-2018 dc power supply monitoring device for power dl/t 857-2004 technical requirements for rectifier and inverter equipment for storage batteries in power plants and substations dl/t 1074-2019 dc and ac integrated uninterruptible power supply equipment for electric power dl/t 329-2010 dlt 860-based communication interface for low-voltage power supply equipment in substations dl/t 1392-2014 dc power supply system insulation monitoring device technical conditions dl/t 1397.1-2014 ~ dl/t 1397.6-2014 general technical requirements for test equipment for dc power supply systems part 1 to 6 dl/t 5044-2014 technical specification for design of dc system in power engineering these standards guide the technical management of my country’s dc power supply personnel and the specific work of on-site operation and maintenance personnel; guide the technical inspection of dc power supply manufacturers, promote the development of my country’s low-voltage dc power equipment production capacity, and also enable the power, petrochemical, and many industries, such as metallurgy and rail transit, have achieved great improvements in safe electricity technology. 03 contribution and inspiration through the technical link of the dc power supply joint design group of the ministry of electric power, we have implemented updated designs and innovatively developed generations of intelligent dc power supply equipment. at present, china has entered the low-voltage dc power supply equipment production capacity and technical level. the world's leading ranks, advanced intelligent low-voltage dc power supply complete sets of equipment have been widely used in the power grids of countries around the world (in the power grids or nuclear power plants of countries in asia, africa, latin america, the middle east, central asia, europe, the united states, and russia), china won glory and gained a good reputation. these achievements are attributed to the top-level design, guidance, coordination and support of the former ministry of electric power safety and health department, as well as to the vast number of low-voltage dc power supply researchers, operation and maintenance personnel and manufacturing companies. under the leadership of the team leader gu nihong, chief designer wang dianwei, yang zhongliang, zhao mengxin and other leading figures, the vast number of scientific and technical personnel in the joint design team have obtained shanghai kaihua power supply equipment co., ltd., zhuhai titan technology co., ltd., and beijing people’s electric factory co., ltd. and shenzhen inkerui technology co., ltd., shanghai aerospace power technology co., ltd. and shuangdeng group co., ltd. and other companies have provided high-quality prototypes for various stages, and have obtained abundant patents; passed a large number of tests, explorations and innovations on dc power supply equipment have enabled the low-voltage dc power supply system of china power grid to form a complete set of management models for product standards, design, testing, manufacturing, and operation and maintenance; making the development and manufacturing intelligent the complete set of high-frequency switching dc power supply equipment has been widely used in ac 10~1000kv substations, dc ±500~±800kv substations and foreign ancillary equipment; it has made a significant contribution to the upgrading of china's power grid low-voltage dc power supply system! review the development history of low-voltage dc power system innovation and make important contributions to the safe and reliable operation of my country’s power generation and power supply. during this period, the implementation of the unified organization of the competent functional departments and the integration of scientific research and manufacturing enterprises; technical directors’ guidance and development, design, and operation backbones combination: insist on combining research and development with unified standards and specifications. the three types of three-in-one spirit have played a major and fundamental role in guaranteeing, and are worthy of summarizing and remembering. we pay high tribute to the above-mentioned star companies and their leading figures for their contributions and their tireless spirit in the course of "three combinations"! we must inherit and carry forward the innovative spirit of "three combinations" and make greater contributions to the sustainable development of my country's power grid low-voltage dc power supply system! about the author wang chengyu, graduated from xi’an jiaotong university in 1993, phd, professor-level senior engineer, deputy chairman of the national high voltage switchgear standards committee, deputy chairman and secretary general of the power industry high voltage switchgear and dc power standards committee, has long been engaged in high voltage switches equipment research, operation and technical management.