The leaders of the State Council has paid much attention to, cared about and supported the development and localization of DC transmission technology in China and Xi'an DC Transmission Base.
From the 1980’s, the state has confirmed China XD Group as the base of scientific research, manufacture and test of DC transmission equipment in China; has supported it in policies and funding. As early as Gezhouba — Shanghai DC Transmission Project, China XD Group imported the design and manufacture technologies, including DC system research, design of complete system, and DC control and protection, through the means of combination of technology and trade. He Guangyuan, the former minister of Ministry of Machine Building, has pointed out in the letter to Premier Li Peng, named “The views of developing DC transmission technologies in China ”in 1994, that “Construction of Xi'an DC Transmission Base must be strengthened for the purpose of realizing localization of DC transmission equipments ”. Premier Li Peng instructed definitely: agree, support. Zou Jiahua, the former vice premier, instructed: the supporting project shall be confirmed firstly. A power transmission line shall be confirmed by applying The Three Gorges Project or power grid planning. The Planning Commission shall discuss this with Ministry of Electricity and Ministry of Machinery and offer report of specific suggestions. Next, discuss the support in work and finance for foreign cooperation, domestic development and localization on the basis of the line. This is a powerful support for construction of Xi'an DC Transmission Base.
The former State Bureau of Machine Building and State Power Corporation submitted a report to Three Gorges Project Construction Commission of the State Council together in 1998. The report named Letter with respect to suggestions of importing manufacture technologies and cooperative production of equipments in the bidding of Three Gorges – Changzhou ?500kv DC Transmission Project（hereinafter referred to as “the Suggestions”）. The Suggestions pointed out that:
According to the indicative spirit of leaders of the State Council with regard to importing the technologies during construction of the first Three Gorges Project and realizing localization of the second Three Gorges Project, when the international purchase of DC transmission equipment of Three Gorges – Changzhou Project is made, meanwhile, the key technologies of DC equipments shall be imported and some equipments shall be manufactured at home by the means of cooperative manufacture through technology introduction to promote localization of DC equipment. Therefore, the imported key technology for DC equipment manufacture is an important component of bid invitation and negotiation tendering of DC equipment of The Three Gorges Project. It put forward on the basis of drawing the past experience and lessons that: The principal of market economic must be followed and attention must be paid to market, benefit and development prospect during the process of import of foreign talents. At the same time, the Suggestions put forward confirmations in three aspects: to confirm the responsibility unit of recipient for technology introduction; to confirm the contents of technology introduction; to confirm the funds needed and its sources.
The objectives of technology introduction confirmed in the Suggestions: providing conditions for trial run of products made by domestic enterprises with the transferred technologies through import of several key technologies of DC equipments at the left side of The Three Gorges （Three Gorges – Changzhou Project）; the objective is that to build the second DC transmission project by using the domestic technologies without importing technology for the second time.
It put forward in the suggestions that: the technology introduction is composed of two parts: system design and manufacture of equipments. The Ministry of Electricity is in charge of introduction of DC system design; the Manufacturing Department is in charge of technology introduction of manufacture of DC equipments.
The suggestions confirmed that the key equipments and components to be introduced are: converter transformer, oil-immersed smoothing reactor, converter valve and components of thyristor. It put forward in the suggestions that the recipients of imported technologies of these key equipments and components are:
（1）Converter transformer: the recipients of technologies are Shenyang Shenbian Transformer Co., Ltd. and XD Transformer Co., Ltd.
（2）Converter valve: the recipient of technologies is Xi'an Power Rectifier Factory.
（3）Components of thyristor: the recipient of technologies is Xi'an Power And Electronic Technology Research Institute.
（4）Oil-immersed smoothing reactor: the recipient of technologies is Xi'an Transformer Factory.
The Suggestions was approved by Three Gorges Project Construction Commission of the State Council at the same day, and was reported to Wu Bangguo, the vice premier, and Zhu Rongji, the prime minister, by Three Gorges Project Construction Commission of the State Council.
The work of combination of technology and trade, and of technology introduction of equipments of converter station of Three Gorges – Changzhou ?500kv DC Transmission Project began from that day.
In order to achieving better achievements from this technology introduction, China XD Group, as one of the recipients of technologies, has made a lot of preparation work carefully in the aspects of technology, organization, personnel and documents, etc.
China XD Group started preparation work very early, implemented the organization measures and documents down-to-earth for the technology introduction. The Group contacted with ABB Corporation, Siemens Corporation and Alstom Corporation one year earlier the bid invitation on the basis of summing up work experience of technology introduction from Gezhouba — Shanghai DC Project, made several technical exchanges with the three corporations and visited the corporations on-the-spot, therefore, deeply understood the state of the art, product level and production capacity of the three corporations. These founded solid technical basis for negotiation of technology introduction. The Group has organized staff to draw up documents both in English and in Chinese to be used for negotiation of technology introduction, such as the equipment that needs imported technology, which cost near two months, and this founded solid document basis for negotiation of technology introduction.
XD DC Transmission Base has already begun to take shape through technical innovation, tackling key problems in science and technology, and practice of ten DC Projects in over 20 years. China XD Group has the ability of designing, manufacturing, and supplying converter transformer, smoothing reactor and thyristor valve used in ?500kv HVDC transmission projects; has two ways for transporting converter transformer and smoothing reactor by rail and by road. It can undertake independently the system research and design of complete set of equipments used in converter station of ?100kv and below HVDC transmission project; can take part in or undertake the system research and design of complete set of equipments used in converter station of ?500kv HVDC transmission project. It is in the leading position in these designs, and has got consent from the official departments, such as National Development and Reform Commission, office of Three Gorges Project Construction Commission of the State Council, and the consent from enterprises of the same profession, such as State Grid Corporation and China Southern Power Grid Company.
Xi'an High Voltage Apparatus Research Institute built a high-voltage DC generator that is needed for research of ?500kv DC transmission project at the end of 1960’s and the beginning of 1970’s, and developed research on high voltage DC technology.
A Back-to-Back converter test station, 8.5kv, 200a, capacity l.7mw, was built in Xi'an High Voltage Apparatus Research Institute in 1974. Matching 6-pulse converters are used on the side of rectifier and on the side of inverter respectively; there are 12 thyristor valves totally, among which, 10 converter valves are composed of sixteen 2000v, 200a thyristor in series; two converter valves are composed of forty-eight 200—1000v, 200a thyristor. Before this, a lot of tests and researches have been made to prototypes of thyristor that are connected by 52 converter valves in series. The converter valve is air isolated, air cooling, indoor structure, electromagnetic trigger; analog phase control is used in the control system. Besides a large quantity of checks and tests of primary equipments and secondary equipments, the test station was used for test and research of control and protection feature of DC transmission and all kinds of failure types. The above-said work has laid good foundation for making equipments used in Zhoushan DC Transmission Project.