Completion of the Jiuquan-Shaoshan ±800KV UHVDC project

Earlier updates from the Jiuquan-Shaoshan ±800 kV UHVDC project reported the start and successful completion of the low-level converter tests  including black start capabilities, protection settings and protection co-ordination among the comprehensive set of more than 640 tests that are necessary before the final commissioning of the UHVDC station.

According to the latest reports, the ±800 kV UHVDC system successfully completed the 168-hour (one-week) continuous operation test with all features reaching the expected standards. This would be the last test for the system before coming fully online and in service.

This project, starting at Qilian converter station in Jiuquan at the northwestern province of Gansu and terminating at the Shaoshan converter station, in Xiangtan, Hunan, covers a total transmission distance of 2384 km with a converter capacity that reaches 8000 MW.

The UHVDC link is one of the many transferring wind and other renewable energy from the northwest part of China, the load centers in the central and eastern provinces of China. At full operation, the annual expected energy from the HVDC system to Hunan is expected to  reach 40 TWh, equalling the output of six coal-fired power plants around the capital city of Changsa, and meet almost 25% of the electricity demand in the whole of Hunan province.

The timetable of the project so far is:

• Authorisation and approval on May 2015.

• Construction commenced on 3rd of September 2015.

• Completion of towers and transmission lines  on 24th of November 2016.

• Completion of converter stations on 21st of December 2016.

• Completion of the low level bipolar UHVDC tests completed on March 2017.

• Completion of the high level bipolar UHVDC tests completed on 20th April 2017.

• Completion of the 168-hour continuous operation on 28th May 2017

Testing begins for a new ±800kV UHVDC transmission line from Northwest to Central China.

Testing of the Qilian converter station in the Jiuquan – Shaoshan ±800kV UHVDC transmission line started earlier this week, on the 10^th of March. Black start capability, protection settings and protection co-ordination as well as current control is among the comprehensive set of more than 640 tests that are necessary before the final commissioning of the UHVDC station.

This converter station is part of the Jiuquan – Shaoshan ±800kV UHVDC transmission line a project designed and constructed with investments from the State Grid Corporation of China (SGCC) connecting the northwestern part of China and Gansu Province to the middle of the country in Hunan Province. The ±800kV UHVDC transmission line, with a total length of 2383 km, crosses four provinces, from Gansu through Shaanxi and Chongqing, to Shaoshan in Hunan. The capacity of the two converter stations is 16 GW and the transmission line will be delivering 20.000 GWh of energy at its initial stages and 40.000 GWh of energy annually, when fully utilized

The project, which aims to facilitate integration of large-scale renewable wind and solar resources from the northwest of China to the load centers in the center of the country, was authorized in 2015 by the Chinese department of national development. Its construction took 18 months with the transmission line completed in late December 2016.

The complete project, that is expected to come into service in June of 2017, costed a total of 26.2 billion RMB (approximately 5 billion Australian dollars). 

A breakthrough of HVDC circuit breaker in China: application and commercial services

Ever since the first Gotland HVDC link in 1954, islands have always been an exceptional testbed for HVDC technologies demonstration. The Zhoushan district in Zhejiang province, with more than 1300 islands and excellent wind resources, offers such a testbed in China to demonstrate new HVDC technology.

Back in July 2014, the island complex become the location for the first five-terminal multiterminal HVDC (MTDC) system, the Zhoushan ±200kV MTDC with Modular Multilevel Voltage Source Converters at each of the terminals.

In order to provide a truly multiterminal operation as a network it is important for the MTDC to have the ability to operate under dc and ac side faults and appropriately isolate faulted terminals. The key device to provide such functionality is the dc breaker.

In the end of 2016, the Zhoushan MTDC became the ground for another breakthrough in HVDC tehnologuy with the installation, commissioning and operation of the first 200kV circuit breaker  with fast isolation. The new circuit breaker is based on the combination of a high-speed mechanical switch and a hybrid cascaded full bridge module which allows fast extinction of bidirectional fault currents,on the dc side of the HVDC networks. The hybrid dc breaker is capable of isolating and disconnecting the dc transmission line for fault currents up to 15kA at 200kV within 3 ms.

Location of the five-terminal in google map : https://www.google.com.au/maps/place/Zhoushan,+Zhejiang,+China/@30.0124857,122.0165304,9.25z/data=!4m5!3m4!1s0x3452c5c61b6c087f:0xa95ffbbca9c810a6!8m2!3d29.985295!4d122.207216

The Zhoushan MTDC project connects the five MMC stations in five different islands by 134 km undersea cable, the overall capacity is 1000 MW. The MTDC has transmitted nearly 500 MWh since its first operation, and enlarges the ability of connecting distributed wind farms throughout the islands and improve the reliability of power supply for all islands.

‘Although VSC-HVDC as a technology has vast advantages, HVDC circuit breaker technology is a bottleneck in the electric engineering field’ said Jiejie Zhang, the vice director of department of HVDC, World Power Grid Research Institution, China.  VSC-based HVDC transmission networks, especially those based on the half-bridge MMC topology has no reliable ability to clear faults on the dc-side. Especially in the current implementation of the MTDC project, a partial fault in one converter station results in blackout in all converter stations leading to a reduced ability in avoiding cascading faults.

VSC-HVDC has significant advantages in MTDC systems as it enables independent control of active reactive power, and is expected to play a significant role in enabling bulk renewable energy integration, enhancement of flexible transmission systems. The application the hybrid breaker in the Zhoushan MTDC is an first step towards future DC transmission networks. 

Chongqing-Hubei back-to-back VSC HVDC: a hybrid interconnection

The National Development and Reform Commission of China formally gave its authorization for the construction of a "Back-to-back HVDC grid interconnection" between the Southwestern province of Chongqing and the Central province of Hubei. This authorization was approved on the 26^th December, 2016.

Currently the interconnection between Chongqing and Hubei is through two 500kV AC transmission lines (Jiupan-Longquan & Zhangjiaba-Enshi) with the two systems connected and operating synchronously. Aiming to improve the stability of power transmission and the two systems , as well as to ensure the increasing electricity output from Southeast China, the State Grid Corporation of China (SGCC) decided to change the synchronous interconnection between the two systems into an asynchronous interconnection using HVDC.

Chinese main power grid 

The interconnections will be built using Voltage Source Converters (VSC) based on Modular Multilevel (MMC) converter technology. Compared with the ‘classic Current-Source Converter HVDC’, VSC-HVDC allows flexible control and fast response on both active power and reactive power respectively allowing decoupling and independent control of active and reactive power (PQ decoupling), avoids commutations failures typical with larger thyristor based systems and avoids the use of large reactive power compensators at the end of the HVDC lines.  

Each of the VSC-HVDC stations will be rated at 2*1250 MW with a DC transmission line voltage of ±400kV, it will be the one of highest voltage and largest capacity Back-to-back VSC-HVDC worldwide. With regards to technical parameters of the project, the converter station in the north lane located in Yichang city, Hubei province, will comprise two converter units at 1250 MW each and will be built in the second stage of the project with an overall capacity of 2500MW.  The B2B converter station in the south lane will be located in the City of Enshi, and will be of identical size and capacity to the North one. The AC system around the HVDC converters is of 500kV. 

The total cost of the project is estimated at 6.5 billion RMB (1.3 Billion AUD)

The following is a single line diagram of the proposed B2B VSC-HVDC station on the north transmission line:

 Geographical map of Project 

The Ximeng-Taizhou ±800kV UHVDC (One of Four UHVAC & UHVDC Project) is nearing completion

The converter stations at the Ximeng-Taizhou UHVDC Project are nearing completion with 70% of main devices already installed and the overall project expected to reach completion by this Chinese Spring Festival (28^th January 2017).

Figure 1 Converter station (from Xinhua Network)

This project is a significant component of the ‘Four UHVAC & Four HVDC plan’ as part of the broader ‘National Air Pollution Control Action Plan’. The ±800kV UHVDC Transmission line starts at the Ximeng converter station, located in the Inner Mongolia Autonomous Region and terminates at the Tazhou converter station, crossing five provinces (Inner Mongolia, Hebei, Tianjin, Shandong, Jiangsu), covering an overall distance at 1620km.  Commissioning and testing is expected to be completed by June, 2017, and the whole system will be operational by August.

Upon its completion, the Ximeng-Taizhou UHVDC Project will have the ability to transmit 55 billion KWh annually, equally transport 25 million tons, and reducing  CO₂ emissions by 49.5 million tons. The project will contribute to the control of air pollution in the Yangtze district.

Figure 2 Construction of converter station

Driven by increased concerns about pollution and air quality, especially in the North-eastern provinces, Premier Li Keqiang hosted, on 18^th April 2014, the first conference of the National Energy Committee, that led to the implemention of the  ‘National Air Pollution Control Action Plan’, and authorized construction of the “Four UHVAC & Four UHDC' Project, to "improve reliability of electricity supply, boost development of clean energy, contribute to a sustainable growth of the economy".

The whole project is expected to cost 174.48 billion RMB (34.2 billion AUD), and included construction and expansion of 10 high voltage converter stations and 15 high voltage substations transformer capacity reaches 140 million kWh. The overall transmission line length of all the projects is above 12,000 km, with all eight transmission lines expected to come into service within 2017.

The following are the details of the eight transmission lines of the “Four UHVAC & Four UHDC' Project.

Name	Voltage	Distance(km)	Capacity (MW)	Operation Time	Status
1 Huainan-Nanjing-Shanghai	1000kV UHVAC	2*789	12000	2016	In Operation
2 Ximeng-Shandong	1000kV UHVAC	2*730	15000	2016	In Operation
3 Mengxi-Tianjin	1000kV	2*608	24000	2016	In Operation
4 Yuheng-Weifang	1000kV UHVAC	2*1049	15000	2017	Under Construction
1 Ningdong-Zhejiang	±800kV UHVDC	1720	16000	2016	Under Construction
2 Jinbei-Nanjing	±800kV UHVDC	1119	16000	2017	Under construction
3 Shanghaimiao-Shandong	±800kV UHVDC	1300	12800	2017	Under construction
4 Ximeng-Taizhou	±800kV UHVDC	1620	14400	2017	Under constrcution

Figure 3 Paths of the 'Four UHVAC & Four UHVDC' Project