Construction of record breaking transmission line is under way

The 1100kV DC Changji-Guquan line will set a new world record in terms of voltage level, transmission capacity and distance. It will be capable of transporting 12 GWe, at least 20% more than the ± 800 kV UHVDC links currently in operation. Transmission distance will be extended from around 2000 km to 3284 km, enabling the integration and transmission of renewables in the north of China on a much larger scale. When fully operational the link will be able to feed eight 500 kV and two 1000 kV AC lines.

The high voltage equipment for the new line is being supplied by two prominent European companies, Siemens and ABB, under separate contracts. Both have recently completed high voltage testing of a major line component, the 1100 kV transformers. These will be the most powerful ever made, and have been developed specifically for this project. Commissioning of what will be the world’s largest and longest HVDC link is scheduled for 2018.

Contracts

Contracts with both main suppliers were signed in July 2016. ABB was awarded over $300 million worth of contracts by State Grid Corporation of China to supply converter transformers, bushings and tap changers, HVDC converter valves, DC circuit breakers, wall bushings and capacitors as well as system design support. The transformers would meet the most stringent performance, reliability and safety standards. Each transformer weighs 800 tonnes, and is 32 metres in length. ABB’s transformer manufacturing and testing facility in Chongqing as well as the local HVDC engineering and technology centre would be actively involved in the delivery and execution of the project.

Together with local partners Siemens has contracted to supply 1100 kV converter transformers and other equipment for the same project. The transformers would be the world’s first 1100 kV converter transformers, and the most powerful, with a capacity of 587.1 MVA.

Testing UHVDC components

Siemens was first out of the blocks. On 7 November last year it declared that the world’s first ±1100 kV HVDC transformer, manufactured in Nuremberg, had passed its type testing phase.

The supplied transformers will be installed in the Guquan converter station of the link to feed power from conventional AC transmission grids into converter stations. The transformers will also be loaded with the very high DC quantities of the transmission voltage and current.

Because it was entering a new dimension in HVDC technology Siemens completely redesigned all key components. The main goal was to meet the extraordinarily stringent requirements imposed on the insulation systems – for example, the two valve bushings through which the current flows from the interior of the transformers into the converters are approximately 19 metres long, owing to the necessary insulation clearance in air. With bushings, the transformers are 37.8 metres long, 5.85 m high and 5.20 m wide. With insulating oil, they weigh 823 metric tons, from a transport weight of 490 metric tons.

ABB’s announcement came in December when transformers and other key equipment to be supplied by ABB successfully completed a ‘stringent’ test phase. The successful test runs of the low and high voltage units, a series of type tests, were carried out in collaboration with SGCC. ABB stated that the technology breakthrough made it possible to connect ±1100 kV DC with 750 kV UHVAC links for the first time. It has also developed and tested a range of other key 1100 kV components, including converter valves, bushings and DC circuit breakers. “In addition to transporting more power across longer distances with lower losses, this breakthrough will enable the interconnection of AC and DC grids and support the future linking of regions and countries.” said Claudio Facchin, president of ABB’s Power Grids division.