The 1100 kV DC giant is one of 28 transformer units that ABB has developed in close collaboration with State Grid Corporation of China (SGCC) to enable unprecedented amounts of electricity to be transmitted over the world’s longest transmission link, with minimal energy losses.
The ABB converter transformers will be deployed at the transmitting end of the Changji-Guquan ultra-high voltage direct current (UHDC) link, where they will enable 12,000 megawatts (MW) of power to be transported over 3,000 km - from remote power plants in northwest China to population centers in coastal regions where the energy is needed.
Increasing the amount of power that can be transported over twice the distance was one of the biggest technical challenges in power transmission history. ABB and one other company were given 15 months to propose and verify an 1100 kV DC transformer design. Only ABB succeeded within the deadline.
The difficulty is that dielectric components do not scale linearly. It is not simply a case of raising existing 800 kV DC designs to a higher voltage. On the contrary, existing designs were of little use. ABB had to redesign the transformer from scratch, rethink existing concepts and innovate new technologies and manufacturing methods.
Because of the tight deadline, ABB also had to create a new way to test and validate the design. There was no time to engineer and build full-scale components and test them at full voltage. Instead, ABB had to devise a new approach, using smaller scale components at existing voltages to simulate conditions at 1,100 kV DC. It was a creative, time saving method that allowed the engineers to meet the challenging deadline.
Type tested in only 7 days
That was the design stage. Now, with the first 1100 kV DC converter transformer completed, the moment of truth had arrived to type test it in extreme conditions.
Type testing is a set of exacting electrical and thermal tests to verify the design and prove that the transformers meet customer requirements and ABB standards of craftmanship.
In the tests the transformers are subjected to huge surges of power as well as temperatures and oper-ating conditions that exceed real-life scenarios. They have to prove that they have the robustness to perform reliably as required over a very long operating life.
In addition, they have to operate with at least 607 megavolt amperes (MVA) of power - which has never been done before and withstand extreme air temperatures.
“The transformer passed all the type tests without incident and in just seven days, 14 days ahead of schedule,” says Markus Heimbach, Managing Director of BU Transformers. “This proves that the designs we produced in record time for the world’s largest converter transformers meet customer specifications flawlessly.”
Transported in sections
Now that the type tests have been completed, the transformers will be dismantled for transportation from the ABB factory in Ludvika, Sweden - the birthplace and home of HVDC and UHVDC power transmission to northwest China. Each transformer weighs over 800 tons, the equivalence of 550 cars, measuring more than 30 meters in length. They are too big to be transported in one piece.
When fully operational this UHVDC link will be able to feed eight 500 kV and two 1000 kV AC lines – delivering power equivalent to twice the average annual power consumption of Switzerland.
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