Passing 1.1 million volts through a wall

ABB is delivering the largest and most powerful wall bushings ever made, capable of conducting 1.1 million volts of electricity safely and reliably through a converter station valve hall wall

The wall bushings are a critical component in the record-breaking ultra-high voltage direct current (UHVDC) technology that ABB has innovated to transport unprecedented amounts of electricity over the longest possible distances with minimal energy losses.

Developed for the world's first 1,100 kV UHVDC link, the wall bushings are part of a comprehensive ABB converter station solution for the longest, most powerful and highest capacity power transmission link on the planet, located in China.

When completed in 2018, the Changji-Guquan UHVDC link will deliver 12,000 megawatts of power - enough to meet the needs of 26.5 million people - at a voltage of 1100 kV DC, almost 50 percent more than the +/- 800 kV UHVDC links currently in operation.

The link enables renewable and conventional energy to be generated at source in a remote part of northwestern China and transported more than 3,000 km on space-efficient overhead lines to industrial and population centers, where the energy is needed.

Wall bushings are used to connect the indoor converter station to the UHVDC transmission lines at each end of the UHVDC link. The bushings protrude through the valve hall wall of the converter station, with part of the bushing inside and part outside the building.

Eight of these giant bushings will secure the transmission of power into and out of the converter sta-tions, while another two bushings will be kept in reserve in case of emergency.

Technical challenges
The technical challenges in designing and manufacturing wall bushings that can handle 50 percent more electrical energy at a higher voltage than was previously possible were huge.

New concepts in insulation, thermal and mechanical design had to be developed by ABB to withstand the extreme performance requirements of operating safely and reliably at 1,100 kV.

The bushing is 40 percent longer, three times heavier and has a 30 percent larger diameter than the 800 kV DC bushing - extreme dimensions which pushed ABB's production and testing halls to the limit.

During type-testing, the bushings had to withstand the potentially disabling effects of extreme operat-ing conditions - air temperatures as low as -42°C, huge surges of power from lightning strikes, and sud-den rises in temperature from current among others.

And, speed was essential. This new transmission voltage for bushings and converter transformers, which ABB has also developed, had to be designed, manufactured and tested within only 18 months.

Besides the 1100 kV DC wall bushings for the two converter stations, ABB is also supplying wall bushings at various voltages for the substations, where the power will be received from, or fed into, the AC transmission system at both ends of the link.

Click here to read about the ABB converter transformers that make 1100 kV DC power transmission possible.


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