Alstom engaged with two of the world’s biggest electrical cable manufacturers – Nexans and Viscas – to undertake some collaborative ground breaking research into the long term behaviour of cable for DC systems.

Traditionally DC systems have used cable designed for AC networks, and the long term effects of this are unknown.

Backed by several partners, Alstom were to pioneer extensive research into the behaviour of HVDC cables. In order to investigate the sustainability of the cables it was essential to prematurely age the cables with an accelerated process to establish the performance of the cable after 30 years of use. Alstom invited GRE to be involved with the project from the outset with the responsibility of designing a system that would put the cable through it’s paces.

In order to simulate years of aging, the equipment needed to heat the cable to +80 °C for 16 hours and then rapidly reduce to +20°C for 8 hours and to maintain this 24 hour cycle indefinitely. All of the parameters had to be fully adjustable, and due to the very high voltage environment the equipment had to be run on ultra-pure water.

GRE manufactured two main systems:

• Heating and cooling interface (Thermal Management Module) which directed the ultra-pure water into various jackets that were positioned
  over the cable.
• PEA Chamber and thermal control – GRE designed a system that mimicked the water jacket but the device had to be kept dry, which was
  achieved using strictly controlled air flow.

The system was split over eight key modules, all of which were individually programmable such that the technicians could modify and control the entire process at every stage. GRE wrote bespoke software for each device, which were all networked and then made available as an entire system over MODBUS via an optical link to the main control centre.

To complete the testing environment, GRE also designed and manufactured a Faraday Cage measuring 20m wide, 10m high and 15m long to encapsulate the entire system.

Following initial pilot trials, the system was further expanded over the following 2 years as the Client’s requirements developed. Both systems continue provide the required functionality.