Quantum Leap in Control
19 November 2008
Implementing a refit of the process control systems at Drax Power Station, which supplies about 7% of the UK’s electricity, was a major project that took over four years to complete and involved addressing many technical challenges. Quantum PLCs and Unity Pro software from Schneider Electric have, however, provided an ideal foundation for the station’s new control architecture.
One of the largest power stations in the UK with six generator sets, each rated at 660MW, construction of Drax began in the mid 1960s. Phase 1 was commissioned in the 1970s and the second phase in the 1980s. It has been in continuous operation ever since. The control systems on the original three generators were refurbished in the 1990s. Unsurprisingly, by the early years of this century, the control systems on the remaining 3 generators were starting to show their age. In particular, they were inflexible and they were becoming increasingly difficult and costly to maintain.
As a result, the decision was taken to refit the entire process control installation with modern equipment. Capula Limited, one the UK’s leading system integrators and a company with extensive experience in large scale systems, was appointed to handle this major project. The engineers at Capula had, however, to contend with many special demands.
Among the technical requirements was the need for the highest possible level of availability for the new system. This dictated the use of redundant architecture with hot standby, so that no single failure could shut down the system.
In addition, the new system would have to provide open connectivity to communicate with the station’s high-end SCADA installation, and it needed to use IEC61131-compliant software. The conclusion was that the project’s needs would best be met by Quantum programmable controllers from Schneider Electric, used in conjunction with Unity Pro programming software.
Among the factors that influenced this decision was the ease with which Quantum controllers can be used in a dual-redundant hot-standby configuration that offers true bumpless transfer.
The new process control system for each generator set comprises 17 hotstandby pairs of Quantum PLCs,
supporting a total of almost 8,000 I/O points. The I/O, all of which is remote, is linked to the PLCs via dual redundant connections, and the PLCs communicate with each other by means of a selfhealing Ethernet fibre-optic ring.
Connections to legacy equipment are implement in Modbus TCP and Modbus, both of which are supported as standard in Quantum products.
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