Drax completes process control refit

Drax, UK -  Drax Power Station has completed a four-year project to refit the process control systems at the Yorkshire coal-fired plant, which supplies about 7% of the UK’s electricity.

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. The control systems on the original three generators were refurbished in the 1990s. Over recent years, however, the ageing control systems on the remaining three generators were proving difficult and costly to maintain.

In response, Drax decided to refit the entire process control installation with modern equipment and appointed Capula Ltd, one the UK’s leading system integrators, to handle this major project. The engineers at Capula had, however, to contend with many challenges, including the need to ensure the highest possible level of availability for the new system.

The demanding requirements of the power plant dictated the use of redundant architecture with hot standby, so that no single failure could shut down the system. The new system also had to provide open connectivity to communicate with the station’s high-end SCADA installation, and it needed to use IEC61131-compliant software.

Engineers, therefore, decided that the various project needs would best be met by Quantum programmable controllers from Schneider Electric, used in conjunction with Unity Pro programming software - in part because the controllers could be used in a dual-redundant, hot-standby configuration that offered bumpless transfer.

The new process control system for each generator set now comprises 17 hot-standby 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 self-healing 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.