Static digital excitation systems retrofitted to power station

Sensonics has retrofitted two static digital excitation systems at Cruachan power station in Scotland. Contracted by Scottish Power for the Unit 3 and Unit 4 upgrade, Sensonics worked closely with Optimised Systems and Solutions (OSyS) to replicate the equipment fitted to Unit 1 and Unit 2 during previous works.

Constructed in the early 1960s, Cruachan Power Station is one of only four pump storage facilities in the UK and, due to its location, presented a number of challenges. The power station is completely concealed within a manmade cave under Ben Cruachan and houses four generator/motor sets that are driven from an upper reservoir; the generators are capable of producing 400MW of electricity. The station can produce electricity for the grid in less than two minutes when demanded, and the need for high-integrity turbine control systems is essential to meet these operational requirements.

Reliability through redundancy

The original AVR (automatic voltage regulation) system offered no hardware redundancy and, with spare parts becoming obsolete, the reliability and availability was becoming of major concern. The new system has been designed to offer extremely high availability by utilising separate and diverse digital controller hardware in combination with dual thyristor bridges providing 100 per cent redundancy. These are all backed up by duplicate power supplies and independent protective trips. A power system stabiliser was also included in the software algorithm to ensure Grid Code compliance.

For the Unit 3 and 4 equipment, Scottish Power contracted Sensonics to provide the same Optimised Systems and Solutions equipment configuration that was fitted to Units 1 and 2 in 2002. Sensonics managed the entire project on a turnkey basis in terms of mechanical design, manufacture, factory testing and installation, through to commissioning the entire system in conjunction with the OSyS engineers.

The successful upgrading of the AVR equipment at Cruachan Power Station is an example of Sensonics' capability as a supplier of high-integrity systems for turbine supervisory, control and protection applications, even in the most demanding environments.

Russell King, Managing Director at Sensonics, comments: "The partnership with OSyS to deliver this critical turbine system to Scottish Power utilised the OSyS technology and expertise in combination with Sensonics turnkey project capability. Working closely with Scottish Power to develop the safe working systems and appropriate procedures to deliver this project half a mile under a Scottish mountain was a real challenge. The project timeframe and working environment were particularly demanding and the retrofit activity was successfully completed within the requested four-week period."