BAC's new for old scheme saves money on cooling water cathodic protection system upgrade for Torness power station
BAC's new for old scheme saves money on cooling water cathodic protection system upgrade for Torness power station
Keywords: Cathodic protection, Coolers
By retaining existing power supply control cabinets but upgrading the internal electronics to provide a state-of-the-art automatic cathodic protection(CP) control system for the cooling water supply and discharge system at the 1,400 MW Torness nuclear power station in Scotland, BAC Corrosion Control has considerably reduced the cost compared with a total replacement.
The station uses four vertical mixed flow pumps each rated at 11 m3/s and 1,490 kW to circulate sea water from the North Sea for cooling. The impressed current cathodic protection system is controlled from four cabinets,originally installed by BAC Corrosion Control in 1985, when the advanced gas cooled reactor station was built. Since that time control technology has advanced apace and various factors prompted the station management to replace the old cabinets with more up-to-date equipment. On site replacement spares were almost exhausted and the old current control system required time consuming manual adjustment.
Unit 1 A power supply cabinet
Being at the forefront of CP system technology, BAC initially took away one cabinet, stripped out the old control gear which used grid coil resistors to vary anode current in the CP system and installed new control modules. This meant that current could be precisely controlled safely and with ease rather than the old manual system of moving a band along a low voltage live wire. New lockable isolator handles were also fitted to improve safety. Subsequently, the remaining three cabinets were similarly upgraded.
The BAC CP system at Torness uses reference cells and sensing electrodes at intervals in the anode circuits on the plant being cathodically protected. The system needs to be more critically controlled than normal pipe runs due to varying tide levels and flowing or static water conditions. These two variables affect the oxygenation levels within the cooling pipe system. When the water is flowing, oxygenation is higher and it is due to these variants the CP system needs to be automatically controlled.
"We have replaced an obsolete control system with one employing cutting edge technology that operates automatically," commented an engineering spokesman for the station. "It is a more reliable system and will provide us with accurate control for many years to come" he added.
