East Yelland Power Station
Photos and article from The Engineer – 13 May 1955, courtesy of Grace’s Guide
Construction of East Yelland started in 1950 at a time when demand for electricity was increasing rapidly and generating capacity was in short supply. Power cuts were regular occurrences after the war and to be sure of meeting demand quickly government ordered stations to be built using tried and tested technology in order to ensure rapid construction and reliable operation. Generators of over a 100MW were in operation, but proven 30 and 60MW turbo-generators were to be used. This was later to prove East Yelland’s downfall as it’s relatively poor station thermal efficiency meant it could not compete against more modern designs. Only it’s strategic importance to maintaining local supplies and supporting grid voltage in the south west kept the station open for so long.
East Yelland was a coal fired station built by the British Electricity Authority (BEA), a nationalized industry formed in 1948 to develop and operate the electricity generation industry across England and Wales. (The BEA became the Central Electricity Generating Board (CEGB) in 1958). The building architecture was built to high standards using expensive colour blended brick to minimize it’s visual impact on the important coastal landscape. The height of the chimneys was also restricted to 120 ft to satisfy the ministry of defence, who were concerned about the proximity of the station to RAF Chivenor. The chimney height was increased much later in the life of the station to 180 feet, but this was still much lower than the normal 300 feet which the CEGB would have liked in order to increase performance and aid dispersal of combustion gases.
The station had a gross nameplate capacity of 180,000 kilowatts, or 180 megawatts. This was produced by six 30 MW Parsons two stage steam turbines. In practice the turbines were found to be so well designed and manufactured they could produce more than 110% of name plate rating giving a maximum station generation in excess of 200 MW. Net output to the grid after supplying on-site auxiliary loads was just over 190 MW. Operating at optimum efficiency the station output was limited to 150MW.
The boilers were of an old, but proven chain grate design by John Thompson boilers. Coal was automatically fed onto a moving chain grate with air blown up through it. These had a poor efficiency compared to pulverized fuel boilers.
Coal supplies came by boat and unloaded at the purpose built jetty where the cranes transferred the coal to conveyors which took the coal to hoppers above the boilers or to an adjacent coal storage yard. Ash from the back of the boiler dropped on to a submerged conveyor belt that took ash away via a further conveyor system to the ash dump East of the station.
In order to provide flexible steam raising capacity the boilers were equipped with variable speed input (forced draft) and output fans (induced draft) operated from a DC drive supply system with large mercury arc rectifiers that looked more like something out of Doctor Who.
The station overall station thermal efficiency was in the order of 25%. To appreciate the magnitude of the losses for every 100 tons of coal burnt the energy of 75 tons was thrown away, mainly as waste heat out in to the river via the sea water cooling system. Sea water cooling to the six turbo-alternator condensers, was provided by large high voltage motor driven pumps mounted below sea level in a separate cooling water pump-house.
Another challenge for the station was the closure of the south wales pit supplying the correct grade of coal shortly after the station was commissioned. From then on most of the coal had to be shipped from Ayrshire.
The relatively low station thermal efficiency combined with high coal costs resulted in the station dropping down the merit order system. The merit order was the name used by the CEGB for the order in which stations would be scheduled on to the grid to meet increasing demand. From the mid-sixties onward the station was used solely for ‘peak lopping’ (a name used in the industry to describe stations being run solely to meet the peaks in demand). By the mid-sixties nuclear stations such as Berkley and Hinkley Point ‘A’ were coming on stream along with much larger 200 and 300MW coal and oil fired steam turbines supplying base load demand.
However even in the late sixties, the grid was stretched at times to meet demand, so much so that on many occasions East Yelland was requested from Bristol grid control to carry out voltage reductions to reduce local load and start up two ex-motor torpedo boat diesel generators of only a few hundred kilowatts in addition to all six main turbo-generators running at max generation to do everything it could to help prevent grid frequency falling to the point where load shedding was required.
The station was closed in the mid-eighties. One major long term advantage to north Devon of East Yelland was the 132kV substation used to connect the station to the national grid. This 132/33kV substation remains today to the west of the old East Yelland site and forms one of two bulk supply points connecting the local north Devon electricity network to the 400kV national grid. The second 132/33kV bulk supply point is south of Barnstaple. These are of strategic importance to Renewable Energy generation in the area particularly for larger wind and solar farms.