Pocket Power Station

In 1963 SSS Gears supplied a 66T Encased Clutch to the Bristol Siddeley Patchway site connected to a Proteus aero-engine for peaking power and voltage support. This was our first synchronous condensing application

In the years between 1959 and 1965, South Western Electricity Board (SWEB) installed a number of small unmanned peaking power stations at remote points on its system. These “Pocket Power Stations” consisted of a turbo-prop aero-engine driving an alternator, together with the control gear and switch-gear and associated oil storage tanks. The sets could be started and stopped remotely via a telephone line and could be run up and put on load in minutes. These pioneer power stations led the way to the use of aero-engines for power generation and were the fore-runners of the large gas turbine sets in use today.

History

The “Pocket Power Station” idea arose from Mr. A.N. (Bill) Irens, the SWEB Chairman (1956-1973). In his previous employment as the Chief Electrical Engineer for the Bristol Aeroplane Company, he had seen generators used to load engines under test (as dynamometers to measure the power output). In such cases the output was usually dissipated in resistance banks. However he realised that aero-engines could be used for power generation.

At the time that Mr. Irens joined SWEB as Chairman, the tariff for electricity levied by the British Electricity Authority (later the Central Electricity Generating Board) incurred a high charge based on peak demand. This peak demand occurred for a relatively short time during the winter and Mr. Irens reasoned that if SWEB could reduce this peak a considerable advantage could be gained. For this purpose small, remotely-controlled generators, which could be started and put on load within minutes, would be required. A gas turbine powered generator would be ideal for this purpose. Such a generator would also be ideal to provide an alternative supply at remote parts of the SWEB system, where amenity problems made the provision of additional circuits difficult. Thus the pocket power station was conceived.

The Engine

The engine chosen was the Bristol Siddeley Proteus. This was originally developed for the Bristol Brabazon and the Princess Flying Boat, but both projects were abandoned before the engine had finished its development. The Proteus was then adapted to power the Bristol Britannia, which had a long and successful career. A version of the engine was also used to power the Bluebird-Proteus CN7 which achieved the land speed record of 403 mph in 1964 on Lake Eyre in Australia.

The Proteus was a 4,250 SHP (shaft horse power) turbo-prop engine. It used the free turbine principle, in which the compressor-driving and power turbines are mounted on concentric, but mechanically independent shafts. This arrangement enables each system to run at its optimum speed under all conditions. Reduction gear, similar to that used on the Proteus aero-engine was used to drive an alternator at 1,000 RPM.

The Power Plant

This consists of a 4,250 SHP Proteus engine coupled to a 1,000 RPM, 3.2 MVA, 3 Phase, 50 Hz, 11,000 Volt Electric Construction Co. alternator and exciter. This, together with its switch-gear and controls, was housed in a small building on light foundations and remotely controlled. There was no cooling water requirement or need for manning of the plant

The output was 3.0MW, later restricted to 2.7MW. The engine initially ran on diesel fuel, but problems with wax in cold weather led to a change to kerosene.

Initially two sets were constructed, one for use at Bristol Siddeley's Patchway Works and the second for installation at Princetown on Dartmoor. SWEB installed and commissioned sets at a further four sites.

These plants fulfilled three functions:

· Peak Lopping

· Security of Supply

· Voltage Support

Princetown claimed to be the world's first unmanned power station and was in use until 2003 after 40 years of service.

A working example of the Pocket Power Station is installed at the Internal Fire Museum of Power near Cardigan, Wales and was given a Heritage Award by the Institute of Mechanical Engineers in 2010.

The SSS Clutch

In 1963, the Bristol Siddeley Patchway site incorporated an SSS 66T Encased Clutch rated at 3MW for 1500 rpm. This was the first synchronous condensing application for an SSS Clutch and it allowed the alternator-generator to remain spinning and synchronised to the grid, still providing reactive power and voltage support when the plant was not delivering power. The SSS Clutch automatically engages when the speed of the turbine matches the speed of the alternator-generator.

We now design SSS Clutches for this application rated at over 300 MW, but many of the original SSS Clutch product features are as relevant today as they were in 1963:

· An automatic mechanical freewheel clutch

· Robust gear teeth design allowing transmission of high power / torque

· Primary and Secondary pawls to enable clutch engagement at different speeds

· A dashpot to cushion clutch engagement

· An internal thrust bearing to locate the alternator shaft

Many thanks to John Gale and Histelec News for the history and background on the “Pocket Power Stations” and to the Internal Fire Museum of Power.