The Grosvenor Gallery Installation

One of the most well-known early electrical generating stations was at the Grosvenor Gallery (now the Aeolian Hall), in Bond Street, London, and it had as its Chief Engineer, Sebastian Ziani de Ferranti. The generating voltage was 2,400 volts single phase a.c. In addition to the supply to the Gallery, supplies were given to adjacent premises. The entire distribution was by means of overhead conductors, radiating from a mast on the roof via masts on convenient buildings. For those taking a supply, a 1 h.p. transformer was provided.

The Grosvenor Gallery installation is of historical significance because it represented a challenge to those experts who championed low voltage d.c. for distribution. It was considered that 100 volts d.c. was a safe voltage. The main disadvantage was the short distance over which low voltage d.c. could be transmitted, namely approximately mile. The contrary views that high voltage a.c. was superior were helped by the introduction of the transformer in 1882. By 1885 the design of transformers had advanced such that high voltage a.c. distribution over fairly large distances became a real prospect.

Deptford

The London Electricity Supply Corporation was formed in 1887 by the directors of the Grosvenor Gallery Company. Ferranti was of the opinion that building a large power station in the crowded heart of London was impracticable and, as was already the trend with gas distributors, he recommended and convinced the directors that a new power station should be built away from the centre at Deptford. For the supply from Deptford, he proposed transmission at 10,000 volts, considerably higher than used up to then. Although nowadays this seems quite ordinary, it caused a sensation since, at that time, the limit of distribution voltage was around 3000V.

Ferranti experimented with two types of cable for 10kV operation; rubber and jute insulated. The first cable was rubber insulated, made by the I. R. G. P. Company. This was short lived because the high permittivity of the rubber, the charging current of a seven mile main was likely to be excessive, also the cost of the rubber was very high. For the majority of the route Ferranti adopted the jute insulated concentric cable manufactured by the Fowler-Waring Company.ferranti1.jpg - 17472 Bytes

Although a few years later, the Deptford mains were laid underground, Ferranti obtained the agreement of the South Eastern Railway Company for the cables to be cleated along the parapet of their railway viaduct, this avoided the hassle of obtaining permission to excavate in the road. The electrical performance of the cable was satisfactory but its disadvantage soon became apparent. It was exposed to sparks and flying cinders from passing locomotives and exhibited a tendency to catch fire.

After this brief but disastrous experience of this type of cable, Ferranti proceeded to design and make one. The result of his work, the "Ferranti Main"carried power at 10,000 volts from Deptford to central London for over 40 years.

Ferranti's proposal for a concentric cable with the outer conductor earthed provoked tremendous criticism from fellow engineers and the Board of Trade. It was however a trait of Ferranti that once he determined he was right, there was no changing his mind. To demonstrate the safety of his proposed cable he arranged a frightening demonstration. His assistant, Harold Kolle stood on an earthed copper plate, holding a cold chisel to the live mains in his bare hands. Another assistant using a sledge hammer drove the chisel through the conductors resulting only of the blowing of the main fuse link. Kolle, when asked if he had been frightened replied yes, because the other guy had not used a sledge hammer before.

The "Ferranti Main"

Ferranti Main
It was no ordinary cable, but a system of concentric conductors in 20 ft lengths. The conductors were two brazed copper tubes, each approximately 0.27 sq. in. in sectional area and 13/16 inch and 115/16 inch in external diameter. The inner copper tube was insulated by wrapping it with layers of brown paper which had been dried and then impregnated with ozokerite wax, (plentiful as a by-product of the making of candles). The paper was rolled tightly around the copper tube, while the wax was warm, in a special machine, until the built-up insulation had reached a thickness of about half an inch. Another copper tube, similarly insulated to 1/8 inch thickness, was drawn tightly over the first. The two were then slipped into an outer protective tube and melted wax forced in. The original patent included the provision of holes in the inner tube to allow the permeation of impregnant into the insulation when introduced under pressure.

Although the main was inherently rigid, bends of ten foot radius were made by shaping the tubes with a rail bender. This caused some distortion of the paper insulation, but no problems were experienced as a result of this practice.

Special plant was installed at Deptford to manufacture the concentric mains under the supervision of H. W. Kolle and laying commenced in the summer of 1890. For a great part of the distance they were cleated to the parapet of the South Eastern Railway viaduct, but in part buried in asphalt-filled troughing beneath roads which followed the route of the railway. The four mains were looped into a switching point in Blackfriars Road and terminated at the London Electric Supply Company's Cockspur Street sub-station in Trafalgar Square. Two continued to the Grosvenor Gallery terminal in the old boiler house at Bloomfield Place. Supplies commenced on February 16th 1891, the mains remained in use until November 1933.

Ferranti Joints

The cable circuit utilised mechanical joints, able to be made by unskilled labour. The connection did not use solder but relied upon intimate mechanical contact. Four cables were laid side by side, there were 1100 joints per mile of trench and out of 8000 joints, only 15 proved to be faulty.

The outer copper tube was cut back for approximately 21 inches and the insulation tapered down to form a long cone. The corresponding end of the adjacent tube was reamed out to provide an exact fit. The inner conductor was jointed by a copper rod and the outer conductor by a copper sleeve. The copper sleeve was then grooved to grip the conductors and to lock the joint firmly after it had been pulled together by means of screw jacks. The outer sleeve was of iron and topped up with bitumen compound. The joint, although electrically efficient, suffered from the lack of provision for expansion of the conductors on load. Although the system operated satisfactorily for over forty years, some problems were experienced with joints as the loads increased.

Subsequent repairs were made using a 10kV flexible paper insulated cable made by B. I. Wire Company at Prescot and the Siemens N-H cable.
John Heath
Heath, Haynes & Trains
When I moved from Cornwall to Congresbury a year ago, I naturally took an interest in the North Somerset area and had a look at the OS map. The only one I had of the area was a 1inch map revised in 1956!

Being interested in old railways I noticed the dotted "track of old railway"between Weston-super-Mare and Clevedon. This was obviously the shortest route between the two towns (6 1/2 miles), the road route prior to the motorway would have been via Yatton - 11 miles!

I began looking into the history of this line and spoke to John Heath (another railway buff) about it. He lent me a very interesting book on the subject (see below). I was intrigued to learn that it had been a light railway, which opened in 1897 and closed to passenger service in 1940. It was known as the "Weston, Clevedon & Portishead Railway". I found out that Colonel H.F.Stevens took over as General Manager in 1911. This name rang a bell, since when living in East Cornwall, I had read that the same man had been associated with the railway between Calstock and Callington along the River Tamar. This had originally been a 3ft 6in gauge mineral railway opened in 1872 serving the local tin mines. I had walked part of the route in my East Cornwall days.

This Tin Line linked up with the Plymouth, Devonport & South Western Railway at Bere Alston. Calstock is on the Cornwall bank of the River Tamar and it was necessary to cross the river. This was achieved with a magnificent viaduct, which still proudly stands to this day.

From John Heath's book, I realised that Col. Stevens had built a little empire of light railways stretching from Ashover Railway in Derbyshire to East Cornwall and across to the East Kent railway. In fact he was associated with 16 light railways between 1898 until his death in 1931, aged 63.

In 1923 he was offered the chance of grouping his lines into the "big four", but declined to do so and remained independent. The lines were all run on a shoe-string budget and hardly made any profit. He used second-hand engines and carriages and carried out minimum maintenance. He even designed a petrol powered rail-bus using a lorry chassis. After his death, the lines slowly declined into bankruptcy and were nearly all closed down. He was certainly an unusual person, who ruled his empire from an office in Tonbridge. However he brought public transport to many rural areas, which then reverted to their former isolation with the "Beeching Axe"1966.

Hooray for old maps and idiosyncratic engineers!
John Haynes
Notes :
1. The Colonel Stevens Railways by John Scott-Morgan 1978.
2. The Light Railway Act 1896 allowed lines to be built to various gauges and to less onerous standards (25mph maximum speed).

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