Cross Channel Power

A talk by M.J. Wrigley Esq., (Member) at Durrington Community Centre – 11th March, 1987.

The President was in the Chair and after a brief introduction he asked the speaker to deliver his talk.
Leading up to the idea of interconnection of electric power systems across the Channel Maurice briefly traced the history of the U.K. grid system. By the turn of the century coal gas was already well established for lighting and electricity was trying to compete.

After the first world war it was evicent that it would be advantageous for electricity generating stations to be interconnected, for reasons of economy of standby plant, peak load sharing etc. The 1926 Act set up the ‘grid’ system which facilitated the spread of electric power useage. By 1946 coal gas was still widely used domestically, but a corresponding interconnection of the many small, often smelly, gas works was not practical and after attempts at using imported liquid gas the situation was resolved by North Sea gas and a network of pipes. Thus interconnection was the key to progress as in many other fields of activity e.g. telecommunications, transport. In electric power, the super grid was the next step – i.e. a load carrying grid, eliminating the bulk transport of coal over long distances – “coal by wire”.

The idea of a ‘connection’ across of channel was a natural extension and in the 1950’s a study was made. By this time the use of direct current (d.c.) for long distance transmission of power was being developed and advocated – the Swedes, Germans and Russians having built experimental systems. The Swedes had a successful 100 km underwater link from the mainland to the island of Gotland and they helped to promote the U.K. – France link in which they would provide the terminal converter equipment (a.c. to d.c. and vice versa) with the U.K. and France providing cable, transformers, power filters and civil works. Direct current is particularly advantageous for underwater transmission, where electric cables are used in contrast to overhead transmission lines, and cables have enormously greater electrostatic capacity which creates problems of charging currents (reactive power) with a.c. but absent with d.c. The critical distance for d.c. to become more economic was given as about 800 km overland and 30 km under water. The Swedes had their eyes on future prospects underwater in New Zealand and Sardinia and overland in Zambia. Also linking of two a.c. power systems through a d.c. link has application if the two systems have different frequencies e.g. 50 Hz /60 Hz in Japan, 60 Hz/ 25 Hz in U.S.A. – where the length may be zero. A further advantage of d.c. is that the control grids of the valves in the converters can be used to switch the power on and off – eliminating expensive circuit breakers.

The converters of the first cross-channel link contained valves of the mercury-arc air cooled pumped type with grids between anode and cathode to control the firing angle – an essential requirment for the inverter at the receiving end. The cable, solid paper insulation lead sheathed and steel wire armoured was laid on the sea bed and only buried, for protection from dragging anchors, where close to the shore.

A second link, rated 2000MW at +&- 270 kV is now in operation and this is based on solid state valves, i.e.thyristers and the cables are buried all the way across the channel.

Maurice gave it as his strong opinion that the French always saw the function of the link as a means of exporting their cheaper electricity and ridiculed the talk of essentially a two way flow for peak loads occurring at different times.

In deference to the considerable number of members who are not electrical engineers Maurice kept away from technical matters and your reporter cannot do justice in a few words to his conversational presentation.

The open discussion was very lively. Messrs. Haynes, Hill, Hammond, Milway and Markwell raised matters relating to the cable itself and in answering Maurice confirmed it was jointless, with solid insulation (P.I.L.C.) operating at 270 kV to earth, that a d.c. link cable could be accommodated in a future Channel Tunnel provided adequate cooling was provided, possibly a service tunnel being built first to house the d.c. cable whether or not the railway tunnel was later built, the cables are of 900 mm copper conductors. He said the Adniralty caused unnecessary expense, requiring the go and return cables to be laid close together and not allowing earth return on the surprising grounds of not interfering with ships compasses. Harry Calverley described a machine, the transverter, built in the early 1920’s rated 2000 kW 100 kV d.c. – he having seen it on test at Dick Kerr’s works when at the age of 9 his father, a coinventor took him to see it. It was shown at the Wembley Exhibition. Bill Bailey said he had worked on this machine, that it worked well but not proceeded with due to lack of promoters in the slump. It was of course superseded by mercury arc converters – some 20 years later. Bill referred to the Thury system in which all machines, generaters and load, were connected in series. In answer to questions by Messrs. Plyer, Hammond, Farebrother, Haynes and others Maurice said the cable of the second link started operation at about the end of the miners strike, that no special provision was needed for thermal expansion, that the principal transformer weighed about 250 tonnes, and that metering of power was compensated to be that at a virtual mid-channel position.

Stan Morley, in expressing the thanks of the meeting recalled some of his early experiences working with the speaker on the grid system and then referred to Maurice’s close involvement with the Cross- Channel link. He thanked him for his effort in preparation and presentation and this was warmly endorsed by the meeting.