An Encyclopedia of the History of Technology part 40. This one of a kind encyclopedia presents the entire field of technology from rudimentary agricultural tools to communication satellites in this first of its kind reference source. Following an introduction that discusses basic tools, devices, and mechanisms, the chapters are grouped into five parts that provide detailed information on materials, power and engineering, transportation, communication and calculation, and technology and society, revealing how different technologies have together evolved to produce enormous changes in the course of history | PART TWO POWER AND ENGINEERING the safety of the system he arranged a demonstration in which a concentric cable of his own design was made live at 10 000 volts and a workman drove a chisel through it. The workman was unhurt and the Board of Trade were satisfied. The main conductors were concentric copper tubes separated by paper impregnated with ozokerite wax. They were entirely successful some remaining in service until 1933. The generators however were less successful and to make matters worse for Ferranti the Board of Trade would only allow the company to supply a much smaller area of London than he had hoped. The directors decided to build only a small part of Ferranti s planned generating plant and in 1891 he resigned from the Corporation. The Deptford scheme was very ambitious and although the subsequent history of electricity supply shows that Ferranti was working on the right lines he may well have been more immediately successful if his plans had been rather more modest. All public electricity supply systems are now entirely AC although the last DC supply in Britain to a Fleet Street newspaper-remained in use until 1985. For transmission over long distances DC systems are sometimes preferred. Very high power mercury arc valves developed in Sweden in the 1930s permit very heavy currents to be rectified transmitted over a DC line and then inverted back to AC. DC transmission is also used when it is desired to link two AC systems which operate at different frequencies or which operate at the same frequency but cannot be kept in synchronism. An example of the former is inJapan where part of the country operates on 50Hz and part on 60Hz and the two networks are interconnected through a DC link. The cables under the English Channel linking the British and French grids also operate on DC. The first Anglo-French link opened in 1962 had a capacity of 160MW. New cables laid in 1986 with a capacity of 2000MW are buried in a trench cut in the sea floor to avoid damage
