A Network Switching Expert System For AC Railway Electrification

This paper reports the development of a PROLOG expert system utilising computer graphics for on-line monitoring and control of the 50-Hz single- phase overhead current collection catenary system currently in operation in Hong Kong. Running as an on-line consultant on a personal computer, this expert system allows operating personels to perform pseudo network switching on each of the six full graphics pictures representing the whole of the catenary line system. This displays may be zoomed in or out to show either details or overall layouts. Users are able to examine from graphics displays effects of their own choice of switching sequence. Legal switching brings about changes in display configurations and/or colours to relcord Circuit- breakers change of ON/OFF status, or relocation of supply points. The,expert system also checks against illegal switching which causes violation of interlocking rules, isolation of catenary sections from the supply, and/or phase-to-phase short-circuit of the utility system. In addition, this paper reports further work to develop a methodology of evaluating voltages across cross-overs which run between parallel catenary lines. A cross-over with excessive voltages across it should not be used to divert a train due to the risk of damaging insulators across the cross-over. An accurate evaluation of cross-over voltages involves the solution of a large set of simultaneous differential equations governing train time-tables, controls, movements as well as power consumptions. This paper would however show how cross-over voltages are derived on the basis of approximate relationships relating these quantities. Finally, the expert system provides a user-friendly environment and a knowledge acquisition sub-system to enable editing of a knowledge base to be made with little or no assistance from a knowledge engineer.