High voltage under-ground cable data communications for high speed unit protection and control

The authors present the findings of an on-going investigation into the use of HV power cables for high security, dedicated data communications between substations. This communications system provides the data transfer required for high speed unit protection of distribution feeder circuits and network automation. The communications system uses a high frequency carrier with the line driver and receiver circuits tuned to pre-defined channels. The propagation characteristics of typical underground HV cables together with the coupling circuits have been examined. The internal protocols and coding techniques used to organise the data into message blocks and to provide error detection and limited correction are introduced. Using 80 kBits/sec bi-directional data transmission along the power circuit, the system provides user data rates of 40.8 kbits/sec for protection and 4.8 kbits/sec for network automation and 4.8 kbits/sec for `house-keeping´