Automatic switching scheme on the city of London 33kV network between Back Hill and Finsbury Market

This paper refers to the Automatic Switching (AS) System implemented on UKPN´s 33kV network between Back Hill and Finsbury Market 132kV/33kV substations. The use of latest technology and peer to peer communications has allowed the implementation of a high speed network recovery system with complex switching regimes whilst incorporating a relatively simple architecture. The advanced control platform allows for flexible switching matrixes to be set at each site for different running arrangements. The scheme design allows for up to ten control inputs to initiate an independent switching sequence that can reconfigure the bus bar running arrangement, change the interconnector group settings groups and send to the remote station a command to reconfigure its bus bar running and feeder group settings. The control inputs are monitoring the incoming grid transformer main protection trip relays, the interconnector group trip relays and the remote end AS unit using the communications protocol IEC 61850 over fibre between the two sites. This allows for signals to be sent to reconfigure remote ends to achieve fast transfer of load between the two sites. Programming of the tripping matrix is achieved using IEC6070-5-103 communications protocol from a remote station or locally via a human machine interface at the substation. Previous design of such systems using fixed switching sequences without the possibility of remote communications has meant that the schemes have been limited in their operation and where they can implemented. By designing the logic in a way that gives full flexibility of operation meant that this can be applied for any possible running configuration.