Enabling future meshed operation for distribution networks

摘要

Distribution networks have traditionally mainly been operated as groups of radial feedersprotected by overcurrent relays, fuses and reclosers. The performance of traditional radialfeeder protection is also limited in the presence of distributed generation. An alternative is toapply a looped or meshed architecture found in transmission. This approach has beenapplied in some distribution networks, typically using pilot-wire differential protection or amodern equivalent. Wide scale application of this is limited due to the requirement for a circuitbreaker and relay at each distribution substation. A more cost effective solution may be todivide the meshed network into wider areas each containing multiple distribution transformersand line segments and having circuit breakers at the boundary terminals. Protection of eachzone would be selective so that any distribution circuit fault only interrupts supply to a singlezone and other zones remain energized via alternative paths.This paper considers the protection system that would be required for this meshed networkconfiguration to operate successfully, even in the case of increasing levels of distributedgeneration. Direct application of existing transmission protection methods may not beappropriate due to differing network characteristics. A much greater number of line terminalsare possible and, as each line section supplies a much smaller load, lowering the overall costof the protection system is more important. The technology available in distribution networksalso differs to that used at higher voltages and is changing rapidly. Rogowski sensors areoften being used in the place of current transformers (CTs), eliminating the need tocompensate for saturation under fault conditions. Dedicated communications networks toeach distribution substation are not common but the installation of Fibre-to-the-Premise(FTTP) networks in urban areas may be a possible means of providing high-bandwidthprotection communications at a low cost as well as a means of reliable time synchronisation.The emphasis of this paper is to illustrate the potential architecture to manage meshedoperation of distribution lines/cables leveraging the broadband communications and cheapersensor development. The chosen biased differential system assumes the availability of nonsaturatingcurrent sensors and a suitable communication network. The GPON standard forFibre-to-the-Premise communications is examined and shown to be suitable as a medium forprotection phasor transfer.A futuristic view of how distribution network will emerge enabled through sensors,communications and standards is the essence of this paper and the authors believe will addvalue to the preferential subject PS1.