Report on New Differential Protection Method After 6 Years in Service

This new protection function was first presented at Georgia Tech in 2012. This paper will discuss how this new approach using a differential type protection schemes on automated distribution feeders performed over a 6 year period. The paper will discuss in detail a number of field operations. The paper will provide detailed information of all considerations that was implemented as part of the protection function to ensure dependable performance. At A&N Electrical a two source loop feeder system and at Wake Electrical a mesh connected 3 source feeder system provided the field operation content that for this paper. This new approach is important as current methods using time coordinated over current curves present real challenges for protection engineers to overcome. This will become more of an issue as Distributed Generation perpetration increase on the distribution system. An Automated Distribution Feeder with an ever changing topology and or power source, required true adaptive protection systems to ensure that protection will accurately operate for all system faults. An adaptive approach can be extremely costly and complex to deploy, test and commission. Current protection systems are well suited to protect simple static feeder topologies. When a feeder system topology changes the protection system must adapt to accommodate this change. Although most protection devices today can provide up to 8 protection setting groups, the calculation of all the time coordinated curves to be implemented can become a time consuming and costly exercise. In addition all settings for all setting groups must be implemented, tested and commissioned on all devices prior to activation of the feeder adding to the implementation costs. The differential approach is immune to changes of feeder topology and provides a simple solution to complex problems.