Loss of mains protection relay performances when subjected to network disturbances / events

Loss of Mains protection (LOM) is the requirement for the connection of Generation to the UK distribution network. Its role is to prevent the generator from accidentally energising an electrically isolated section of network. Such requirements are derived from Statutory Regulations, and the method of achieving it are described in Engineering Recommendation G59/1 and Engineering Technical Recommendation 113 — often referred to as ETR 113 [1,2]. There is however a general concern, within the power system fraternity, that the existing generation of LOM protective relays are unduly influenced by, and sensitive to, network disturbances. Whilst standard settings [1,2] are used, the level of sensitivity has been found to be primarily determined by the type and make of protection relay used. This can directly impact on the level of ‘false tripping’ for connected distributed generation, which in turn increases maintenance requirements, reduces their availability, and can affect the overall performance of the distribution network. This paper presents an overview of the high level performance of several Loss of Mains protection relays. Real network disturbances were used in the testing, captured using installed data loggers, and a range and variety of network disturbances were used and applied to the relays. These disturbances were not true LOM events and so enabled the performance and immunity of the relays to be evaluated under controlled conditions.