Problems and solutions for protective relay applications in petroleum facilities-some protection applications for generators and transformers

Two areas of medium and high voltage protective relaying for industry applications are addressed: (1) generator backup protection and (2) protection of transformers with relatively high values of available fault currents. The presentation is a series of cases that were studied on electrical power systems at different industry facilities. The first part of this paper discusses the use of voltage controlled or voltage restraint time-overcurrent (51V) relays and distance (21) relays applied as generator backup protection. Actual applications on bus-connected and unit-connected generators are presented with a discussion of the protective relay settings and problems encountered. The second part of this paper discusses the application of proper protective devices, including protective relays and instrument transformers to protect transformers installed on buses with relatively high available primary fault currents. Problems encountered with the instrument transformer and protective relay selection are addressed, including saturation, burden, and protection from failure. Emphasis is placed on routine and special applications, lessons learned on real projects, and trouble spots to avoid.