Discussion on the revision of DL/T 684—2012 guide of calculating settings of relay protection for large generator and transformer

Abstract

DL/T 684—2012 Guide of Calculating Settings of Relay Protection for Large Generator Transformer （hereinafter referred to as the “2012 Guide”） has played a significant role in improving the correct operation rate of relay protection devices for generator transformers and ensuring the safe operation of electrical equipment in power plants. However， with the increase in capacity of individual generator units in China and the emergence of new faults， the “2012 Guide” has proved inadequate， requiring revision to better guide engineering practice. Therefore， this paper analyzes the problems in the “2012 Guide” and puts forward specific revision suggestions to address problems such as misoperation of generator differential protection under sympathetic inrush current， misoperation of false power-on protection under poor synchronous conditions， and tripping of gap zero-sequence current protection of main transformer before reclosing in the case of transient single-phase ground faults on the line. The suggestions can provide reference for the revision of the “2012 Guide”.

Keywords

• generator differential protection
• stator grounding protection
• out-of-step protection
• reverse power protection
• false power-on protection
• stator overload protection
• negative sequence overload protection
• gap zero-sequence protection of main transformer