A microprocessor based protective system for generator-transformer units

The authors describe a general concept of a digital protective system for large generator-transformer units. The main principle of this system is presented and some of its protective functions are discussed. Special attention is given to the overall impedance protective scheme which integrates all the tasks realised separately in conventional techniques by individual relays, i.e. back-up distance, loss of excitation and loss of synchronism (pole-slipping) protection