DESIGN AND SIMULATION OF SOFTWARE FOR A HIGH SPEED DIGITAL DISTANCE RELAY

Abstract

Distance relays are used for the protection of transmission lines in electric power systems. These relays estimate an apparent impedance of the protected line from the relay location to the fault and compare it with the relay settings for making decisions. Many approaches have been suggested in the past for developing distance relaying criteria that can be implemented using digital processors. One of the approaches used modal components for developing the distance relaying criterion. The work reported in this thesis investigates the previously suggested distance relaying criterion that used modal transformations. Depending on the type of fault, this criterion requires that some coefficients be computed in the on-line mode. An improved criterion is proposed in this thesis which eliminates the on-line computations of the coefficients. Also, the proposed criterion minimizes the number of divisions. Consequently, it reduces the computational burden on the digital processor. The derivation of the proposed criterion is described. The proposed criterion is used for developing the relay software that is written in the assembly language of the TMS-32010 digital processor. The performance of the relay software was evaluated using the fault data generated by the Electro-Magnetic Transient Program (EMTP). A six bus representation of the Saskatchewan Power Corporation system was modelled in the EMTP. Some of the results of the simulation studies are reported in this thesis.