High Speed Distance Relaying Using Least Error Squares Method

Abstract

Due to the increasing scale and complexity of modern power grids, the demand for high-speed protection is growing. Distance relays are the most commonly used type for transmission line protection. Fast sub-cycle numerical distance elements are useful, especially for EHV/UHV transmission systems (400 kV and above). A primary advantage of the LES method is that the length of the window for phasor estimation can be varied and therefore it can be used as a sub-cycle algorithm. And a mho characteristic is adopted to achieve a trip decision.

The proposed LES technique is tested on a two generator power system configuration. The method is tested using three-phase voltage and current data generated from a PSCAD/EMTDC simulation model. The relay module developed has three functional components: fault detection, phasor estimation, and protective elements. The code for the relay module is developed in MATLAB. Next, different scenarios are considered taking into account the various fault types and locations. Some of the essential practical considerations such as coupled capacitor voltage transformer (CCVT) and current transformer (CT) saturation are also taken into account for the modelled 375 kV (EHV) test system.

In this MSc work, a preliminary prototype is developed with the necessary interfaces for the LES-based distance relay. With the interface, the operating data are imported into FPGA in Comtrade99 format, and then the voltage and current instantaneous values are transformed into single-precision floating type variables.

The thesis work shows that the proposed LES scheme is a straightforward and reliable technique, can run faster than some other sub-cycle techniques, and can be applied to any power system configuration. The main contribution of this research is the application of the LES technique for distance relaying with a faster trip time. The other contributions are developing an FPGA interface for simulation and testing of the proposed relay and addressing some of the hardware implementation issues.