Modelling of numerical distance relays using MATLAB

Numerical relays are the result of the application of microprocessor technology in relay industry. Numerical relays have the ability to communicate with its peers, are economical and are easy to operate, adjust and repair. Modeling of numerical relay is important to adjust and settle protection equipment in electrical facilities and to train protection personnel. Computer models of numerical relays for the study of protection systems are greatly enhanced when working along with an Electromagnetic Transient Program (EMTP). This paper describes distance relay model built using MATLAB environment. The behavior of the distance relay model has been verified using data about different faults generated by the Electromagnetic Transient Program (EMTP-ATP). Data generated by EMTP-ATP describes the voltage and current signals at the relay location both immediately before and during the fault. The signals include the DC offset and the high frequency traveling waves. The data is applied to the relay simulator, which then evaluates whether the impedance trajectory of the fault enters one or more of the operating zones. The results are presented in graphical form using an R-X diagram. The model is then verified by checking the model impedance measurement at different fault locations, and resistive faults. The paper demonstrates the benefits achieved when using a computer simulation of a relay in conjunction with a transient power system simulation.