A new method for measuring the exact impedance of digital distance relay based on harmonic and inter-harmonics elimination

The increasing importance of electrical energy, technology development and the growth of irregular energy consumption has increased the importance of power system protection or minimizing the losses from damages and errors caused by human mistakes, weather conditions and drawbacks of other equipment. The relays, which are responsible for power system protection, are important equipment in these networks. Today, the use of digital relays is extended due to the need for fast and high precision measurements in various terms of use. On the other hand, the power networks are affected by various harmonics due to different factors like network errors. The presence of harmonics causes the speed and precision to decrease so that the existing methods are usually sensitive to the harmonics and their results are not sufficiently accurate. In this paper, a method for calculating the error impedance in distance relay and removing the harmonic and inter-harmonic components and decaying DC component using the Kalman Filter and Taylor series and their combination is proposed. Two cases are considered in general. In case one, a permanent three-phase fault occurs in the middle of the first line and in the second line, a permanent three-phase fault is simulated in the middle of the second line. Finally, the results of the simulation are proposed and compared with the other methods.