محمدكاظم حاجي ماهاني

The most important protection for the transmission line is the distance relay, which works based on the distance estimation using the impedance calculation from the relay to the fault location. To estimate the location of the fault, the distance relay must be able to correctly calculate the voltage and current phasor. One of the powerful methods to calculate the voltage and current phasor is discrete Fourier transform and least square error. The fault current signal is not a symmetrical sinusoidal signal and is usually contaminated with a decaying DC component. This component is an exponential signal that add to the sinusoidal waveform of the fault current, and the reason for its existence is the energy stored in the transmission fault selfie property, before the fault occurs. The damping DC component causes errors and fluctuations in the current phasor estimation, and this will prevent the coordination and correct operation of the distance relay in the set area. For this reason, a fast method with high precision is needed to protect the power system, which is not negatively affected by the damping DC component. In this thesis, a hybrid method is presented based on the integration of two separate methods to improve the performance of the least squares method. The first proposed method uses a short information window with a variable size, which gives high speed to the distance relay, and the second proposed method uses a fixed information window, which has a strong frequency response against harmonics and noise. The proposed algorithm is first tested using mathematical formulation in different conditions such as different modes of decaying DC component, noise, harmonic and frequency deviation. In order to check the performance of the presented algorithm by more realistic examples, it is tested in a simple transmission system simulated in Simulink MATLAB under different conditions and all the tested items such as flexibility, speed and accuracy of the proposed algorithm are eva‎luated and confirmed.

رله ديستانس , مولفه نمايي , شكل موج جريان خطا , اثرDC ميراشونده

distance relay , exponentialy component , waveform of fault current , decaing DC offset

Mohamad kazem Hajimahani

Dr. Sadegh jamali