Resumo:
The transfer of electrical energy, from generation to final consumers, is carried out through a system, normally called the Electric Power System (EPS), which must have quality, reliability and present as few as possible interruptions with a quick reestablishment of service to its customers.
Regarding protection, the transmission lines (TL) are protected by means of IEDs (Intelligent Electronic Devices), containing the ANSI 21 function (distance), often with redundancy to obtain greater reliability in the detection and classification of faults and, consequently, in the immediate operation of shutting down the section under fault of the transmission line.
This master's dissertation aims to analyze the factors that impact the correct measurement of relay 21, for single-phase faults on double circuit lines, considering the influence of the mutual zero sequence coupling of the parallel lines. This work was conducted, firstly, by evaluating the various documents in the literature, which talk about the theoretical problems involved in the correct measurement of relay 21. Secondly, the program Matlab was used to calculate the theoretical errors and then carry out simulations on a real-time platform, in this case a Real-Time Digital Simulator (RTDS).
The system considered in Matlab and modeled in RTDS contains a 440 kV TL double circuit (operating in parallel), sometimes with one of these circuits disconnected and grounded, as well as two power supplies at the ends. However, a distance element is influenced by several factors, such as: fault resistance, remote infeed, soil resistivity, line loading, zero sequence mutual coupling existing in double circuits which, in theory, could be minimized using correct parameterization of 21 function, including compensated currents in the case of earth faults.
The mentioned system was modeled in the real-time digital simulator (RTDS), including virtual protection relays (ANSI 21 function) in each of the parallel line circuits, with the aim of analyzing the simulation results regarding impedance measurements during faults phase-to-ground in different positions along one of the circuits, also considering different fault resistance values and the mutual compensation factor set (or not) in the relays. The values obtained are qualitatively compared with theoretical results calculated by a MatLab routine and presented in the form of tables and various graphs.
