Browsing by Author "Martins, L. Sousa"
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- A computer-based testing system to evaluate protective relays as a tool in power system protection educationPublication . Martins, L. Sousa; Fortunato, Carlos; Pires, V. FernãoTeaching power system relaying is a fundamental issue in a power system high-level course. However, for an effective instruction of this topic an experience with real equipments can be considered as fundamental. To achieve this purpose, in this paper a new approach for the practical learning of power system relaying is presented. This consists of a computer-based testing system of relay-operating characteristic. Different relay types and developed specific software are also an important piece of the laboratory practice. Using this system it is possible to understand the performance and limitations of different protective relay systems and to test a real relay disoperation. The benefit of using this system is not available through traditional lectures and textbooks.
- A current differential line protection using a synchronous reference frame approachPublication . Martins, L. Sousa; Fortunato, Carlos; Pires, V. FernãoThis paper presents a new approach for a current differential protection of the transmission lines. This approach is based on the Park transformation or ABC-dqo transformation. Using the ABC-dqo transformation the three phase quantities are transformed into a synchronous rotating reference frame. In this way, the line currents of the three phase system are measured and transformed into three dc components. So, immunity to problems such as sampling misalignment and time delay of the communication channel will be improved. Several test results are presented in order to show the effectiveness of the proposed approach.
- A power amplifier system for testing of distance relay operating characteristicPublication . Marçal, Rui; Rodrigues, Ricardo; Fortunato, Carlos; Martins, L. Sousa; Pires, V. FernãoThis paper describes a power amplifier system for testing of distance relay operating characteristic. This power amplifier is based on two three phase inverters with a neutral wire. The output power currents and voltages are controlled by a sliding mode controller. A developed matlab/simulink digital simulator generates the test signals. This test signals are converted in current and voltage references using a microcontroller to connect the digital simulator to the power converter amplifier. Experimental results from a laboratory prototype are presented and discussed.
- Transmission lines protection based on the current eigenvalues differential conceptPublication . Pires, V. Fernão; Guerreiro, M.; Fortunato, Carlos; Martins, L. SousaThis work presents a new approach for a current differential protection of the transmission lines. The proposed approach is based on the Clarke-Concordia transformation and principal component analysis. First the acquired current signals are transformed into “αβo” components by applying the Clarke-Concordia transformation. This allows obtaining typical patterns. To identify these patterns a principal component analysis is performed. Several tests under different fault conditions were performed. The obtained results allow verifying the effectiveness of the proposed approach.