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Transient Measurement


 Considering the growing interest in evaluating the interaction between the electric power system and high voltage equipment, some utilities in the Brazilian electric sector have asked Cepel for measurements and evaluations regarding transients subjected by equipment, mainly in transformers, autotransformers and reactors. This situation began to gain relevance in cases where there is a need to identify the reasons for equipment failures.


In order to identify the type of electrical request an equipment is subjected to, it is instrumented, and transient voltages arising from maneuvers in the substation are acquired during a few months. In some cases, the equipment is previously characterized in the frequency domain (SFRA - sweep frequency response analysis) to obtain amplitudes, resonant frequencies and natural anti-resonance.


The transient voltages values are stored on a specific hardware and made available via intranet for the necessary analyzes. Events resulting from lightening discharges are not considered.


Based on the acquisitions of the transient voltages reaching the equipment, the signals are analyzed, and their main frequencies are identified through the use of an FFT (Fast Fourier Transform) routine.

From the identification of the natural frequencies of equipment oscillation and the frequency spectrum of transient voltages capable of reaching the equipment under analysis, it is possible to infer if there is any interaction between the equipment and transient voltages generated by maneuvers in the substation or in the system.

Based on the information of frequencies and amplitudes of the acquired signals, the following evaluations are performed: effect of the maneuvers on the natural frequencies of oscillation of the equipment, and evaluation of the risk involved in the maneuvers measured by means of the frequency domain severity factor (FSDF)


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