Structural health monitoring systems are employed to evaluate the state of structures to detect damage, bringing economical and safety benefits. The electromechanical impedance technique is a promising damage detection tool since it evaluates structural integrity by only measuring the electrical impedance of piezoelectric transducers bonded to structures. However, in real-world applications, impedance-based damage detection systems exhibit strong temperature dependence; therefore, variations associated with temperature changes may be confused as damage. In this article, the temperature effect on the electrical impedance of piezoelectric ceramics attached to structures is analyzed. Besides, a new methodology to compensate for the temperature effect in the electromechanical impedance technique is proposed. The method is very general since it can be applied to nonlinear (polynomial) temperature and/or frequency dependences observed on the horizontal and vertical shifts of the impedance signatures. A computer algorithm that performs the compensation was developed, which can be easily incorporated into real-time damage detection systems. This compensation technique is applied successfully to two aluminum beams and one steel pipe, minimizing the effect of temperature variations on damage detection structural health monitoring systems in the temperature range from −40°C to 80°C and the frequency range from 10 to 90 kHz.

Pipelines have been widely used for the transportation of chemical products, mainly those related to the petroleum industry. Damage in such pipelines can produce leakage with unpredictable consequences to the environment. There are different structural health monitoring (SHM) systems such as Lamb wave, comparative vacuum, acoustic emission, etc. for monitoring such structures. However, those based on piezoelectric sensors and electromechanical impedance technique (EMI) measurements are simple and efficient, and have been applied in a wide range of structures, including pipes. A disadvantage of such technique is that temperature changes can lead to false diagnoses. To overcome this disadvantage, temperature variation compensation techniques are normally incorporated. Therefore, this work has developed a complete study applied to damage detection in pipelines, including an innovative technique for compensating the temperature effect in EMI-based SHM and the modeling of piezoceramics bonded to pipeline structures using finite elements. Experimental results were used to validate the model. Moreover, the compensation method was tested in two steel pipes—healthy and damaged—compensating the temperature effect ranging from −40 °C to +80 °C, with analysis on the frequency range from 5 kHz to 120 kHz. The simulated and experimental results showed that the studies effectively contribute to the SHM area, mainly to EMI-based techniques.

The growing use of nonlinear devices has raised the harmonic levels in power systems. A challenging power quality problem is determining how much each installation contributes to the harmonic voltages measured at a point of common coupling so that the costs of mitigation solutions can be fairly divided. Currently, there is still no practical worldwide established method to solve this problem. The IEEE PES Task Force on Harmonic Modeling and Simulation developed a Benchmark Test System to support this line of research. Therefore, this study uses the IEEE PES Benchmark to evaluate and compare harmonic contribution determination (HCD) methods. To do so, this Benchmark Test System was implemented in MATLAB/Simulink and used to test five HCD methods proposed in the literature under different network operating cases, including cases with background distortions and resonance. The methods are the Voltage Harmonic Vector Method, the IEC Method, the Dominant Impedance Method, the Capacitor Switching Method, and the Harmonic Current Injection Method. It has been found that the HCD methods generally led to similar contribution percentages, proving the convergence of the methodologies. In addition, an analysis of the methods' sensitivity to input measurement errors was done.

Short-term voltage variations (STVVs) are phenomena manifested as voltage sags, voltage swells, or interruptions lasting up to 1 minute. Despite their short duration, they greatly influence the operations of loads. In fact, residential, commercial, and industrial consumers can be strongly affected when facing supply discontinuities, loss of production, physical damages, and other issues. Under such circumstances, conflicts may arise between suppliers and consumers. Thus, a strategy that identifies whether the STVV phenomenon was produced upstream or downstream of a given point of common coupling between two agents interconnected by a transformer is proposed in this paper. The methodology is based on the transference mechanism of imbalance indicators through this connecting transformer. The current process is not about determining the physical location of the disturbance in the network but only about establishing the responsibility for the disturbance. The effectiveness of the process is determined through computational and experimental studies, for which typical electrical systems are employed. To this end, unbalanced STVVs are imposed on these systems, and the voltage and current imbalance levels on the primary and secondary sides of transformers are correlated to validate the proposal.