Marko Zubčić

This paper investigates the detection of broken rotor bar in squirrel cage induction motors using a novel approach of randomly positioning a triaxial sensor over the motor surface. This study is conducted on two motors under laboratory conditions, where one motor is kept in a healthy state, and the other is subjected to a broken rotor bar (BRB) fault. The induced electromotive force of the triaxial coils, recorded over ten days with 100 measurements per day, is statistically analyzed. Normality tests and graphical interpretation methods are used to evaluate the data distribution. Parametric and non-parametric approaches are used to analyze the data. Both approaches show that the measurement method is valid and consistent over time and statistically distinguishes healthy motors from those with BRB defects when a reference or threshold value is specified. While the comparison between healthy motors shows a discrepancy, the quantitative analysis shows a smaller estimated difference in mean values between healthy motors than comparing healthy and BRB motors.

Energy efficiency generally implies the efficient use of energy in all sectors of final consumption—industry, services, agriculture, households and transport. Shipping accounts for nearly 3% of global greenhouse gas emissions, making it the sixth largest CO₂ producer in the world. This is a result of inefficient ship design, lack of planning and optimal use of resources. As the transport sector expands, so does the pressure for a greener and cleaner maritime industry. Reducing fuel consumption is a major driver of the need for energy efficiency on ships. In this paper, due to the importance of maritime transport, we observed the impact of reducing the dimensions of the main switchboard as a contribution to energy efficiency. This contribution is not of great importance as is the case with the optimization of the navigation route, etc., but it certainly affects the weight and, thus, the fuel consumption, which contributes to energy efficiency in the designed system. The aim of this paper is to optimize the design of the main switchboard by using 2D simulations of possible bus topologies, in order to develop six different busbar models and find one that best meets the requirements. The simulation results indicate the optimal location and dimensions of the busbars in the main switchboard in accordance with the switchgear parameters. Apart from the change in layout and dimensions of the busbars, the replacement of conventional instrument transformers with new current/voltage sensors contributes to a significant reduction in the weight and size of the switchboard, which ultimately benefits energy efficiency.

The chosen electrical equipment, i.e., the earthing switch has its application in marine switchgear. In this paper, the reduction of dimensions is considered with the purpose of making it more energy efficient in terms of onboard application. This test validates that the earthing switch as an electromechanical device is capable of withstanding electrodynamic forces. Two approaches are applied and compared. Both approaches are based on a simplified three-dimensional (3D) model of the earthing switch. The first approach is analytical: the electrodynamic forces are calculated with the assumption that currents flow in concentrated lines. Maximum static stress is compared to the yield point of the earthing knife material. The second approach applies the finite element method in the time domain. The results show that the rectangular cross-section can withstand the electrodynamic forces produced by the given currents. Simple cost analysis shows how much material is saved by changing the design from standard earthing knifes with C channel profile to the rectangular profile. Material savings make this study interesting for marine switchgear application. The paper shows qualitative influence of the obtained results on the Energy Efficiency Design Index of the ships.

Maja Krčum, Marko Zubčić, Anita Gudelj; Review, pp. 284-288 Download