The paper deals with impact of electric asymmetry of rotor coil on induction machine on the time course of electromagnetic flow inside the machine as well as any change to the course of electromagnetic leakage flux on the surface of machine frame and in its immediate vicinity. Familiarity with dependency between the course of flux and specific failures of the machine helps with measuring of the leakage flux by simple means, with records to be utilised as a value easy to obtain and measure to proceed with non-contact diagnostics of a specific machine failure. The paper further refers to results of mathematical modelling to show the indication of a specific failure, including its comparison with measurement.

Contact connections in electrical machines and apparatus are important elements in the whole power supply network and a high level of reliability is expected there. Contact resistance is a fundamental criterion in the design of an electrical contact or contact system. The contact resistance should be as low as possible to minimize losses due to the current passage and the related heating of the contact connection. The value of the contact resistance depends on the material used, the value of the applied force, the type of contact, and, last but not least, the quality of the surface and chemical layers. In this paper, an initial diagnosis of the contact material is performed based on the determination of the sample’s specific resistivity by the four-wire method and the evaluation of the measurement uncertainty. The work is followed by the design of a testing device that uses crossed bars to measure the change in contact resistance as a function of the magnitude of the applied force. An analysis of the sample mounting method is performed here using FEM simulations of the current field and shows the interaction between the holder and the sample in terms of current line transfer. The proposed system is then used for experimental measurements of the material-dependent coefficient K_C for verification of existing or newly developed materials in electrical engineering, where the values of the K_C coefficient are not known. Finally, the paper also deals with the measurement of fritting voltage for individual contact pairs having surface quality corresponding to brushing.

A short-circuit tripping device is an integral part of a miniature low-voltage circuit breaker. As far as its design is concerned, the release mechanism comprises a metal case with a moving armature and a compression spring; the armature is further surrounded with winding (coil) made of copper wire. Short-circuit current flowing through the protected circuit brings the release armature in motion and the force produced acts on the mechanism lock to arm the breaker. This paper will present application of electromagnetic FEM analysis to calculate the static and dynamic characteristics of force acting in short-circuit release of a circuit breaker. The both analysis are compared to the real measurement of armature moving by the help of high-speed camera.

Hydrogen is one of the modern energy carriers, but its storage and practical use of the newest hydrogen technologies in real operation conditions still is a task of future investigations. This work describes the experimental hydrogen hybrid energy system (HHS). HHS is part of a laboratory off-grid system that stores electricity gained from photovoltaic panels (PVs). This system includes hydrogen production and storage units and NEXA Ballard low-temperature proton-exchange membrane fuel cell (PEMFC). Fuel cell (FC) loses a significant part of heat during converting chemical energy into electricity. The main purpose of the study was to explore the heat distribution phenomena across the FC NEXA Ballard stack during load with the next heat transfer optimization. The operation of the FC with insufficient cooling can lead to its overheating or even cell destruction. The cause of this undesirable state is studied with the help of infrared thermography and computational fluid dynamics (CFD) modeling with heat transfer simulation across the stack. The distribution of heat in the stack under various loads was studied, and local points of overheating were determined. Based on the obtained data of the cooling air streamlines and velocity profiles, few ways of the heat distribution optimization along the stack were proposed. This optimization was achieved by changing the original shape of the FC cooling duct. The stable condition of the FC stack at constant load was determined.

This paper focuses on description of the operation principle inherent to the Adams' electric motor-generator fitted with permanent magnets made of rare earth (NdFeB). For checking of the basic design we have used the FEM electromagnetic simulation made by Ansys Workbench and Ansys Maxwell. The Adams' motor generator is basically assembled with slight deviations from the original patent with respect to the stator magnetic circuit design. The resultant speed-torque characteristics obtained by measurement and the input power values have been processed to determine the machine's efficiency.

The article deals with the influence of the shape Boucherot's cage on induction motor parameters, which are mainly values of starting torque, breakdown torque, but also power factor, efficiency and starting current. Torque curve of induction motor with Boucherot's cage is characterized by a high value of starting torque with a relatively low starting current. The waveform of the resulting torque characteristics is the sum of characteristic of outer cage and characteristic of the inner cage. These partial waveforms are given by their impedances which are given by active part - so by cross-section of rotor slot, and by reactive part - so by self-inductance respectively reactance which is associated the depth of rotor slot, the width of the rotor tooth, width and height of bar etc. The principle of calculating the reactance and resistance of the machine is given in the article and also to analyze the equivalent circuit according to the choices we derive formulas for equations required torques. We are finding the optimum of shape of rotor slot for the maximum size of the relative starting torque and minimum size of relative starting current while maintaining favorable power factor and efficiency the motor.