Petr Kacor

Results from hybrid off-grid power system operation analysis

Hybrid off-grid power systems are used for supplying electrical devices in case a connection to the normal distribution system is not possible for some reasons. In this article, we draw conclusions from the operation of the hybrid power system used for supplying street lighting systems. Photovoltaic and wind power plants are used as energy sources in this case.

Indication of failures of rotor bar on induction machine with squirrel cage rotor in its external electromagnetic field

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.

Analysis of force characteristic of short-circuit release in low voltage circuit breaker

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.

Modelling of Antiphase Noise Reduction of a Transformer

This article discusses about development of research of using antiphase elimination of noise reduction. It dedicated to modeling of acoustic phenomena by software AnSys and possibility of simulation and modeling of acoustic short-circuit over the antiphase elimination. The team of authors of this article have been involved in the issue of eliminating noise emissions by electronic equipment from the year 2009. This theme is extremely relevant at present since the health of the human population is a definite priority in human efforts. The first functional prototype for an Antiphase Eliminator, which was installed on a power transformer, was successfully constructed in 2012 on the basis of research. The team develops anti phase eliminator for over 6 years. Now after completion of analog prototype began with digitization and thus building another prototype. This new prototype will processes the signals into digital form. Because the efficiency of the analog prototype is relatively low, the team began together with the digitization also work on computer models that would reveal possible causes of low efficiency. These models already subtracted signals only, as it was on the start of research. These models simulate real acoustic propagation in space, his reflections and the resulting impact of the action of antiphase eliminator.

CFD analysis of temperature distribution of PEM type fuel cell

The paper deals with analysis of temperature rise in a fuel cell module using the CFD numerical model. The module is based on a low-temperature fuel cell with polymer electrolytic membrane. There is a simulation of stable condition, when the cell supplies constant output and the system generates waste heat exhausted through the cooling fins. The aim of analysis was to find potential problematic spots with higher temperature rise values. The results of simulation serve for design of an optimal cooling for the fuel cell.

Possibilities of program EMTP - ATP to analyze the starting current of induction motor in frequent switching

Program EMTP ATP is a very effective tool for solving and analysis of transients of various electrical circuits. We used this program for analysis energy stored in inductance of induction motor and the influence to starting current. Paper deals with the situation repeating the induction motor starting, that occurs immediately follow each other. During such repeating induction motor starting the influence of already existing magnetic field in the motor is applied. Is is caused by energy stored in main inductance of induction motor. We performed a simulation in EMTP ATP and after that we made measurement.

Adjustment of pull characteristics of lever magnet with variable reluctance

Lever magnets, often defined s magnets with variable reluctance or open C-frame magnets, belong to significant components of automation system, heir thrust being based on the force generated upon convenient curvature of flux lines within the magnetic field gained through specific geometrical layout of the magnetic circuit. Their main advantages include a relatively high tensile force at the beginning of armature path, especially with the noiseless operation that predestines such magnets for utilization in automation systems, electric-pneumatic circuits as well as in electric-pneumatic controls of wind music instruments. Other applications comprise electric switching gear, mainly multiple-pole contact relays with low noise operation. Pull characteristics can be greatly affected by supplementing magnetic circuit with n extra permanent magnet. This paper describes characteristics of this type of magnets and the impact of the extra permanent magnet on the resultant pull characteristics.

Influence of rotor slot shape on the parameters of induction motor

The article deals with the influence of the shape Boucherots 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 Boucherots 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.

Coupling of finite and boundary elements for transient eddy current problems

A symmetric coupling of methods of finite and boundary elements for numerical solution of transient eddy current problems is described. This is an essential step in modelling of electromagnetic forming of metalic sheets. The finite element method is employed in the conducting region of the metalic sheet. The boundary element method relies on the Stratton-Chu representation formula and it models the electromagnetic field in the air including its decay at infinity. We impose external currents by the Biot-Savart law.

Small-scale wind power in off-grid and its controlling by variable load

This article solves problem of small-scale wind power in off-grid. Article offers solution for controlling load by prototype. Prototype manages the load so that the induction generator is still in his optimum. The article focuses on controlling by prototype. The whole design of prototype, suitable value of capacitors and load is also discussed in this paper. Prototype is created from MOSFETs and microcontroller structure it allows really low price of whole prototype. The prototype is designed so that it can be used for different powers of induction generator and different weather conditions. The prototype has got self education program for learning of optimum of induction generator. Article shows waveforms from measurements, where the prototype operates in education mode and where the prototype operates in full educated mode.