International Scientific Journals
of Scientific Technical Union of Mechanical Engineering "Industry 4.0"

Тhe widespread use of hydro power plants is well known. In addition to such plants that have been in operation for decades, there is currently an increased interest in the design and construction of new plants. In this regard, the accumulation of statistical data on the change in certain quantities and parameters for different periods of time and operating modes is important. On the other hand, subsequent processing of such accumulated data according to certain rules is possible. The main goal of this paper is statistical processing of data for a specific hydro power plant, in order to identify certain trends and prepare recommendations for improving activities.

Paper deals with testing of a specific centrifugal fan under different conditions – changes in supply voltage and flow rate regulation by throttling, as well as the application of frequency control. A digital portable multifunctional device has been used for measuring and analyzing three-phase electrical circuits. Some intrinsic electrical variables have been measured and recorded, and others have been subsequently calculated. Comments, conclusions and recommendations have been done. The results obtained would be interesting for specialists dealing with this technical equipment.

Paper deals with determining the possible savings of electrical energy in a passenger elevator. After carrying out calculations with a set number of floors of an administrative building and number of passengers according to a proven and widely used methodology in Bulgaria, an appropriate three-phase squirrel-cage induction motor has been selected to drive the considered elevator system. Calculations have been also carried out on the possible recovery, i.e. returning electrical energy back to the supply power grid when the driving rotating electrical machine is switched to generator mode. Variants with different number of passengers and movement of the cabin in upward and downward directions were theoretically studied. The active power, time to work in recovery mode and the active energy returned to the power grid are defined for each specific case. Calculations of possible electrical energy return in generator mode would be of interest to specialists dealing with these technical facilities.

The paper deals with an operating photovoltaic plant in Bulgaria. The wide application of photоvoltaic plants in the energy system is known. At the same time, subject matters about their normal functioning are fundamental. The goal of the paper set is to analyze data from the operation of a photovoltaic power plant , which is ultimately related to improving its behavior. Relevant conclusions have been dоne.

Paper deals with determining the permissible number of switches on per hour depending on the load and operating mode parameters – starting and stopping times, pause duration, etc. The criterion is that the overheating of the stator winding does not exceed the overheating at nominal mode and load. The basis of the chosen method is the assumption that the electric motor is assumed to be a conditionally uniform body, i.e. a body made of the same material with an infinitely large thermal conductivity and therefore having the same temperature throughout its volume under all possible modes and loads. The results of the calculations with a computer program
implemented are presented in tabular form.

Paper deals with a newly designed three-phase asynchronous electric motor with an application as a traction motor for driving compact battery-powered electric vehicles mainly in urban environments. The main characteristics of the motor are presented. The problems and solutions related to the sizing and optimization of the motor in the design according to various criteria and conditions are analyzed, with energy efficiency being the main determining factor.

Paper focuses on the use of renewable energy sources and in particular the use of water energy. A hydro power plant is a complex of facilities and equipment for converting the energy of the water flow into electrical energy. The advantages of hydro power plants are obvious – a supply of energy constantly renewed by nature itself, simplicity of operation, absence of environmental pollution. Taking into account the growing role of small and medium-sized enterprises in the economic development, both of an individual country and on a global scale, as well as the widespread orientation towards the use of renewable energy sources in the production of electricity, the main goal of the current development is the analysis of the operation of the electrical part of a specific hydro power plant with small power. Statistical processing of operational data on the change of certain variables was carried out. In conclusion, it is summarized that the hydro power plant under consideration has good operational indicators.

Paper deals with low power photovoltaic system implemented by means of flexible module. Flexible modules powered by sunlight are really a very interesting and promising novelty, being one of the newer alternative energy sources. A selected technical solution with specific characteristics of the individual components is presented. Measurements with digital measuring equipment were performed and experimental results were presented. In conclusion, it is summarized that the tested flexible module gives good results.

This paper is devoted to some up-to-date computational tools, which are on-line available and appropriate to remote learning as well as to scientific research implementation relevant to mathematics and their applications.
The following aspects are concerned and discussed: some of the opportunities and benefits afforded by the software tools which are taken into consideration; necessary requirements which have to be met in order to use these tools; some disadvantages and drawbacks which may arise.
Comparison of fees and prices for different mathematical software tools is done.
For purpose of illustration realistic examples are also given.

In specific energy saving measures, special attention is paid to driving technologies, as electric drives account for two thirds of industrial energy consumption. Paper deals with appropriate selection of electric motor with higher efficiency for shuttleless weaving grapple machine in order to retrofitting the electric drive. Such machines are not single pieces, but are always a certain set of a given production company. Once electricity consumption is reduced by investing in energy-saving engines, this can be the basis for intelligent and efficient energy management, accurate predictions of electricity consumption for future periods, which ultimately leads to increased energy efficiency of manufacturing enterprises.and systems.

Paper deals with general overview of the electric vehicles on-board chargers, available in operation – both for new such vehicles and for those that have been obsolete, but are still moving on the roads in our country and around the world. Studies have been conducted and useful information on battery-powered electric vehicles and plug-in hybrid electric vehicles has been systematized. All this is done in connection with the ubiquitous decisive steps for large-scale and global introduction of electric vehicles, such as appropriate choice and necessity and the related topics for drastic change of the car fleet, which will cover firstly urban vehicles, the energy balances of power grids of the individual countries with a careful analysis of the expected load for normal operation, the environmental benefits, the energy efficiency and economic benefits from the use of electric vehicles and their technical improvement in the long run. In addition, under good management, the development of electric mobility can be one of the ways for achievment of employment and industrial growth.