On the issue of occurrence of fire-hazardous situations with unbalanced power consumption

The influence of phase current unbalance on the probability of occurrence of fire-hazardous situations in industrial premises that receive power in various power supply systems is considered. The theoretical prerequisites for the occurrence of fire-hazardous situations are described. It is shown that zero-sequence flows flowing through a neutral conductor in an unbalanced mode significantly heat it, which can lead to short circuits and conditions for the occurrence of fires. The results of studies of unbalanced conditions in Russia and abroad are presented. It is shown that the zero-sequence flows resulting from current unbalance lead to an increase in additional losses of active power and electrical energy. It is proved that additional heat losses caused by unbalanced power consumption can destroy the insulation of neutral and phase conductors, which is the main cause of short circuits and, as a result, fires. Based on the use of the Matlab graphical editor, dynamic characteristics of variations in phase and interphase currents and voltages, as well as the power loss coefficient, which characterizes the increase in heat losses, are constructed. The analysis of fires and their consequences for various objects in the Russian Federation is made. A computational unit has been developed in Matlab, which is used for calculating and plotting the dynamics of fires and their consequences over the investigated period of time. It is shown that the occurrence of fires and their consequences due to violations of the rules of operation of electrical installations occurs in any premises and sometimes reaches more than 20% of all possible causes of fires. Methods and technical means of minimizing zero-sequence currents as a means of preventing the occurrence of fire-hazardous situations are considered. The principle of operation of an automatically controlled shunt-symmetric device with a minimum resistance to zero-sequence currents is described.

Statistical Analysis of Electric Power Distribution Grid Outages

Power systems in general supply consumers with electrical energy as economically and reliably as possible. Reliable electric power systems serve customer loads without interruptions in supply voltage. Electric power generation facilities must produce enough power to meet customer demand. Electrical energy produced and delivered to customers through generation, transmission and distribution systems, constitutes one of the largest consumers markets the world over. The benefits of electric power systems are integrated into the much faster modern life in such extent that it is impossible to imagine the society without the electrical energy. The rapid growth of electric power distribution grids over the past few decades has resulted in a large increment in the number of grid lines in operation and their total length. These grid lines are exposed to faults as a result of lightning, short circuits, faulty equipment, mis-operation, human errors, overload, and aging among others. A fault implies any abnormal condition which causes a reduction in the basic insulation strength between phase conductors or phase conductors and earth, or any earthed screens surrounding the conductors. In this paper, different types of faults that affected the electric power distribution grid of selected operational districts of Electricity Company of Ghana (ECG) in the Western region of Ghana was analyzed and the results presented. Outages due to bad weather and load shedding contributed significantly to the unplanned outages that occurred in the medium voltage (MV) distribution grid. Blown fuse and loose contact faults were the major contributor to unplanned outages in the low voltage (LV) electric power distribution grid.

Overhead power lines magnetic field reducing in multi-story building by active shielding means

Aim. Reducing of magnetic flux density of magnetic field in multi-storey building, generated by overhead power lines to the sanitary standards level by active shielding means. The tasks of the work are the synthesis, computer simulation and experimental research of three-circuits system of active shielding, which includes three shielding coils. Methodology. When synthesizing the system of active shielding of magnetic field, are determined their number, configuration, spatial arrangement and of shielding coils as well as the shielding coils currents and resulting magnetic flux density value in the shielding space. The synthesis is based on the multi-criteria game decision, in which the payoff vector is calculated on the basis on quasi-stationary approximation solutions of the Maxwell equations. The game decision is based on the stochastic particles multiswarm optimization algorithms. Results. Computer simulation and experimental research of three-circuit system of active shielding of magnetic field, generated by overhead power lines with phase conductors triangle arrangements in multi-storey building are given. The possibility of initial magnetic flux density level reducing in multi-storey building to the sanitary standards level is shown. Originality. For the first time to reducing of magnetic flux density of magnetic field in multi-storey building the synthesis, computer simulation and experimental research of three-circuit system of active shielding of magnetic field generated by single-circuit overhead power line with phase conductors triangular arrangements carried out. Practical value. Practical recommendations from the point of view of the practical implementation on reasonable choice of the spatial arrangement of three shielding coils of three-circuit system of active shielding of the magnetic field generated by single-circuit overhead power line with phase conductors triangular arrangements in multi-storey building are given.

Utilization of Six-Phase Systems to Reduce Technical Losses in Subtransmission Networks of Power Distribution Companies

The objective of this work is to find solutions for the reduction of energy losses in the distribution systems, focusing on the number of phase conductors. In the transmission segment, there are many surveys with six-phase systems. Due to the current regulatory framework in Brazil, the economic viability of this solution is highly restricted. In the distribution segment, the situation is different and there is little research on this alternative. The segment’s valuation model (PRICE-CAP) enables greater technical and economic viability. The main objective of this work is to demonstrate the reduction in technical losses by transforming a three-phase double circuit line into a six-phase line. The work presents: the regulatory framework that shows the advantage of investing in the distribution segment; and performs simulations considering OpenDSS to illustrate the reduction of technical energy losses.

Secured wired BPL voice transmission system

Designing a secured voice transmission system is not a trivial task. Wired media, thanks to their reliability and resistance to mechanical damage, seem an ideal solution. The BPL (Broadband over Power Line) cable is resistant to electricity stoppage and partial damage of phase conductors, ensuring continuity of transmission in case of an emergency. It seems an appropriate tool for delivering critical data, mostly clear and understandable voice messages. This paper describes such a system that was designed and evaluated in real-time operating conditions. It involved a two-way transmission of speech samples in American English and Polish. The efficiency of the designed solution was evaluated in the subjective study on a group of 15 people.

Determination of the Operating Temperature of the Gas-Insulated Transmission Line

Gas-insulated lines (GILs) have been increasingly used as high-current busducts for high-power transmission. Temperature is one of the most important factors affecting the performance and ampacity of GILs. In this paper, an analytical method was proposed to determine the temperature of a three-phase high-current busduct in the form of a single pole GIL. First, power losses in the phase conductors and enclosures were determined analytically with the skin, and proximity effects were taken into account. The determined power losses were used as heat sources in thermal analysis. Considering the natural convection and radiation heat transfer effects, the heat balance equations on the surface of the phase conductors and the screens were established, respectively. Subsequently, the temperature of the phase conductors and the enclosures were determined. The validation of the proposed method was carried out using the finite element method and laboratory measurements.

Thermal Distortion of Signal Propagation Modes Due to Dynamic Loading in Medium-Voltage Cables

Temperature variation from dynamic cable loading affects the propagation characteristics of transient signals. The distortion of modal signal components as a function of temperature in a three-phase medium-voltage cable is investigated. The temperature influence arises mainly through the complex insulation permittivity, which has a non-linear relationship with temperature. Near the maximum operating temperature of the cross-linked polyethylene insulation, the propagation velocity increases by 0.56% per degree centigrade but is an order of magnitude less sensitive at ambient temperature. The paper presents modeling results based on cable impedance and admittance matrices obtained from electromagnetic field simulation, taking into account the time-varying temperature distribution in the cable cross-section. The results are verified by applying Rayleigh–Schrödinger perturbation analysis. In the time domain, signal patterns shift when the modal propagation velocities change upon cable loading. Moreover, separation of degenerate modes is observed when the cable phase conductors carry an unbalanced current. The perspectives for exploiting the temperature dependency of signal propagation for pinpointing cable defects and for dynamic rating of underground power cables are discussed.

Optimized Protection of Pole-Mounted Distribution Transformers against Direct Lightning Strikes

Direct lightning strikes on overhead phase conductors result in high overvoltage stress on the medium voltage (MV) terminals of pole-mounted transformers, which may cause considerable damage. Therefore, introducing an efficient protection strategy would be a remedy for alleviating such undesirable damages. This paper investigates the optimized protection of MV transformers against direct lightning strikes on the phase conductors. To this end, first, the impacts of grounding densities (number of grounded intermediate poles between every two successive transformer poles) on the probability of overvoltage stress on transformer terminals are investigated. Then, the implications of guy wire, as a supporting device for ungrounded intermediate poles, on reducing the overvoltage stress on transformers, are studied. Finally, the role of a surge arrester in mitigating the overvoltage stress of non-surge-arrester-protected transformer poles is scrutinized. The investigations are conducted on a sample MV network with 82 wood poles comprising 17 pole-mounted transformers protected by spark gaps. To provide in-depth analysis, two different poles, namely creosote- and arsenic-impregnated poles, are considered under wet and dry weather conditions. A sensitivity analysis is performed on grounding distances and on a combination of guy wire and grounded intermediate poles while taking into account soil ionization. The results provide a clear picture for the system operator in deciding how many grounded intermediate poles might be required for a system to reach the desired probabilities of transformers experiencing overvoltage stress and how the surge arrester and guy wires contribute to mitigating undesirable overvoltage stress.