Marinko Stojkov

Simulation of lightning transients on 110 kV overhead-cable transmission line using ATP-EMTP

Due to construction of a highway in the eastern part of Croatia, a nesurge arrestersw 110/x kV substation was built with two parallel connecting underground cables. Cables were connected to already existing 110 kV overhead lines. At the place where the transition between overhead lines and cables is made, surge arresters were installed. In this paper lightning stroke at the grounding wire on the overhead line and its impact on underground cables were studied. Transient program Electromagnetic Transients Program (ATP-EMTP) is used to create a model of the system and to perform simulation of the transient process during lightning stroke. The results of the simulation are briefly presented and discussed in the paper.

Technical losses in power distribution network

This article introduces a new method of permanent inspection of technical active power losses. It is based on analytical computer code calculation with examples from the actual power system. Based on the incoming data from the remote control supervising system as well as technical and commercial information data, the result of the calculation is technical losses for every single element of the network. Further calculation result analysis enables global understanding of commercial losses as well as more quality planning and operating of the distribution network

Estimation of electrical energy not supplied in reliability analysis of distribution networks

There are many aspects about the electrical energy not supplied (EENS) price, about estimation of the economies losses and the social economic benefit losses in the different kinds of human activity, education and life or about similar estimation in suppliers money losses due to not charged EENS. Detailed technical analyzes of some real power system faults, real demands and real deliveries are described in this paper. The EENS quantity evaluation during real power lines faults is given here. Power supplier aspect of the EENS evaluation is presented in the paper. Fault period without voltage of the day is compared with the same time period of the next or previous day. The values of EENS calculated until now have been overestimated due to magnified initial power demand neglects. The real value of EENS is evaluated by integrating function power (or electric current) in depends on time for each day (two consecutive days).

Illegal connection location on main power cable

The main goal of this paper is initiation of the method for determination of possible stealing of electrical energy and for estimation of exact length location of illegal connection. Method is based on time domain reflectometer (TDR) principles and function.

Optimizacija uklopnog stanja u distribucijskom elektroenergetskom sustavu

Original scientific paper To improve function of distribution power subsystem, systematic researches of optimization methods based on modern analytic techniques, have been performed recently. Therefore, several specialized algorithms for power flow and power losses calculations in electric distribution subsystem are developed. Distribution power subsystem 10 kV with 212 buses and 72 switches is analysed in this paper. Stochastic optimization based on simulated annealing method is applied. The aim of analysis is to determine the optimal network switching condition of minimum losses, with the precondition of keeping the stable voltages on all buses. Simulations are performed for two initial configurations with different initial annealing temperatures and cooling speeds. All parameters of distribution network components have constant values. The results show that the obtained solutions are with better efficiency than those that are chosen initially.

Review of Non-Traditional Optimization Methods for Allocation of Distributed Generation and Energy Storage in Distribution System

The integration of distributed energy sources transforms passive distributed grid, in which the energy flows only in one direction (from the source to the consumer), in an active one, in which energy flows in both directions. To maximize positive impacts, which distributed generation (DG) can provide to the distribution network, it is necessary to determine the optimal allocation of distributed generation. The optimal allocation can be determined by using the optimization method. There are two main categories: exact methods (traditional) and heuristic (non-traditional) methods. Exact methods search for global optimum while heuristic methods achieve satisfactory solutions with greater computation speed. This paper gives a brief review of non-traditional methods used for determining optimal location and optimal power of DG with the aim to reduce real power losses and to improve voltage characteristics. Also, there is a review of the application of those methods in determining the optimal power, optimal location and optimal cycle of charging/discharging of electrical energy storage systems.

Development of a new type of finned heat exchanger

Original scientific paper A new geometric form of fins (needle fins) for finned heat exchangers of gas-liquid type is described. It achieves a higher heat transfer coefficient and lower mass of the heat exchange surface relative to the heat exchangers with circular fins which in this case served as a basis for comparison. For the analysis of the heat transfer, the computational fluid dynamics analysis with ANSYS Fluent software was applied. Numerical simulation was performed for the round fins and fins with a new, innovative geometric shape at air flow speeds of 1 m/s to 5 m/s. The results of numerical simulations, with regard to the exchanged heat and pressure drop were verified by the correlations available in the literature and compared to the simulation results for tubes with innovative fins. Results show an increase in the amount of Nu from 20 % to 30 % for 2300 >Re > 12000 while reducing mass of heat exchange surfaces of 23,8 %.

Power System Fault Data and Time Series

Power system reliability and continuous electric power supply without downtimes or with a few as shorter as possible interruptions are basic for financial success in today’s power market (EN50160). So, modern customer oriented relationships and efficient electricity service have to be included in nowadays power system management.