Srete Nikolovski

Measurements and computation of electromagnetic field in transformer station 400/110 kV ernestinovo

This paper presents results of measurements and computations of the electric and magnetic fields of complex busbars, transformers and transmission line structures at transformer station 400/110 kV. The fundamental sources of low frequency electromagnetic fields in the transformer station are the primary elements of the 400 and 110 kV open substations and associated overhead lines. Due to the complexity of the geometry of the substation elements, it was necessary to apply a three-dimensional approach to the computation of the electromagnetic field. Measurements were performed by EMS 100 field meter and computations of electromagnetic fields were conducted for quasi-static states of electrical values at a power frequency of 50 Hz. The calculated electric and magnetic fields were compared with measured values and permissible levels according to Croatian regulations. Measurements were performed for real working conditions for twelve different profiles in the transformer station.

Hybrid Evolutionary-Heuristic Algorithm for Capacitor Banks Allocation

Hybrid Evolutionary-Heuristic Algorithm for Capacitor Banks Allocation The issue of optimal allocation of capacitor banks concerning power losses minimization in distribution networks are considered in this paper. This optimization problem has been recently tackled by application of contemporary soft computing methods such as: genetic algorithms, neural networks, fuzzy logic, simulated annealing, ant colony methods, and hybrid methods. An evolutionaryheuristic method has been proposed for optimal capacitor allocation in radial distribution networks. An evolutionary method based on genetic algorithm is developed. The proposed method has a reduced number of parameters compared to the usual genetic algorithm. A heuristic stage is used for improving the optimal solution given by the evolutionary stage. A new cost-voltage node index is used in the heuristic stage in order to improve the quality of solution. The efficiency of the proposed two-stage method has been tested on different test networks. The quality of solution has been verified by comparison tests with other methods on the same test networks. The proposed method has given significantly better solutions for time dependent load in the 69-bus network than found in references.

Agent-based modelling application possibilities for Croatian electricity market simulation

Croatia is today in the first phase of restructuring and opening its electricity market. At this moment, electricity market is open to eligible customers only. Eligible customers are able to choose their supplier and currently these are all non-households. Starting from July 1st, 2008 all customers, including households, will become eligible and the market will hence be fully open. Therefore, a suitable method for Croatian market simulation is needed. This paper presents possibilities of using an agent-based model to simulate the Croatian electricity market. Agent-based models represent each market participant as an independent software agent. Each agent has its own strategy and decision-making process. Agents are able to learn and adapt to their environment. EMCAS (electricity market complex adaptive system) is a computer simulation program for agent-based simulation. This paper presents an EMCAS case representing mutual influences of market participants in the emerging Croatian market. Simulations and future developments are presented.

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

Distribution Network Restoration Using Sequential Monte Carlo Approach

The paper describes a developed procedure for modeling restoration after a fault and calculating associated switching time using sequential Monte-Carlo approach. The procedure is based on the experience and knowledge of distribution system operators, thus represents an attempt in regarding the realistic issues influencing the duration of fault isolation and customer restoration, i.e. the actual switching and eventually repair time needed for restoration of each affected customer. In addition to expected duration of switching, the associated probability density functions can be computed. Further more, Visual Basic software using the proposed procedure has been developed and some examples of switching time expectations and probability distributions calculations are presented

ANFIS as a method for determinating MPPT in the photovoltaic system simulated in MATLAB/Simulink

Photovoltaic systems as part of larger distribution systems for the production of electricity have non-linear current-voltage characteristics. These characteristics depend on the temperature of the solar cells and insolation of panels. The method for the search of the maximum power or MPPT is widely known, and there are many offered algorithm solutions. The aim of this paper is to present ANFIS (Adaptive Neural Fuzzy System Inference) as a method of computer intelligence in the search function of maximum power or maximum utilization of the PV system, without prior knowledge of the system. MPPT ANFIS will be located between the PV panels and devices for voltage regulation. Inputs used to go inside the fuzzy regulators and outputs of the fuzzy regulators are going into power changing device. The advantage of this method is the low cost of implementation because it uses embedded computer systems and does not require additional sensors for measuring temperature and insolation. It is very easy to upgrade in the case of increasing the knowledge base used in FIS membership function. Everything is simulated by MATLAB/Simulink software on the one-phase IBC system.

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).

Frequency domain analysis of 110/35 kV transformer station grounding system subject to lightning strike

Lightning transients processes appear when lightning strikes hit tall objects, such as transmission and communication towers or transformer substations. Large currents generated by the stroke flow in the grounding system and dissipate in the soil. The electromagnetic fields (EMF) generated by such high currents may cause damage to equipment and may be dangerous to personnel. The field theory method is used to examine the transient behaviour of the lightning processes in the grounding system.

The influence of wind park krš-pađene on reliability indices of 110 kV transmission network

This paper presents the reliability assessment of the southern part of Croatian transmission network and the influence of the wind farm on reliability indices. Croatian Electric Utility (HEP) Renewable Energy Sources with partner C.E.M.P. is developing wind farm in the region near town Knin. Wind farm will have installed capacity of 100 MW in the first phase. In the second phase additional 40 MW is planned to be installed. For the purpose of this paper, it was assumed that wind farm consist of the 50 turbine units, 2 MW each. Reliability assessment was performed, and reliability indices were computed for the case before and after construction of the wind farm. The reliability is analyzed using state enumeration method and NEPLAN software. Input data were obtained from annual reports of HEP TSO (Transmission System Operator) and statistic analysis of data was performed first. Since there are no statistical data for new cables and transformer stations that are constructed, input data for them were taken from the relevant literature. Probability of wind farm production level is taken from measured wind statistics. In reliability assessment Markov state space model of the wind generator, busbars, transformers, breakers and disconectors was used. Load is modeled at the output substation busbars with maximum active and reactive power. The simulations are performed in order to calculate reliability indices before and after the construction of wind farm. Conclusions and comments on the results are presented at the end of the paper.