SREĆKOVIĆ, N., TRBUŠIČ, M., BELIČ, E., ŠTUMBERGER, G.
PROVIDING THE PROPER VOLTAGE PROFILES WITHIN THE MEDIUM VOLTAGE DISTRIBUTION NETWORK WITH PV SYSTEMS
KOMUNALNA ENERGETIKA / POWER ENGINERING, 32
Proliferation of the distributed electric power generation (DG) units requires the evaluation of different effects that DG units may have on the electricity network operation. Photovoltaic (PV) systems that are properly placed and sized, as well as equipped with the suitable control systems, may have positive impact on the voltage profiles and the reduction of losses of electric energy within the network. This paper discusses the possibility of providing the proper voltage profiles within the medium voltage distribution network, using the optimal reactive power generation and/or optimal reduction of active power generation from PV systems. Time – discrete calculation of the network operating conditions throughout the year were performed on two existing medium voltage distribution networks. Optimal values of reactive power generation and the reduction of active power generation were determined using the differential evolution in time points, where voltage rise, higher than the allowed, occurred. The results obtained suggest that reactive power generation from the existing PV systems should be used in voltage control, followed by the reduction of active power generation when necessary.
BELIČ, E., VOH, J., SUKIČ, P., ŠTUMBERGER, G.
IMPACT OF PHOTOVOLTAIC SYSTEMS’ REACTIVE POWER GENERATION ON ACTIVE POWER GENERATION AND TRANSMISSION LOSSES IN
THE LOW VOLTAGE DISTRIBUTION NETWORK
KOMUNALNA ENERGETIKA / POWER ENGINERING, 33
This paper evaluates the impact of photovoltaic systems’ reactive power generation on active power generation and transmission losses in the low voltage distribution network. The introduced experimental system consists of two major parts. The photovoltaic system represents the first part, in which every photovoltaic module is connected to the low voltage network by the individual microinverter. Two way communication is established to each microinverter by the communication gateway. The second part consists of a control system with data acquisition system. The flexible experimental system offers a possibility to add and establish different network connections of the single-phase or three-phase smart grids. Within the scope of this work, additional cable was installed to establish one phase low voltage network with the photovoltaic system on one side and network on the other. The results of the analysis and measurements performed for operation of experimental low voltage network show that the reactive power generation in photovoltaic systems increases the amount of active power that can be generated in photovoltaic systems without to violate voltage profile. However, with both of these actions transmission losses in the low voltage network increase.
BELIČ, E., DEŽAN, K., LUKAČ, N., ŠTUMBERGER, G.
EVALUATION OF ENERGY SAVINGS ACHIEVED WITH OPTIMUM PHOTOVOLTAIC SYSTEMS REACTIVE POWER GENERATION IN LOW VOLTAGE DISTRIBUTION NETWORK
KOMUNALNA ENERGETIKA / POWER ENGINERING, 32
This paper deals with the evaluation of energy savings that can be achieved in low voltage distribution network by photovoltaic systems (PVS) reactive power generation according to the network needs. Whole analysis is done on the model of real low voltage distribution network, where two 50 kWp PVS are installed. For evaluation of energy savings, time frame of one year is considered. Active powers of PVS are determined on the basis of average measured solar irradiance in half hour intervals and loads active powers on the basis of load profile. Since installed photovoltaic systems are relatively large, the analysis is also performed for smaller PVS with rated power of 5 kWp. The presented results shows, that energy savings can be achieved with existing PVS when they generate optimal reactive power. However, savings can be even improved if instead of big, smaller PVS are installed at sites where consumption is present.
SREĆKOVIĆ, N., BELIČ, E., ŠTUMBERGER, G.
COMPARISON OF METHODS FOR LOAD FLOW CALCULATION IN LOW VOLTAGE DISTRIBUTION NETWORK WITH CONNECTED DISPERSED PRODUCTION
KOMUNALNA ENERGETIKA / POWER ENGINERING, 8
Load flow analysis represents one of the core methods used in modern distribution system operation. Therefore, it is necessary to provide efficient, numerically robust load flow algorithms with fast convergence and minimum usage of memory, suitable for variety of operating scenarios. The paper presents, compares and evaluates two efficient methods for load flow calculation in distribution network – backward/forward sweep method and direct method. The procedure of modeling the distribution network elements – line sections, loads, distributed generation units, as well as the implementation of algorithms, has been presented. The analysis has been performed on low voltage distribution network system.
BELIČ, E., DEŽELAK, K., ŠTUMBERGER, G.
A LINE VOLTAGE DEPENDENCY ANALYSIS ON ACTIVE AND REACTIVE POWER FLOW AT DIFFERENTC LOW VOLTAGE LINES
KOMUNALNA ENERGETIKA / POWER ENGINERING, 9
The paper provided presents a line voltage dependency analysis on active and reactive power flow. The line voltage dependency is studied based on analytical expression. For the analysis it is assumed that one end of the line is connected to infinite bus, while at the other end voltage is observed in dependency of active and reactive power flow. The analysis covers three different low voltage cables with two different lengths. The results shows that in low voltage network voltage significantly depends on active power flow, while reactive power flow dependency is minimal. Voltage dependency increases, when low voltage lines are extended.
SUKIČ, P., DREVENŠEK, D., BELIČ, E., ŠTUMBERGER, G.
EFFICIENCY OF INVERTERS IN SOLAR POWER PLANTS WITH REACTIVE POWER GENERATION
KOMUNALNA ENERGETIKA / POWER ENGINERING, 14
The paper discusses possibilities for reactive power generation using inverters for solar power plants. Measurements performed on an inverter for solar systems were performed for different values of generated active and reactive power in order to determine the efficiency characteristic. The obtained characteristic is approximated with a surface. It is applied to evaluate increase of inverter losses due to reactive power generation as well as to evaluate the potential of inverters in solar power plants for reactive power generation.
DEŽELAK, K., KOTNIK, S., DEŽAN, K., BELIČ, E., IVANECKÝ, J., ŠTUMBERGER, G.
ACCEPTANCE INDICATORS OF A MICRO HYDRO POWER PLANT INVESTMENT FOR A MICRO HYDRO POWER PLANT "KOTNIK"
KOMUNALNA ENERGETIKA / POWER ENGINERING, 5
This paper deals with the impact of the energy cost, produced by a micro hydro power plant, on the acceptance indicators of a micro hydro power plant investment. The aforementioned acceptance indicators are the net present value and the internal rate of return. All calculations are performed for a micro hydro power plant "Kotnik" with power of 10 kW, where technical and essentially financial parts are observed.
DEŽELAK, K., JAKL, F., BELIČ, E., ŠTUMBERGER, G.
EMISSIONS OF ELECTRIC AND MAGNETIC FIELDS CAUSED BY 400 KV OVERHEAD POWER LINES TYPE DONAVA
KOMUNALNA ENERGETIKA / POWER ENGINERING, 8
In proposed paper the emissions of electric and magnetic fields caused by 400 kV overhead power lines type Donava are dealt. Firstly, the classical Donava type overhead power line is dealt, while different varity of conductor bundle are considered. Secondly, the Austrian type of overhead line is considered, firstly without and after with additional 110 kV system on the same tower.
BELIČ, E., SUKIČ, P., DEŽELAK, K., ŠTUMBERGER, G.
DYNAMICAL MODEL OF DISTRIBUTION NETWORK WITH DISTRIBUTED GENERATION
KOMUNALNA ENERGETIKA / POWER ENGINERING, 18
In this paper a dynamical model of distribution network with distributed generation is presented. Model of distribution network was developed using software package Matlab/Simulink with its blockset SymPowerSystems. Elements of utility network like supply network, power lines, load, and distribution transformer were modeled with elements which are already included in this blockset, but the distributed generator model was developed based on the current injection to the grid, considering references of active and reactive power. The aim of network modeling was to analyze the voltage profiles and transmission loses before and after connection of the distributed generation to the grid. Presented are the results of performed analysis.
DEŽELAK, K., DEŽAN, K., DEŽELAK, D., BELIČ, E., ŠTUMBERGER, G.
INTERNAL RATE OF RETURN FOR A SOLAR POWER PLANT IN CASE OF MOVABLE PHOTOVOLTAIC MODULS
KOMUNALNA ENERGETIKA / POWER ENGINERING, 8
In proposed paper the internal rate of return for a solar power plant investment is mainly dealt. The main parts of the solar power plant are represented by the photovoltaic moduls, which could be static or movable. In case of movable photovoltaic moduls, where moduls are following to the movement of the sun, the amount of the produced energy could be even up to 30 % higher than in case of static photovoltaic moduls. On the other hand an investment in movable solar plant leads to the higher initial costs of the whole investment.