Gheorghe Lazaroiu

Voltage unbalance vulnerability areas in power systems supplying high speed railway

High speed railway loads fed by the three phase power system represent an important source of unbalance perturbation in the grid. The degree of voltage and current unbalances depends on the train motion, load condition and power system supply configuration. The present paper deals with the identification procedure of a vulnerability area in which the voltage unbalance presents values that exceed the standard limits. A case study referred to the 63 buses CIGRE network analyzed in the paper gives rise to interesting comments and discussion.

Transient analysis of DG interfaced low voltage dc system

The paper deals with the analysis of a low voltage dc distribution system. This dc system efficiently uses the opportunities that distribution generators (DG) offers for the power quality improvement, considering the more easily interconnection of the energy storage devices. The analysis of the energy management system and the behavior of the dc system during faults in the ac grid and dc grid are conducted.

Harmonic summation in power systems with power electronic interfaced loads

The growth of equipments incorporating nonlinear elements in the power system imposes to adopt efficient measures for limiting the current and voltage waveforms distortion. The paper deals with the determination of the values for the summation coefficient for the 5, 7, 11, and 13 harmonic orders.

Sustainable building for the quality of power supply

The photovoltaic (PV) systems, together with energy storage devices, interconnected in parallel with the utility can improve the reliability during power quality perturbations in the main system supply. The paper presents a possible solution with high level of power supply continuity, where a hybrid system is simulated in case of power quality negative events. Reference is made on an existing plant relevant to a case of building integrated PV system installed in Italy. An economic analysis is also developed in order to weigh also the power quality aspect into the revenue indices.

Mathematical model and experimental tests of hydrogen diffusion in the porous system of biomass

ABSTRACT The paper deals with mathematical model and experimental tests of hydrogen (pure or mixed) diffusion in the porous system of biomass. A mathematical model has been developed for gas diffusion in a porous system and based on it a numerical simulation for hydrogen absorption gas been carried out. The results are presented graphically and they point out that the concentration variation inside the pore decreases with the increases of pore length and increases with the increase of hydrogen flux. Also, the absorbed hydrogen quantity decreases with the increase of the pore length and for a given pore length the absorbed hydrogen quantity increases with the increases of hydrogen flux and internal pore surface. Research regarding hydrogen diffusion in the porous system of biomass is part of wider research focusing on using hydrogen as an active medium for solid biomass combustion. In parallel with hydrogen diffusion in solid biomass, tests regarding biomass combustion previously subjected to a hydrogen flux will be carried out.

HVDC transmission corridor — Cost benefit analysis

Constructed in 1986, the 750 kV line connecting the Ukrainian and Romanian transmission networks went out of service in the mid-1990s due to damage to the lines. Although the Romanian TSO and the Ukrainian TSO carry plans to restore the line, each has experienced significant development of their transmission networks since the line went out of service. This article identifies the optimal configuration of the corridor to serve the transmission requirements of the system operators in Romania, Ukraine and Moldova. Currently the transmission corridor, which had consisted of a 750kV AC Over Head Line (OHL), is not in operation and is in a state that cannot be easily repaired. The OHL has been damaged so that it could be considered as “non-existent” for each party. The investment scenarios themselves are comprised two voltage levels considered for the corridor: 400 kV and 750 KV. In turn, these voltages can be analyzed in terms of synchronous AC or asynchronous DC connection via a back-to-back station that may be located in either Moldova or Romania.

Aspects of the animal fat use at the diesel engine fuelling

The general objective of the research is analyzes of the preheated gas oil-animal fat blends use at the experimental diesel engine, type CFR- IT9-3M, adequate instrumentation. The engine was fuelled firstly with diesel fuel then with different diesel fuel-animal fats blends (5%, 10%, 15% animal fats content in mixture with diesel fuel). The main animal fat advantages - cetane number and calorific value close to diesel fuel, higher oxygen content it recommend a good alternative fuel for diesel engines. But, the high viscosity and poor vaporization characteristics of animal fats need prior their heating. The results of experimental investigations show the animal fats effects on auto ignition delay, on the combustion parameters and on the pollutants emissions level. Thus, at the animal fats content increase in mixture with diesel fuel, for same engine adjustments, were obtained the follow results: auto ignition delay increases with ~20%; maximum gas pressure decreases with 10%; gas temperature decreases with 8%; indicate efficiency decreases with 10%; NOx emissions level decreases with 30%; CO emission level increases with 28%; HC emissions level increases with 58%; CO2 emission level decreases with 3.5% and smoke emissions decreases with 65%. Was established the animal fats effects on the fuel auto ignition and combustion. Animal fats can be considered a good alternative fuel for diesel engine, assuring the replace of the fossil fuels and resolving the major problem of animal wastes.

Hydrogen — An energy vector in efficient combustion of energy willow

The paper analyzes the experimental combustion efficiency of solid biomass in the form of willow chips in hydrogen jet (gas enriched in hydrogen - HRG). The experiments has been performed on a 2 MW boiler from the Polytechnic University of Bucharest. The thermo-economic analysis is carried out for a 200 kW steam turbine used for valorizing energy willow, resulting from its harvesting experience in Romania.

Influence on the power quality of the connection of wind power into the electricity grid transmission

Lately, in operation of power system installation have found numerous perturbations affecting the normal functioning of connected users, mainly at 110 kV network, in vicinity of large disturbing users. The monitoring of power quality within the network nodes, which are connected directly disturbing users to the transmission network, allowed to know how specific the requirements on power quality and how quality parameters are within the limits permitted. Power quality problem on connecting wind farms to the electricity transmission network is currently very topical given the diversity of plants and induced risks - in each case - the deviations from normal operation.

System monitoring of energy quality for wind power generators

The interconnection of wind sources characterized by a significant variability of generated power and the continuous growth of installed power in wind farms raises a number of specific problems both to the utilities and to the power system operator. One of these issues is the injection of current and voltage harmonics into the electrical networks, affecting the quality of energy delivered to customers. Due to the output power variations of the wind turbines, electrical flicker is produced. Thus, on-line monitoring systems are required to obtain information about the influence of these generators over the electrical network.