Gloria Ciumbulea

Induction motor's broken bars detection by using Stockwell transform

This paper presents a Stockwell transform-based method for processing starting angular speed data from an induction motor and transforming it into some forms that are useful for fault detection and diagnostics of rotor broken bars. The proposed method generates angular speed frequency-time spectrum that is dependent to the number of rotor broken bars and of the motor load level. The angular speed signal energy, the amplitude of its spectral component with the highest frequency and the amplitude-time diagrams of its spectral components are analyzed as number of broken rotor bars indicators. The results are obtained by simulation in Matlab/Simulink of a faulty induction motor.

Space phasor geometrical loci in polar coordinates as voltage unbalance monitoring tool

Voltage unbalance is a common phenomenon in AC power network. This disturbance can cause on the three-phase induction motors connected to the power supply system serious ill effects such as overheating, drop of efficiency and reduction in output torque. Therefore, operation of an induction motor for any length of time above 5% of voltage-unbalance condition is not recommended and on-line voltage unbalance monitoring is required from economical reasons. In this paper a new method of evaluating the degree of unbalanced voltage in power network is proposed. This new approach uses voltage space phasor geometrical locus in polar coordinates based on a modified “a-b-c” to “d-q” coordinate transformation which gives the possibility to localize the unbalanced phases and to appreciate the severity of the voltage unbalance.

Building integration of 30 kWp photovoltaic system at University Politehnica of Bucharest, Romania

A Building Integrated Photovoltaic Power System of 30 kWp was recently installed at University Politehnica of Bucharest, Romania. It is the first grid-connected and largest PV system of the country. With this opportunity, an innovative non-penetrating system that uses the modules and mounting hardware as ballast was designed and implemented. Personnel with no previous experience with the roof PV systems, putting an innovative mounting system and documentation to the test, performed array installation. In the paper, the PV power system and its installation process are described, special attention being accorded to the complex mounting system. The provided information can be useful to anyone implementing a PV system.

Use of surface response methodology for the fuel cells mathematical modelling

The objective of this work was to use Box - Wilson experimental plan to establish the relation between a dependent variables P (the delivered power) and three independent variables X1 (current density), X2 (air pressure) and X3 (air stoichiometry) in order to obtain the optimal values of the independent variables which give the maximum values of the fuel cell electric delivered power. The development of a PEM Fuel Cells mathematical model based on the design of experiment and surface response methodologies are described.

The use of experimental design to find the operating maximum power point of PEM fuel cells

Proton Exchange Membrane (PEM) Fuel Cells are difficult to model due to their complex nonlinear nature. In this paper, the development of a PEM Fuel Cells mathematical model based on the Design of Experiment methodology is described. The Design of Experiment provides a very efficient methodology to obtain a mathematical model for the studied multivariable system with only a few experiments. The obtained results can be used for optimization and control of the PEM Fuel Cells systems.

A new graphic evaluator of the voltage unbalance in power networks

Voltage unbalance is a common phenomenon in AC power network. This disturbance can bring to the three-phase induction motors connected to the power supply system important drawbacks such as overheating, drop of efficiency and reduction in output torque. Therefore, operation of an induction motor with voltage unbalance above 5% is not recommended and therefore continuous monitoring of voltage unbalance o the supply system is need. In this paper a new method of evaluating the voltage unbalanc index in power distribution networks is proposed. This new approach uses voltage space phasor geometrical locus in polar coordinates based on a modified “a-b-c” to “d-q” coordinate transformation which gives the possibility to localize the unbalanced phases and to estimate the severity of the voltage unbalance.

The PV grid-connected demonstration system of University “Politehnica” of Bucharest

In 2006, at University Politehnica of Bucharest, in the framework of the European demonstration project PV-Enlargement, and of the Romanian project “PV grid”, a rooftop grid-connected photovoltaic power generation system of 30 kWp has been installed. This is a Double Array PV System containing two kinds of silicon modules: crystalline and amorphous. The installed power of crystalline modules is of 27.36 kWp and that of amorphous modules is of 3.24 kWp. This paper gives a survey of amorphous Silicon array performances during 12 representative working months under specific operational and environmental conditions of Bucharest geographical location.