Francisco Blázquez

Characterization of the Rotor Magnetic Field in a Brushless Doubly-Fed Induction Machine

The large increase in wind generation could improve the final development of wind systems with brushless doubly-fed induction machines (BDFIM) as an alternative to the doubly-fed asynchronous machines. For this reason, a detailed study of several aspects of the BDFIM design, as well as of its rotor configuration, is absolutely essential. In this paper, the authors present an alternative formulation of the BDFIM operating principle in synchronous mode. Besides the basic equation of the machine operation, it presents as main advantage the precise characterization of all the magnetic field components in a BDFIM with idealized stator windings and an idealized rotor cage. Based on this formulation, the paper provides a standard that may be used to compare the fields created by different real BDFIMs. This standard has been validated by laboratory tests.

A Novel Rotor Ground-Fault-Detection Technique for Synchronous Machines With Static Excitation

This paper presents a novel ground-fault-detection technique for synchronous machines. This technique is suitable for synchronous machines with static excitation systems, whose excitation field winding is fed by rectifiers through an excitation transformer. The main contribution of this new technique is that it can detect and discriminate both ac- and dc-side ground faults in the excitation system, without the need for traditional power injection sources. This detection technique is based on the frequency analysis of the voltages or currents at a grounding impedance placed at the excitation transformer neutral terminal. This technique has been validated through computer simulations and experimental laboratory tests.

Computer-Based Simulation and Scaled Laboratory Bench System for the Teaching and Training of Engineers on the Control of Doubly Fed Induction Wind Generators

Among the existing renewable sources, wind energy is reaching production rates that are becoming important on the worldwide energy scene. Since the control of these wind generators is a very technical discipline, practical teaching methodologies are of special relevance. Paradoxically, in the past, the training of engineers specializing in this area has lacked the practical component represented by field tests, due to the difficulty of access to this kind of installation. This paper presents a system designed for use both in teaching and training procedures for control strategies for wind generators with doubly fed induction generator (DFIG) technology. The system includes two phases or levels of use: the first being a simulation phase based on computer models, and the second, an advanced level which allows for the conducting of tests on a laboratory scaled workbench composed of a wind turbine emulator coupled to an electric generator. With this equipment, the effectiveness of the wind generator regulation systems can be analyzed from the point of view of the maximum power point tracking control strategy, as well as from that of the contribution produced by the wind generator to the control of the operation of the electric grid to which it is connected.

Influence of Rotor Position in FRA Response for Detection of Insulation Failures in Salient-Pole Synchronous Machines

Frequency response analysis (FRA) is a very common test for the diagnosis of power transformers. This paper presents some relevant results on the application of FRA to the diagnosis of rotating machines. First, a reference rotor position for obtaining the reference FRA response of a rotating machine is proposed. Then, FRA with the proposed rotor position is used to identify faults in the stator of the machine. This paper studies turn-to-turn and ground faults in the stator for different fault resistance values. Several laboratory tests demonstrate the applicability and value of the use of FRA in the diagnosis of rotating machines.

New On-Line Rotor Ground Fault Location Method for Synchronous Machines With Static Excitation

This paper presents a novel on-line rotor ground fault location method for synchronous machines, which, combined with rotor ground fault protection, can detect and locate faults in the rotor. This method is suitable for synchronous machines with static excitation systems, whose excitation field winding is fed by rectifiers through an excitation transformer. The main contribution of this new technique is that it can locate the position of a ground fault in the rotor winding online, reducing the repair time. The proposed technique is based on the analysis of the ac and dc components of the excitation voltage and the voltage measured in a grounding resistance located in the neutral terminal of the excitation transformer. This technique has been validated through computer simulations and experimental laboratory tests.

Adaptation of Floating Point DSP-Based Technology for Small Variable-Speed Wind Turbine

In this article we present the design and development of a control board that uses of two floating point digital signal processors to control a double converter inside a small wind turbine induction generator. The algorithms programmed on the processors have the ability to perform a vector control over the transient torque on the generator, controlling at the same time the flux of active and reactive power supplied to the network. Bearing in mind that requirements for robustness and maintenance reduction are a must when designing a micro wind turbine generator, the developed control system eliminates the need for position and shaft speed sensors and greatly reduces the size of the filter in the network connection.

Coordinated Power Quality Improvement in Multiunit Diesel Power Plants

Power quality is a main concern in power systems with generators driven by internal combustion engines, especially by low- and medium-speed diesel engines. The torque in internal combustion engines, which is the superposition of the torques from each cylinder, has periodic oscillations. These torque oscillations, once the generator is connected to the grid, result in power fluctuations and voltage flicker problems, which clearly reduce power quality. This paper presents a new control strategy to improve power quality in multiunit diesel power plants, based on the compensation of the electrical fluctuations between individual generators. This compensation is performed by properly controlling the mechanical rotor phase angle between the different generators during the synchronization process. The proposed control strategy is verified using a case study.

New Fault-Resistance Estimation Algorithm for Rotor-Winding Ground-Fault Online Location in Synchronous Machines With Static Excitation

This paper presents a new algorithm for estimating the ground-fault resistance value in rotor windings. This new algorithm is an improvement of an online ground-fault location method previously presented. This location method is suitable for synchronous generators with static excitation, whose excitation field winding is fed by controlled rectifiers through an excitation transformer. The estimation of the fault resistance is obtained through the comparison between the third-harmonic voltage measured in a grounding resistance placed in the neutral of the excitation transformer and the third-harmonic voltage calculated by the algorithm. This latter variable is obtained with the dc component of the output voltage of the controlled rectifier and the ac supply voltage of this converter. The fault resistance value is used in the novel technique of online ground-fault location, and it allows improving the accuracy of the location of the defect. This new algorithm, integrated in the complete location method, has been tested with satisfactory results in a 5-kVA laboratory synchronous generator and in a 106-MVA hydro-generating unit.

High-Efficiency Voltage Regulator for Rural Networks

This paper presents a high-efficiency voltage regulator, which combines robustness, low costs and easy maintenance without power electronics components. These characteristics make it suitable for rural networks, where investments and operational cost in power quality improvement are limited. The regulator consists of a multiwinding reduced-power transformer, and provides serial voltage compensation. Different voltage compensation steps are obtained by modifying the connection and the polarity between the primary and secondary windings. The transformer design has been optimized to obtain a high-efficiency and low-cost regulator. An automatic controller monitors the output voltage and sets the optimal compensation step. At present more than 400 units of the voltage regulator are in operation. Field test results are presented to show the operation of the voltage regulator.

Real time power plant simulation platform for training on Electrical Protections and Automatic Voltage Regulators

Electrical Protection systems and Automatic Voltage Regulators (AVR) are essential components of actual power plants. Its installation and setting is performed during the commissioning, and it needs extensive experience since any failure in this process or in the setting, may entails some risk not only for the generator of the power plant, but also for the reliability of the power grid. In this paper, a real time power plant simulation platform is presented as a tool for improving the training and learning process on electrical protections and automatic voltage regulators. The activities of the commissioning procedure which can be practiced are described, and the applicability of this tool for improving the comprehension of this important part of the power plants is discussed. A commercial AVR and a multifunction protective relay have been tested with satisfactory results.