F. Blázquez

Low-Voltage Ride-Through Capability for Wind Generators Based on Dynamic Voltage Restorers

The increasing penetration of wind energy in power systems has forced operators worldwide to develop new grid codes to integrate this form of generation. One important aspect of the problem is the low-voltage ride-through capability of wind generators. This paper describes a solution for wind farms with squirrel-cage asynchronous generators based on the use of a dynamic voltage restorer. Along with a specifically developed control scheme, it provides the wind generator the ability to remain connected during a voltage disturbance and, at the same time, to fulfill the demanding reactive power requirements imposed by recent grid codes. The main experimental results of extensive laboratory tests on system performance are also presented.

High-efficiency voltage regulator and stabilizer for outdoor lighting installations

This paper presents a high performance system of regulation and stabilization of luminous flux for public street lighting installations. Its purpose is to reduce the luminous flux of the luminaries efficiently by reducing their voltage supply, resulting in the improvement of energy efficiency in the installation. The system is basically composed of electromagnetic components which provide robustness and high-performance to the device, as well as minimum maintenance requirements. However, the voltage regulation is based on the application of voltage steps. Aging studies of the luminaries have been carried out to analyze the impact of this discrete voltage regulation. A specific prototype of this voltage and stabilizer regulator have been in operation in a real outdoor lighting installation for more than one year.

Novel Rotor Ground-Fault Detection Algorithm for Synchronous Machines With Static Excitation Based on Third-Harmonic Voltage-Phasor Comparison

This paper presents a new algorithm for detecting ground faults in rotor windings. This location method is suitable for synchronous generators with static excitation, whose excitation field winding is fed by controlled rectifiers through an excitation transformer. This new algorithm is an improvement of an online ground-fault location method presented previously, in which the effect of the rotor capacitance has a high influence in the correct detection of the fault. The detection of the ground fault is performed by the supervision of the phase angle between two phasor voltages. The first one is the third-harmonic phasor voltage obtained from the measurement of the field voltage, which is used as a reference. The second one is the third-harmonic voltage phasor obtained by the measurement in a grounding resistance placed in the neutral of the excitation transformer. It allows not only detecting the ground fault along the field winding but also distinguishing the cases of ground fault in the rotor winding, from the cases of high influence of the rotor capacitance in healthy condition. This new algorithm has been tested with satisfactory results in a 106-MVA hydro generating unit.

A Monitoring System for Diesel Engine Driven Generators Based on Electric Power Output Oscillation Assessment

Diagnosis is a main concern in power systems with generators driven by internal combustion engines, especially by low- and medium-speed diesel engines. The purpose of this paper is to develop a new diagnostic method that avoids generator operation in dangerous torque imbalance conditions. Torque in internal combustion engines has a periodic oscillation due to variations in the combustion process and pressure development between cylinders. A defective combustion in one or more cylinders produces an imbalance in torque oscillation. Analyzing the harmonic order of the generator power output makes it possible to detect and identify the cylinder that is producing the imbalance. This method has been tested with satisfactory results in a 11.6-MVA/600–r/min/10-kV diesel engine driven generator.

Energy, Materials and Person-hour Savings through a New Decentralized Power Supply for HVAC in Large Buildings. A Case Study: A Shopping Center in Spain.

Abstract Currently, heating and cooling systems used for achieving thermal comfort in commercial buildings represent a significant energy consumption. Traditionally, power supply installations of these Heating, Ventilation and Air Conditioning Systems (HVAC) present low efficiency. In these installations the power is supplied from the substation to the HVAC system by low voltage cables. Due to the long distances of the power distribution, the system suffers considerable energy losses. This paper proposes a decentralized power supply installation based on a power distribution at medium voltage, which achieves not only significant energy savings, but also important savings in material and person-hours. These improvements entail substantial savings in cost and CO2 emissions.

New On-Line Excitation-System Ground Fault Location Method Tested in a 106 MVA Synchronous Generator

In this paper, a novel excitation-system ground-fault location method is described and tested in a 106 MVA synchronous machine. In this unit, numerous rotor ground-fault trips took place always about an hour after the synchronization to the network. However, when the field winding insulation was checked after the trips, there was no failure. The data indicated that the faults in the rotor were caused by centrifugal forces and temperature. Unexpectedly, by applying this new method, the failure was located in a cable between the excitation transformer and the automatic voltage regulator. In addition, several intentional ground faults were performed along the field winding with different fault resistance values, in order to test the accuracy of this method to locate defects in rotor windings of large generators. Therefore, this new on-line rotor ground-fault detection algorithm is tested in high-power synchronous generators with satisfactory results.

Design and construction of a laboratory bench system for the teaching and training of engineers on diagnostics of permanent magnet motors

Permanent magnet synchronous motors PMSM are widely used in industry due to their higher torque and higher power to volume ratio. Moreover they have a better dynamic performance compared to the motors with electromagnetic excitation. Despite its robustness electrical, mechanical and magnetic faults has been described. It has led to the development of specific diagnostic systems for such machines. These systems are constantly evolving according to the literature. In this situation of increasing use of PMSM it is necessary to teach and train professionals in diagnostic techniques. This paper describes the design process of an experimental bench on which can be studied all types of faults associated with the PMSM operation. The design of a PMSM prototype, which is the most important equipment of this bench, is described in more detail.

Enhancement of a high speed de-excitation system for brushless synchronous machines by large blocking voltage semiconductors

One of the main disadvantage of the synchronous machines with brushless excitation is that the field winding is not accessible for the de-excitation. The de-excitation process is very slow as the field current flows through the rotating diodes which operate in freewheel mode. Therefore in case of an internal fault, despite the correct operation of the protection relays, the machine could have severe damages. A high-speed de-excitation system for these machines was developed. The de-excitation is achieved by inserting a resistance in the field circuit by a static switch semiconductor based, obtaining a dynamic response similar to that achieved in machines with static excitation. This paper presents the improvement in the de-excitation system in the second commercial 20 MVA hydro generator in operation. In this case, high blocking voltage semiconductor was used, making the dynamic response even better, than in the first hydro generator.

Combustion problem identification based on electric power output oscillation assessment for Diesel-Engine driven generators

One of the most critical situations in the operation of medium and low speed synchronous generators appears when they are subjected to torque imbalances. This could be the case of internal combustion engines driven generators. In these engines, torque has a periodic oscillation due to variations in the combustion process and pressure development between cylinders. Consequently, a fuel excess or a fuel deficiency in a cylinder produces an imbalance in the torque oscillation. So the detection of combustion failures is very important in order to avoid problems in generator performance. In a prior work, the authors have presented a diagnostic method that detects combustion failures caused by a fuel deficiency in a cylinder, even in their first stages. The purpose of this paper is to improve this diagnostic technique by including the effects of fuel excess. Thus, another cause of dangerous torque imbalances in generator operation can be avoided. Analyzing the harmonic order of the generator power output makes it possible to detect and identify the cylinder that is producing the imbalance. This new technique has been verified with adequate results in a 11.6 MVA/ 600 rpm/10 kV Diesel-Engine Driven Generator.

A novel educational proposal: Devising an electric power system

The study of electric power systems within the field of Electrical Engineering is usually approached by computer simulation because any actual test is quite complex to be implemented, especially with renewable energies. Having the aim to improve student learning about this topic, a new subject called “Devising an Electric Power System” was organized following a CDIO (Conceive-Design-Implement-Operate) approach. The subject is programmed for one academic year and based entirely on laboratory work. The students are divided into three teams. Every team would have to work on a power system that includes a solar PV generator and a pumping controlled drive, both connected to a three-phase grid. The third and last part of the subject is focused on “electric utility” business strategy. In the final day of the course a competition between the three teams takes place.