Anabela Pronto

Agent-Based Simulation of Wholesale Energy Markets: A Case Study on Renewable Generation

Variable generation (VG), such as wind power, has increased significantly in recent years. VG has several unique characteristics compared to those of traditional power plants, including significant fixed capital costs but near-zero variable production costs. Large penetrations of VG tend to influence the prices and schedules of energy markets. Specifically, increasing levels of VG tend to reduce market prices, increase price volatility, and reduce the cleared energy levels of existing generating plants. This paper describes some important features of an agent-based system to simulate energy markets. Special attention is devoted to a case study aiming at analysing the behaviour of the system in situations with increasing levels of wind generation, notably comparing market schedules and prices in situations with either low or high levels of wind generation.

Analysis of Characteristic Hysteresis Loops of Magnetic Shielding Inductive Fault Current Limiters

Magnetic shielding inductive fault current limiters with high temperature superconducting cylinders have previously been described by a characteristic (or maximum) hysteresis loop, built from properties of their constitutive parts, which allowed predicting their behavior in electrical grids. These preliminary results were based on finite element simulations, but posterior experiments suggested limitations in the models. In order to investigate the application of these previous models to real devices, two laboratory-scale prototypes were built with different types of superconducting material in the secondary, either bulk cylinder or tape. Although the behavior of both devices is still approximately defined by a maximum hysteresis loop, differences in the shielding current response, when compared with previous model, must be incorporated in future models.

Analysis of Electromagnetic Forces in Superconducting Fault-Current Limiters Under Short-Circuit Condition

Electrodynamic forces developed under short-circuit events must be well characterized in power-grid applications, as they can compromise the integrity of network systems, particularly power transformers, but also inductive superconducting fault current limiters (SFCLs). These strains can destroy windings causing failure of the devices and affecting power-grid operation. In this paper, the analysis of electrodynamic forces developed in an inductive SFCL of transformer type under such extreme conditions is carried out based on finite-elements method (FEMs). The secondary of the envisaged devices is built by high-temperature superconducting (HTS) coated conductors and distinct configurations (radially and axially distributed windings) are analyzed in order to determine the most adequate for electromagnetic forces minimization. FEM results for developed radial and axial forces are evaluated and compared, as well as current distribution and normal magnetic induction in each winding.

A Methodology for Modeling and Simulation of Saturated Cores Fault Current Limiters

Inductive fault current limiters, such as saturated cores topology, have been considered as an enabling technology for the advent of modern power grids. Thereby, several full-scale prototypes have been developed in recent years aiming, e.g., supporting increased penetration of dispersed generation, mostly from renewable sources. For the advent of these devices and technology, the development of straightforward design tools that allow simulating them in electrical power grids with different voltage ratings and characteristics is required. In this paper, a methodology for simulating the behavior of saturated cores limiters is presented as an alternative to techniques based on finite elements methods (FEM), thereby dramatically reducing computation time. This methodology is based on characteristic parameters of those limiters and is compared with FEM simulations. Experimental measurements in a laboratory scale prototype are also carried out to validate the proposed methodology.

Analysis of the effects of asymmetric faults in three-phase superconducting inductive fault current limiters

Inductive fault current limiters of magnetic shielding type can be described in terms of the excursion in the plane defined by flux linked with primary and line current, and this methodology has been previously applied to single-phase devices. Practical applications, however, require three-phase limiters, which, for the sake of compactness, may be built by three legged cores, instead of three single phase units. This has the advantage of using well established methods of power transformers industry, but the performance of the devices depends on the type of fault, e.g. phase to ground or phase to phase. For instance, in a three legged core, a phase to ground fault affects healthy phases, and these are the most frequent faults in distribution grids, where such systems are envisaged. The effects of asymmetric faults are analysed in this paper, by means of measured excursions in the linked flux-current plane.

Validation and Application of Sand Pile Modeling of Multiseeded HTS Bulk Superconductors

Sand pile and Bean models have already been applied to describe single grain HTS bulks. An extension to that approach was used to model multiseed bulks, needed for several practical applications as electric motors or flywheels with superconducting bearings. The use of genetic algorithms was then proposed to determine intra- and intergrain current densities, and application to two and three seeds samples using trapped flux experimental measurements was exemplified. However, this model assumed some simplifications, as equal properties in grain boundaries between neighboring grains. In this paper an extension to this methodology is proposed and evaluated by analyzing measurements performed in plans at different distances from surfaces of samples with three seeds. Discussion of its influence on a practical application is also explored.

Design Aspects and Test of an Inductive Fault Current Limiter

Abstract Magnetic shielding inductive fault current limiters with high temperature superconducting tapes are considered as emerging devices that provide technology for the advent of modern power grids. The development of such limiters requires magnetic iron cores and leads to several design challenges regarding the constitutive parts of the limiter, namely the primary and secondary windings. Preliminary tests in a laboratory scale prototype have been carried out considering an assembly designed for simplicity in which the optimization of the magnetic coupling between the primary and secondary was not the main focus. This work addresses the design configuration of an inductive current limiter prototype regarding the assembly of the primary and secondary windings in the core. The prototype is based on a closed magnetic core wound by a primary, built from a normal electric conductor, and a short-circuited secondary, built from first generation superconducting tape. Four different design configurations are considered. Through experimental tests, the performance of such prototype is discussed and compared, in terms of normal and fault operation regimes. The results show that all the configurations assure effective magnetic shielding at normal operation regime, however, at fault operation regime, there are differences among configurations.

Electricity Usage Efficiency in Large Buildings: DSM Measures and Preliminary Simulations of DR Programs in a Public Library

The programs and actions to rationalize energy consumption and increase energy efficiency, such as demand-side management (DSM) and demand response (DR), are receiving increasing attention. DSM involves the selection, planning, and implementation of measures intended to have an influence on the demand or customer-side of the electric meter. DR includes programs designed to encourage end-users to make short-term reductions in energy demand in response to price signals from the market or triggers initiated by electricity grid operators. This paper aims at studying DSM actions and DR programs to improve electricity efficiency in a public library (large building), taking into account a time of use (TOU) tariff. It presents a model of the library developed with the software DesignBuilder and using real data. It also proposes DSM actions to improve efficiency and reduce energy costs. Specifically, the analysis of the building equipment and their usage constraints lead to the development of load shifting and peak clipping mechanisms. Regarding DR programs, the library manager adopts a load direct control program proposed by a retailer and involving a reduction in consumption in the peak period of the day. The agents negotiate the terms and conditions of a bilateral contract, notably energy prices and contract duration. The DSM actions, the DR program and the negotiated rate allow the library manager to reduce consumption by 4 % and lead to savings of about 7 % in total annual costs.

Development of a Simulink Model of a Saturated Cores Superconducting Fault Current Limiter

Superconducting fault current limiters are considered as emerging devices for the advent of modern power grids. Those limiters as well as other electric power grid applications have been developed in the last years in order to support the increased penetration of dispersed generation. The development of such limiters requires new design tools that allows to simulate those devices in electrical power grids with different voltage ratings and characteristics. This work presents a methodology to simulate the behaviour of saturated core type limiters based on its characteristic curves. A prototype is tested to obtain its characteristic and then the methodology is implemented in Simulink. The simulation carried out by the proposed methodology is compared with a real test.

Study of an axial flux disc motor with superconductor rotor

The integration of high temperature superconductors (HTS) in electrical machines potentially allows reduction in devices dimensions or performance improvement for the same active volume, when compared with their conventional ones. The use of polycrystalline HTS samples allows big bulk samples. An axial disc motor with HTS material or conventional aluminium in the rotor and conventional armature has been designed and developed. This paper describes simulations and laboratory experiments performed at liquid nitrogen temperature (77 K) in order to analyze the motors behaviour and its electromechanical characteristics and to define an electric equivalent circuit that allows describing its operation. In order to evaluate the superconducting quality of the bulks and flux pinning phenomena, Hall probe mapping system was performed in order to define the field profiles at 77 K for different polar configurations. The analysis of the obtained results allows confirm the flux pinning phenomena, being the entire rotor magnetized and conclude that the motor with the HTS rotor behaves as a conventional hysteresis motor even though with a different nature, while the motor with aluminium rotor behaves as a conventional induction motor. In asynchronous regime, the HTS motor exhibits a constant torque, higher than the conventional aluminium one. For both cases, the developed torque is proportional to the poles pairs.