| Περίληψη : | This master thesis analyzes the usage, necessity and effects of sensors in modern smart electrical grids, emphasizing on security issues that arise. It is comprised of four chapters. The first chapter provides a mathematical background and deals with the characteristics, the functionality, the limitations and the future form of electricity grids. The second chapter presents the reasons behind the growing need for measurements, the usage of sensors in Smart grids and the qualities and usage of the produced data. The third chapter discusses general issues of security, provides a bottom-up security approach and presents solutions and security guidelines. The fourth chapter records some case studies of Smart Grid implementations from all over the world and presents overall conclusions. Electricity, the greatest scientific achievement of the nineteenth century, was shaped to its current form by economic, political, social, and environmental factors. Faraday and Tesla were the pioneers that made large scale electricity production possible. Electric companies grew and generating facilities were interconnected to a common transmission network, thus making the grid more reliable and efficient. The most important characteristics of electrical systems are voltage, current, impedance, power and the power factor. We are mostly concerned with electric power in a power system rather than the currents and voltages. Cosine waveforms and rotating vector diagrams are used when representing time alternating values like ac voltage. Electrical power is a complex quantity and is divided in active (real part) and reactive (imaginary part). The active power is the useful power, while the reactive does not provide any work and should be kept at lowest levels possible. The apparent or complex power is the product of the current and voltage of a circuit. The power factor is a measure of quality of the transported power. Three-phase systems are preferred over single-phase due to their ability to produce constant power and not pulsating. The per unit system was invented to simplify calculations over multiple voltage levels throughout the grid. In this system, electrical quantities are expressed as fractions of a defined base unit quantity. An interconnected classical power system can be divided into the generation, transmission, distribution and utilization subsystems. The generation includes generators, mostly synchronous ac three-phase motors, and transformers. The transmission network transfers electric power from the generating facilities to the distribution over elevated power lines (overhead transmission) or underground cables. The part from the distribution substations to the consumer’s service entrance equipment composes the distribution, while the loads of the power system in general are referred to as the utilization. The power demand varies throughout the day and can be represented with a daily demand curve diagram. The efficiency of a generating plant is assessed by the load factor, the ratio of average load over a designated period of time to the peak load occurring in that period. Electrical power systems currently have many problems and limitations. Electricity is difficult to be stored in large scale, thus the supply of power should be continuously adjusted to balance the varying demand. Regional and national power grids are interconnected to national and international level while their supervision and control is broken down to many stakeholders due to the de-regulation. The electrical power flows to all points of a power grid and the effects of a change in transmission or generation are propagated to the whole grid and cannot be easily anticipated or controlled. The extension of transmission lines makes power delivery inefficient, while the quality of power must be maintained at high levels or else instabilities arise that could lead to blackouts. New and efficient technologies will be introduced to resolve these problems by transforming the current electrical grids into Smart Grids. Many different definitions of the term ‘smart grid’ have been given worldwide. The most inclusive one is that a Smart Grid is a next-generation network that integrates communication and information technology into the existing power grid to optimize energy efficiency. Sensing and measurements are the cornerstones of this transformation, while security concerns are raised along the way. The most important reasons to deploy sensors and take measurements in a Smart Grid are of technical - environmental and economical nature. Technical and environmental reasons include resilience and reliability, security, efficiency and the integration of emerging technologies. Resilience, the capability to withstand and recover from unpredicted actions, will be provided by sensors spread in all parts and subsystems of the grid that report their values in real-time. Security, both physical and cyber, is enforced by monitoring sensors. Greater efficiency is accomplished by measuring the qualitative characteristics of the flowing electrical power and making real-time adjustments to the grid. Integration of renewable technologies and reduction of greenhouse and toxic gas emissions is realized by being able to predict and control their fluctuating power output with the help of grid and weather sensors. Economical reasons include the elimination of the grid’s over-dimensioning by reducing peaking units, the adoption of Demand Side Management, by leveraging the Advanced Metering Infrastructure and smart appliances, and the integration of cheaper, renewable resources. Sensors are devices that measure a physical property by responding to a physical stimulus and convert it into an electrical signal. They can be categorized into active and passive, depending on their power source and into wireless and satellite, wired, optical fiber and hybrid, depending on their way of communication. They can also be grouped according to their placement inside the Smart Grid’s systems to: generation, transmission, distribution and utilization system sensors. Sensors in generation are utilized by PLCs, G-SCADA and HMI systems. Sensors in transmission are used by T-SCADA, PMUs, EMS, line protection and monitoring systems. The distribution system encompasses field sensors, D-SCADA, DMS, field controllers, devices and meters forming the AMI. The utilization system takes advantage of various technologies with built-in sensing capabilities like HANs, HEMS, IHDs and BMS. A Smart Grid can be divided into three layers, where each layer is composed of digital and non-digital technologies and systems from the domains of telecommunication, information, and energy technology. It can be viewed as an additional communication layer that is virtually overlaid on to the existing power grid and on which an application layer is built. This layered approach reduces the complexity, by creating independent components and subcomponents, leading to the creation of a system of systems. A communication layer lies on top of the power layer but, currently, there is no endto- end communication available because there is a communications gap between customers’ premises and the rest of the components and actors in the energy chain. The AMI, or FAN, will bridge this gap by linking the existing utilities’ communication networks with smart meters. Smart meter data are needed mainly by ESPs to provide innovative, value added services like sending price signals to consumers, controlling appliances and changing tariffs. The data exchanged through Smart Grid communication systems have different behavioral characteristics, regarding the network’s Quality of Service potential and can be categorized in various classes according to specific attributes. Other important aspects of the data that is generated are: its increasing volume, the preservation ofconsumer’s and businesses’ privacy and the cost effectiveness. The power grid constitutes a primary, critical infrastructure for a country, whereas its growing dependency on ICT brings along new threats and risks. Threats can be divided in intentional and unintentional. Unintentional threats can come from human-originated factors or from natural phenomena. Vulnerabilities inherited from the Smart Grid’s composing elements also present a danger for security. Intentional human threats constitute a smaller threat to the power grid in total, for the time being, but are expected to increase dramatically. The capabilities of attackers have evolved and the motives behind their actions include: curiosity, notoriety, revenge or extortion, financial gain, terrorism and cyber electronic warfare. Data privacy is also a major security concern, with private data used by utilities and third parties to further increase profits.
|
|---|
Copyright © 2013 Βιβλιοθήκη Ο.Π.Α. Με την επιφύλαξη παντός δικαιώματος.