All industrialized countries rely heavily on electricity supply systems. Such power systems are complex interconnected networks of overhead lines, underground cables and transformer for the transmission and distribution of electrical energy over long distances from power station to consumers. Power system analytical techniques have been developed in order to design and operate efficient power system.
One of the main design, and operation, issues involves voltage drop along long current-carrying transmission lines. In order to carry large load currents economically but without excessive loss, circuit impedance has to be carefully managed and therefore conductor cross-sections need to be appropriately sized.
Power system engineers use a per-unit method for analysis. It considerably simplifies such calculations in complex, interconnected networks operating at many different generation, transmission and distribution voltages.
Historical Development of Power System Analysis
It took a few centuries for the modern day electrical energy system to develop. The development first started in the early of 1800. Scientists like Alessandro Volta, C. A. de Coulomb, Benjamin Franklin, Luigi Galvani etc had worked on the principles of electric and magnetic field. Though by that time they were probably just motivated by the intellectual curiosity and none of them realize that their work will lead to huge engineering innovation in later time.
The harness and use of electrical energy is not possible until around 1810. With the research efforts of scientists like Sir Humphrey Davy, Andre Ampere, George Ohm and Karl Gauss, the use of electrical energy started to dawn upon the scientific community.
Between 1821 and 1831, two scientists worked on their induction principle individually and contributed a lot to the development of electrical energy – Michael Faraday and Joseph Henry. Michael Faraday built a machine to generate voltage while Joseph Henry successfully applies his work on electromagnets and telegraphs.
In 1840, for about 30 years, primitive generators were built using the induction principle by many engineers like Alfred Varley, Charles Wheatstone, Siemens brothers Werner and Carl etc. At the same time brilliant electric arcs were formed by observing current carrying carbon electrodes drawling apart. In the decade of 1870s the arc lighting was made available to commercial. Arc lamps were used in street lightings and lighthouses. However domestic lighting was still mainly depending on gas light. Arc lamps are rarely used indoor by that time due to high intensity of these lights.
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Although the idea of heating a current carrying conductor could be use for illumination this idea is very hard to be realize. This is due to the incandescent materials burnt very quickly to be any of use. By the time of October 1879 first light bulb was invented by Thomas Alva Edison. The glass bulb was lighted with a carbonized cotton thread in a vacuum enclosed space and it lasted for 44 hours before burning out. Edison later on improved the design of the lamp and proposed a new generator design.
In 1882 the Pearl Street power station was established in New York City. The system was direct current three-wire, 220/110v. The main purpose of the power company is for illumination. The lighting load peaks in the evening till midnight, the power consumption at other times reduces drastically. It was obvious to the power companies that their complex and pricey set up are laid idle for other time thus the design of electric motors is further improved to make them commercially possible. The motors became popular is short time and used widely in many applications. By this time the electric energy era truly begins.
In 1890s alternating current electricity was formed by Westinghouse Company. Nicola Tesla, a Serbian engineer who worked in the company, invented polyphase induction motor and also conceived the entire polyphase electrical power system. When the new discovery was proposed he faced severe objections from the proponents of dc. However the battle between ac and dc was won by ac due to a few factors:
Ac voltage could be boost by transformers and could step it down for distribution.
Figure :Milestones of the early electric utility industry Ac generators were easy to construct.
Ac motors were easy to construct compared to dc motors. Even thought ac motors is simple they are stronger and cheaper than dc motors.
With this new ac technology the electric power becomes more affordable and accessible by people.
Power system analysis software tools
Figure : Harmonics example sourced from www.era.co.ukBasically, power system software tools can be divided into two group: commercial softwares and educational softwares. Simulator software like SIMPOW, PSCAD, CYMDIST and PowerWorld are belongs to the commercial group while educational software packages like UWPFLOW, MATPOWER AND PSAT etc.
This power system analysis software was often use by power engineers for study purposes. With both hand calculations and estimation are time consuming and having the risk of doing errors resulting in significant safety. As this design of power system software is able to predict the system behavior under both normal and abnormal operating conditions.
ERACS is a suite of programs which allow harmonics, fault, arc flash, transient stability and protection co-ordination studies to be done via GUI (graphical user interface). The calculation programs are carried out and its results obtained through the single line diagram.
Rectifier has the capability of drawing a non-sinusoidal current from a sinusoidal voltage supply. The current drawn can be divide into its harmonic components by using Fourier series and the harmonic current source(in this case, rectifier) will propagate into the system and harmonic voltage is disappeared due to the reaction harmonic current and network impedance.
The harmonic characteristic are stored as one of the library elements and the program calculates its total harmonic voltage and current distortion across the network.
Figure : Transient stability example sourced from www.era.co.ukTransient stability program is able to study the behavior of generator, motor starting, fault and load application etc. Several results are programmed into ERACS with the outcome shown graphically on the single line diagram.
Figure : Loadflow example sourced from www.era.co.uk
Loadflow section calculates the steady state conditions of a power system network. The section will find out the transformer tap changer positions, real and reactive power flows in given limitation. The network above arrows shows the direction of power flow and warning will be given for overloaded system.
Figure : Protection Co-ordination example sourced from www.era.co.uk
Protection co-ordination program is three programs in one. Relays, circuit breaker, fuses are included to single line diagram as well. With chosen characteristics, the suitability of the settings for current system is checked by the protection program under steady state loadflow conditions.
PSAT(Power System Analysis Toolbox)
PSAT is one of the software packages for power system analysis and developed using Matlab, which runs operating system like Mac OS, Linux and Windows. In addition, PSAT is able to run on GNU/Octave (Matlab clone) for analysis and designing electric power system. PSAT includes;
Continuation power flow
Optimal power flow
Small signal stability analysis
Figure : Synoptic scheme of PSAT (source from IEEE- An Open Source Power System Analysis Toolbox)Time domain simulation
Static and dynamic models
PSAT hold interfaces to UWPFLOW (supplies algorithm for power flow analysis) which have increases PSAT ability to solve power flow problems. So as to obtain a complete and accurate analysis, PSAT supports several static and dynamic models such as: Power Flow Data, Market Data, Transmission line faults, Bus frequency measurements, Loads, Synchronous machine, Regulating Transformers and so on.
The synoptic scheme of PSAT shown below roughly tells how PSAT works overall.
Furthermore, more figures were sourced for self understanding on PSAT.
Figure : Main GUI of PSAT
Figure : GUI for data format conversion
Figure : GUI for user defined models
Figure : PSAT-Simulink library
PSAT allows drawing electrical schemes by pictorial blocks. Its computational engine is solely Matlab based the Simulink environment is used only as graphical tool.
In summary, PSAT have several models of standard, static dynamic analysis ,a complete GUI and a Simulink based network editor. PSAT is ideal for education and basic power system analysis learning and useful for creating bridges between Matlab and other software packages like, GAMS .
PSS/VIPER is an incorporated program for evaluating, simulate and optimizing power system performance. It has a one line diagram with highly developed features, like lone loading graphs and animated flows. Several organizations use it for power system analysis and as a marketing and scheduling tool.
Figure : PSS/VIPER single line diagram
PSS/VIPER is a power system analysis tool for PSS/E, which has become the defacto world standard for transmission analysis. This software is not only capable of letting user to use PSS/E data, but to able to exchange data with electrical utilities. The analysis functions include:
Advanced Short Circuit Analysis
PSS/VIPER’s short circuit analysis takes in all machine contributions, which are calculated at user-defined times after event of a fault. The advanced time-decremented short circuit engine that represents the concepts of all major international standards is included in PSS/VIPER including UK Electricity Association recommendation.
Figure : Short-circuit analysis(circuit breaker make and break and overstress)
PSS/VIPER has industry-standard harmonic dispersion calculations that allow user to model the effects of natural harmonic properties of the network along with user-defined harmonic injections and filters. The obtained harmonic result can be shown on a single line diagram as plots of harmonic voltage, impedance against frequency, harmonic spectrum are existed.
Figure : Harmonics results
Protection / Co-ordination
Modelling for transformers, fuses, conductors and relays can be found on the protection and coordination module. By drawing a protection pack on the diagram, PSS/VIPER is able to create the protection devices and supply a Microsoft Accessâ„¢ database. Nonetheless, users are able to change the fuse and relay characteristic as they like.
Figure : Protection and Coordination
Alternative choice of Power system analysis software tools
PSCAD of Manitoba HVDC Research Centre is a fast, accurate and easy-to-use power system simulator for the design and verification of all types of power systems. It is a powerful and flexible design tool and graphical user interface to EMTDC. It comes with a library of preprogrammed and tested models, ranging from simple passive elements and control systems to more complex models, such as machines, FACTS devices, lines, and cables
PowerWorld is a comprehensive, robust power flow solution engine capable of efficiently solving systems of up to 60,000 buses. Basically, this power system analysis package is designed to simulate high voltage power system operation on a time frame ranging from several minutes to several days. The
package is “extremely user-friendly and highly interactive”, including one-line diagrams with animated flow, color contours, support for panning, zooming, and conditional display of all or a subset of various devices available in the system, such as buses, loads, generators to areas, and zones. This package is not only limited to transmission line simulation but also simulates OPF, security-constrained OPF, and hence is useful for simulating power market and internal education of power systems.
ASPEN is basically a stand-alone PC-based graphical user-machine interface for power system applications and analysis. It is equipped with integrated modules like Power Flow, DistriView, OneLiner, Breaker Rating Module, Relay Database, and Line Constants. The Power Flow program is designed for the planning, design and operating studies of transmission, sub-transmission and distribution networks. OneLiner is a short-circuit and relay coordination program for relay engineers. Relay Database is designed to be a repository of relay information for electric utilities and industrial facilities. DistriView is an integrated suite for voltage drop, short-circuit, and relay coordination software for utility distribution systems. The ASPEN modules also have data import-export facilities and built-in scripting language using the BASIC programming.
CYME International’s PSAF is integrated power system analysis software, equipped with simulation modules for conducting a wide array of system studies for utilities and industries. Currently available analysis modules of PSAF include CYMFLOW for power flow, motor starting, and AC contingency analysis, CYMFAULT for short-circuit analysis, CYMHARMO for harmonic analysis, CYMSTAB for transient-stability analysis, CYMLINE for one-line diagram, WECS for wind energy conversion systems, and CYME programs for line and cable parameter calculations. CYMDIST is another analysis package for distribution network planning and studies with various optional add-on modules.
ETAP of Operational Technology, Inc. is for the design, simulation, and analysis of generation, transmission, distribution, and industrial power systems. The ETAP software suite has various program modules like power system analysis, real-time simulation, advanced monitoring, optimization control, intelligent load shedding, energy usage cost analysis, and device coordination. The ETAP PowerStation family of programs is a fully integrated analysis tool used to design, maintain, and operate electric power systems in a totally graphical and virtual reality environment. Other integrated tools include ETAP PSMS for PowerStation Management System, ETAP STAR for System Protection and Device Coordination, and ETAP PanelSystems for panel system design and analysis.
SPICE is a powerful general-purpose analog circuit simulator that is used to verify circuit designs and predict the circuit behavior. Especially for integrated circuits, SPICE was originally developed at the Electronics Research Laboratory of the University of California, Berkeley (1975). PSpice is a PC version of SPICE developed by MicroSim Corp (OrCAD), and HSpice is a version, developed by Avant! (Synopsys Corp.) that runs on workstations and larger computers. SPICE can perform many kinds of electronic circuits-level analysis, such as DC-AC, transient, noise, sensitivity, distortion, Fourier, and Monte Carlo. SPICE has an analog as well as digital library of all standard components
ESA’s EasyPower is a suite of power system analysis software products that can be used for power system analysis, design, measurement, and control and that can be used to simulate a power system with unlimited busses. It offers an integrated one-line diagram with multiple analysis functionalities. The EasyPower suite of products includes EasyPower ShortCircuit, EasyPower PowerFlow, EasyPower PowerProtector (for protective device coordination and device database), EasyPower Spectrum (for harmonic and PQ problems), EasyPower ArcFlash, and EasyPower Measure.
DIgSILENT PowerFactory software is an integrated power system analysis tool that combines reliable and flexible system modeling capabilities with state-of-the-art solutions algorithms and unique object-oriented database management. One can develop detailed power system models in a single database with a wide range of steady-state, frequency-domain, time-domain, and stochastic system characteristics. The package supports the simulation and analysis for a system with a maximum of 100 buses, 250 buses, and an unlimited number of buses. Among the packages are PowerFactory Distribution, PowerFactory Transmission, PowerFactory Industrial, and PowerFactory Enterprise. PowerFactory is not only limited to analysis of respective sectors but also does reliability analysis, production planning, contingency analysis, power electronics device modeling, and interface for SCADA/GIS, and is compatible with a third-party product such as PSS/E & PSS/U.
CAPE, developed by Electrocon International, Inc. is the world’s most powerful protection engineering software. It has an extensive database for protection engineering and the largest library of detailed relay models. CAPE consists of series of core and optional modules for analysis and reporting, linked by a general-purpose database. All CAPE modules contain an important set of standard features. CAPE’s working space is user-friendly, GUI-based, which has the ability to define sets of buses, lines, transformers, and protective devices for batch operations or for use in macros (short programs). CAPE’s user programming language (CUPL) helps to extend any module to perform an almost limitless number of useful, repetitive tasks such as CUPL macros that can be easily developed to perform automatic fault studies. The package includes built-in macros to compute fault locations, relay settings, reaches of instantaneous overcurrent and distance elements, generator breakers flashover currents, and state simulation data for end-to-end relay testing.
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In summary, there are a lot more power system analysis software tools available in the market. However, research is mainly on ERACS as it is regularly use by power engineers for system design and planning purposes. Therefore, they have direct key into the program development to incorporate best practices currently in electrical industry. Nevertheless, one can always find ERACS at most universities in UK.
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