Electrical power system simulation involves power system modeling and network simulation in order to analyze electrical power systems using design/offline or real-time data. Power system simulation software's are a class of computer simulation programs that focus on the operation of electrical power systems. These types of computer programs are used in a wide range of planning and operational situations for electric power systems.
Multiple elements of a power system can be modelled. A power-flow study calculates the loading on transmission lines and the power necessary to be generated at generating stations, given the required loads to be served. A short circuit study or fault analysis calculates the short-circuit current that would flow at various points of interest in the system under study, for short-circuits between phases or from energized wires to ground. A coordination study allows selection and setting of protective relays and fuses to rapidly clear a short-circuit fault while minimizing effects on the rest of the power system. Transient or dynamic stability studies show the effect of events such as sudden load changes, short-circuits, or accidental disconnection of load on the synchronization of the generators in the system. Harmonic or power quality studies show the effect of non-linear loads such as lighting on the waveform of the power system, and allow recommendations to be made to mitigate severe distortion. An optimal power-flow study establishes the best combination of generating plant output to meet a given load requirement, so as to minimize production cost while maintaining desired stability and reliability; such models may be updated in near-real-time to allow guidance to system operators on the lowest-cost way to achieve economic dispatch.
There are many power simulation software packages in commercial and non-commercial forms that range from utility-scale software to study tools.
Load flow calculation
The load-flow calculation[1] is the most common network analysis tool for examining the undisturbed and disturbed network within the scope of operational and strategic planning.
Using network topology, transmission line parameters, transformer parameters, generator location and limits, and load location and compensation, the load-flow calculation can provide voltage magnitudes and angles for all nodes and loading of network components, such as cables and transformers. With this information, compliance to operating limitations such as those stipulated by voltage ranges and maximum loads, can be examined. This is, for example, important for determining the transmission capacity of underground cables, where the influence of cable bundling on the load capability of each cable has to be taken also into account.
Due to the ability to determine losses and reactive-power allocation, load-flow calculation also supports the planning engineer in the investigation of the most economical operation mode of the network.
When changing over from single and/or multi-phase infeed low-voltage meshed networks to isolated networks, load-flow calculation is essential for operational and economical reasons. Load-flow calculation is also the basis of all further network studies, such as motor start-up or investigation of scheduled or unscheduled outages of equipment within the outage simulation.
Especially when investigating motor start-up,[2] the load-flow calculation results give helpful hints, for example, of whether the motor can be started in spite of the voltage drop caused by the start-up current.
Short circuit analysis
Short circuit analysis analyzes the power flow after a fault occurs in a power network. The faults may be three-phase short circuit, one-phase grounded, two-phase short circuit, two-phase grounded, one-phase break, two-phase break or complex faults. Results of such an analysis may help determine the following:
Magnitude of the fault current
Circuit breaker capacity
Rise in voltage in a single line due to ground fault
The goal of transient stability simulation of power systems is to analyse the stability of a power system from sub-second to several tens of seconds. Stability in this aspect is the ability of the system to quickly return to a stable operating condition after being exposed to a disturbance such as for example a tree falling over an overhead line resulting in the automatic disconnection of that line by its protection systems. In engineering terms, a power system is deemed stable if the substation voltage levels and the rotational speeds of motors and generators return to their normal values in a quick and continuous manner.
Figure 1. Specifies the acceptable amount of time it takes grid voltages return to their intended levels, which may vary depending on the magnitude of voltage disturbance.
Models typically use the following inputs:
Number, size and type of generators with any available mechanical, electrical, and control (governor, voltage regulation, etc.) parameters,
a mix of residential, commercial and industrial load at each bus,
location and specifications for distributed control devices such as tap-changing transformers, switched shunt compensation, static Var compensators, flexible AC transmission systems, etc.,
location and specifications for protection devices such as relays and load shedding, and
location and specifications of any other relevant control and/or protection devices.[4]
The acceptable amount of time it takes grid voltages return to their intended levels is dependent on the magnitude of voltage disturbance, and the most common standard is specified by the CBEMA curve in Figure. 1. This curve informs both electronic equipment design and grid stability data reporting.[5]
Electricity flows through an AC network according to Kirchhoff's Laws. Transmission lines are subject to thermal limits (simple megawatt limits on flow), as well as voltage and electrical stability constraints.
The simulator must calculate the flows in the AC network that result from any given combination of unit commitment and generator megawatt dispatch, and ensure that AC line flows are within both the thermal limits and the voltage and stability constraints. This may include contingencies such as the loss of any one transmission or generation element - a so-called security-constrained optimal power flow (SCOPF), and if the unit commitment is optimized inside this framework we have a security-constrained unit commitment (SCUC).
In optimal power flow (OPF) the generalised scalar objective to be minimised is given by:
where u is a set of the control variables, x is a set of independent variables, and the subscript 0 indicates that the variable refers to the pre-contingency power system.
The SCOPF is bound by equality and inequality constraint limits. The equality constraint limits are given by the pre and post contingency power-flow equations, where k refers to the kth contingency case:
The equipment and operating limits are given by the following inequalities:
represent hard constraints on controls
represents hard/soft constraints on variables
represents other constraints such as reactive reserve limits
The objective function in OPF can take on different forms relating to active or reactive power quantities that we wish to either minimise or maximise. For example we may wish to minimise transmission losses or minimise real power generation costs on a power network.
Other power flow solution methods like stochastic optimization incorporate the uncertainty found in modeling power systems by using the probability distributions of certain variables whose exact values are not known. When uncertainties in the constraints are present, such as for dynamic line ratings, chance constrained optimization can be used where the probability of violating a constraint is limited to a certain value.[6] Another technique to model variability is the Monte Carlo method, in which different combinations of inputs and resulting outputs are considered based on the probability of their occurrence in the real world. This method can be applied to simulations for system security and unit commitment risk, and it is increasingly being used to model probabilistic load flow with renewable and/or distributed generation.[7]
Models of competitive behavior
The cost of producing a megawatt of electrical energy is a function of:
fuel price
generation efficiency (the rate at which potential energy in the fuel is converted to electrical energy)
operations and maintenance costs
In addition to this, generating plant incur fixed costs including:
plant construction costs, and
fixed operations and maintenance costs
Assuming perfect competition, the market-based price of electricity would be based purely on the cost of producing the next megawatt of power, the so-called short-run marginal cost (SRMC). This price however might not be sufficient to cover the fixed costs of generation, and thus power market prices rarely show purely SRMC pricing. In most established power markets, generators are free to offer their generation capacity at prices of their choosing. Competition and use of financial contracts keeps these prices close to SRMC, but inevitably offers price above SRMC do occur (for example during the California energy crisis of 2001).
In the context of power system simulation, a number of techniques have been applied to simulate imperfect competition in electrical power markets:
Cournot competition
Bertrand competition
Supply function equilibrium
Residual Supply Index analysis
Various heuristics have also been applied to this problem. The aim is to provide realistic forecasts of power market prices, given the forecast supply-demand situation.
Long-term optimization
Power system long-term optimization focuses on optimizing the multi-year expansion and retirement plan for generation, transmission, and distribution facilities. The optimization problem will typically consider the long term investment cash flow and a simplified version of OPF / UC (Unit commitment), to make sure the power system operates in a secure and economic way. This area can be categorized as:
A well-defined power systems study requirement is critical to the success of any project as it will reduce the challenge of selecting the qualified service provider and the right analysis software. The system study specification describes the project scope, analysis types, and the required deliverable. The study specification[9] must be written to match the specific project and industry requirements and will vary based on the type of analysis.
Power system simulation software
Over the years, there have been several power system simulation software used for various analysis. The first software with a graphical user interface was built by the University of Manchester in 1974 and was called IPSA[10][11] - Interactive Power Systems Analysis (now owned by TNEI Services Ltd).[12][13][14][15][16][17] The recently reformatted cinefilm 'A Blueprint for Power', shot in 1979 shows how this revolutionary software bridged the gap between user-friendly interfaces and the precision required for intricate network analyses.[18][19]
General Electric's MAPS (Multi-Area Production Simulation) is a production simulation model used by various Regional Transmission Organizations and Independent System Operators in the United States to plan for the economic impact of proposed electric transmission and generation facilities in FERC-regulated electric wholesale markets.[20][21][22][23][24] Portions of the model may also be used for the commitment and dispatch phase (updated on 5 minute intervals) in operation of wholesale electric markets for RTO and ISO regions. Hitachi Energy's PROMOD is a similar software package.[25] These ISO and RTO regions also utilize a GE software package called MARS (Multi-Area Reliability Simulation) to ensure the power system meets reliability criteria (a loss of load expectation (LOLE) of no greater than 0.1 days per year). Further, a GE software package called PSLF (Positive Sequence Load Flow), Siemens software packages called PSSE (Power System Simulation for Engineering) as well as PSS SINCAL (Siemens Network Calculator), and Electrical Transient Analyzer Program (ETAP) by Operation Technology Inc.[26] analyzes load flow on the power system for short-circuits and stability during preliminary planning studies by RTOs and ISOs.[27][28][29]
Related Research Articles
An electrical network is an interconnection of electrical components or a model of such an interconnection, consisting of electrical elements. An electrical circuit is a network consisting of a closed loop, giving a return path for the current. Thus all circuits are networks, but not all networks are circuits. Linear electrical networks, a special type consisting only of sources, linear lumped elements, and linear distributed elements, have the property that signals are linearly superimposable. They are thus more easily analyzed, using powerful frequency domain methods such as Laplace transforms, to determine DC response, AC response, and transient response.
Electric power transmission is the bulk movement of electrical energy from a generating site, such as a power plant, to an electrical substation. The interconnected lines that facilitate this movement form a transmission network. This is distinct from the local wiring between high-voltage substations and customers, which is typically referred to as electric power distribution. The combined transmission and distribution network is part of electricity delivery, known as the electrical grid.
In electrical engineering, the power factor of an AC power system is defined as the ratio of the real power absorbed by the load to the apparent power flowing in the circuit. Real power is the average of the instantaneous product of voltage and current and represents the capacity of the electricity for performing work. Apparent power is the product of root mean square (RMS) current and voltage. Due to energy stored in the load and returned to the source, or due to a non-linear load that distorts the wave shape of the current drawn from the source, the apparent power may be greater than the real power, so more current flows in the circuit than would be required to transfer real power alone. A power factor magnitude of less than one indicates the voltage and current are not in phase, reducing the average product of the two. A negative power factor occurs when the device generates real power, which then flows back towards the source.
A high-voltage direct current (HVDC) electric power transmission system uses direct current (DC) for electric power transmission, in contrast with the more common alternating current (AC) transmission systems.
Electric power distribution is the final stage in the delivery of electricity. Electricity is carried from the transmission system to individual consumers. Distribution substations connect to the transmission system and lower the transmission voltage to medium voltage ranging between 2 kV and 33 kV with the use of transformers. Primary distribution lines carry this medium voltage power to distribution transformers located near the customer's premises. Distribution transformers again lower the voltage to the utilization voltage used by lighting, industrial equipment and household appliances. Often several customers are supplied from one transformer through secondary distribution lines. Commercial and residential customers are connected to the secondary distribution lines through service drops. Customers demanding a much larger amount of power may be connected directly to the primary distribution level or the subtransmission level.
In power engineering, the power-flow study, or load-flow study, is a numerical analysis of the flow of electric power in an interconnected system. A power-flow study usually uses simplified notations such as a one-line diagram and per-unit system, and focuses on various aspects of AC power parameters, such as voltages, voltage angles, real power and reactive power. It analyzes the power systems in normal steady-state operation.
In electrical engineering, particularly power engineering, voltage regulation is a measure of change in the voltage magnitude between the sending and receiving end of a component, such as a transmission or distribution line. Voltage regulation describes the ability of a system to provide near constant voltage over a wide range of load conditions. The term may refer to a passive property that results in more or less voltage drop under various load conditions, or to the active intervention with devices for the specific purpose of adjusting voltage.
This is an alphabetical list of articles pertaining specifically to electrical and electronics engineering. For a thematic list, please see List of electrical engineering topics. For a broad overview of engineering, see List of engineering topics. For biographies, see List of engineers.
A microgrid is a local electrical grid with defined electrical boundaries, acting as a single and controllable entity. It is able to operate in grid-connected and in island mode. A 'stand-alone microgrid' or 'isolated microgrid' only operates off-the-grid and cannot be connected to a wider electric power system.
A phase angle regulating transformer, phase angle regulator, phase-shifting transformer, phase shifter, or quadrature booster, is a specialised form of transformer used to control the flow of real power on three-phase electric transmission networks.
A phasor measurement unit (PMU) is a device used to estimate the magnitude and phase angle of an electrical phasor quantity in the electricity grid using a common time source for synchronization. Time synchronization is usually provided by GPS or IEEE 1588 Precision Time Protocol, which allows synchronized real-time measurements of multiple remote points on the grid. PMUs are capable of capturing samples from a waveform in quick succession and reconstructing the phasor quantity, made up of an angle measurement and a magnitude measurement. The resulting measurement is known as a synchrophasor. These time synchronized measurements are important because if the grid’s supply and demand are not perfectly matched, frequency imbalances can cause stress on the grid, which is a potential cause for power outages.
In an electric power system, a fault or fault current is any abnormal electric current. For example, a short circuit is a fault in which a live wire touches a neutral or ground wire. An open-circuit fault occurs if a circuit is interrupted by a failure of a current-carrying wire or a blown fuse or circuit breaker. In three-phase systems, a fault may involve one or more phases and ground, or may occur only between phases. In a "ground fault" or "earth fault", current flows into the earth. The prospective short-circuit current of a predictable fault can be calculated for most situations. In power systems, protective devices can detect fault conditions and operate circuit breakers and other devices to limit the loss of service due to a failure.
The merit order is a way of ranking available sources of energy, especially electrical generation, based on ascending order of price and sometimes pollution, together with amount of energy that will be generated. In a centralized management, the ranking is so that those with the lowest marginal costs are the first ones to be brought online to meet demand, and the plants with the highest marginal costs are the last to be brought on line. Dispatching generation in this way, known as economic dispatch, minimizes the cost of production of electricity. Sometimes generating units must be started out of merit order, due to transmission congestion, system reliability or other reasons.
In electrical power engineering, power systems CAD is computer-aided design (CAD) software that is used to design and simulate electrical power systems in commercial and industrial buildings.
An electric power system is a network of electrical components deployed to supply, transfer, and use electric power. An example of a power system is the electrical grid that provides power to homes and industries within an extended area. The electrical grid can be broadly divided into the generators that supply the power, the transmission system that carries the power from the generating centers to the load centers, and the distribution system that feeds the power to nearby homes and industries.
From 1929 to the late 1960s, large alternating current power systems were modelled and studied on AC network analyzers or transient network analyzers. These special-purpose analog computers were an outgrowth of the DC calculating boards used in the very earliest power system analysis. By the middle of the 1950s, fifty network analyzers were in operation. AC network analyzers were much used for power-flow studies, short circuit calculations, and system stability studies, but were ultimately replaced by numerical solutions running on digital computers. While the analyzers could provide real-time simulation of events, with no concerns about numeric stability of algorithms, the analyzers were costly, inflexible, and limited in the number of buses and lines that could be simulated. Eventually powerful digital computers replaced analog network analyzers for practical calculations, but analog physical models for studying electrical transients are still in use.
The unit commitment problem (UC) in electrical power production is a large family of mathematical optimization problems where the production of a set of electrical generators is coordinated in order to achieve some common target, usually either matching the energy demand at minimum cost or maximizing revenue from electricity production. This is necessary because it is difficult to store electrical energy on a scale comparable with normal consumption; hence, each (substantial) variation in the consumption must be matched by a corresponding variation of the production.
Claes Göran Andersson, is a Swedish academic. He was a full Professor of Power Systems in the Department of Information Technology, Swiss Federal Institute of Technology in Zurich, Switzerland, in 2010–2016 and is now emeritus. He is a Fellow of the Royal Swedish Academy of Engineering Sciences, Royal Swedish Academy of Sciences, and the Swiss Academy of Engineering Sciences. He was also elected as an International Member of the US National Academy of Engineering in 2016 for contributions to the development of high-voltage direct current (HVDC) technology and methods of power system voltage stability analysis.
This glossary of electrical and electronics engineering is a list of definitions of terms and concepts related specifically to electrical engineering and electronics engineering. For terms related to engineering in general, see Glossary of engineering.
Performance modelling is the abstraction of a real system into a simplified representation to enable the prediction of performance. The creation of a model can provide insight into how a proposed or actual system will or does work. This can, however, point towards different things to people belonging to different fields of work.
↑ Hui, Zhu (2014). "The Simulation Analysis of Motor Startup Based on the ETAP Platform". 2014 International Conference on Mathematics and Computers in Sciences and in Industry. Vol.10.1109/MCSI.2014.36. pp.245–248. doi:10.1109/MCSI.2014.36. ISBN978-1-4799-4324-1. S2CID24691998.
↑ Giraldo, Juan S., Juan Camilo López, Jhon A. Castrillon, Marcos J. Rider, and Carlos A. Castro. "Probabilistic OPF model for unbalanced three-phase electrical distribution systems considering robust constraints." IEEE Transactions on Power Systems 34, no. 5 (2019): 3443-3454. https://doi.org/10.1109/TPWRS.2019.2909404
↑ Banerjee, Binayak, and Syed Islam. "Modelling and Simulation of Power Systems." Smart Power Systems and Renewable Energy System Integration. By Dilan Jayaweera. Vol. 57. Cham: Springer International, 2016. 15-26. Studies in Systems, Decision and Control. Springer Link. Web. 22 Nov. 2016. http://link.springer.com/book/10.1007%2F978-3-319-30427-4
↑ "Computer Aided Design for Electricity Networks"; presentation at IEE Centre Meeting, Chester, UK, 2 February 1976. Farquhar, D.; Lynch, C.A.; Ravenscroft, G.; Nield, B.
↑ "Power System Simulation using Interactive Computing and Graphical Display"; IFAC Symposium, Melbourne, Australia, 21-25 February 1977, p369-373. Lynch, C.A.; Brameller, A.; Cale, K.R.
↑ "Interactive Design and Operation of Power Systems"; PhD Thesis, University of Manchester Institute of Science and Technology (UMIST), 1977. Lynch, C.A.
↑ "An Established CAD System for Electrical Power System Analysis"; CAD78 Conference, Brighton, UK, 14-16 March 1978, p170-181. Lynch, C.A.; Brameller, A.
↑ "Network Graphics Based Interactive Power System Analysis"; IEEE Winter Power Meeting, New York, 4-9 Feb 1979; Paper A 79 019-1.3. Lynch, C.A.; Efthymiadis, A.E.
↑ "Use of Interactive Network Graphics Based Power System Analysis in Distribution Network Operation"; IEE Conference on Power System Monitoring and Control, London, UK, 24-26 June 1980. Lynch, C.A.; Smith, A.A.; Efthymiadis, A.E.
↑ "IPSA – A Blueprint for Power"; a short film (18 mins) produced by the Manchester University Audio Visual Service for UMIST and Manweb; first shown May 1979.
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