The new Contingency Analysis tool in DIgSILENT PowerFactory has been designed to offer a high degree of flexibility in configuration, calculation methods and reporting options. Single- and multiple- time-phase contingency analyses are available, both of which offer automatic or user-defined contingency creation based on events, and the consideration of controller time constants and thermal (short-term) ratings.
Calculation Options for Contingency Analysis:
- Support of three calculation methods:
- AC load flow calculation
- DC load flow calculation
- Combined DC/AC calculation; i.e. full DC load flow calculation and automatic recalculation of critical contingencies by AC load flow
- Single- and Multiple- Time-Phase calculations. Multiple time-phase contingency analysis facilitates user-defined post-fault actions within discrete time periods.
- Generator Effectiveness and Quad Booster Effectiveness calculation:
This calculation feature assists the planner in defining appropriate measures for overstressed components in critical contingency cases: During contingency analysis, the possible impact of individual generator re-dispatch or transformer tap changes on overstressed lines is evaluated. Corresponding reports are available that list the generator and quad booster effectiveness on a per-case basis.
- Ultimate Performance via Grid Computing: Possibility to perform the contingency analysis calculation in parallel (on multi-core machines and/or clustered PCs)
Management of Contingencies/Fault Cases:
- User-friendly definition of contingencies (n-1, n-2, n-k, busbar) as ‘Fault Cases’ supporting user-defined events to model post-fault actions (re-switching, re-dispatching, tap adjustment, load shedding)
- Clustering of ‘Fault Cases’ into ‘Fault Groups’ for efficient data management
- Special Operational Libraries to manage ‘Fault Cases’ and ‘Fault Groups’ for future re-use
- Automatic creation of contingency cases based on Fault Cases, considering current network topology
Result File Management:
- Recording of results in (sparse) result file; accessible for any kind of export and/or customer-specific post-processing
- Predefined and user-definable monitoring lists for recording of results; selection of individual components, component classes and their associated variables to be recorded. Any available calculation result for a standard load flow calculation is accessible during contingency analysis.
- User-defined limits for recording of results (thermal loadings, voltage limits, voltage step change)
A wide range of standard reports is available, facilitating summary views or the presentation of results on a per-contingency basis:
- Maximum Loadings Report
- Loading Violations (per case) Report
- Voltage Ranges Report
- Voltage Violations (per case) Report
- Generator and Quad Booster Effectiveness Report
Other key features:
- Tracing Facilities: Use of the new ‘Trace’ function to step through events in a multiple time-phase contingency, while viewing updated results in the single-line graphic
- Support of component-wise Short-Term Ratings based on pre-fault loading and post-fault time
- Special “Contingency Analysis” toolbar for user-friendly configuration, calculation and reporting
Parallel Computing Option:
Calculation of contingencies in parallel represents an important required computation time reduction depending on the number of cores being used.
- Management of the parallel computation function
- Dedicated settings for the execution of the contingency analysis
- Support of three calculation methods:
Quasi Dynamic Simulation
- All load flow calculation variabes are available for storing and plotting
- Statistical data for the variables
- Results such as maximum, minimum, average, variance, etc. are provided
- Energy estimation for the studied time interval
- Tabular reports for the most relevant results as loading/voltage ranges and non-convergency cases
- Export to HTML or Excel options
The typical application of the network reduction tool is a project where a specific network has to be analyzed but cannot be studied independently of a neighbouring network of the same or of a higher or lower voltage level. In this case, one option is to model both networks in detail for the calculation. However, there may be situations in which it is not desirable to perform studies with the complete model; for example when the calculation time would increase significantly, or when the data of the neighbouring network is confidential. In such cases it is good practise to provide a representation of the neighbouring network which contains the interface nodes (connection points) which may be connected by equivalent impedances and voltage sources.
The objective of Network Reduction is to calculate the parameters of a reduced AC equivalent of part of a network, as defined by a boundary. This boundary must completely split the network into two parts. The equivalent network is valid for both load flow and short-circuit calculations. ,Following this, a model variation can be optionally created in the PowerFactory database, whereby the full representation of the portion of network that has been reduced is replaced by the equivalent.
- Flexible definition and maintenance of network boundaries with Boundary Definition Tool. Various features such as colouring of boundaries and topological checks
- Network Reduction can be calculated at any appropriate boundary
- Support of load, standard Ward (PQ-equivalent), extended Ward (PV-equivalent) and REI-DIMO equivalents
- Support of short-circuit equivalents for transient, subtransient, peak-make and peak-break currents
- The reduced network can be created in a network variation. This allows for simple comparison and swapping between reduced and non-reduced cases.
- Robust reduction algorithms based on the sensitivity approach, i.e. reduced network matches for the current operating point as well as for network sensitivities
- Implicit result verification feature
The basic functional model library of DIgSILENT PowerFactory’s protection analysis tool has been extended to include additional devices such as CTs, VTs, relays, fuses and more complex protection schemes including user-defined modelling capabilities. Additionally, there are specially designed interactive VIs (Virtual Instruments) for displaying system quantities and, more importantly, for modifying protection settings in the graphical environment. This last feature is especially useful, as coordinated settings between different protection schemes can be modified via the cursor in the graphical environment, following which the settings in both the database and the simulation environment are also updated.
All protective devices are fully-functional under steady-state and transient conditions, allowing device response assessment under all possible simulation modes, including load flow calculation, fault analysis, RMS and Instantaneous Values (EMT) simulation.
PowerFactory’s main protection features are:
- Accurate steady-state relay checking via short-circuit and load flow (balanced & unbalanced)
- Precise dynamic relay checking with RMS and EMT simulations
- Consideration of current transformer saturation
- Diagrams for overcurrent and distance coordination:
- Time-overcurrent diagrams
- R-X characteristic diagrams
- Time distance diagrams
- Automatic Protection Coordination Wizard for time-overcurrent protection schemes
- Short-circuit trace to examine the performance of a protection scheme in response to a fault or combination of faults
Protection Model Library and Functionality
The DIgSILENT PowerFactory protection analysis tool contains a comprehensive protection device model library. All relays are modelled for steady-state calculations (short-circuit, load flow), RMS and EMT simulation modes. The definition of relay types is highly flexible via block diagrams. For RMS and EMT simulation purposes, relays may be extended and adopted to cope with user specific requirements via the PowerFactory DSL language The features of the protection model library are listed below.
Fuses are represented by their melting curves. It is possible to take minimum and maximum melting curves into account.
Time-Overcurrent Relays for 1-phase, 3-phase, ground and negative sequence time over-currents. Additionally, the relay characteristics can incorporate the following standards and solution methods:
- IEC 255-3, ANSI/IEEE and ANSI/IEEE squared
- ABB/Westinghouse CO (Mdar)
- Linear approximation, Hermite-spline approximation
- Analytical expressions via built-in formula editor and analyser (DSL)
Instantaneous Overcurrent Relays for 1- phase, 3-phase, ground and negative sequence time over-currents.
Directional Relays for overcurrent, power, ground current, and any combination of time and instantaneous overcurrent relays. Additionally, voltage and current polarization is used for the detection of negative and zero sequence components considering also dual polarization. Optional: with voltage memory.
Distance Relays for phase, ground and zone distance protection. Provision is available for incorporating overcurrent and under-impedance starting units (U-I or Z) as well as angle under-impedance.
Different characteristics are available for distance relay zones including:
- MHO, offset MHO
- Polygonal, offset polygonal
- Tomatoes, lens and circle
- R/X Blinders and quadrilateral
Support of various polarisations such as:
- Cross polarised (90ø connection)
- Positive, negative sequence polarised
- Optional: voltage memory
Zero sequence and parallel line compensation
Voltage Relays for under-voltage, instantaneous voltage, voltage balance and unbalance.
Additional devices such as: Breaker Fail, Motor Protection, Generator Protection, Differential Protection, Reclosing Relays, Low Voltage Circuit Breakers, and Out-of-Step Relays.
In addition to these protection functions and relays, DIgSILENT PowerFactory provides further devices and characteristics for more detailed protection system modelling, such as:
- Current and voltage transformers that include saturation effects
- Conductor, cable damage curves, cable overload curves and inrush peak current modelling
- Transformer damage curves (ANSI/IEEE Standard C57.109-1985) and inrush peak current modelling
- Motor starting curves, cold and hot stall, in-rush peak current modelling, and any user-defined curves
All protection device models are implemented within the composite model frame environment. This allows users to easily design and implement their own models, by utilising the graphical user interface for constructing block diagrams.
Output & Graphical Representation
- Overcurrent curve adjustment using drag & drop
- Display of tripping curve tolerances during drag & drop
- User-defined labels
- Tripping times are automatically displayed for calculated currents in time-overcurrent diagrams
- Display of an unlimited number of overcurrent curves in diagrams
- Simple creation and addition of diagrams via single line graphics
- Display of motor starting curves, conductor/cable and transformer damage curves
- Balloon help showing name of relay, etc.
- Double-click on curves to change relay settings
- Additional axis for voltage levels
- Display of single line diagram paths in time-overcurrent diagrams
R-X Characteristic Diagrams
- Display branch impedances with several options
- Automatic display of calculated impedances
- Adding relays with offset
- Flexible display of zones (starting zones, etc.)
Time Distance Diagrams
- Different methods for calculating curves: kilometrical or short-circuit sweep method
- Forward and/or reverse diagram
- Selectivity check of distance and overcurrent relays/fuses in same diagram
- Separate overreach zone representation
- Additional axis showing relay locations and busbars/terminals
- Selectable x-axis scaling (length, impedance, reactance, 1/conductance)
Single Line Diagram
- Colouring of switches according to relay locations, relay tripping times
- Display of relay tripping times in result boxes
- Additional text boxes for relay settings
Relay Setting Report
- Simplified ASCII reports genertaed in the output window
- Tabular report command can be customised to deal with the structure of complex relay models and for a protective device class
Relay Tripping Report
The coordination of overcurrent-time protection is performed graphically using the current-time diagram as the basis. Relay settings are modified using drag & drop to move characteristics. Short-circuit currents calculated by the short-circuit command, are shown in the diagram as a vertical line. In addition, the corresponding tripping times of the relays are displayed. Coordination between relays at different voltage levels is available. Therefore, currents are automatically based on the leading voltage level, which can be selected by the user.
For distance protection coordination, two powerful graphical features are integrated. The first of these features is the R-X diagram for displaying the tripping zone of distance relays and the line impedances. Several relays can be visualised in the same R-X diagram. This can be useful for the comparison of two relays that are located at different ends of the same line. The relay characteristics and the impedance characteristic of the connecting line will be shown in the same R-X diagram. Following short-circuit calculations, the measured impedances are visualised with a marker in the shape of a small arrow or cross. From the location of the marker the user can see the tripped zone and its associated tripping time. For dynamic simulation, measured impedances of the relays can be displayed, thereby visualising the functioning of power swing blocking or out-of-step tripping relays.
The second powerful graphical feature is the time-distance diagram, which is used for checking the selectivity between relays along a coordination path. The relays on a coordination path can be displayed in diagrams for forward, reverse or for both directions. Consequently, it is very easy to check the selectivity of the relays along a coordination path. Two different methods for calculation of the tripping curves are provided. These are the kilometric and the short-circuit method.
- Kilometric method: The reach of the zones is calculated from the intersection of the given positive sequence impedance of the lines, and the impedance characteristic of the relays.
- Short-circuit method: This is the main method for checking the selectivity. Short-circuits (user-defined fault type) are calculated along the coordination path. The tripping times for the time-distance curve are determined using the calculated impedances. The starting signal of a relay is also considered.
A special feature of the distance protection is the consideration of blocking signals or POTT (permissive over-reach transfer tripping), PUTT (permissive under-reach transfer tripping), which are also taken into account. In addition to tripping curves of distance relays, the curves of overcurrent relays can be displayed and coordinated in the same diagram using the short-circuit method.
Both the kilometric and the short-circuit method consider breaker opening times in the calculation of tripping times. The breaker opening time can be optionally ignored.
The coordination assistant helps the protection engineer to quickly find well-structured and consistent network protection solutions and afterwards easily analyse, tune and implement the chosen settings in the protection devices. The algorithm is flexible, automated and comprehensive featuring the following options:
- User-definable coordination area
- Automatic coordination of distance protection relays
- Determination of relay protection zones
- Reactive reach via zone-factors (independent, cumulative, ref. to line 1)
- Resistive reach based on prospective fault/load resistance
- Output options:
- Tabular report
- Time-distance diagram
- Automatic update of protection devices
- Time distance plots are automatically obtained after the algorithm
Arc-Flash Hazard Analysis
PowerFactory offers the possibility to perform calculations to determine Personal Protective Equipment (PPE) requirements by means of the Arc-Flash Hazard Analysis tool:
- Arc-Flash calculations can be performed using globally or individually specified circuit-breaker tripping times, or protection clearing times based on actual protection settings; the calculation takes into account the arc resistance when determining protection clearing times
- Incident Energy and PPE requirements can be displayed on the Single Line Graphic
- Easy preparation and use of Arc-Flash labels based on the calculation results
- IEEE-1584 2002
- NFPA 70E 2008
- German Standard BGI/GUV-I 5188
With the first method, IEEE-1584 2002, the arcing current is calculated based on the equations presented in the standard. Interally, PowerFactory calculates the arc resistance required to limit the fault current to the balanced value. When the NFPA method is selected, the bolted fault current is used for the calculation. For either method, when the user selects to use relay tripping times, a second calculation is performed at a reduced fault current and the associated clearing time. PowerFactory compares the results of these two cases and reports on the worst case result.
The Arc-Flash Hazard analysis tool in PowerFactory offers different option to visualise results:
- Result boxes and colouring mode in the Single Line Graphic
- Arc-Flash reports dialogue to configure tabular result output
- Arc-Flash labels to export a selected set of variables to Microsoft Excel
- Automatic cable sizing based on IEC 60364-5-52, NF C15-100, NF C13-200, and BS 7671, etc.
- Cable reinforcement optimisation
- Verification of global and/or individual thermal and short-circuit constraints
- Verification of user-defined voltage drops per terminal and/or feeders
- Balanced (positive sequence) or unbalanced calculation with support of all phase technologies (1-, 2- and 3-phase systems, w/o neutral conductor)
- System phase technology and cable type consistency checks in the feeder
- Various verification reports and automatic modification of cable types in the existing network via network Variations
Cable Ampacity Calculation
- Cable Ampacity calculation based on IEC 60287 or Neher-McGrath method
- Evaluation of maximum allowable current for cables based on cable material, laying arrangement and environmental data
- Rich reports and automatic modification of cable derating factors in the existing network via network Variations
Power Quality and Harmonic Analysis
The harmonic analysis functionality is ideal for applications in transmission, distribution and industrial networks for filter design, ripple control signal simulation or for the determination of network resonance frequencies.
For analysing the impact of harmonics in power systems, DIgSILENT PowerFactory provides two harmonic analysis functions.
Harmonic Load Flow
The DIgSILENT PowerFactory harmonic load flow features the calculation of harmonic voltage and current distributions based on defined harmonic sources and grid characteristics. It allows the modelling of any user-defined harmonic voltage or current source, both in magnitude and phase including inter-harmonics. The harmonic sources can be located at any busbar in the power system and may be implemented within any network topology.
Harmonic current sources can be associated with any load, SVC (TCR injection), rectifier or inverter. Harmonic voltage sources can be modelled using the AC voltage source model or the PWM AC/DC converter model. The built-in rectifier models inject the spectrum of ideal 6-pulse rectifiers if no other injection has been defined.
DIgSILENT PowerFactory supports any type of characteristic harmonic, un-characteristic harmonic (even harmonics etc.) and non-integer (inter-) harmonics. Unbalanced harmonic sources (e.g. single-phase rectifiers) are also fully-supported. The analysis of inter-harmonics or unbalanced harmonic sources is based on a complete abc-phase network model.
Because of the phase correct representation of harmonic sources and network elements, the superposition of harmonic currents injected by 6-pulse rectifiers (via Y-Y and Y-D transformers leading to a reduction in 5th, 7th, 17th, 19th etc. harmonic currents) is modelled correctly.
DIgSILENT PowerFactory calculates all symmetrical and asymmetrical harmonic indices for currents and voltages, as defined by relevant IEEE standards, including harmonic current indices and harmonic losses, such as:
- THD and HD ((Total) Harmonic Distortion)
- TAD (Total Arithmetic Distortion)
- IT product
- Harmonic losses
- Active and reactive power at any frequency
- Total active and reactive power, displacement and power factor
- RMS values
- Unbalance factors
- Integer and non-integer harmonic order values
- Flicker Assessment:
- Pst, Plt (short- and long-term flicker disturbance factors; continuous an switching operation)
- Relative voltage change value
Results can be represented:
- In the single line diagram (total harmonic indices)
- As histograms (frequency domain)
- As waveform (transformation into the time domain)
- As profile (e.g. THD versus busbars)
The frequency dependent representation of network elements such as lines, cables, two- and three-winding transformers, machines, loads, filter banks etc. for considering skin effects is fully-supported.
The frequency sweep performs a continuous analysis in the frequency domain. The most common application is the calculation of self- and mutual network impedances for identifying the resonance points of the network and for supporting filter design.
- All impedances are calculated simultaneously in the same run. Since DIgSILENT PowerFactory uses a variable step-size algorithm, the calculation time of frequency sweeps is very low while the resolution around resonance points remains very high (typically 0.1 Hz)
- Frequency sweeps can either be performed with the positive-sequence network model (very fast) or the complete three-phase abc-network model
- Calculation of self- and mutual network impedances
- Calculation of voltage amplification factors
- Impedance plots may be created in either Bode, Nyquist or magnitude/phase forms
In addition to common applications relating to harmonic distortion, PowerFactory’s Frequency Sweep function can also be used for subsynchronous resonance studies. The calculation of damping and undamping torques is supported by special scripts.
The skin effect is considered by associating frequency characteristics with line or transformer resistances and inductances. These characteristics can be specified by either setting the parameters of a polynomial expression or by entering the characteristic point by point using tables. DIgSILENT PowerFactory uses cubic splines or hermite polynoms for appropriate interpolation.
- Lines are modelled either by approximate PI sections or by the highly-accurate distributed parameter line model that should always be used for long lines or high frequency applications. The skin effect can be included in both line models.
- Filters can be specified by either ‘layout’ parameters or ‘design’ parameters. ‘Layout’ parameters are typically the rated reactive power, the resonance frequency and the quality factor. ‘Design’ parameters are the actual R, L, and C values.
In addition to the explicit specification of frequency dependent resistance or inductance via parameter characteristics, overhead lines can be modelled by defining the tower geometry and cables can be modelled by specifying the cable layout. In such cases, frequency dependent effects, such as the skin effect or frequency dependent earth return, are automatically calculated and considered by the model.
Ripple Control Signals
DIgSILENT PowerFactory provides full support for analyzing and dimensioning ripple control systems. Series and parallel coupling of ripple control systems can be modelled including all necessary filter elements.
- The level of the ripple control signal in the entire network is calculated and reported in the single line diagram, the output window or the browser.
DIgSILENT PowerFactory features a special, easy-to-use function for calculating the rating of all components of a filter. All relevant voltages across all components are calculated and made available in the ‘Filter Sizing’ report.
Power Quality Assessment according to D-A-CH-CZ Guideline
The Connection Request Assessment tool ia a very useful feature for power quality calculations according to D-A-CH-CZ guideline "Technical Rules for the Assessment of Network Disturbances" as used in Germany, Austria, Switzerland and Czech Republic. A new Connection Request Assessment command is available as well as the Connection Request element. This element represents a new load installation which is to be connected to the grid.
Full assessment of the D-A-CH-CZ guideline is performed based on the following criteria:
- Voltage changes and flicker
- Voltage unbalance
- Commutation notches
- Interharmonic voltages
Following the calculation, a detailed report and summary are made available for further analysis.
Connection Request Assessment
- According to D-A-CH-CZ guidelines
- Assessment at PCC:
- Voltage changes and flicker
- Voltage unbalance
- Commutation notches
- Interharmonic voltages
- HV resonances
Transmission Network Tools
PV Curves Calculation
- Voltage stability assessment by determination of critical point of voltage instability
- Support contingency analysis, i.e. detection of “limiting contingency”
QV Curves Calculation
- Voltage stability limit assessment by evaluating the bus voltage change w.r.t. variation of injected reactive power
- Evaluating of stable operating points for various system loading scenarios, including contingencies
- Determination of reactive power compensation by superposition of capacitor characteristics in QV plots
Power Transfer Distribution Factors
- Analysis of the impact of a power exchange between two regions
- Various load and generation scaling options
Transfer Capacity Analysis
- Determination of maximum power transfer capacity between two regions
- Various load and generation scaling options for exporting and importing region
- Thermal, voltage and contingency constraints options
Distribution Network Tools
In order to reduce network unbalance and improve quality of supply, DIgSILENT PowerFactory incorporates features to assist the user in distribution network optimisation:
- Optimal capacitor placement
- Open tie optimisation
- Cable reinforcement optimisation
- Feeder tools for voltage/technology change
- Auto-balancing to minimise voltage unbalance
Optimal Capacitor Placement
PowerFactory’s Optimal Capacitor Placement determines the optimal locations, types and sizes of capacitors to be installed in radial distribution networks. The economic benefits due to energy loss reduction are weighted against the installation costs of the capacitors while keeping the voltage profile within defined limits. This feature includes:
- User-definable library of proposed capacitor candidates together with annual installation costs
- Consideration of:
- Benefits due to loss reduction
- Voltage limits
- Maximum total investment costs
- Support of load profiles
- Calculated results: set of locations where capacitors should be installed, which type of capacitor(s) should be installed at each site, and whether or not a switched capacitor is proposed
- User-friendly presentation of results with fully-integrated post-processing features
Open Tie Optimisation
PowerFactory’s Open Tie Optimisation finds a loss-minimal switch configuration of the network, which results in a radial topology while maintaining all thermal limits. This feature includes:
- Heuristic algorithm which explores all potential meshes in the grid to evaluate the optimal tie-points to open
- Consideration of loading limits
- User-definable section of the network where optimal open tie-points should be determined
- Report mode to propose switch status changes or automatic switch reconfiguration
Cable Reinforcement Optimisation
PowerFactory’s Cable Reinforcement Optimisation determines the most cost-effective option for upgrading overloaded cables. The objective function is to minimize annual costs for reinforcing lines (i.e. investment, operational costs and insurance fees). Constraints for the optimization are the admissible voltage band and cable loading limits for the planned network.
- Optimisation along pre-definable feeder
- User-definable library of available cable/OHL types with costs that can be used for reinforcement
- Consideration of:
- Admissible voltage band limits
- Maximum voltage drop limit at the end of the feeder
- Maximum admissible Cable/OHL overloading
- Various plausibility checks for final solution
- Calculated results: report of the recommended new cable/overhead types for lines and cost evaluation for the recommended upgrading
- Report mode to propose cable/OHL type changes or automatic type replacement
- Report on short-circuit loading of lines and cables
- Automatic balancing of feeders such that voltage unbalance at terminals is minimised
- Reconfiguration of phasing of loads, lines, or transformers and combinations thereof
- Supports fixed phasing elements
- Colouring modes to visualize phase technology before and after change
Reliability calculations are essential for the evaluation and comparison of electrical power systems in terms of both design and operation. Although non-stochastic contingency analyses (i.e. n-1) are able to highlight obviously unacceptable operational events, they cannot rank these events in terms of either frequency or duration. The DIgSILENT PowerFactory Reliability Analysis tool incorporates standard reliability assessment features together with sophisticated modelling techniques that enable all forms of reliability assessment to be carried out.
Failure models are defined using mean yearly failure frequency and repair duration data. For lines and cables, this data is entered in per-length terms. Detailed models are available for generators that enable de-rated states to be represented, with maintenance and common mode models also available.
Load forecast and growth curves can be imposed via time-varying load characteristics. Load models are additionally available for hard-to-predict industrial situations, and each can be assigned its own interruption cost using one of the following cost functions: cost/customer/interruption, cost/kW/interruption or cost/interruption.
All failure and load models can be represented either by the Markov method, where simple mean repair durations are modelled, or by the sophisticated Weibull-Markov method, where repair duration variance is additionally modelled. The Weibull-Markov model also has the unique property that annual interruption cost indices such as load and process (industrial) interruption costs can be calculated both analytically and quickly. Consequently, PowerFactory’s Reliability Analysis tool enables the comparison and justification of alternative investment proposals on a financial basis.
The basic calculation method used is analytical state enumeration. This method is very efficient, produces exact results and is flexible for addressing a wide range of reliability calculation problems. The network reliability analysis can be carried out on the basis of a simple connectivity check (primarily intended for distribution networks) or on the basis of AC load flow calculations which consider load curtailments due to overloading or voltage constraints (for bulk power system analysis).
The approach combines fast topological analysis for fault clearance, fault isolation and power restoration, with AC load flow and optimisation techniques for addressing energy at risk, load transfer and load shedding.
Finally, the results of all reliability assessments can be presented in text format, as user-defined graphs, or within the single-line graphics environment.
The failure models for network reliability assessment include:
- Failures of lines, cables, transformers, generators/external grids and busbars
- Independent second failures ("n-2")
- Common mode failures
- Double earth faults
- Protection/circuit breaker malfunction
- Transient fault model (for momentary interruption indices)
In addition to the above-listed failure models, planned outages such as scheduled maintenance can also be considered.
Special failure models can be used by various network components to share failure data. The failure models hold stochastic failure information (mean yearly failure frequency for sustained, transient and earth faults on a per km basis, as well as mean repair durations). PowerFactory’s user-interface allows for both an easy setup, as well as for simple modification of input data for various studies.
The Maintenance feature simulates the effects of network reliability under predefined planned outage scenarios. Maintenance of individual network components can be modelled on an hourly basis.
Based on the network model and the given failure data, the reliability analysis generates and analyses the resulting contingency cases.
In addition, the user can model load forecast and growth curves by imposing time-varying load characteristics. PowerFactory has a very efficient handling of the reliability assessment over time with varying load data, through the use of the following techniques:
- Clustering of load states in the state enumeration algorithm
- Analysing load variation correlations, thereby reducing the overall number of load states
- Using linear approximation techniques to improve performance in the case of large numbers of load states
Failure Effect Analysis (FEA)
The Failure Effect Analysis simulates both the automatic and manual reactions to faults of installed protection and of the system operators during each reliability assessment. The FEA can be checked and fine-tuned in an interactive way to exactly match the real system and operator reactions.
The Failure Effect Analysis comprises:
- Automatic fault clearance by protection devices
- Automatic or manual fault isolation
- Automatic or manual power restoration by network reconfiguration.
This includes sophisticated sectionalizing and strategic power restoration methods that operate in three distinct phases:
- Phase 1: Sectionalising by remote controlled switch devices
- Phase 2: Sub-sectionalising of strategic areas
- Phase 3: Full system restoration
- Overload alleviation by optimised generator re-dispatch, load transfer and load shedding, under consideration of load priorities and the amount of load that is available for shedding.
- Under-voltage load-shedding
For classical bulk power system analysis, it is assumed that post-fault overloads may occur. A full AC load flow, incorporating basic generator re-dispatch and automatic tap changing, is used to analyse post-fault system conditions. Additional load transfer and/or load shedding will then be simulated.
In cases where it can be assumed that system restoration will not lead to any overloading, the overload alleviation can be omitted and a fast network connectivity analysis is sufficient.
System Indices and Results
PowerFactory’s Network Reliability Assessment calculates all common reliability indices. Among others, the following indices are available:
System indices (also available for user-defined feeders, zones, and areas):
- SAIFI, System Average Interruption Frequency Index
- CAIFI, Customer Average Interruption Frequency Index
- SAIDI, System Average Interruption Duration Index
- CAIDI, Customer Average Interruption Duration Index
- ASIFI, Average System Interruption Frequency Index
- ASIDI, Average System Interruption Duration Index
- ASAI, Average Service Availability Index
- ASUI, Average Service Unavailability Index
- ENS, Energy Not Supplied
- AENS, Average Energy Not Supplied
- ACCI, Average Customer Curtailment Index
- EIC, Expected Interruption Cost
- IEAR, Interrupted Energy Assessment Rate
- SES, System Energy Shed
- LOLE, Loss of Load Expectancy
- LOEE, Loss of Energy Expectation
- LOLF, Loss of Load Frequency
- LOLD, Loss of Load Duration
- MAIFI, Momentary Average Interruption Frequency Index
- AID, Average Interruption Duration
- ACIF, Average Customer Interruption Frequency
- ACIT, Average Customer Interruption Time
- LPIT, Load Point Interruption Time
- LPIF, Load Point Interruption Frequency
- LPENS, Load Point Energy Not Supplied
- LPEIC, Load Point Expected Interruption Costs
- LPCNS, Load Point Customers Not Supplied
- LPPNS, Load Point Power Not Supplied
- LPPS, Load Point Power Shed
- LPES, Load Point Energy Shed
- LPIC, Load Point Interruption Costs
- TCIF, Total Customer Interruption Frequency
- TCIT, Total Customer Interruption Time
- AID, Average Interruption Duration
- LPIF, Yearly Interruption Frequency
- LPIT, Yearly Interruption Time
The Network Reliability Assessment is fully-integrated into PowerFactory, thus profiting from the extremely flexible data management and data management and data handling for setting up individual studies.
Each contingency case is created and analysed based on events (i.e. switch events, load shedding events, generator re-dispatch events). By default, the events are created automatically by the reliability calculation algorithm. This allows the user to analyse, adjust and fine-tune the individual cases in a very flexible manner. The reliability calculation will then consider user-defined events for the FEA instead of creating them automatically.
Tracing of Individual Cases
The user can examine the results of a single fault by running the fault case of interest in the trace mode, a step-by-step analysis that sweeps over the individual actions of the FEA. The switching actions and load shedding/generator dispatch events created by the reliability calculation will then be applied to the network and the results can be viewed and analysed after each time step.
Powerful Output Tools for Result Representation
Results can be viewed in a variety of ways:
- Formatted reports
- Tabular result views (integrated into the PowerFactory Data Manager)
- Graphical result representations
- Various clouring modes
Contribution to Reliability Indices
Post-processing tools allow the calculation of individual components' contributions to system indices. In this way the user can study the impact of certain network components (such as lines/cables, transformers, etc.) on the overall system indices. Likewise, loads can be grouped into load classes (industrial, agricultural, domestic, etc.) and their contribution to, for example, energy indices can be evaluated.
Development of indices over years
Taking into account the evolution of the network model and the failure data over time, PowerFactory supports the calculation and visualisation of the reliability indices over years.
Optimal Power Restoration
PowerFactory offers Power Restoration tools for distribution networks incorporating Tie Open Point optimisation methods to achieve an utmost level of resupply. For example, PowerFactory is automatically evaluating - as part of the Power Restoration strategy - the benefits of any move of tie open points in any neighboring feeder.
- Unbalanced calculations
- Handle of feeder constraints
- Calculation of reliability indices
- Use of load distribution states
- Use of Time Tariffs and Energy Tariffs
Optimal Power Restoration
Optimal Power Restoration studies can be conducted for single case to obtain a "Recovery Scheme Report" - even in the case where no failure data is available for the network components. This function includes the feature to trace the stages of the restoration and view the impacts oh the restoration on the single line graphic.
- Animated tracing of individual cases
- Optimal Remote Control Switch (RCS) placement
- Optimal Manual Restoration
Optimal Power Flow (OPF)
The PowerFactory Optimal Power Flow serves as the ideal complement to the existing load flow functions. Where the standard load flow calculates branch flows and busbar voltages based on specified “set points” (active/reactive power generation, generator voltage, transformer tap positions, etc.), the OPF also calculates the “best possible” values for optimising a user-specified objective function and a number of user-defined constraints. In this way, the OPF adds intelligence and consequently improves efficiency and throughput of power system studies significantly.
Reactive Power Optimisation (OPF I)
- Minimisation of total or partial grid losses
- Maximisation of reactive power reserve
- Reactive power optimisation (interior point method)
- Various controls such as:
- Generator reactive power
- Transformer and shunt taps
- Flexible constraints such as:
- Branch flow and voltage limits
- Generator reactive power limits
- Reactive power reserve
- Boundary flows
Economic Dispatch (OPF II)
- Various objective functions, e.g.:
- Minimisation of losses
- Minimisation of costs (eco dispatch)
- Minimisation of load shedding
- Optimisation of remedial post-fault actions, e.g. booster tap changes (pre- to post-fault)
- AC optimisation (interior point method)
- DC optimisation (linear programming)
- Various controls such as:
- Generator active and reactive power
- Transformer, quad booster and shunt taps
- Flexible constraints such as:
- Branch flow and voltage limits
- Generator active and reactive power limits
- Active and reactive power reserve
- Boundary flows
- Contingency constraints (DC only)
Techno-economical calculations are used to perform an economic assessment and comparison of network expansions (projects) through an analysis of:
- Cost of electrical losses
- Economic impact of failure rates (reliabilty)
- Investment costs (including initial costs, initial value, scrap value and expected life span)
- Project timing
The output of the techno-economical calculation is the Net Present Value (NPV) of the project over the selected period. The command can optionally reconfigure the network at each step of the calculation to minimise losses (using the Tie open Point optimisation command).
Output results are:
- Reference to the result object
- Summary report of selected calculation options, and annual costs, total costs and Net Present Value in the output window
The PowerFactory State Estimator provides an accurate real-time analysis of the full operating system based on the information provided by selectively monitored data, e.g. that of an installed SCADA system. The objective of the state estimator is to assess the generator and load injections in a way such that the resulting load flow solution matches as closely as possible the measured branch flows and busbar voltages. The features of PowerFactory’s State Estimation tool include:
- Flexible definition of external measurement devices in the network model supporting the following measurement types:
- Active and reactive power branch flows
- Branch current (magnitude)
- Busbar voltage (magnitude)
- Breaker status
- Transformer tap position
- User-definable selection of system states to be estimated/optimised:
- Loads: Active and reactive power demand, or alternatively the scaling factor
- Generators and static generators: Active and reactive power generation
- Asynchronous machines: Active power generation
- Static Var Systems: Reactive power injection
- Transformers: Tap positions
- High-precision estimation of full system state that minimises deviations from measurements
- Fast-converging non-linear optimisation algorithms
- Observability check based on a novel sensitivity analysis approach
- Detection of unobservable system states
- Grouping of unobservable states in equivalence classes
- Detection of redundant measurement locations
- Innovative patch strategies for unobservable areas; usage of automatically created pseudo-measurements
- Bad data detection in the loop
- Measurement plausibility checks as pre-processing, such as:
- Node sum checks for active and reactive power
- Check for consistent active power flow directions at each side of branch elements
- Check for unrealistic branch losses and unrealistic branch loadings
- Check for negative losses on passive branch elements
- Check for large branch flows on open-ended branch elements
- Statistical report and colouring modes to visualise measurement qualities
- Fully featured, large scale AC/DC system representation
The PowerFactory State Estimator is supporting a variety of communication options such as OPC (OLE for Process Control) or Shared Memory Interface for implementing data interchange with any kind of SCADA system.
- Flexible definition of external measurement devices in the network model supporting the following measurement types:
Stability Analysis Functions (RMS)
RMS Simulation with a-b-c Phase Representation
The a-b-c phase, steady-state component representation of the power system, features the fundamental frequency analysis of any asymmetrical grid operation condition.
- Initialisation via balanced or unbalanced power flow
- Simulation of unbalanced loading conditions in 1-, 2- and 3-phase AC and DC systems
- Simulation of any number and combination of unbalanced faults including single- and double-phase line interruptions
- The a-b-c phase system representation mode avoids tedious hand-calculations of equivalent fault impedance
- It also allows for accessing any a-b-c phase quantity for plotting or precise modelling purposes (e.g. protection devices)
In many cases stability calculations must be run for long periods thus taking into account effects of slower control systems such as boiler control, network exchange control or transformer tap-changer control. Other applications are varying loads or applications of wind power where the impact of wind speed fluctuations must be analyzed. In such cases, short-term and mid-term dynamics have already reached steady-state but slower transients are still being observed.
- Long-term stability simulations based on adaptive step-size algorithms with accuracy-controlled step-size adaptation ranging from milliseconds to several minutes without any decrease in precision or even manipulation of transient behaviour.
- A-stable simulation algorithm which fully covers fast transients as well as slow, semi steady-state dynamics with high-precision event handling (stiff systems).
- Voltage stability analysis considering effects of load variations, tap-changer control and reactive power limits
- Long-term flicker analysis in cases such as fluctuating renewable generation or varying loads
- Secondary control analysis and optimisation
Electromagnetic Transients (EMT)
DIgSILENT PowerFactory provides an EMT simulation kernel for solving power system transient problems such as lightning, switching and temporary over-voltages, ferro-resonance effects or sub-synchronous resonance problems. Together with a comprehensive model library and a graphical, user-definable modelling system (DIgSILENT Simulation Language (DSL)), it provides an extremely flexible and powerful platform for solving power system electromagnetic transient problems.
Any combination of meshed 1-, 2-, and 3-phase AC and/or DC systems can be represented and solved simultaneously, from HV transmission systems, down to residential and industrial loads at LV distribution levels. Standard built-in models include:
- Lumped and distributed parameter line/cable models; constant and frequency-dependent.
- 2- and 3-winding transformers and autotransformers for 1-, 2- or 3-phase systems, including stray capacitances, tap dependent impedance and saturation effects. Flexible definition of non-linear magnetising reactance: two-slope, polynomial, flux-current values
- Passive RLC branches, capacitor banks and filters of multiple layouts
- Surge arresters, including calculation of energy absorption
- Voltage and current, AC-, DC- sources
- Impulse sources (to be modelled via DSL)
- VT, CT and PT models, including saturation effects
- Series capacitor, including MOV and bypass switches
- Discrete power electronic components such as diodes, thyristors, IGBTs
- HVDC valve groups (6- and 12-pulse Graetz bridge configurations) and other FACTS devices such as SVCs, UPFCs, TCSCs and STATCOMs
- Synchronous and asynchronous machine, doubly-fed induction generator
- Circuit breaker models (to be modelled via DSL)
- Stochastic switching (procedures to be implemented via DPL scripts).
The package provides a powerful user-friendly graphical environment for the evaluation of simulation results characterised by:
- User-customisable plots for waveform visualisation, including filtering options, scaling, etc.
- Calculation of Fast Fourier Transform (FFT)
- Export capability to COMTRADE-Files, spreadsheet-format, CSV-files, WMF-files, etc.
Motor Starting Functions
PowerFactory’s Transient Motor Starting functionality analyses motor starting scenarios where the effect of a motor starting on the grid frequency is negligible. In such situations, the typical questions to be answered are:
- What is the maximum voltage sag? (This is typically not the initial voltage sag at t=0)
- Will the motor be able to be started against the load torque?
- What is the time required to reach nominal speed?
- How will the supply grid be loaded and which starting options should be considered?
Static Motor Starting
The Static motor Starting simulation makes use of the load flow and static short-circuit calculation by executing a series of calculations to analyse the scenario:
- First, execution of a load flow calculation when the motors are disconnected from the system
- Then, execution of a short-circuit calculation, using the complete method, simultaneously with the occurance of the motors being connected to the network
- Finally, execution of a load flow calculation after the motors have been connected to the system
Transient Motor Starting
The Transient Motor Starting function makes use of the PowerFactory stability module by providing a pre-configured shortcut for easy-to-use motor starting analysis. The motor starting is initiated by selecting the respective motors within the single line diagram and initiating the motor starting calculation.
- A complete symmetrical or asymmetrical AC/DC load flow will be computed prior to the motor starting event; pre-selected and pre-configured VIs are automatically created and scaled with full flexibility for user-configuration
- Consideration of high-precision, complex motor models with built-in parameter estimation. A comprehensive library of low voltage, medium voltage and high voltage motors is provided
- Typical motors supported are: single- and double cage asynchronous machines, squirrel and slip-ring motors, double-fed induction machine, synchronous motors
- Access to the model library for built-in motor driven machine characteristics (torque-speed characteristics) with flexible user-modelling support
- Support of various starting methods such as direct start, star-delta starting, variable rotor resistor, thyristor softstarter, transformer softstarter, variable speed drives, etc.; start from any rotational speed
- Full flexibility in considering starting sequences
- Completion of motor voltages before, during, and after starting as well as successfully motor starting assessment
Full representation of generators with exciter/AVR model support on the basis of built-in models (e.g. IEEE models) as well as user-defined models utilising the DSL approach; consideration of protection devices such as under-voltage protection, over-current protection, automatic restarting relays (EMR) or transformer OLTC.
Small Signal Stability
The DIgSILENT PowerFactory modal analysis tool features small signal analysis of a dynamic multi-machine system. System representation is identical to the time domain model. It covers all network components such as generators, motors, loads, SVS, FACTS, or any other component used in the system representation, including controllers and power plant models.
Analysis of eigenvalues and eigenvectors is appropriate for applications such as low-frequency oscillatory stability studies, PSS tuning, determination of interconnection options and its basic characteritics, and is a natural complement to the time domain simulation environment. It also allows for the computation of modal sensitivities with respect to generator or power plant controllers, load characteristics, reactive compensation or any other dynamically-modelled equipment.
PowerFactory’s Eigenvalue Analysis is very user-friendly, requiring minimal configuration of the command. Its calculation steps are as follows:
- Based on a converged and adjusted power flow, the modal analysis starts with the calculation of the system initial conditions. Alternatively, any interrupted status of a time domain simulation could be used as the initial condition.
- The system A-matrix is constructed automatically for the complete system (including generators, general loads, predefined system plant and controller models as well as DSL devices).
- System and model linearisation - including user-defined models - is performed by iterative procedures. Limiting devices are disabled automatically. The representation of the network model is equivalent to the simulation model, allowing a direct comparison/validation between time domain simulations and modal analysis results.
- Support of QR-algorithm as well as the Arnoldi-Lanczos method.
- Calculation of all eigenvalues based on QR algorithm
- Selective eigenvalue calculation:
- computation of a certain part of the eigenvalue spectrum: calculation of a user-definable number of (closest) eigenvalues around a complex reference point
- based on the Arnoldi-Lanczos method
- recommended as a fast approach for higher order systems for which calculation of all eigenvalues by QR algorithm is too time-consuming
- Calculation results include eigenvalues (together with oscillation information such as damped frequency, damping, damping ratio, damping time constant, etc) and left and right eigenvectors. From eigenvectors, the individual machines’ controllability, observability, and participation factors are derived with respect to each mode.
- Powerful post-processing tools for result visualisation
- Tabular result representation of:
- Eigenvalues (including all oscillation information such as damped frequency, damping, damping ratio, damping time constant, etc)
- Eigenvectors (individual controllability, observability, participation of individual machines for any selected mode)
- Eigenvalue Plot
- Visualisation of calculated eigenvalues in the Gaussian plane
- Various filter and scaling options
- Automatic determination of stability border, highlighting of stable/unstable eigenvalues
- Plot has interactive features that facilitate detailed analysis of individual modes; convenient creation of phasor plots/bar diagrams for each mode
- Mode Bar Plot
- Bar diagram visualisation of controllability, observability and participation factors of individual machines for a given mode
- Various filter options (e.g. restriction to minimum participation, and/or individual generators)
- Mode Phasor Plot
- Phasor diagram visualization of controllability, observability and participation factors of individual machines for a given mode
- Various filter options
- Automatic detection and highlighting of clusters for convenient identification of inter-area modes
- Tabular result representation of:
- Possibility to obtain MATLAB compatible output results and system matrices
System Parameter Identification
Built-in system identification and general optimisation procedures provide an easy and accurate method to perform model parameter identification on the basis of system tests and field measurements. The PowerFactory Parameter Identification tool is suitable for parameter estimation of multi-input multi-output (MIMO) systems, which are described by any type of nonlinear DSL model. The identification procedure is fully integrated into the graphical frame definition and block diagram, and also features parameter estimation for integrated models (such as loads or generators) which form part of a power system model.
The optimisation procedures provided are highly generic and can also be used for optimally tuning parameters such as PSS settings according to defined model response functions.
Scripting and Automation
DPL (DIgSILENT Programming Language)
The DPL-Programming Language offers a flexible interface for automating PowerFactory execution tasks. The DPL scripting language adds a new dimension to PowerFactory software by allowing the implementation of new calculation functions. Typical examples of user-specific DPL-scripts are:
- Parametric sweep calculations (e.g. sliding fault location, wind profile load flows)
- Implementation of user-specific commands (e.g. transfer capability analysis, penalty factor calculation)
- Automatic protection coordination and device response checks
- Specific voltage stability analysis via PV-/QV-curve analysis, etc.
- Contingency screening according to user-specific needs
- Verification of connection conditions
- Data pre-processing including input/output handling
- Equipment sizing and dimensioning
- Report generation
The DPL object-oriented scripting language is intuitive and easy to learn. The basic set of commands includes:
- C++- like, object-oriented syntax
- Flow commands such as "if-then-else", "do-while"
- Input/import, output/export and reporting routines
- Mathematical expressions, support of vectors and matrices
- Access to any PowerFactory object and parameter including graphical objects
- Definition and execution of any PowerFactory command
- Object filtering and batch execution
- PowerFactory object procedure calls and DPL subroutine calls
- New: Calling of external libraries (DLLs) for linking and executing other applications
DPL’s basic syntax allows for the quick creation of simple high-level commands to automate tasks. Such tasks may include renaming objects, search and replace, post-processing calculation results and creating specific reports.
All parameters of all objects in the network models are accessible. DPL can be used to query the entire database and to process all user-input and result parameters without restrictions.
The DPL language can be used to create new 'standardised' DPL commands that can be used over and over again. DPL commands allow input parameters to be defined, and can be executed for specific selections of objects. Proven DPL commands can be safely stored in DPL command libraries and be used from there without the risk of damaging the scripts.
DPL commands can configure and execute all PowerFactory commands. This includes not only the load flow and short-circuits calculation commands, but also the commands for transient simulation, harmonic analysis, reliability assessment, etc. New objects can be created by DPL in the database, and existing objects can be copied, deleted and edited. New reports can be defined and written to the output window; new graphs can be created and existing graphs can be adjusted to reflect a user-defined selection or the current calculation results.
A DPL command may contain other DPL commands as subroutines. This modular approach allows the execution of subroutines as independent commands. Existing commands can be combined to quickly create more complex commands.
PowerFactory offers support for the Python scripting language. Python can now be used for various kinds of automation tasks within PowerFactory and integration tasks from external applications. Although the proprietary built-in scripting language will be supported, there are several good reasons to start using Python:
- Non-proprietary, widely spread and very popular scripting language
- Open source licenced
- Extensive standard libraries and third party modules
- Interfaces to external databases and MS-Office like applications
- Web-services, etc.
- Support for debugging
PowerFactory Module in Python
The functionality of PowerFactory is offered in Python through a dynamic module with the name "powerfaytory.pyd". Some facts about this module:
- Dynamic modeule implemented in Boost.Python using PowerFactory API
- Offers access to:
- all objects
- all attributes (element data, type data, results)
- all commands (load flow calculation, etc.)
- lots of special built-in functions (DPL functions)
- Usable from:
- within PowerFactory though the new command ComPython
- external (PowerFactory is started by the module as an engine
Integration of a Python Script into PowerFactory
Every Python script file (*.py) is represented in PowerFactory by a ComPython object. A ComPython object holds only the path, not the file itself. With the " Open in external editor" button it is possible to edit the file directly. The "Execute" button executes the script.
Python scipts (ComPython) objects can be executed like DPL scripts (ComDpl objects) and interrupted with the "Break" button in the main toolbar.
API (Application Interface)
C++ interface for full external automation of PowerFactory
Task Automation Tool for parallelised execution of calculation functions and scripts