Fault Analysis
Network Reduction
Voltage Stability Analysis
Load Flow Sensitivities
Contingency Analysis
Overhead Line and Cable Parameter Calculation
Distribution Network Analysis
Power Flow Analysis
Within the Load Flow analysis environment, the accurate representation of a variety of network configurations and power system components is possible.
- DIgSILENT PowerFactory offers a selection of calculation methods, including a full AC Newton-Raphson technique (balanced and unbalanced) and a linear DC method. The enhanced non-decoupled Newton-Raphson solution technique with current or power mismatch iterations, typically yields round-off errors below 1 kVA for all buses. The implemented algorithms exhibit excellent stability and convergence. Several iteration levels guarantee convergence under all conditions, with optional automatic relaxation and modification of constraints. The DC load flow, solving for active power flows and voltage angles, is extremely fast and robust (linear system; no iterations required).
- 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 voltage levels. Neutral conductors can be modelled explicitly.
- The Load Flow tool accurately represents unbalanced loads, generation, grids with variable neutral potentials, HVDC systems, DC loads, adjustable speed drives, SVSs and FACTS devices, etc., for all AC and DC voltage levels.
- DIgSILENT PowerFactory offers a new, intuitive and easy-to-use modelling technique which avoids the definition of bus types such as SL, PV, PQ, PI, AS, etc. PowerFactory simply provides the control mechanisms and device characteristics which are found in reality.
More Load Flow Analysis Features
- Consideration of reactive power limits: detailed model for generator Mvar capability curves (including voltage-dependency).
- Practical station control features with various local and remote control modes for voltage regulation and reactive power generation. Reactive power is automatically adjusted to ensure that generator output remains within its capability limits.
- Various active power control modes, e.g. as dispatched, according to secondary or primary control, or inertial response.
- Supports device characteristics, such as voltage-dependent loads and asynchronous machines with saturation and slip dependency, etc.
- Comprehensive area/network power exchange control features using Secondary Controllers (SCO) with flexible participation factors.
- Transformer OLTC able to control local or remote bus voltages, reactive power flows and voltage-drop compensation (LDC) within distribution systems. Special transformer controller model for parallel transformers. Transformer tap adjustment supports discrete and continuous methods.
- Device controllers for shunts, doubly-fed asynchronous machines and other power electronics elements such as self-commutated converters (VSC), thyristor/diode converters or integrated FACTS devices.
- Local and remote control mechanisms for SVCs. Automatic and continuous control of TCR and TSC switching is performed within component ratings to hold the voltage at a given value.
- Correct representation of transformer vector groups and phase displacement.
- Shunts can be modelled to consist of a combination of series and/or parallel connected capacitors, reactors and resistors. Shunts can be connected to busbars and feeders or to the remote ends of cables and lines. Filters may consist of any number of shunt combinations, and automatic shunt switching can be included in the automatic voltage regulation.
- Support of the Virtual Power Plant model for generator dispatch based on merit order algorithm.
- Feeder load scaling to control power flows at feeder entry point – including nested and parallel feeders.
- Full support of any parameter characteristic and scale to allow parametric studies or easy definition of loading scenarios or load profiles.
- All operational data (generation and demand patterns, switch positions, etc) can be saved and maintained in distinct Operational Scenarios.
Further Special Functions
- Analysis of system control conditions
- Consideration of protection devices
- Determination of ‘Power at Risk’
- Calculation of Load Flow Sensitivities. Evaluation of expected active/reactive power flow and voltage changes in the network based on the effect of demand/generation or transformer tap change.
- Support of DPL scripts; e.g. to perform load balancing, determination of penalty factors or any other parameter required.
Load Flow Results
- Implicit calculation of a large number of individual result variables and summary figures
- Display of any variable within the single line graphic, station diagram, and a tabular Flexible Data Page
- Various colouring modes for the single line graphic to visualize quantities such as calculated loading and/or voltage levels
- Detailed analysis reporting, which can list overloaded system elements, unacceptable bus voltages, system islands, out-of-service components, voltage levels, area summaries, and more
- Detailed textual output with pre-defined or user-defined filters and levels
- DPL interactivity with all results
- Result export to other software applications such as MS-EXCEL
Fault Analysis
DIgSILENT PowerFactory features fault calculation functionality based on international standards as well as the most accurate DIgSILENT General Fault Analysis (GFA) method.
The following features and options are supported by all implemented fault analysis methods:
- Calculation of fault levels at all busbars.
- Calculation of short-circuit quantities at a selected busbar or along a defined section of line/cable, including all branch contributions and busbar voltages
- Calculation of all symmetrical components as well as phase quantities.
- User-definable fault impedance
- Provision of specially designed graphs and diagrams including all quantities typically required by the protection engineer
- Thermal overloads highlighted on the single line graphic for busbars and cables, with all equipment overloads available in a summary text report
- Calculation of Thevenin impedances as seen from the faulty node
- Calculation of apparent phase impedances (magnitude and angle) at any location along a transmission line/cable or busbar, for all branches, selected subsets thereof, or 1, 2 or 3 nodes from the faulted node
Supported Standards
IEC 60909 and VDE 0102/0103
PowerFactory provides a strict and complete implementation of the most frequently used standard for component design world-wide; the IEC 60909 and VDE 0102/0103 fault calculation standard, according to the most recently published versions.
- Calculation of the initial symmetrical peak current Ik" and short-circuit power Sk", peak short-circuit current ip, symmetrical short-circuit breaking current Ib, and thermal equivalent current Ith (IEC 60909-0 2001). Both minimum and maximum short-circuit currents can also be calculated based on network voltage c-factors
- Support of all fault types (three-phase, two-phase, two-phase to ground, single-phase to ground)
- Calculation of Ik with selectable “Decaying Aperiodic Component”
- Selectable method for calculating the peak short-circuit current in meshed networks
- User-definable fault impedance, conductor temperature and c-voltage factor.
- Fault calculation can optionally include or exclude motor contribution to the fault current
- Provision of specially designed graphs and diagrams required by the protection engineer for protection coordination and design
IEEE 141 / ANSI e 37.5
PowerFactory provides a thorough implementation of the IEEE 141/ANSI e37.5 fault calculation standard according to the latest published version. Special features are:
- Transformer tap positions can be included in the fault current calculation
- User-defined fault impedance and pre-fault voltage can be included in the fault current calculation
Other Standards
G 74 and IEC 61363
Complete Method/Multiple Faults
DIgSILENT PowerFactory’s Complete Method is especially designed for protection coordination purposes or for analyzing observed system contingencies. It provides the required algorithms and precision for determining the “true” or “operational” short-circuit currents without considering the simplifications or assumptions typically made in standard fault analysis.
In addition to the high precision network model, multiple faults which occur simultaneously in the system or unusual fault conditions such as inter-circuit faults or single-phase interruptions can be analysed.
- The Multiple Fault Analysis executes a complete network analysis based on subtransient and transient representations of electrical machines taking into account all specified network devices with their full representation and pre-faulted load conditions.
- Combination with IEC60909 principles for the calculation of aperiodic components and peak short-circuit currents
- Calculation of peak-break and break-RMS currents
- Consideration of a complete multi-wire system representation. Applicable to single-phase or two-phase networks.
- Analysis of multiple fault conditions
- Calculation of any asymmetrical, single or multiple fault condition with or without fault impedance, including single- and double-phase line interruptions.
Fault Analysis Results (all Methods)
PowerFactory offers many reporting options, including detailed reporting on all short-circuit levels for all faults, or alternatively, a specific report for a particular fault type. Special protection reports can also be generated to include impedance, current and voltage information.
- Display of any variable within the single line graphic, station diagram and Flexible Data Page
- Fully flexible filter mechanisms to display objects in colour mode
- Detailed analysis reporting, which can list overloaded system elements, unacceptable bus voltages, system islands, out-of-service components, voltage levels, area summaries and more
- Detailed text output with pre-defined or user-defined filters and levels
- DPL interactivity with all results
- Result export to other software applications such as MS-EXCEL or MS-ACCESS
Network Reduction
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.
General Features
- Flexible definition and maintenance of network boundaries. Various features such as colouring of boundaries and topological checks
- Network Reduction can be calculated at any appropriate boundary
- Support of Standard Ward (PQ-equivalent), Extended Ward (PV-equivalent) and equivalent loads
- 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
Voltage Stability Analysis
PV Curves
PowerFactory supports the calculation of PV curves by applying specifically implemented scripts. These scripts perform the calculation of voltage variations against:
- Load variation in a selected area
- Load shift across boundaries (keeping the total load constant)
- Generator shift across boundaries (keeping the total generation constant)
PV curves can be calculated for a selected set of contingencies. Diagrams are automatically created.
Q-V Analysis
For analyzing the required reactive power reserve at individual busbars, PowerFactory provides scripts for the calculation of Q-V curves.
Load Flow Sensitivities
Supplementing PowerFactory’s voltage stability analysis suite is the Sensitivity Analysis tool. It is often required to not only know the critical point of a system, but also how this critical point is affected by changes in system conditions. PowerFactory’s Sensitivity Analysis tool performs a static voltage stability calculation according to the following options:
- Sensitivity to a single busbar (calculation of the voltage sensitivities of all busbars and branch flow sensitivities according to variations in power (ΔP and ΔQ) at the selected busbar).
- Option to calculate sensitivities with respect to all busbars simultaneously.
- Sensitivity to a transformer tap position change (calculation of the voltage sensitivities of all busbars and branch flow sensitivities according to changes of a transformer/quad booster tap).
- Modal analysis
- Identification of “weak” and “strong” parts of the network based on modal transformation of the δv/δQ sensitivity matrix.
- Eigenvalue calculation on the δv/δQ sensitivity matrix, with a user-defined number of eigenvalues to be calculated.
- Results of eigenvalues are displayed (in descending order according to magnitude), and branch/bus sensitivities can be displayed for each mode.
Contingency Analysis
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)
Reports:
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
Overhead Line and Cable Parameter Calculation
DIgSILENT PowerFactory incorporates the automatic calculation of the electrical parameters of any cable/overhead line configuration starting from layout and geometric characteristics which are typically available in manufacture’s datasheets. The calculation is applicable over a wide range of frequencies and supports the step-up process of highly accurate line and cable models for harmonic analysis, frequency sweep and EMT-simulation among others. The supported options are described below.
Overhead Line Parameter Calculation
- Any combination of line circuits (1-, 2- and 3-ph), neutral conductors and earth wires, with/without automatic reduction of earth wires
- A flexible definition of tower types and tower geometries, including conductor sags, allowing a multiple combination of tower geometries and conductor types that avoids entry of redundant data
- Circuit-wise, symmetrical and perfect transposition and user-defined phasing for the definition of any non-standard transposition scheme
- Solid and tubular conductor types, including sub-conductors for phase circuits and earth wires
- Skin effect
- Equivalent impedance and admittance matrices in natural, reduced and symmetrical components
Cable Parameter Calculation
- Multi-phase single core and pipe type cable systems
- Flexible definition of cable layouts, including conducting, semi-conducting and insulating layers
- Compact and hollow core shapes, filling factor for stranded conductors
- Consideration of skin effect
Calculation of layer impedances and admittances in natural, reduced and symmetrical components, including sheath and armour reduction, cross-bonding
Distribution Network Analysis
Feeder Analysis
- Feeder Plots: Graphical display feature (Virtual Instrument, VI) to increase transparency in grid loading and voltage profile analysis along the feeder. Displayed result variables are freely configurable. Full interactivity is given via the VI to access all relevant data of the components belonging to the feeder.
- Schematic Visualization of Feeder: Automatic generation of single line diagram to visualize components of the feeder with distance/index view.
- Feeder Load Scaling: A load flow calculation feature that allows the automatic adjustment of individual bus loads to match a specified total feeder load. The selection of loads which are to participate in the feeder scaling procedure is user-defined. This method allows for complex scaling scenarios with nested and parallel feeders.
Low-Voltage Network Analysis
PowerFactory integrates enhanced features designed especially for the analysis of LV networks. These functions enable the user to:
- Consider load diversity
- Perform a load flow analysis that considers load diversity for calculating maximum voltage drops and maximum branch current
- Perform cable reinforcement optimization to either automatically reinforce selected cables, or to provide a report of recommendations
- Perform voltage drop and cable loading analysis
- Perform statistical calculations of neutral currents caused by unbalanced single-phase loading and load diversity, to represent a realistic network
Stochastic Load Modelling
On the basis of defined ‘customer units’ the user may specify a number of customers connected to a line. Load flow options are provided to define the load per unit customer according to:
- Power per customer unit
- Power factor
- Coincidence factor for an infinite number of loads (i.e. ‘simultaneity factor’)
- Stochastic evaluation (theoretical approach, also applicable to meshed networks)
- Maximum current estimation (application of stochastic rules for estimating maximum branch flow and maximum voltage drops)
The Load Flow with stochastic load modelling then provides maximum currents for each branch component, maximum voltage drops, and minimum voltages at every bus bar..
The usual variables for currents and voltages in this case represent average values of voltages and currents.
Losses are calculated based on average values; the maximum circuit loading is calculated using maximum currents.
Cable Reinforcement Optimization
PowerFactory’s Cable Reinforcement Optimization 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.
- Optimization 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
Feeder Tools
The PowerFactory Feeder Tools comprise a set of tools for radial systems to change voltage levels, phase technology or to optimize phasing from a particular point downwards.
Voltage and Phase Technology Change Tool
- Automatic change of the voltage level and/or phase technology inside a pre-defined feeder
- Automatic replacement of type data (for transformers, lines, loads and motors) according to pre-configurable type mapping tables – including automatic creation of new compatible types if necessary
Auto-Balancing Tool
- Automatic balancing of feeders such that voltage unbalance at terminals is minimized
- 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
