Simpow® – Technical info

SIMPOW – Power-flow analysis module

The power-flow module simulates steady-state symmetrical conditions, considering the power-frequency voltages and currents. A single-phase model using positive-sequence quantities represents the power system. The node voltages, injected active and reactive power and some other variables give the state of the system.

Either the Dynamic method or the Newton-Raphson method is the numerical technique employed to solve the power flow.

A variety of constraints on variables and limits can be specified. Multi power-flow runs are defined by run instructions in a Command File. User defined modelling in power-flow computations is possible with the modelling language Dynamic Simulation Language, DSL.

SIMPOW – Dynamic simulation module

In Simpow there are two dynamic simulation modes in Simpow: Transient stability and instantaneous value mode. Each mode can be characterised as dynamic simulation of a power system under steady state or disturbed symmetrical or unsymmetrical conditions.

Transient stability mode calculates by phasor models the power-frequency components of AC system and the average values of DC system voltages and currents. The primary components are represented as positive, negative and zero sequence quantities.

The instantaneous value mode calculates the instantaneous values of voltages and currents. The primary components are represented as dq0 quantities.

During a time-domain simulation, users are able to switch between transient stability mode and instantaneous value mode.

An implicit predictor-corrector method of integration for simultaneous solution of all algebraic and differential equations is employed in dynamic simulation. The default method is a combination of Gear’s integration method and the trapezoidal integration method, with automatically controlled variable time step. The solution method assures retained accuracy and numerical stability also for long-term simulations.

There is a comprehensive set of models available for dynamic simulations including HVDC and SVC systems.

SIMPOW – Fault analysis module

The fault analysis module simulates steady-state symmetrical or asymmetrical conditions, considering power-frequency voltages and currents. Fault analysis processes a linearized ”frozen” state of dynamic simulation at an arbitrary point of time after the occurrence of an event, normally at zero time.

The fault analysis module performs calculation of power-frequency short-circuit currents and can be specified to include short-circuit currents, their distribution, their positive, negative and zero sequence components, as well as the corresponding short-circuit impedances seen from the faulty nodes.

The fault analysis module calculates also according to the procedure and rules of the Standard IEC 909, which results in maximum and minimum values of initial, peak, breaking and steady-state short-circuit currents on arbitrary nodes can be calculated.

SIMPOW – Frequency domain analysis

Simpow employs Eigenvalue calculation and frequency response techniques in the frequency domain. These include linearization of the power system equations at the actual operating point and consider only incremental changes of the state variables around the operating point.

The frequency domain analysis allows e.g.:

•Calculation of sensitivity of an Eigenvalue with respect to parameters.

•Displaying Eigenvalues in locus diagram in the complex plane. Useful when manipulating a parameter and observing its influence of the Eigenvalue.

•Single-line diagram of the power system with ”vector” visualization of the generator speedcomponents of the Eigenvectors related to a selected pair of complex Eigenvalues corresponding to a particular mode of generator electromechanical oscillations.

•Calculation of participation factors.

•The Eigenvalue technique can be applied at any time during a simulation.

•Frequency scanning technique which calculates the response of selected variables to a sinusoidal perturbation, either in the form of a current injected to a selected node or by adding a signal to a selected variable. Frequency scanning is performed for a specified range of frequencies.

•Calculating of the frequency dependant impedance of the network at any perturbed bus.

These techniques are excellent means for the study of the small signal stability of generators and automatic control systems.

SIMPOW – User modelling

Dynamic Simulation Language (DSL) is a built-in programming language allowing user defined modelling of any power system component implying regulators and primary components, e.g. FACTS devices, drive systems and special machines.

A graphical tool, the DSL Code Generator, is available by which the user can define and generate the required DSL code to be used in dynamic simulation. Exciters, voltage regulators, power system stabilisers, turbines, turbine governors, protective relays, etc., can be modelled by selecting and connecting pre-defined block diagrams from a library.