NEPLAN | Stability Analysis (RMS)

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The module RMS Stability Analysis is one of the most advanced tool for dynamic simulations on the market and allows to simulate symmetrical and unsymmetrical networks and events. It implements a unique mathematical framework for large-scale, nonlinear system with fast/slow continuous and discrete (hybrid) events. The initialization of the mathematical model is performed by high sophisticated algorithms in an automatic way and is fully integrated. The time-consuming model-specific initialization process could be omitted. The NEPLAN Simulation Language (NSL-SymDef) is used for user-defined models, but an extensive built-In library for e.g. Wind turbines (IEC 61400-27-1 standards), Photovoltaic (CIRED standard) and CIM ENTSO-E models is also available.

Main characteristics:

  • Short-term, mid-term and long-term dynamic simulations
  • Symmetrical and asymmetrical AC and DC networks (same as for steady state calculation)
  • Simulation of symmetrical conditions and events in DQ0 reference frame for higher performance
  • Simulation of unsymmetrical conditions and events in ABC reference frame (multi-phase system)
  • High accuracy and performance (simulation in real-time) with fixed and variable step-size algorithm
  • Simulation of any fault or event, see examples below
  • Behavior of protection devices in pre-defined library are considered during simulation, see examples below
  • User defined protection models described by equations or function blocks
  • Transient Motor starting for synchronous and asynchronous machines with start-up devices
  • Model definition through NEPLAN Simulation Language and compiling to Dynamic Link Library (DLL)
  • Graphical editor for creating models (AVR, relay, etc.) through function blocks and automatic compilation to Dynamic Link Library (DLL)
  • Open framework to monitor and control any variable in the network system
  • Co-simulation with external systems
  • Frequency Analysis with Fast Fourier Transform (FFT)


Typical applications

  • Grid Interconnection Studies for Renewable Energy and verification of grid code compliance
  • Machine dynamics and startup simulations
  • Rotor angle stability with several different type of regulators
  • HVDC-(light), FACTS, SVC design and regulation
  • Load shedding and protection schemes
  • Automatic generation control (AGC)
  • PSS tuning with Eigenvalue and Sensitivity analysis
  • Wide area network controllers

Typical protection models

  • Min-max relays (e.g. over current, under voltage, power and frequency): modeled with the possibility to trigger of any desired event (e.g. switching in/off an element, increase/decrease load, loss of excitation). Various load shedding schemes can be easily simulated
  • Overcurrent relays, circuit breakers and fuses
  • Pole slip relays, including binary input signals from external sources
  • Out-of-step protection including Power Swing Blocking (PSB) and Out of Step Tripping (OSP)
  • Distance protection with any characteristic: pickup and tripping stages, impedance diagrams, binary input signals from external sources


Typical disturbances (events)

  • Possibility of defining and saving various disturbance groups, with different single event per case
  • Definition of  different faults (symmetrical and unsymmetrical) on buses, bus elements, branches
  • Different switching operations (feed-forward control in control circuits, cross coupling of protective devices, in/out of branches, etc.)
  • Loss of generator excitation
  • Start-up of motors with different start-up devices
  • Transformer tap modification
  • Load shedding scenarios (even in relation with frequency relay)
  • Disturbances with function activation (step, ramp, sinusoidal function or combination)
  • User-defined disturbances (every variable can be modified in the network/control)
  • Definition of specific voltage profile on buses for Low Voltage Ride Through (LVRT) and Over Voltage Ride Through (OVRT)

Brochure: Introductory brochure for stability analysis could be found here.


  • Introductory video to Dynamic (Stability) analysis could be found here.
  • Learning video for modelling controllers for Stability analysis with NSL-SymDef could be found here.


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