Stability analysis with ANDES

Two dynamic studies run on ANDES: transient stability simulates the response to a fault or line trip over time, and eigenvalue analysis shows how well oscillation modes are damped.

Transient Stability (ANDES Time-Domain Simulation)

ANDES

Transient Stability shows how the network responds over time to a bus fault or line trip: rotor swings, voltage recovery, and whether machines stay in synchronism. Standalone overview: Transient stability guide.

Where to find it

Simulate → Transient Stability (ANDES). Requires a subscription. You need at least one Generator with dynamics. An External Grid alone is not enough.

When to use

  • Synchronism after a fault (speed and angle swings)
  • Comparing clearing times and fault locations
  • Voltage recovery after a clear or line trip

How to run

  1. Place a synchronous Generator and fill the Dynamics tab (defaults are applied if fields are empty).
  2. Click Simulate → Transient Stability (ANDES).
  3. Set end time, optional fault bus and clear times, and optional line outage.
  4. Run and inspect generator speed/angle and bus voltage vs time.
How Electrisim maps the diagram to ANDES
  1. Electrisim serialises the diagram (buses, lines, transformers, loads, generators) to the backend.
  2. The backend builds an ANDES system: static models (Bus, Line, PQ, PV/Slack) plus dynamic models (GENROU or GENCLS, exciters, governors).
  3. Missing Dynamics-tab fields receive textbook defaults (reported in the result).
  4. Optional disturbances from the study dialog: bus fault (apply/clear times) and/or a line outage at a given time.
  5. PFlow.run() establishes the operating point; TDS.run() integrates to tf.
  6. Results return as time series: generator ω, δ, bus voltages, and an approximate system frequency from mean ω.

Input Parameters

Parameter Description Type Typical values Default
Frequency System base frequency number 50 or 60 Hz 50
System Base (MVA) ANDES system MVA base for per-unit conversion number 100 100
tf Simulation end time (s) number 5–20 10
Fault Bus Bus where a three-phase fault is applied (optional) select Any bus on the diagram (none)
fault_tf / fault_tc Fault apply and clear times (s) number 1.0 / 1.1 1.0 / 1.1
Line Outage Optional line to trip via ANDES Toggle select Any AC line (none)
toggle_t Line outage time (s) number 2.0 2.0

Results

  • Multi-series charts: generator speed ω (pu), rotor angle δ (rad), bus voltage (pu), mean frequency (Hz)
  • Summary: tf, point count, generator/bus counts, event settings
  • List of applied dynamic defaults and mapping warnings (e.g. skipped DC lines, static generators)
  • CSV export of the time series

Requirements & Limitations (MVP)

  • At least one synchronous Generator; mark one generator as slack (or include an External Grid plus generators)
  • Static generators are not modelled as SynGen in this MVP (warned in results)
  • Three-winding transformers and DC lines are skipped
  • Full ANDES model catalogue (100+ models) is not exposed — GENROU/GENCLS, EXDC2/SEXS, TGOV1 only

Technical References

Based on: ANDES PFlow + TDS. Demo model: transient_stability_two_machine_demo.py (File → Import).

Related: Eigenvalue Analysis · Generator Dynamics tab · Motor Starting (dynamic)

Eigenvalue Analysis (ANDES Small-Signal Stability)

ANDES

Eigenvalue analysis linearises the system around the current operating point and plots modes in the complex plane: damping and oscillation frequency. Negative real parts are stable; positive real parts grow.

Where to find it

Simulate → Eigenvalue Analysis (ANDES). Same requirement as Transient Stability: at least one Generator with dynamics.

When to use

  • Small-signal stability at the current dispatch
  • Poorly damped local or inter-area modes
  • Effect of inertia, droop, or exciter gains (Generator Dynamics tab)

How to run

  1. Use the same dynamic network as for transient stability (no fault is required).
  2. Click Simulate → Eigenvalue Analysis (ANDES).
  3. Run and inspect the s-plane plot, damping ratios, and optional participation factors.
Solver steps
  1. Build the ANDES system as for time-domain simulation (no fault or line-trip disturbances).
  2. Run power flow, then the eigenvalue study.
  3. Return all eigenvalues plus the least-damped oscillatory modes (frequency and damping ratio).
  4. Optionally include participation factors for the top modes.

Input Parameters

Parameter Description Default
Frequency / System Base Same as TDS (Hz / MVA) 50 / 100
n_modes Number of least-damped oscillatory modes to highlight 10

Results

  • Stability verdict: stable, marginally_stable, or unstable
  • Counts: positive / zero / negative eigenvalues
  • s-plane scatter plot and table of σ, ω, f (Hz), damping ratio ζ
  • Participation factors for highlighted modes (when available)

Technical References

Based on: ANDES eigenvalue tutorial.

Related: Transient Stability · Generator Dynamics tab

Last updated: October 2026

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