Nordic Test System

The Nordic test system is a well-established benchmark for voltage stability and long-term dynamics studies, originally defined in the IEEE PES Technical Report on Test Systems for Voltage Stability Analysis and Security Assessment. It represents a realistic multi-area transmission network and is used extensively in research and education.

IEEE-Nordic-Test-system RepositoryComplete RAMSES data set: all operating points, disturbance scenarios, documentation, example scripts, and a Jupyter notebook tutorial

Watch it

Episode 10 of the video series, Capstone: Voltage Collapse on the Nordic System, covers this page.

System Overview

Property	Value
Nominal frequency	50 Hz
Buses	74
Synchronous generators	20 (g1–g20)
Transformers	50 (`TRFO` records, step-up and distribution)
Transmission lines	52
Voltage levels	15 kV, 20 kV, 130 kV, 220 kV, 400 kV
Installed generation	16,550 MVA (11,500 MW dispatched at operating point A)

The system is divided into several areas interconnected through a meshed 400 kV transmission network. Lower voltage levels (130 kV, 220 kV) serve sub-transmission, while 15 kV and 20 kV buses connect generators and distribution loads.

One-line Diagram

Dynamic Models

Each generator is modeled as a detailed synchronous machine (SYNC_MACH) with:

Machine model: Subtransient model with d- and q-axis dynamics (round-rotor or salient-pole depending on unit type)
Excitation system: EXC GENERIC1. a generic AVR with field current limiter, OEL, and optional PSS (SPEEDIN type)
Governor/turbine:
- Hydro units (g1–g5, g8–g12, g19–g20): TOR HYDRO_GENERIC1, hydraulic turbine with governor
- Thermal units (g6–g7, g13–g18): TOR CONSTANT: constant mechanical torque

Loads are represented using the INJEC vfd_load model (variable-frequency-dependent exponential recovery load) with voltage-dependent active and reactive power characteristics.

Under-load tap changers are modeled with DCTL LTC2 discrete controllers on all distribution transformers.

Operating Points

The repository provides two main operating points plus a family of load-increase variants:

File	Description
`lf_A.dat` / `dyn_A.dat` / `volt_rat_A.dat`	Operating Point A, base case, moderately stressed
`lf_B.dat` / `dyn_B.dat` / `volt_rat_B.dat`	Operating Point B, heavily stressed, closer to voltage collapse
`lf_B_plus_.dat` / `volt_rat_B_plus.dat`	Operating Point B with total load increased by 25 to 500 MW

Operating Point B is the primary case for voltage stability studies; it features higher load levels in the central area and reduced reactive power reserves. The B_plus variants (documented in doc/variants.pdf) progressively stress the system further and are useful for tracing the loadability limit.

Repository Contents

Path	Description
`lf_.dat` / `dyn_.dat` / `volt_rat_*.dat`	Load-flow data, dynamic data, and power-flow solutions for all operating points
`settings1.dat`	Solver configuration (time step, tolerances, threading)
`obs.dat`	Observation file, monitors all buses, branches, machines, injectors
`uvls.dat`	Undervoltage load-shedding (UVLS) controllers
`nothing.dst`	Empty disturbance file (undisturbed simulation)
`trip_gen.dst` / `trip_branch.dst`	Generator and branch trip disturbance scenarios
`short_trip_branch.dst`	Short-circuit followed by branch trip (`_changeLTCs` variant modifies tap-changer behavior)
`eigen.dst` / `dampJac.dst`	Jacobian export runs for eigenanalysis
`cmd.txt` / `sim_*.cfg`	RAMSES command file and STEPSS GUI simulation configurations (`sim_nothing`, `sim_trip`, `sim_short_trip`)
`doc/`	Detailed system report (`Nordic_test_system_V6.pdf`) and operating-point variants description (`variants.pdf`)
`jupyterhub-tutorial/`	Self-contained tutorial with `Execute.ipynb`, a step-by-step voltage collapse notebook

Disturbance Scenarios

Generator Trip (`trip_gen.dst`)

Trips generator g2 at $t = 1$ s and observes the long-term system response:

0.000 CONTINUE SOLVER BD 0.020 0.001 0.0 ABL
1.000 BREAKER SYNC_MACH g2 0
100.000 STOP

Short-Circuit with Branch Trip (`short_trip_branch.dst`)

Applies a three-phase fault on bus 4032 at $t = 1$ s, cleared after 100 ms by tripping the faulted branch:

0.000 CONTINUE SOLVER BD 0.020 0.001 0.00 ABL
1.000 FAULT BUS 4032 0. 0.
1.100 CLEAR BUS 4032
1.100 BREAKER BRANCH 4032-4044 0 0
200.000 STOP

The jupyterhub-tutorial/ folder contains its own variants of these scenarios (e.g. with shunt compensation switching) used by the tutorial notebook.

Quick Start

Prerequisites

Python 3 with stepss installed
JupyterLab (recommended) or any Python environment

Install stepss following the installation guide.

Running a Simulation

Clone the repository:

git clone https://github.com/SPS-L/stepss-IEEE-Nordic-Test-system.git
cd stepss-IEEE-Nordic-Test-system

Open jupyterhub-tutorial/Execute.ipynb in Jupyter and run cells sequentially, or use the following Python script from the repository root:

Python Script
Jupyter Notebook

import stepss

case = stepss.cfg()
case.addData("dyn_B.dat")
case.addData("volt_rat_B.dat")
case.addData("settings1.dat")
case.addObs("obs.dat")
case.addDst("trip_gen.dst")

ram = stepss.sim()
ram.execSim(case, 150.0)

# Extract and plot results
ext = stepss.extractor(case.getTrj())

Open Execute.ipynb directly. It contains a complete guided tutorial with inline plots for:

Bus voltage evolution
Generator frequency deviations
Governor valve output and mechanical power
Active and reactive power output

What to Observe

After a generator trip on Operating Point B, the simulation demonstrates:

Frequency transient: immediate frequency drop followed by primary governor response from hydro units
Voltage dynamics: progressive voltage decline in the central area as load restoration (tap changers, thermostatic loads) increases demand beyond available reactive reserves
Long-term voltage instability: if the system lacks sufficient reactive support, voltages collapse over tens of seconds. a classic long-term voltage stability phenomenon

License

The stepss-IEEE-Nordic-Test-system repository is licensed under the Apache License 2.0. The IEEE PES-TR19 report itself is not redistributed; obtain it from the IEEE Resource Center link below.

References

IEEE PES Task Force on Test Systems for Voltage Stability Analysis and Security Assessment (chaired by T. Van Cutsem), “Test Systems for Voltage Stability Analysis and Security Assessment,” IEEE PES Technical Report PES-TR19, Aug. 2015. Available from the IEEE Resource Center
STEPSS project page at the Sustainable Power Systems Lab