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.

Nordic_JhubStart Repository Ready-to-run PyRAMSES simulation files with Jupyter notebook tutorial

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System Overview

Property	Value
Nominal frequency	50 Hz
Buses	74
Synchronous generators	20 (g1–g20)
Transformers	20
Transmission lines	52
Voltage levels	15 kV, 20 kV, 130 kV, 220 kV, 400 kV
Total generation capacity	~10,000 MW

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.

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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.

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Operating Points

The repository provides two operating points:

File	Description
dyn_A.dat / volt_rat_A.dat	Operating Point A — base case, moderately stressed
dyn_B.dat / volt_rat_B.dat	Operating Point B — heavily stressed, closer to voltage collapse

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.

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Repository Contents

File	Description
Execute.ipynb	Jupyter notebook with step-by-step simulation tutorial
dyn_A.dat / dyn_B.dat	Dynamic data files (generators, controllers, network, loads)
volt_rat_A.dat / volt_rat_B.dat	Power flow solutions (bus voltages and angles)
settings1.dat	Solver configuration (time step, tolerances, threading)
obs.dat	Observation file — monitors all buses, branches, machines, injectors
nothing.dst	Empty disturbance file (undisturbed simulation)
trip_gen.dst	Generator trip disturbance scenario
short_trip_branch.dst	Short-circuit followed by branch trip
variants.pdf	Documentation of system variants and operating points

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Disturbance Scenarios

Generator Trip (trip_gen.dst)

Trips generator g2 at $t = 1$ s and observes the system response. Additional shunt compensation is switched at $t = 11$ s and $t = 21$ s:

0.000 CONTINUE SOLVER BD 0.010 0.001 0.0 ALL
1.000 BREAKER SYNC_MACH g2 0
5.000 CONTINUE SOLVER BD 0.010 0.001 0.0 ALL
120.000 STOP
11.000 CHGPRM SHUNT SH1042 QNOM 80
21.000 CHGPRM SHUNT SH1042 QNOM 80

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. ABL
1.000 FAULT BUS 4032 0. 0.8
1.100 CLEAR BUS 4032
1.100 BREAKER BRANCH 4032-4044 0 0
5.000 CONTINUE SOLVER BD 0.020 0.001 0. ABL
240.000 STOP

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Quick Start

Prerequisites

• Python 3 with PyRAMSES installed
• JupyterLab (recommended) or any Python environment

Installation

pip install pyramses matplotlib numpy

Running a Simulation

1. Clone the repository:

   git clone https://github.com/SPS-L/Nordic_JhubStart.git
   cd Nordic_JhubStart

2. Open Execute.ipynb in Jupyter and run cells sequentially, or use the following Python script:

Python Script

import pyramses

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

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

Jupyter Notebook

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

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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

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References

• T. Van Cutsem, M. Classes, “Description, modelling and simulation results of a test system for voltage stability analysis,” IEEE PES Technical Report PES-TR19, 2013. Available from the IEEE Resource Center
• RAMSES project page at the Sustainable Power Systems Lab
• STEPSS project page at the Sustainable Power Systems Lab