Thevenin Impedance for voltage stability: Estimation of the thevenin Impedance in power Transmission Systems

Stefan Christian Polster

Research output: ThesisMaster's Thesis


Increasing energy consumption and the declared intention to meet it with renewable energy sources and smart grid solutions require transmission and distribution grids to be more flexible and better monitored than in former times to be able to withstand fast changes in generation and load. Due to the often long distances between generation units and load centers it is essential to monitor the voltage stability of the system as one of its limiting factors. So far, research on voltage stability focused on providing solutions for off-line applications.
The possibility to acquire real time data from phasor measurement units (PMUs) in concerned buses provides the basic means to develop a real time monitoring of the voltage stability by using the Thevenin theorem to estimate the possible maximum power. A simple stability indicator can be found by comparing the actual load power with the estimated maximum power. The advantage of the proposed algorithm is that, apart from the data from PMUs, only the topology of the examined subsystem and the operational status of included generators must be known. In this work a solution is developed to estimate the Thevenin impedance of a simple network topology, which takes the operational borders of the generators into account. The algorithm is validated by simulating a test network. Moreover, a feasible way to reduce the real time measurements needed and to evolve the algorithm to suit general network topologies is proposed.
Original languageEnglish
QualificationMaster of Science
  • Renner, Herwig, Supervisor
  • Uhlen, Kjetil, Supervisor, External person
Publication statusPublished - 2016


  • PMU, voltage stability, Thevenin Impedance, generation limits


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