Long term dynamics of a power system

Large scale system disturbances caused by an imbalance between loads and generation have been a contributing factor in promoting cascading circuit interruptions resulting in widespread blackouts. Such large scale system failures as the New York Blackout of July 1977 [1] and Brittany, France in December 1965 and November 1976 [2] are characterised by cascading failure and as such cannot be simulated effectively or efficiently by using conventional transient stability programs since system failure occurred over a period of many minutes.

The study of power system behaviour for periods up to say 15 minutes has become known as power system Long Term Dynamics. If the long term behaviour of a system is to be investigated following a fault, the long term simulation would commence after the initial transients had damped sufficiently, this would usually occur after 10 seconds. Alternatively other system simulations may be carried out entirely in long term mode. Thus system planners and operations staff have an additional analysis tool with which to investigate power system behaviour.

It is therefore apparent that it is not feasible to study long term power system dynamics with conventional transient stability programs because of the prohibitive computer time involved together with the unsuitability of models used in transient stability studies. When there is loss of generation or major tie line in the power system the QEC is interested in ensuring the stability of the system. Immediately after a disturbance the behaviour of the system is studied using a transient stability program, such studies usually run for up to 10 seconds of real time. Because of the nature of the Queensland system the long term behaviour of the system is of interest and particularly in terms of voltage response. In this regard the action of transformer tapchanging, machine excitation, load response and capacitor switching needs to be monitored over a period of some minutes.

This thesis describes a digital computer program developed to simulate the long term dynamics of a power system and includes models of turbogenerators and other power system components together with results of simulations made with the program.

The appendices summarise the data used in all simulations and show comparison between program simulation and field test data.