Proper representation of load is important in power system stability studies, but it is a difficult task. Load modeling is qualitatively different from generator modeling in many aspects. Composition of load needs to be reliably estimated, models of different components must be combined to obtain a reasonably manageable overall system model, and field measurements are not at all easy.

Load Representation in Power System Stability Studies

In order to include an accurate representation of loads in steady state stability investigations a method based on state space theory is suggested which due to its flexibility can be applied to any type of terminal equipment. In the present paper it is shown how the dynamical behaviour of loads may have a decisive influence on the stability limit of a power system.

Effect of Load characteristic on the Dynamic Stability of Power Systems

A 100-machine transient stability program has been developed which represents the effects of machines much more completely than has been available previously. Both d-and q-axis quantities are fully represented and saturation effects in both axes are incorporated. The speed-governing and voltage-regulating systems available are extensive and complete, thus allowing a very close approximation to any physical system. Facilities for nonlinear loads and induction motor transients are also included.

New Techniques for the Calculation of Dynamic Stability

The dynamic behavior of complex asynchronous motor loads has been investigated by means of a digital computer program based on general equations for induction machines. The paper is devoted to load-voltage relationships. Load-frequency characteristics are not discussed in detail.

Dynamic Equibalents of Asynchronous Motor Loads in System Stability Studies

A method is described of calculating the effect of large induction motors on the transient performance of a multimachine power system under fault conditions. The representation of an induction motor is similar to that used for synchronous machines, and is therefore suitable for describing composite systems. The method is based on Park's equations and, unlike earlier methods, allows for the ‘deep-bar effect’ usually present in large cage induction motors. The most accurate result is obtained by using the full set of equations, but more approximate methods using simplified equations are considered. The method is verified by tests on model machines connected by impedances representing transmission lines. Preliminary tests were made on a simple system comprising an induction motor connected to an infinite busbar through an impedance, and were followed by tests on a composite system containing a synchronous machine and an induction motor connected in parallel parts of the system. The results slow that good results are obtained with the accurate calculation which, however, requires a large amount of computer time, but that any approximation introduces considerable error.

J. E. Rowe

Papers

Digital Computation of Induction-Motor Transient Stability