Equipment and Stability Constraints in System Operation

Module 2 : Equipment and Stability Constraints in System Operation

Lecture 8 : Large disturbance Angle stability

For example, if the restoring force of the spring is almost a linear function upto a certain stretch but reduces to zero beyond that value, then for a large disturbance it is possible that the spring will break (as shown in the figure below).

To avoid instability (breaking of the spring), the following can be done:

1) Make the spring more stiff.
2) Reduce the disturbance.
3) Keep the equilibrium stretch of the spring small (so that it has more margin to stretch in case of disturbances).

The behavior of SMIB system is similar. Under normal operating conditions, there are restoring torques which tend to keep the synchronous machine in synchronism with the infinite bus. However when disturbances are large, the torque may not be able to "pull back" the machine to synchronism. We now illustrate this by an example.