PMU based real-time monitoring for delayed voltage response

Voltage instability due to large disturbances plays a major role in many blackout incidents. Online tools that can assess stability of the system have been recommended in order to reduce the occurrences of large scale blackouts. This paper proposes a model free algorithm that can assess the short term voltage stability of the system in real time based on voltage measurements from PMU´s. This approach uses simple calculations to determine the Lyapunov Exponent whose sign indicates the stability (negative) or instability (positive) of the system. A new method to identify the problem of delayed voltage recovery at a bus based on a virtual reference and the Lyapunov exponent is proposed and is tested on the IEEE 162 bus system. It is successful in detecting the delayed recovery which was not detected by using the conventional Lyapunov exponent. The implementation of the Lyapunov exponent in a real time cyber-physical test bed is described using the Phasor models in Opal-RT and the usefulness of implementing the method in the test bed is described.