Local identification of voltage emergency situations

This paper proposes a simple procedure to identify the onset of long-term voltage instability from the time evolution of the distribution voltages controlled by load tap changers. The moving average of sampled measurements is computed and used to trigger local emergency signals. The method is validated on voltage signals obtained from time simulation of a realistic test system. The ability to identify instability in the critical area is demonstrated in three test cases. Index Terms--Emergency detection, load tap changer, long-term voltage stability, overexcitation limiter, voltage collapse.