Patent ID: 9077208
Filing Date: 2015-07-07
Classification: H02J

Abstract:
1. A method of automatically identifying a probable instability condition of an islanded electrical system, the method comprising: receiving, using a controller, an indication that power to a plurality of loads has been transferred from a primary power source to an alternate power source electrically isolated from the primary power source to form an islanded electrical system that includes the alternate power source and the loads, the alternate power source providing electrical power to the loads; responsive to receiving the power source change signal, receiving a load status change signal from a load in the islanded electrical system indicating that an operational status of the load has changed; responsive to receiving the first load change signal, receiving frequency magnitude values, according to a first periodicity corresponding to at least one per 100 ms, of the alternating current or voltage measured by an intelligent electronic device (IED) coupled in the islanded electrical system to the alternate power source, and storing frequency data indicative of the measured frequency magnitude values and associated timestamp values corresponding to a time or cycle count each of the frequency magnitude values are measured; based on the received frequency magnitude values, identifying a pickup time corresponding to a detected deviation from a nominal or fundamental frequency of the electrical power and a dropout time corresponding to a restoration of the frequency of the electrical power to the nominal or fundamental frequency; based on at least the pickup time and the dropout time, calculating a rate of recovery for the detected frequency deviation from the nominal or fundamental frequency; the controller determining whether an anomalous condition exists in the islanded electrical system based on at least whether the calculated rate of recovery exceeds a rate of recovery threshold; and responsive to the rate of recovery exceeding the rate of recovery threshold, storing in a memory an indication that the anomalous condition exists.