A new noise-immune method to detect protective CT saturation and its release instants

CT saturation is a phenomenon that can cause inaccurate fault current measurement and may result in related protective relay failure to block the high current flow under a fault condition in a power system. Hence, it is required to develop a method to detect occurrence of CT saturation with a good accuracy under presence of noise in a power system. In this paper, a new method having the afore-mentioned characteristics is presented. The main benefit of exploiting the introduced approach here for detecting CT saturation is its high level of reliability as well as its reasonable operational speed in CT saturation detection. In other words, these two properties are implemented to this method. Moreover, in addition to the conventional assumption in the past works to consider the fault current as the sum of one sinusoidal current component, and an exponential current component; it is assumed here that the fault current can also be in form of a double-exponential waveform as it is observed in some switching fault currents even if the lightning fault currents which preserve a very short duration are ignored. This is a new assumption which seems has not been analyzed in the past published works. In this paper first the existing CT saturation detection methods are classified, and then the new method with its formulation is presented. Finally this method is compared with some of the past published works through some simulations.