Fast and in situ remanent flux detection method for a protection current transformer based on the fluxgate theory

This paper proposes a fast and in situ remanent flux detection method for a protection current transformer (CT) based on the fluxgate theory. A high frequency voltage source is connected to the secondary side of the CT, and saturates the core slightly in the positive or negative direction. The polarity of the remanent flux is decided by the sign of integral of the voltage. The remanent flux is calculated with the linear relationship between the remanent flux and the second harmonic of the high frequency component of the voltage. The linear relationship can be obtained in advance considering the fluxgate theory. To verify the performance of the proposed remanent flux detection method, different levels of remanent flux, with and without primary current, are considered with Electromagnetic Transient Program - Restructured Version simulations. The results indicate that the proposed method can quickly and effectively detect the remanent flux of a protection CT in situ, which means that the CT is not required to be removed from the substation.