Low Current Transformer Utilizing Co-Based Amorphous Alloys

Metal oxide surge arresters have been widely used for protection of power system networks against overvoltages caused by atmospheric discharges or malfunction of devices connected to the network. During its operation, a surge arrester structure is degradated, which can be observed as an increase of a surge arrester leakage current. This paper presents an implementation of a new, high-permeability, Co₆₄Fe₄Ni₁Si₁₅B₁₄ amorphous alloy as a current transformer for monitoring of a leakage current in low voltage surge arresters. The characteristics of the current transformer for different loads have been measured in the system using very sensitive current-voltage converter. Experimental results confirmed that low current transformer utilizing Co₆₄Fe₄Ni₁Si₁₅B₁₄ amorphous alloy in annealed state gives a possibility to measure a leakage current about several μA with operating frequency 50 Hz. Moreover, the results indicate that the leakage current waveforms have a different shape than a pure sine wave voltage applied to the surge arrester enabling an evaluation of the device nonlinearity as a measure of its degradation by means of a resistive component of the leakage current.