Abstract: The present disclosure relates to a method for preventing a maloperation of differential protection of an optical fiber caused by saturation of a single Current Transformer (CT) of 3/2 connection. By applying a combination of the differential judgment and the sub-CT current judgment, reliable identification of internal and external faults is ensured, and the problem of misjudging of the internal fault as the external fault can be prevented as well.

Abstract: The present disclosure relates to a method for preventing a maloperation of differential protection of an optical fiber caused by saturation of a single Current Transformer (CT) of 3/2 connection. By applying a combination of the differential judgment and the sub-CT current judgment, reliable identification of internal and external faults is ensured, and the problem of misjudging of the internal fault as the external fault can be prevented as well.

Abstract: The invention relates to a frequency measuring method and measuring device. The method comprises: firstly sampling the current signal to be measured, and discretizing the sampled signals; secondly obtaining sampling matrixes [In] and [In,] of the current signal to be measured at time n and time n?1 from the discrete sampled signals, setting a reference frequency fref, constructing a reference voltage signal u(t) from fref, and discretizing u(t) to gain reference matrix; finally, attaining phase values of time n and time n?1 from the eigenvalues of matrixes [In]+[U] and [In?1]+[U], and determining a calculation frequency fcomp. The invention uses sampled matrixes constructed from the reference signals and the signals to be measured.