| 摘要 |
The invention relates to a method for protecting an electrical supply network in the event of a fault (K). In this case, at least one electrical time-periodic signal (i(t)) from the supply network is measured and is transformed to the frequency domain. The complex variables are modified by means of modified filter coefficients (I1D) of the transformed time-periodic signal (i(t)) by combining imaginary part filter coefficients of the first and second harmonics (I1, I2). In a first alternative, a check is then carried out for each sample in order to determine whether the modified imaginary part (I1D) has the same sign as the imaginary part of the first harmonic (I1) and whether the magnitude of the modified imaginary part (I1D) is greater than the magnitude of the imaginary part of the first harmonic (I1). An output imaginary part (I1A) is then set equal to the modified imaginary part (I1D) if the conditions from step d1) are satisfied or is set equal to the imaginary part of the first harmonic (I1) if the conditions from step d1) are not satisfied. In a second alternative, a first impedance (Z1) is determined using the first harmonic (I1) and a second impedance (Z2) is determined using the modified imaginary part (I1D). Either the impedance having the smaller magnitude from the first and second impedances (Z1, Z2) or the impedance with the imaginary part having the smaller magnitude from the first and second impedances (Z1, Z2) is then selected and is set as the line impedance (ZL). The line impedance (ZL) determined is compared with at least one predefined value. Finally, a control signal (B) for an interruption component (2) of the supply network is output if the line impedance (ZL) is lower than the at least one predefined value. |
