Protection of electrical power supply systems

Claim 1

Apparatus for detecting the occurrence of a fault in a section of an electrical power supply system comprising: means for measuring the values of the voltage and current at a predetermined location to develop measured voltage and current representations, means for filtering out high frequency components in the measured voltage and current representations, means for calculating an approximation to the Fourier transform of a moving window of the filtered voltage representation over a predetermined interval of time and at a predetermined frequency, said Fourier transform of the voltage representation being modified by a continuous phase change at the said frequency, means for calculating an approximation to the Fourier transform of a moving window of the filtered current representation over the said time interval and at the said frequency, said Fourier transform of the current representation being modified by a continuous phase change at the said frequency, means for calculating the impedance of said section from said modified Fourier transforms of the voltage and current representations, and means for generating a trip signal when the value of said calculated impedance indicates a fault.

Claim 5

A method for detecting the occurrence of a fault in a section of an electrical power supply system comprising the steps of: measuring the values of the voltage and current at a predetermined location to develop measured voltage and current representations, filtering out high frequency components in the measured voltage and current representations, calculating an approximation to the Fourier transform of a moving window of the filtered voltage representation over a predetermined interval of time and at a predetermined frequency, said Fourier transform of the voltage representation being modified by a continuous phase change at the said frequency, calculating an approximation to the Fourier transform of a moving window of the filtered current representation over the said time interval and at the said frequency, said Fourier transform of the current representation being modified by a continuous phase change at the said frequency, calculating the impedance of said section from said modified Fourier transforms of the voltage and current representations, and generating a trip signal when the value of said calculated impedance indicates a fault.

Claim 6

A method for detecting the occurrence of a fault in a section of an electrical power supply system comprising the steps of: measuring the values of the voltage and current at a predetermined location to develop measured voltage and current representations, filtering out high frequency components in the measured voltage and current representations, calculating an approximation to the Fourier transform of a moving window of the filtered voltage representation over a predetermined interval of time and at a predetermined frequency, said Fourier transform of the voltage representation being modified by a continuous phase change at the said frequency, calculating an approximation to the Fourier transform of a moving window of the filtered current representation over the said time interval and at the said frequency, said Fourier transform of the current representation being modified by a continuous phase change at the said frequency, calculating the impedance of said section from said modified Fourier transforms of the voltage and current representations, and generating a trip signal when the value of said calculated impedance indicates a fault.

Claim 7

A method for detecting the occurrence of a fault in a section of an electrical power supply system comprising the steps of: measuring the values of the voltage and current at a predetermined location to develop measured voltage and current representations, converting the measured current and voltage representations to digital representations thereof, digitally filtering out high frequency components in the measured voltage and current representations, calculating an approximation to the Fourier transform of a moving window of the filtered voltage representation over a predetermined interval of time and at a predetermined frequency, said Fourier transform of the voltage representation being modified by a continuous phase change at the said frequency, calculating an approximation to the Fourier transform of a moving window of the filtered current representation over the said time interval and at the said frequency, said Fourier transform of the current representation being modified by a continuous phase change at the said frequency, calculating the impedance of said section from said modified Fourier transforms of the voltage and current representations, and generating a trip signal when the value of said calculated impedance indicates a fault.

Claim 8

A method for detecting the occurrence of a fault in a section of an electrical power supply system comprising the steps of: measuring the values of the voltage and current at a predetermined location to develop measured voltage and current representations, converting the measured current and voltage representations to digital representations thereof, digitally filtering out high frequency components in the measured voltage and current representations, calculating an approximation to the Fourier transform of a moving window of the filtered voltage representation over a predetermined interval of time and at a predetermined frequency, said Fourier transform of the voltage representation being modified by a continuous phase change at the said frequency, calculating an approximation to the Fourier transform of a moving window of the filtered current representation over the said time interval and at the said frequency, said Fourier transform of the current representation being modified by a continuous phase change at the said frequency, calculating the impedance of said section from said modified Fourier transforms of the voltage and current representations, and generating a trip signal when the value of said calculated impedance indicates a fault.