Apparatus and method for measurement from the ground for high voltage overhead lines

Claim 1

An apparatus for measuring current in a plurality of high voltage overhead electrical lines which form a group of n high voltage electrical lines above ground level, said apparatus comprising: detecting means including a plurality p of devices (2) for detecting and measuring magnetic fields induced in the lines, said devices being at the ground level and in proximity to corresponding ones of said lines, wherein p is greater than n; wherein the current is calculated by matrix calculation; wherein a voltage is filtered at terminals of each of said devices (2); wherein a formula, Em i =A ij I j , where Em i is the electromotive force measured in device N°i, i lying in the range of 1 to p, I j is the current in line No. j, j lying in the range 1 to n, and A ij is a matrix of proportionality coefficients a ij relating the electromotive force to a current intensity, is applied for each of a plurality of non-zero harmonic frequencies f k so as to obtain the relationships linking complex components of the current I d (f k ) to the complex components of the electromotive voltage, the sum of harmonic currents being calculated so as to obtain an instantaneous current i d (t); and wherein the calculation of the instantaneous current i d (t) in line No. d is performed according the formula, i d (t)=sum of real parts of Id(f k )exp(2πf k tj), where t represents time, j is the imaginary number whose square equals -1, f k is the k-th harmonic of 10 Hz, I d (f k ) is the complex alternating component at frequency f k of the instantaneous current in line No. d, and d lies in the range 1 to n.

Claim 2

An apparatus for measuring current in a plurality of high voltage overhead electrical lines which form a group of n high voltage electrical lines above ground level, said apparatus comprising: detecting means including a plurality p of devices (2) for detecting and measuring magnetic fields induced in the lines, said devices being at the ground level and in proximity to corresponding ones of said lines, wherein p is greater than n; wherein the current is calculated by matrix calculation; wherein a voltage is filtered at terminals of each of said devices (2); wherein a formula, Em i =A ij I j , where Em i is the electromotive force measured in device N°i, i lying in the range of 1 to p, I j is the current in line No. j, j lying in the range 1 to n, and A ij is a matrix of proportionality coefficients a ij relating the electromotive force to a current intensity, is applied for each of a plurality of non-zero harmonic frequencies f k so as to obtain the relationships linking complex components of the current I d (f k ) to the complex components of the electromotive voltage, the sum of harmonic currents being calculated so as to obtain an instantaneous current i d (t); and wherein the calculation of the instantaneous current i d (t) in line No. d is performed according the formula, i d (t)=sum of real parts of Id(f k )exp(2πf k tj), where t represents time, j is the imaginary number whose square equals -1, f k is the k-th harmonic of 10 Hz, I d (f k ) is the complex alternating component at frequency f k of the instantaneous current in line No. d, and d lies in the range 1 to n.