Detection of faults a power transmission line

Claim 2

Apparatus for the detection of faults on a power transmission line connected between a control station and a distant station, said apparatus comprising: a plurality of voltage sensing means, one for each said station, each connected for producing a signal representing the voltage level V on the transmission line at its respective station; a plurality of current sensing means, one for each said station, each connected for producing a signal representing the current level I in the transmission line at its respective station; a plurality of calculating means, one for each said station, connected to said voltage sensing means and said current sensing means of its respective station for producing an output signal U equal to V +K I, where k is proportional to the characteristic impedance of the transmission line, the value of each said output signal representing a test quantity for its associated station; signal multiplying means connected to said calculating means of said distant station for multiplying the test quantity associated with said distant station by a quantity representing the propagation factor of the transmission line; and comparison means connected to said calculating means of said control station and to said multiplying means for comparing the output values therefrom and providing an indication of the result of such comparison.

Claim 3

Apparatus as claimed in claim 1 wherein saiD voltage sensing means for each said station comprises a voltage stepdown device; and said calculating means for each said station comprises a digital converter connected to receive the signals from said voltage sensing means and current sensing means of its associated station and for converting such signals into digital form, and a calculating unit connected to receive the digital signals from said digital converter for producing said output signal u in digital form.

Claim 4

Apparatus as claimed in claim 2 wherein the transmission line is of the flat three-phase type, said calculating means prepare two test quantities U1 and U2 at each said station, and said comparison means prepare the quantities S1, S2, Q1, Q2 and Q3, where: U1 V1 +K1 V2 +V3 -Zc 1 (I1 +C1 I2 +I3) V1, V2 and V3 being the voltages of the three phases, I1, I2 and I3 are the currents of the three phases, taken positively from said control station to said distant station, K1 and C1 are interphase propagation mode coefficients corresponding to the voltages and currents, respectively, and Zc 1 is the characteristic impedance corresponding to the interphase propagation mode; U2 V1-V3-Zc2 (I2-I3) Zc2 being the characteristic impedance corresponding to the bifular propagation mode; S1 e1d U1 (B)--U1 (A) S2 e2d U2 (b)-U2 (A) (A) identifying test quantities associated with said control station, (B) identifying test quantities associated with said distant station, 1 being the propagation constant for the interphase mode, 2 being the propagation constant for the bifilar mode, and d being the distance between said stations; and Q1 (S1/Zc1) -(S2/Zc2) Q2 S2/Zc2 Q3 (S1/Zc1)+ (S2/Zc2); and wherein apparatus further comprises a logical selection element connected to said comparison means for receiving the quantities Q1, Q2, Q3, for analyzing such quantities to determine the existence of a line fault and to identify the line on which such fault appears.

Claim 5

Apparatus as claimed in claim 1 further comprising a memory disposed at the control station and connected to receive the test quantity for at least one said station and to temporarily store such quantity for a period sufficient to compensate for any difference between times of arrival of said test quantities at said comparison means and the propagation time between said stations over said transmission line.