Protective relay system

Claim 2

A machine implemented method for protecting an electric power system comprising the steps of: providing signals indicative of instantaneous values of sampled electrical quantities or their synthetic values, determining or discriminating the distance in accordance with the equation: ##EQU17## where L represents the inductance of that portion of the electric power system which lies between the relay location and the fault point, v k (k=n, n-1, m, or m-1), i k (k=n, n-1, m, or m-1), and j k (k=n+p, n-p-1, m+p, or m-p-1) represent said instantaneous values or said synthetic values for the time point k, n and m represent sampling time points as expressed by consecutive integers, with n and m differing from each other, p represents integers 0, 1, . . . N, N represents a predetermined natural number, K p (p=0, 1, . . . N) represents constants, with at least K 0 and K 1 being values other than zero and being so determined that the errors in the approximation for the inductance is zero for specificed frequencies, and producing a signal to be used for the protection of the electric power system according to the result of the determination or the discrimination.

Claim 3

A method according to claim 1, wherein the constants K p are determined by solving a set of simultaneous equations derived by substituting the specified values ω q (q=1, 2, . . . N+1) for ω in the equation ##EQU18##

Claim 4

A method according to claim 1, wherein N=1.

Claim 5

A method according to claim 1, wherein the difference between n and m is 1.

Claim 6

A protective relay system for an electric power system comprising: means for providing signals indicative of instantaneous values of sampled electrical quantities or their synthetic values, means for determining or discriminating the distance in accordance with the equation: ##EQU19## where L represents the inductance of that portion of the electric power system which lies between the relay location and the fault point, v k (k=n, n-1, m, or m-1), i k (k=n, n-1, m, or m-1), and j k (k=n+p, n-p-1, m+p, or m-p-1) represent said instantaneous values or said synthetic values for the time point k, n and m represent sampling time points as expressed by consecutive integers, with n and m differing from each other, p represents integers 0, 1, . . . N, N represents a predetermined natural number, K p (p=0, 1, . . . N) represents contants, and with at least K 0 and K 1 being values other than zero and being so determined that the errors in the approximation for the inductance is zero for specified frequencies, and means for producing a signal to be used for the protection of the electric power system according to the result of the determination or the discrimination.

Claim 7

A protective relay system for an electric power system comprising: means for providing signals indicative of instantaneous values of sampled electrical quantities or their synthetic values, means for determining or discriminating the distance in accordance with the equation: ##EQU19## where L represents the inductance of that portion of the electric power system which lies between the relay location and the fault point, v k (k=n, n-1, m, or m-1), i k (k=n, n-1, m, or m-1), and j k (k=n+p, n-p-1, m+p, or m-p-1) represent said instantaneous values or said synthetic values for the time point k, n and m represent sampling time points as expressed by consecutive integers, with n and m differing from each other, p represents integers 0, 1, . . . N, N represents a predetermined natural number, K p (p=0, 1, . . . N) represents contants, and with at least K 0 and K 1 being values other than zero and being so determined that the errors in the approximation for the inductance is zero for specified frequencies, and means for producing a signal to be used for the protection of the electric power system according to the result of the determination or the discrimination.

Claim 8

A system according to claim 5, wherein the constants K p are determined by solving a set of simultaneous equations derived by substituting the specified values ω q (q=1, 2, . . . N+1) for ω in the equation ##EQU20##

Claim 9

A system according to claim 5, wherein N=1.

Claim 10

A system according to claim 5, wherein the difference between n and m is 1.

Claim 11

A machine implemented method for protecting an electric power system wherein signals indicative of instantaneous values of sampled electrical quantities or their synthetic values are produced, a differential equation v=L(di/dt)+Ri is solved by using an approximate expression ##EQU21## to determine the inductance L and to measure or discriminate the distance from the determined inductance, where v represents the voltage, i represents the current, R represents the resistance, t represents the time, t k and t k-1 represent time points, i k+p and i k-p-1 represent values of the current i for time points represented by t k+p and t k-p-1 , p represents integers (0, 1, . . . N), N represents a nautral number, K p (p=0, 1, . . . N) represents constants, with at least K 0 and K 1 being values other than zero and being so determined that the errors in the approximation for the inductance is zero for specified frequencies, and a signal to be used for protection of the electric power system is produced according to the result of the measurement or the discrimination.

Claim 12

A machine implemented method for protecting an electric power system wherein signals indicative of instantaneous values of sampled electrical quantities or their synthetic values are produced, a differential equation v=L(di/dt)+Ri is solved by using an approximate expression ##EQU21## to determine the inductance L and to measure or discriminate the distance from the determined inductance, where v represents the voltage, i represents the current, R represents the resistance, t represents the time, t k and t k-1 represent time points, i k+p and i k-p-1 represent values of the current i for time points represented by t k+p and t k-p-1 , p represents integers (0, 1, . . . N), N represents a nautral number, K p (p=0, 1, . . . N) represents constants, with at least K 0 and K 1 being values other than zero and being so determined that the errors in the approximation for the inductance is zero for specified frequencies, and a signal to be used for protection of the electric power system is produced according to the result of the measurement or the discrimination.

Claim 13

A method according to claim 9, wherein the constants K p are determined by solving a set of simultaneous equations derived by substituting the specified values ω q (q=1, 2, . . . N+1) for ω in the equation ##EQU22##

Claim 14

A method according to claim 9, wherein N=1.

Claim 15

A method according to claim 9, wherein the difference between n and m is 1.