Method for locating a fault on a power line and equipment for carrying out the method

Claim 2

Method for locating a fault on a power line located between a first (P) and a second (Q) station , which line is included in a multi-phase distribution or transmission system, with measurement of the instantaneous values of the current and the voltage in each phase at the two end points (P, Q) of the transmission line, with converting the measured values into corresponding digital values, which are then supplied to a travelling wave model (2, 3) in the respective station, and with obtaining the voltage distribution along the transmission line, seen both from station P to station Q and from station Q to station P, with the aid of the travelling wave models, characterized in that ap =|ΔU Pp | is formed as the difference between the voltage (U' P ), measured in the first station (P) or calculated by means of the travelling wave model, and the corresponding voltage (U"p) one period/half-period earlier, that aq =|ΔU Qq | is formed as the difference between the voltage (U' Q ), measured in the second station (Q) or calculated by means of the travelling wave model, and the corresponding voltage (U" Q ) one period/half-period earlier, that bp =|ΔU Pq | is formed as the difference between the voltage (U' P q) in the second station (Q), calculated in the travelling wave model in the first station (P) with values of currents and voltages measured in the first station, and the corresponding voltage (U"p ) one period/half-period earlier, that bq =|ΔU Qp | is formed as the difference between the voltage (U' Qp ) in the first station (P), calculated in the travelling wave model in the second station (Q) with values of currents and voltages measured in the second station, and the corresponding voltage (U" Qp ) one period/half-period earlier, that c is formed as the vectorial difference between the voltages corresponding to a p and b p , that c is formed as the vectorial difference between the q voltages corresponding to a and b q , that with the aid of the voltage differences formed, the following equations are formed and where with and that the distance between the first station and a fault point (F) on the transmission line between the first station and the second station with a mutual distance PQ is obtained as

Claim 3

Method according to claim 1, characterized in that when the difference in argument between the complex impedances of the power sources and the transmission line is less than 10 degrees, AP and AQ can be expressed, respectively, as and

Claim 4

Method according to claim 1 or 2, characterized in that in the travelling wave models the voltage distribution along the whole transmission line, seen from the respective station, can be calculated.

Claim 5

Method according to claim 1 or 2, characterized in that in the travelling wave models, only the voltage in the first and the second station can be calculated.

Claim 6

Method according to any of the preceding claims, characterized in that voltages delivered from the travelling wave models are generated as phase voltages.

Claim 7

Method according to any of claims 1 to 4, characterized in that the voltages delivered from the travelling wave models are generated as principal voltages.

Claim 8

Method according to any of the preceding claims, characterized in that the voltages delivered from the travelling wave models are generated as negative or zero sequence voltages.

Claim 9

Method according to any of the preceding claims, characterized in that the value of a , b , c and a q , b , c may consist of the rectified mean value, the R.M.S. or the peak value of the corresponding voltages.

Claim 10

Equipment for carrying out the method according to any of the preceding claims comprising devices in both stations, which devices consist of analog-digital convertors (1, 2), travelling wave models (3, 4), summators (5, 6, 7, 8, 15, 18, 19), devices for division (16), devices for multiplication (17), a transmitter (9), a receiver (10) and a calculator (20), characterized in that a first summator (5) is arranged to form a difference voltage ap =|ΔU Pp | as the difference between the voltage (U' P ), measured in the first station (P) or calculated by means of the travelling wave model, and the corresponding voltage (U" P ) one period/half-period earlier, that a second summator (7) is arranged to form a difference voltage a q =|ΔU Qq | as the difference between the voltage (U' Q ), measured in the second station (Q) or calculated by means of the travelling wave model, and the corresponding voltage (U" Q ) one period/half-period earlier, that a third summator (6) is arranged to form a difference voltage b p =|ΔU Pq | as the difference between the voltage (U' Pq ) in the second station (Q), calculated in the travelling wave model in the first station (P) with values of currents and voltages measured in the first station, and the corresponding voltage (U" P q) one period/half-period earlier, that a fourth summator (8) is arranged to form a difference voltage b q =|ΔU Qp | as the difference between the voltage (U' Qp ) in the first station (P), calculated in the travelling wave model in the second station (Q) with values of currents and voltages measured in the second station, and the corresponding voltage (U" Qp ) one period/half-period earlier, that a fifth summator (18) is arranged to form the vectorial difference c p between the voltages corresponding to a p and b p , that a sixth summator (19) is arranged to form the vectorial difference c q between the voltages corresponding to a q and b q , that the difference voltages a , b q and c are adapted to be transmitted, via the transmitter and the receiver, from the second station Q to the first station (P), that the difference voltages a , b p and c p are adapted to be supplied, together with the values of a , band c q transmitted to the first station, to the calculator, that the calculator is arranged to calculate and with that a seventh summator (15) is arranged to form the sum of ΔP and ΔQ, that the quotient between ΔP and the sum of ΔP and ΔQ is adapted to be generated in the member (16) for division, that the distance PF between the first station and a fault point F on the transmission line between the first and the second stations with a mutual distance PQ is adapted to be obtained by multiplying PQ in a multiplier (17) by the quotient between ΔP and the sumΔP + ΔQ, obtained from said member (16).

Claim 11

Equipment according to claim 9, characterized in that when the difference in argument between the complex impedances of the power sources and the transmission line is smaller than 10 degrees, ΔP is adapted to be generated in an eighth summator (11) as the difference between ΔU Qp and ΔU Pp and ΔQ is adapted to be generated in an ninth summator (12) as the difference between ΔU Pq and ΔU Qq .