Method of locating a fault in a power transmission scheme
The technology described herein is generally directed to a method of locating a fault in a multi-terminal electrical power transmission scheme, such as implemented in a power transmission scheme where each of six terminals is connected with one of four junctions via a power transmission section and each junction interconnects a plurality of power transmission sections. Aspects of the described technology can be directed to measuring the voltage and current at each terminal, calculating from the measured voltage and current at each terminal corresponding voltage and current phasors, determining from the calculated voltage and current phasors a synchronization difference between the measured voltage and current at a designated terminal and the measured voltage and current at each other terminal, modifying the calculated voltage and current phasors to compensate for each synchronization difference, and determining from the compensated voltage and current phasors the location of the fault.
1. A method of locating a fault in a multi-terminal electrical power transmission scheme in which each terminal is connected with a junction via a power transmission section and the each junction interconnects a plurality of power transmission sections, the method comprising:
(a) measuring the voltage and current at each terminal;
(b) calculating from the measured voltage and current at each terminal corresponding voltage and current phasors;
(c) determining from the calculated voltage and current phasors a synchronization difference between the measured voltage and current at a designated terminal and the measured voltage and current at the or each other terminal, wherein the synchronization difference is a time difference;
(d) modifying the calculated voltage and current phasors to compensate for the or each synchronization difference; and
(e) determining from the compensated voltage and current phasors the location of the fault.
2. The method of claim 1 , wherein (a) measuring the voltage and current at each terminal further comprises resampling the measured voltage and current from one or more terminals.
3. The method of claim 1 , wherein the power transmission scheme is a multi-phase power transmission scheme, wherein (a) measuring the voltage and current at each terminal further comprises measuring the voltage and current of each phase at each terminal, and wherein (b) calculating from the measured voltage and current at each terminal corresponding voltage and current phasors further comprises converting the measured voltage and current at each terminal into respective phase phasors and then transforming the phase phasors into respective positive and negative sequence voltage phasors and positive and negative sequence current phasors.
4. The method of claim 2 , further comprising determining from the measured current from the one or more terminals whether a fault has occurred and if a fault has occurred whether it effects all phases of the power transmission scheme.
5. The method of claim 4 , wherein if the fault effects all phases of the power transmission scheme then the positive sequence voltage and current phasors are used in subsequent operations, otherwise the negative sequence voltage and current phasors are used.
6. The method of claim 1 , wherein (c) determining from the calculated voltage and current phasors a synchronization difference between the measured voltage and current at a designated terminal and the measured voltage and current at the or each other terminal further comprises:
calculating, with respect to the designated terminal, an equivalent current flowing at the or each other terminal;
equating, in respect of the or each other terminal, a sum of the measured current and the calculated equivalent current to zero according to Kirchhoff's first law; and
extracting, in respect of the or each other terminal a synchronization difference between the measured voltage and current at the designated terminal and the measured voltage and current at the said respective other terminal from a corresponding equated sum of currents.
7. The method of claim 5 , wherein calculating, with respect to the designated terminal, an equivalent current flowing at the or each other terminal comprises establishing an equivalent admittance matrix for the power transmission scheme.
8. The method of claim 1 , wherein (e) determining from the compensated voltage and current phasors the location of the fault further comprises:
designating a terminal at a first end of the power transmission scheme as a first end terminal and a terminal at a second end of the power transmission scheme as a second end terminal;
obtaining a first set of voltage phasors, wherein the first set of voltage phasors comprises the compensated voltage phasor at the first end terminal and further comprises respective voltage phasors at each of the second end terminal and the or each junction that are determined based on the compensated first end terminal voltage phasor;
obtaining a second set of voltage phasors, wherein the second set of voltage phasors comprises the compensated voltage phasor at the second end terminal and further comprises respective voltage phasors at each of the first end terminal and the or each junction that are determined based on the compensated second end terminal voltage phasor; and
comparing the first and second sets of voltage phasors to identify the power transmission section or junction corresponding to the location of the fault, wherein each voltage phasor of the first set of voltage phasors is compared to the respective voltage phasor of the second set of voltage phasors that corresponds to the same end terminal or junction.
9. The method of claim 8 , further comprising, if a given power transmission section is identified as the location of the fault, determining the distance of the fault along the power transmission section using corresponding voltages and currents of an equivalent two-ended system.