Direct-current transmission line protection method and system based on pure current characteristics

A system for protecting a Direct-Current (DC) transmission line based on pure current characteristics, comprising a processor and a memory configured to store instructions executable by the processor, wherein the processor is configured to implement:

• collecting a line current iM(k0) of an M side of a first DC transmission line at a time point k0 and a line current iM(k0−ts) of the M side of the first DC transmission line at a time point k0−ts, computing a current difference diM(k0) of the M side of the first DC transmission line at the time point k0 according to the line current iM(k0) and the line current iM(k0−ts), and determining whether the current difference diM(k0) meets a protection starting criterion, the first DC transmission line being one of transmission lines, the M side of the first DC transmission line being one of an inverter side and a rectifier side of the first DC transmission line, the ts being a sampling interval, the k0 being greater than the ts;
• in response to the current difference diM(k0) of the M side of the first DC transmission line at the time point k0 meeting the protection starting criterion, starting DC protection at the M side of the first DC transmission line, collecting a line current iM(j) of the M side of the first DC transmission line at a time point j and a line current iM(j−ts) of the M side of the first DC transmission line at a time point j−ts, and computing a current difference diM(j) of the M side of the first DC transmission line at the time point j according to the line current iM(j) and the line current iM(j−ts);
• collecting a line current iM(k) of the M side of the first DC transmission line at a time point k and a line current iM(k−ts) of the M side of the first DC transmission line at a time point k−ts, and computing a current difference diM(k) of the M side of the first DC transmission line at the time point k according to the line current iM(k) and the line current iM(k−ts);
• collecting a line current iN(j−Ttran) of an N side of the first DC transmission line at a time point j−Ttran and a line current iN(j−ts−Ttran) of the N side of the first DC transmission line at a time point j−ts−Ttran, and computing a current difference diN(j−Ttran) of the N side of the first DC transmission line at the time point j−Ttran according to the line current iN(j−Ttran) and the line current iN(j−ts−Ttran);
• collecting a line current iM′(j) of an M side of a second DC transmission line at the time point j and a line current iM′(j−ts) of the M side of the second DC transmission line at a time point j−ts, computing a current difference diM′(j) of the M side of the second DC transmission line at the time point j according to the line current iM′(j) and the line current iM′(j−ts), computing a current change iM(k) of the M side of the first DC transmission line at the time point k according to the current difference diM(j) of the M side of the first DC transmission line, and computing a current change ΔiN(k−Ttran) of the N side of the first DC transmission line at the time point k−Ttran according to the current difference diN(j−Ttran) of the N side of the first DC transmission line, the time point of starting DC protection at the M side of the first DC transmission line being denoted as t0, the second DC transmission line being a DC transmission line other than the first DC transmission line, the M side of the second DC transmission line being located on a same side as the M side of the first DC transmission line, the N side of the first DC transmission line being opposite the M side of the first DC transmission line, the Ttran being a DC line transmission channel delay, t0≤j≤k;
• computing a difference accumulating action amount iΣ(t) of the first DC transmission line according to the current difference diM(k) of the M side of the first DC transmission line and the current change ΔiN(k−Ttran) of the N side of the first DC transmission line, computing a difference accumulating threshold isetz of the first DC transmission line according to the current difference diM(k) of the M side of the first DC transmission line, and determining whether the difference accumulating action amount iΣ(t) of the first DC transmission line and the difference accumulating threshold isetz of the first DC transmission line meet an opposite-end boosted differential current accumulation criterion preset, the t being a data collecting time point after start of DC protection at the M side of the first DC transmission line, t0≤k≤t;
• computing a direction action amount iΣΔ(t) of the first DC transmission line according to the current change ΔiM(k) of the M side of the first DC transmission line and the current change ΔiN(k−Ttran) of the N side of the first DC transmission line, and determining whether the direction action amount iΣΔ(t) of the first DC transmission line meets an accumulation low value direction criterion of an opposite-end boosted change current and an accumulation high value direction criterion of the opposite-end boosted change current preset;
• determining, within a time period t0˜tlimit, whether the current difference diM(j) of the M side of the first DC transmission line and the current difference diM′(j) of the M side of the second DC transmission line meet a first pole amplitude-comparison change current pole selecting criterion and a second pole amplitude-comparison change current pole selecting criterion preset, determining, within a time period t0˜tf, whether the current difference diM(j) of the M side of the first DC transmission line meets the first pole amplitude-comparison change current pole selecting criterion preset, determining, after the time point tf, whether the direction action amount iΣΔ(t) of the first DC transmission line meets a ratio braked current pole selecting criterion, wherein in response to that the first pole amplitude-comparison change current pole selecting criterion and the second pole amplitude-comparison change current pole selecting criterion are not met within the time period t0˜tlimit, that the first pole amplitude-comparison change current pole selecting criterion is met at one time point within the time period t0˜tf, or that the ratio braked current pole selecting criterion is met at a time point after the time point tf, a stage-wise current pole selecting criterion is met, the first pole being the M side of the first DC transmission line, the second pole being the M side of the second DC transmission line, the tlimit and the tf being two time points after the t0, tf>tlimit;
• computing a difference quantity iΔ(k) of the M side of the first DC transmission line at the time point k according to the current difference diM(k) of the M side of the first DC transmission line and the current change ΔiN(k−Ttran) of the N side of the first DC transmission line, determining a reverse difference quantity iΔ′(k) of the M side of the first DC transmission line at the time point k based on the difference quantity iΔ(k), and determining whether the reverse difference quantity iΔ′(k) of the M side of the first DC transmission line meets a difference accumulation large number preventing protection criterion preset,
• computing a large number preventing change iz(k) of the first DC transmission line at the time point k according to the current change ΔiM(k) of the M side and the current change ΔiN(k−Ttran) of the N side of the first DC transmission line, and determining whether the large number preventing change iz(k) of the first DC transmission line meets a current change large number preventing protection criterion;
• and
• in response to that the opposite-end boosted differential current accumulation criterion, the accumulation high value direction criterion of the opposite-end boosted change current, and the difference accumulation large number preventing protection criterion are all met at the time point t, and within a time period t0−t a number of sampling points meeting the current change large number preventing protection criterion is greater than a preset point number threshold and a number of sampling points not meeting the current change large number preventing protection criterion, or in response to that the opposite-end boosted differential current accumulation criterion, the accumulation low value direction criterion of the opposite-end boosted change current, the stage-wise current pole selecting criterion, and the difference accumulation large number preventing protection criterion are all met at the time point t, and within the time period t0˜t the number of sampling points meeting the current change large number preventing protection criterion is greater than the preset point number threshold and the number of sampling points not meeting the current change large number preventing protection criterion, exporting a protection action on the M side of the first DC transmission line.

A non-transitory computer-readable storage medium, having stored thereon instructions which when executed by a processor of a computer, allow the computer to perform:

• collecting a line current iM(k0) of an M side of a first DC transmission line at a time point k0 and a line current iM(k0−ts) of the M side of the first DC transmission line at a time point k0−ts, computing a current difference diM(k0) of the M side of the first DC transmission line at the time point k0 according to the line current iM(k0) and the line current iM(k0−ts), and determining whether the current difference diM(k0) meets a protection starting criterion, the first DC transmission line being one of transmission lines, the M side of the first DC transmission line being one of an inverter side and a rectifier side of the first DC transmission line, the ts being a sampling interval, the k0 being greater than the ts;
• in response to the current difference diM(k0) of the M side of the first DC transmission line at the time point k0 meeting the protection starting criterion, starting DC protection at the M side of the first DC transmission line, collecting a line current iM(j) of the M side of the first DC transmission line at a time point j and a line current iM(j−ts) of the M side of the first DC transmission line at a time point j−ts, and computing a current difference diM(j) of the M side of the first DC transmission line at the time point j according to the line current iM(j) and the line current iM(j−ts);
• collecting a line current iM(k) of the M side of the first DC transmission line at a time point k and a line current iM(k−ts) of the M side of the first DC transmission line at a time point k−ts, and computing a current difference diM(k) of the M side of the first DC transmission line at the time point k according to the line current iM(k) and the line current iM(k−ts);
• collecting a line current iN(j−Ttran) of an N side of the first DC transmission line at a time point j−Ttran and a line current iN(j−ts−Ttran) of the N side of the first DC transmission line at a time point j−ts−Ttran, and computing a current difference diN(j−Ttran) of the N side of the first DC transmission line at the time point j−Ttran according to the line current iN(j−Ttran) and the line current iN(j−ts−Ttran);
• collecting a line current iM′(j) of an M side of a second DC transmission line at the time point j and a line current iM′(j−ts) of the M side of the second DC transmission line at a time point j−ts, computing a current difference diM′(j) of the M side of the second DC transmission line at the time point j according to the line current iM′(j) and the line current iM′(j−ts), computing a current change ΔiM(k) of the M side of the first DC transmission line at the time point k according to the current difference diM(j) of the M side of the first DC transmission line, and computing a current change ΔiN(k−Ttran) of the N side of the first DC transmission line at the time point k−Ttran according to the current difference diN(j−Ttran) of the N side of the first DC transmission line, the time point of starting DC protection at the M side of the first DC transmission line being denoted as t0, the second DC transmission line being a DC transmission line other than the first DC transmission line, the M side of the second DC transmission line being located on a same side as the M side of the first DC transmission line, the N side of the first DC transmission line being opposite the M side of the first DC transmission line, the Ttran being a DC line transmission channel delay, t0≤j≤k;
• computing a difference accumulating action amount iΣ(t) of the first DC transmission line according to the current difference diM(k) of the M side of the first DC transmission line and the current change ΔiN(k−Ttran) of the N side of the first DC transmission line, computing a difference accumulating threshold isetz of the first DC transmission line according to the current difference diM(k) of the M side of the first DC transmission line, and determining whether the difference accumulating action amount iΣ(t) of the first DC transmission line and the difference accumulating threshold isetz of the first DC transmission line meet an opposite-end boosted differential current accumulation criterion preset, the t being a data collecting time point after start of DC protection at the M side of the first DC transmission line, t0≤k≤t;
• computing a direction action amount iΣΔ(t) of the first DC transmission line according to the current change ΔiM(k) of the M side of the first DC transmission line and the current change ΔiN(k−Ttran) of the N side of the first DC transmission line, and determining whether the direction action amount iΣΔ(t) of the first DC transmission line meets an accumulation low value direction criterion of an opposite-end boosted change current and an accumulation high value direction criterion of the opposite-end boosted change current preset;
• determining, within a time period t0˜tlimit, whether the current difference diM(j) of the M side of the first DC transmission line and the current difference diM′(j) of the M side of the second DC transmission line meet a first pole amplitude-comparison change current pole selecting criterion and a second pole amplitude-comparison change current pole selecting criterion preset, determining, within a time period t0˜tf, whether the current difference diM(j) of the M side of the first DC transmission line meets the first pole amplitude-comparison change current pole selecting criterion preset, determining, after the time point tf, whether the direction action amount iΣΔ(t) of the first DC transmission line meets a ratio braked current pole selecting criterion, wherein in response to that the first pole amplitude-comparison change current pole selecting criterion and the second pole amplitude-comparison change current pole selecting criterion are not met within the time period t0˜tlimit, that the first pole amplitude-comparison change current pole selecting criterion is met at one time point within the time period t0˜tf, or that the ratio braked current pole selecting criterion is met at a time point after the time point tf, a stage-wise current pole selecting criterion is met, the first pole being the M side of the first DC transmission line, the second pole being the M side of the second DC transmission line, the tlimit and the tf being two time points after the t0, tf>tlimit;
• computing a difference quantity iΔ(k) of the M side of the first DC transmission line at the time point k according to the current difference diM(k) of the M side of the first DC transmission line and the current change ΔiN(k−Ttran) of the N side of the first DC transmission line, determining a reverse difference quantity iΔ′(k) of the M side of the first DC transmission line at the time point k based on the difference quantity iΔ(k), and determining whether the reverse difference quantity iΔ′(k) of the M side of the first DC transmission line meets a difference accumulation large number preventing protection criterion preset;
• computing a large number preventing change iz(k) of the first DC transmission line at the time point k according to the current change ΔiM(k) of the M side and the current change ΔiN(k−Ttran) of the N side of the first DC transmission line, and determining whether the large number preventing change iz(k) of the first DC transmission line meets a current change large number preventing protection criterion;
• and
• in response to that the opposite-end boosted differential current accumulation criterion, the accumulation high value direction criterion of the opposite-end boosted change current, and the difference accumulation large number preventing protection criterion are all met at the time point t, and within a time period t0˜t a number of sampling points meeting the current change large number preventing protection criterion is greater than a preset point number threshold and a number of sampling points not meeting the current change large number preventing protection criterion, or in response to that the opposite-end boosted differential current accumulation criterion, the accumulation low value direction criterion of the opposite-end boosted change current, the stage-wise current pole selecting criterion, and the difference accumulation large number preventing protection criterion are all met at the time point t, and within the time period t0˜t the number of sampling points meeting the current change large number preventing protection criterion is greater than the preset point number threshold and the number of sampling points not meeting the current change large number preventing protection criterion, exporting a protection action on the M side of the first DC transmission line.