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

Patent metadata

Field	Value
Publication number	US-11973340-B2
Application number	US-202017596826-A
Country	US
Kind code	B2
Filing date	Jun 18, 2020
Priority date	Jul 4, 2019
Publication date	Apr 30, 2024
Grant date	Apr 30, 2024

Abstract

A line current i M (k 0 ) of an M side of a first direct-current transmission line is collected at a moment k 0 . A line current i M (k 0 −t s ) thereof is collected at k 0 −t s . At a moment k 0 , a differential value di M (k 0 ) of a current of the side of the first direct-current transmission line is calculated according to the line current i M (k 0 ) and the line current i M (k 0 −t s ). It is determined whether the differential value di M (k 0 ) of the current meets a protection enabling criteria. If so, direct-current protection for the M side of the first direct-current transmission line is enabled. A line current i M (j) of the M side of the first direct-current transmission line is collected at a moment j. A line current i M (j−t s ) thereof is collected at a moment j−t s . A differential value di M (j) of the current of the M side of the first direct-current transmission line at the moment j is calculated according to the line current i M (j) and the line current i M (j−t s ).

First claim

What is claimed is:

1. A method for protecting a Direct-Current (DC) transmission line based on pure current characteristics, comprising:
collecting a line current i M (k 0 ) of an M side of a first DC transmission line at a time point k 0 and a line current i M (k 0 −t s ) of the M side of the first DC transmission line at a time point k 0 −t s , computing a current difference di M (k 0 ) of the M side of the first DC transmission line at the time point k 0 according to the line current i M (k 0 ) and the line current i M (k 0 −t s ), and determining whether the current difference di M (k 0 ) 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 t s being a sampling interval, the k 0 being greater than the t s ;
in response to the current difference di M (k 0 ) of the M side of the first DC transmission line at the time point k 0 meeting the protection starting criterion, starting DC protection at the M side of the first DC transmission line, collecting a line current i M (j) of the M side of the first DC transmission line at a time point j and a line current i M (j−t s ) of the M side of the first DC transmission line at a time point j−t s , and computing a current difference di M (j) of the M side of the first DC transmission line at the time point j according to the line current i M (j) and the line current i M (j−t s ); collecting a line current i M (k) of the M side of the first DC transmission line at a time point k and a line current i M (k−t s ) of the M side of the first DC transmission line at a time point k−t s , and computing a current difference di M (k) of the M side of the first DC transmission line at the time point k according to the line current i M (k) and the line current i M (k−t s ); collecting a line current i N (j−T tran ) of an N side of the first DC transmission line at a time point j−T tran and a line current i N (j−t s −T tran ) of the N side of the first DC transmission line at a time point j−t s −T tran , and computing a current difference di N (j−T tran ) of the N side of the first DC transmission line at the time point j−T tran according to the line current i N (j−T tran ) and the line current i N (j−t s −T tran ); collecting a line current i M ′(j) of an M side of a second DC transmission line at the time point j and a line current i M ′(j−t s ) of the M side of the second DC transmission line at a time point j−t s , computing a current difference di M ′(j) of the M side of the second DC transmission line at the time point j according to the line current i M ′(j) and the line current i M ′(j−t s ), computing a current change Δi M (k) of the M side of the first DC transmission line at the time point k according to the current difference di M (j) of the M side of the first DC transmission line, and computing a current change Δi N (k−T tran ) of the N side of the first DC transmission line at the time point k−T tran according to the current difference di N (j−T tran ) 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 t 0 , 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 T tran being a DC line transmission channel delay, t 0 ≤j≤k;
computing a difference accumulating action amount i Σ (t) of the first DC transmission line according to the current difference di M (k) of the M side of the first DC transmission line and the current change Δi N (k−T tran ) of the N side of the first DC transmission line, computing a difference accumulating threshold i setz of the first DC transmission line according to the current difference di M (k) of the M side of the first DC transmission line, and determining whether the difference accumulating action amount i Σ (t) of the first DC transmission line and the difference accumulating threshold i setz 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, t 0 ≤k≤t;
computing a direction action amount i ΣΔ (t) of the first DC transmission line according to the current change Δi M (k) of the M side of the first DC transmission line and the current change Δi N (k−T tran ) of the N side of the first DC transmission line, and determining whether the direction action amount i ΣΔ (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 t 0 ˜t limit , whether the current difference di M (j) of the M side of the first DC transmission line and the current difference di M ′(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 t 0 ˜t f , whether the current difference di M (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 t f , whether the direction action amount i ΣΔ (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 t 0 ˜t limit , that the first pole amplitude-comparison change current pole selecting criterion is met at one time point within the time period t 0 ˜t f , or that the ratio braked current pole selecting criterion is met at a time point after the time point t f , 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 t limit and the t f being two time points after the t 0 , t f >t limit ;
computing a difference quantity i Δ (k) of the M side of the first DC transmission line at the time point k according to the current difference di M (k) of the M side of the first DC transmission line and the current change Δi N (k−T tran ) of the N side of the first DC transmission line, determining a reverse difference quantity i Δ ′(k) of the M side of the first DC transmission line at the time point k based on the difference quantity i Δ (k), and determining whether the reverse difference quantity i Δ ′(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 i z (k) of the first DC transmission line at the time point k according to the current change Δi M (k) of the M side and the current change Δi N (k−T tran ) of the N side of the first DC transmission line, and determining whether the large number preventing change i z (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 c

Assignees

• China Electric Power Res Inst
• State Grid Corp China

Inventors

• Zhou Zexin
• Liu Huanzhang
• Lv Pengfei
• Cao Hong
• Wang Xingguo
• Ruan Siye
• Du Dingxiang
• Li Yong
• Yang Guosheng
• Jin Mingliang

Classifications

• H02H7/268 Primary

  for DC systems · CPC title

• H02H1/0007

  concerning the detecting means (in general G01R or other subclasses of G01; reed switches H01H71/2445) · CPC title

• H02H1/0092

  concerning the data processing means, e.g. expert systems, neural networks · CPC title

• G01R19/16538

  in AC or DC supplies (G01R19/16519 and G01R19/16528 take precedence) · CPC title

• H02H3/286

  involving comparison of similar homopolar quantities · CPC title