CN104078948B - Electric transmission line positive sequence electric current phase segregated differential protection method based on short-data windows - Google Patents

Abstract

The invention discloses a kind of electric transmission line positive sequence electric current phase segregated differential protection method based on short-data windows.First the three-phase current instantaneous value of each for transmission line of electricity two ends sampling instant is transformed into the current instantaneous value of each sampling instant in transmission line of electricity two ends under α β 0 coordinate axes by it, calculate the forward-order current instantaneous value of each sampling instant in transmission line of electricity two ends under α β 0 coordinate axes, the forward-order current instantaneous value of each sampling instant in transmission line of electricity two ends under α β 0 coordinate axes is carried out coordinate axes inverse transformation and obtains the three-phase forward-order current instantaneous value of each sampling instant in transmission line of electricity two ends, then the three-phase forward-order current instantaneous value utilizing each sampling instant in transmission line of electricity two ends constitutes forward-order current phase segregated differential protection criterion.The inventive method algorithm principle is simple, and program realizes easily, and operand is few, calculates speed fast, relay protection speed of action can be greatly improved.Having phase-selecting function, performance is not affected by transition resistance and load current, it is adaptable to the transmission line of electricity main protection function of whole failure process after completing fault.

Description

Power transmission line positive sequence current split-phase differential protection method based on short data window

Technical Field

The invention relates to the technical field of power system relay protection, in particular to a power transmission line positive sequence current split-phase differential protection method based on a short data window.

Background

The current differential protection is always the main protection of the transmission lines with various voltage grades because the current differential protection is not influenced by the operation mode of a power system and a power grid structure and has a natural phase selection function. The current differential protection can be divided into abrupt magnitude current differential protection and steady magnitude current differential protection. Because the sudden change exists only in a short time within two cycles after the line fault, the sudden change current differential protection is only suitable for the main protection function of the power transmission line within two cycles after the fault. Because the current phasor used by the abrupt variable current differential protection algorithm and the steady state current differential protection algorithm needs to be calculated by a whole cycle data window, the inherent delay of the abrupt variable current differential protection algorithm and the steady state current differential protection algorithm is one cycle, the algorithm has insufficient rapidity, and the algorithm cannot be suitable for main protection of the ultra-high voltage alternating current transmission line.

The current phasor used by the steady-state current differential protection algorithm comprises load current, when a heavy-load power transmission line has a single-phase high-resistance earth fault, the fault current component is very small and even smaller than the load current, so that the differential current is smaller than the braking current, the steady-state current differential protection refuses action when the heavy-load power transmission line has a permanent single-phase high-resistance earth fault, and the zero-sequence current differential protection is taken as backup protection to jump off the three-phase power transmission line, so that strong impact is caused to a power grid, and the power grid operation instability is easily caused.

Disclosure of Invention

The invention aims to overcome the defects in the prior art, and provides a positive sequence current split-phase differential protection method which has a phase selection function, has action performance not influenced by transition resistance and load current and utilizes 1/4 period short data windows to realize the transmission line.

The technical scheme adopted by the invention for solving the technical problem is as follows:

a positive sequence current split-phase differential protection method for a power transmission line based on a short data window comprises the following sequential steps:

(1) the protection device collects A, B, C three-phase current instantaneous values i of the power transmission line at t sampling time of m transformer substation protection installation positions in real time_mA(t)、i_mB(t)、i_mC(t), A, B, C three-phase current instantaneous values i of the power transmission line at t sampling time of n transformer substation protection installation positions are collected in real time_nA(t)、i_nB(t)、i_nC(t)；

(2) The protection device carries out t sampling on A, B, C three-phase current instantaneous values i at the time of m transformer substation protection installation positions_mA(t)、i_mB(t)、i_mC(t) transition to current transient i at time t sample off axis αβ 0_mα(t)、i_mβ(t)、i_m0(t)：

$\left[\begin{array}{c}{i}_{m\mathrm{\α}}\left(t\right)\\ i_{m\mathrm{\β}}\left(t\right)\\ i_{m0}\left(t\right)\end{array}\right]=\frac{2}{3}\left[\begin{array}{ccc}1& -\frac{1}{2}& -\frac{1}{2}\\ 0& \frac{\sqrt{3}}{2}& -\frac{\sqrt{3}}{2}\\ \frac{1}{2}& \frac{1}{2}& \frac{1}{2}\end{array}\right]\left[\begin{array}{c}{i}_{mA}\left(t\right)\\ i_{mB}\left(t\right)\\ i_{mC}\left(t\right)\end{array}\right]$

(3) The protection device carries out t sampling on A, B, C three-phase current instantaneous values i at n transformer substation protection installation places_nA(t)、i_nB(t)、i_nC(t) switch over toαβ 0 instantaneous value i of current at sampling time t under coordinate axis_nα(t)、i_nβ(t)、i_n0(t)：

$\left[\begin{array}{c}{i}_{n\mathrm{\α}}\left(t\right)\\ i_{n\mathrm{\β}}\left(t\right)\\ i_{n0}\left(t\right)\end{array}\right]=\frac{2}{3}\left[\begin{array}{ccc}1& -\frac{1}{2}& -\frac{1}{2}\\ 0& \frac{\sqrt{3}}{2}& -\frac{\sqrt{3}}{2}\\ \frac{1}{2}& \frac{1}{2}& \frac{1}{2}\end{array}\right]\left[\begin{array}{c}{i}_{nA}\left(t\right)\\ i_{nB}\left(t\right)\\ i_{nC}\left(t\right)\end{array}\right]$

(4) The protection device calculates αβ 0 positive sequence current at t sampling time of m transformer substation protection installation under coordinate axis

$i_{m\mathrm{\α}}^{+}\left(t\right)=0.5i_{m\mathrm{\α}}\left(t\right)-0.5i_{m\mathrm{\β}}(t-\frac{T}{4})$

$i_{m\mathrm{\β}}^{+}\left(t\right)=0.5i_{m\mathrm{\α}}(t-\frac{T}{4})+0.5i_{m\mathrm{\β}}\left(t\right)$

$i_{m0}^{+}\left(t\right)=i_{m0}\left(t\right)$

Wherein,is β axis direction under αβ 0 coordinate axisSampling current instantaneous values of m transformer substation protection installation positions at the moment; i.e. i_mβ(t) is a current instantaneous value of the protection installation place of the m transformer substation at the sampling moment of β axis direction t under the coordinate axis of αβ 0;is α axis direction under αβ 0 coordinate axisSampling current instantaneous values of m transformer substation protection installation positions at the moment; i.e. i_mα(T) is the current instantaneous value of m transformer substation protection installation positions at α axial direction T sampling time under the coordinate axis of αβ 0, T is fundamental wave period time, i_m0(t) is a current instantaneous value of the protection installation place of the m transformer substation at the sampling moment of the 0-axis direction t under the coordinate axis of αβ 0;

(5) t sampling of n transformer substation protection installation position under coordinate axis of αβ 0 calculation of protection devicePositive sequence current of time

$i_{n\mathrm{\α}}^{+}\left(t\right)=0.5i_{n\mathrm{\α}}\left(t\right)-0.5i_{n\mathrm{\β}}(t-\frac{T}{4})$

$i_{n\mathrm{\β}}^{+}\left(t\right)=0.5i_{n\mathrm{\α}}(t-\frac{T}{4})+0.5i_{n\mathrm{\β}}\left(t\right)$

$i_{n0}^{+}\left(t\right)=i_{n0}\left(t\right)$

Wherein,is β axis direction under αβ 0 coordinate axisSampling the current instantaneous value of the n transformer substation protection installation positions at the moment; i.e. i_nβ(t) is a current instantaneous value of n transformer substation protection installation positions at the sampling time of β axis direction t under the coordinate axis of αβ 0;is α axis direction under αβ 0 coordinate axisSampling the current instantaneous value of the n transformer substation protection installation positions at the moment; i.e. i_nα(T) is the current instantaneous value of n transformer substation protection installation positions at α axial direction T sampling time under the coordinate axis of αβ 0, T is fundamental wave period time, i_n0(t) is a current instantaneous value of n transformer substation protection installation positions at the sampling time of the axis direction t of 0 under the coordinate axis of αβ 0;

(6) the protection device calculates A, B, C phase positive sequence current instantaneous values at t sampling time of m transformer substation protection installation positions

$\left[\begin{array}{c}{i}_{mA}^{+}\left(t\right)\\ i_{mB}^{+}\left(t\right)\\ i_{mC}^{+}\left(t\right)\end{array}\right]=1.5{\left[\begin{array}{ccc}1& -\frac{1}{2}& -\frac{1}{2}\\ 0& \frac{\sqrt{3}}{2}& -\frac{\sqrt{3}}{2}\\ \frac{1}{2}& \frac{1}{2}& \frac{1}{2}\end{array}\right]}^{-1}\left[\begin{array}{c}{i}_{m\mathrm{\α}}^{+}\left(t\right)\\ i_{m\mathrm{\β}}^{+}\left(t\right)\\ i_{m0}^{+}\left(t\right)\end{array}\right]$

(7) The protection device calculates A, B, C phase positive sequence current instantaneous values at t sampling time of n transformer substation protection installation positions

$\left[\begin{array}{c}{i}_{nA}^{+}\left(t\right)\\ i_{nB}^{+}\left(t\right)\\ i_{nC}^{+}\left(t\right)\end{array}\right]=1.5{\left[\begin{array}{ccc}1& -\frac{1}{2}& -\frac{1}{2}\\ 0& \frac{\sqrt{3}}{2}& -\frac{\sqrt{3}}{2}\\ \frac{1}{2}& \frac{1}{2}& \frac{1}{2}\end{array}\right]}^{-1}\left[\begin{array}{c}{i}_{n\mathrm{\α}}^{+}\left(t\right)\\ i_{n\mathrm{\β}}^{+}\left(t\right)\\ i_{n0}^{+}\left(t\right)\end{array}\right]$

(8) Protection device judgmentWhether the phase of the power transmission line is established or not is judged, if so, the protection device sends tripping signals to circuit breakers at two ends of the A-phase power transmission line; protection device judgmentWhether the phase of the power transmission line is established or not is judged, if so, the protection device sends tripping signals to circuit breakers at two ends of the B-phase power transmission line; protection device judgmentWhether the current is established or not is judged, if so, the protection device sends tripping signals to circuit breakers at two ends of the C-phase power transmission line; wherein k is₁Setting coefficient; i is_setIs a setting current threshold value.

Compared with the background technology, the technical scheme has the following advantages:

the method comprises the steps of firstly converting three-phase current instantaneous values of sampling moments at two ends of a power transmission line into current instantaneous values of the sampling moments at two ends of the power transmission line under an alpha beta 0 coordinate axis, calculating positive sequence current instantaneous values of the sampling moments at two ends of the power transmission line under the alpha beta 0 coordinate axis, carrying out coordinate axis inverse transformation on the positive sequence current instantaneous values of the sampling moments at two ends of the power transmission line under the alpha beta 0 coordinate axis to obtain three-phase positive sequence current instantaneous values of the sampling moments at two ends of the power transmission line, and then forming a positive sequence current split-phase differential protection criterion by using the three-phase positive sequence current instantaneous values of the sampling moments at two. The method does not relate to complex operation, only relates to simple real algebraic operation, has simple algorithm principle, easy program realization, less operation amount and high calculation speed, and can greatly improve the action speed of relay protection. The method has the phase selection function, the action performance is not influenced by the transition resistance and the load current, and the method is suitable for the main protection function of the power transmission line in the whole fault process after the fault. The method realizes the main protection function of the power transmission line by using 1/4-period short data windows, and can correctly and reliably act to jump off a fault phase when the power transmission line has a single-phase high-resistance earth fault.

Drawings

The invention is further illustrated by the following figures and examples.

Fig. 1 is a schematic diagram of a power transmission system to which the present invention is applied.

Detailed Description

Fig. 1 is a schematic diagram of a power transmission system to which the present invention is applied. In fig. 1, CT is a current transformer. In this embodiment, the protection device collects A, B, C three-phase current instantaneous values i of the power transmission line at t sampling time of m transformer substation protection installation places in real time_mA(t)、i_mB(t)、i_mC(t), A, B, C three-phase current instantaneous values i of the power transmission line at t sampling time of n transformer substation protection installation positions are collected in real time_nA(t)、i_nB(t)、i_nC(t)。

The protection device carries out t sampling on A, B, C three-phase current instantaneous values i at the time of m transformer substation protection installation positions_mA(t)、i_mB(t)、i_mC(t) transition to current transient i at time t sample off axis αβ 0_mα(t)、i_mβ(t)、i_m0(t)：

$\left[\begin{array}{c}{i}_{m\mathrm{\α}}\left(t\right)\\ i_{m\mathrm{\β}}\left(t\right)\\ i_{m0}\left(t\right)\end{array}\right]=\frac{2}{3}\left[\begin{array}{ccc}1& -\frac{1}{2}& -\frac{1}{2}\\ 0& \frac{\sqrt{3}}{2}& -\frac{\sqrt{3}}{2}\\ \frac{1}{2}& \frac{1}{2}& \frac{1}{2}\end{array}\right]\left[\begin{array}{c}{i}_{mA}\left(t\right)\\ i_{mB}\left(t\right)\\ i_{mC}\left(t\right)\end{array}\right]$

The protection device carries out t sampling on A, B, C three-phase current instantaneous values i at n transformer substation protection installation places_nA(t)、i_nB(t)、i_nC(t) transition to current transient i at time t sample off axis αβ 0_nα(t)、i_nβ(t)、i_n0(t)：

$\left[\begin{array}{c}{i}_{n\mathrm{\α}}\left(t\right)\\ i_{n\mathrm{\β}}\left(t\right)\\ i_{n0}\left(t\right)\end{array}\right]=\frac{2}{3}\left[\begin{array}{ccc}1& -\frac{1}{2}& -\frac{1}{2}\\ 0& \frac{\sqrt{3}}{2}& -\frac{\sqrt{3}}{2}\\ \frac{1}{2}& \frac{1}{2}& \frac{1}{2}\end{array}\right]\left[\begin{array}{c}{i}_{nA}\left(t\right)\\ i_{nB}\left(t\right)\\ i_{nC}\left(t\right)\end{array}\right]$

The protection device calculates αβ 0 positive sequence current at t sampling time of m transformer substation protection installation under coordinate axis

$i_{m\mathrm{\α}}^{+}\left(t\right)=0.5i_{m\mathrm{\α}}\left(t\right)-0.5i_{m\mathrm{\β}}(t-\frac{T}{4})$

$i_{m\mathrm{\β}}^{+}\left(t\right)=0.5i_{m\mathrm{\α}}(t-\frac{T}{4})+0.5i_{m\mathrm{\β}}\left(t\right)$

$i_{m0}^{+}\left(t\right)=i_{m0}\left(t\right)$

Wherein,is β axis direction under αβ 0 coordinate axisSampling current instantaneous values of m transformer substation protection installation positions at the moment; i.e. i_mβ(t) is a current instantaneous value of the protection installation place of the m transformer substation at the sampling moment of β axis direction t under the coordinate axis of αβ 0;is α axis direction under αβ 0 coordinate axisSampling current instantaneous values of m transformer substation protection installation positions at the moment; i.e. i_mα(T) is the current instantaneous value of m transformer substation protection installation positions at α axial direction T sampling time under the coordinate axis of αβ 0, T is fundamental wave period time, i_m0And (t) is the current instantaneous value of the protective installation place of the m transformer substation at the sampling moment of the 0-axis direction t under the coordinate axis of αβ 0, and t is the sampling time.

The protection device calculates αβ 0 positive sequence current at t sampling time of n transformer substation protection installation under coordinate axis

$i_{n\mathrm{\α}}^{+}\left(t\right)=0.5i_{n\mathrm{\α}}\left(t\right)-0.5i_{n\mathrm{\β}}(t-\frac{T}{4})$

$i_{n\mathrm{\β}}^{+}\left(t\right)=0.5i_{n\mathrm{\α}}(t-\frac{T}{4})+0.5i_{n\mathrm{\β}}\left(t\right)$

$i_{n0}^{+}\left(t\right)=i_{n0}\left(t\right)$

Wherein,is β axis direction under αβ 0 coordinate axisSampling the current instantaneous value of the n transformer substation protection installation positions at the moment; i.e. i_nβ(t) is a current instantaneous value of n transformer substation protection installation positions at the sampling time of β axis direction t under the coordinate axis of αβ 0;is α axis direction under αβ 0 coordinate axisSampling the current instantaneous value of the n transformer substation protection installation positions at the moment; i.e. i_nα(T) is the current instantaneous value of n transformer substation protection installation positions at α axial direction T sampling time under the coordinate axis of αβ 0, T is fundamental wave period time, i_n0And (t) is the instantaneous value of the current at the protective installation position of the n transformer substations at the sampling time of the axis direction t of 0 under the coordinate axis of αβ 0.

The protection device calculates A, B, C phase positive sequence current instantaneous values at t sampling time of m transformer substation protection installation positions

$\left[\begin{array}{c}{i}_{mA}^{+}\left(t\right)\\ i_{mB}^{+}\left(t\right)\\ i_{mC}^{+}\left(t\right)\end{array}\right]=1.5{\left[\begin{array}{ccc}1& -\frac{1}{2}& -\frac{1}{2}\\ 0& \frac{\sqrt{3}}{2}& -\frac{\sqrt{3}}{2}\\ \frac{1}{2}& \frac{1}{2}& \frac{1}{2}\end{array}\right]}^{-1}\left[\begin{array}{c}{i}_{m\mathrm{\α}}^{+}\left(t\right)\\ i_{m\mathrm{\β}}^{+}\left(t\right)\\ i_{m0}^{+}\left(t\right)\end{array}\right]$

The protection device calculates A, B, C phase positive sequence current instantaneous values at t sampling time of n transformer substation protection installation positions

$\left[\begin{array}{c}{i}_{nA}^{+}\left(t\right)\\ i_{nB}^{+}\left(t\right)\\ i_{nC}^{+}\left(t\right)\end{array}\right]=1.5{\left[\begin{array}{ccc}1& -\frac{1}{2}& -\frac{1}{2}\\ 0& \frac{\sqrt{3}}{2}& -\frac{\sqrt{3}}{2}\\ \frac{1}{2}& \frac{1}{2}& \frac{1}{2}\end{array}\right]}^{-1}\left[\begin{array}{c}{i}_{n\mathrm{\α}}^{+}\left(t\right)\\ i_{n\mathrm{\β}}^{+}\left(t\right)\\ i_{n0}^{+}\left(t\right)\end{array}\right]$

Protection device judgmentWhether the phase of the power transmission line is established or not is judged, if so, the protection device sends tripping signals to circuit breakers at two ends of the A-phase power transmission line; wherein k is₁Setting coefficient; i is_setIs a setting current threshold value.

Protection device judgmentWhether or not to becomeIf the phase B is established, the protection device sends tripping signals to circuit breakers at two ends of the phase B power transmission line; wherein k is₁Setting coefficient; i is_setIs a setting current threshold value.

Protection device judgmentWhether the current is established or not is judged, if so, the protection device sends tripping signals to circuit breakers at two ends of the C-phase power transmission line; wherein k is₁Setting coefficient; i is_setIs a setting current threshold value.

The method comprises the steps of firstly converting three-phase current instantaneous values of sampling moments at two ends of a power transmission line into current instantaneous values of the sampling moments at two ends of the power transmission line under an alpha beta 0 coordinate axis, calculating positive sequence current instantaneous values of the sampling moments at two ends of the power transmission line under the alpha beta 0 coordinate axis, carrying out coordinate axis inverse transformation on the positive sequence current instantaneous values of the sampling moments at two ends of the power transmission line under the alpha beta 0 coordinate axis to obtain three-phase positive sequence current instantaneous values of the sampling moments at two ends of the power transmission line, and then forming a positive sequence current split-phase differential protection criterion by using the three-phase positive sequence current instantaneous values of the sampling moments at two. The method does not relate to complex operation, only relates to simple real algebraic operation, has simple algorithm principle, easy program realization, less operation amount and high calculation speed, and can greatly improve the action speed of relay protection. The method has the phase selection function, the action performance is not influenced by the transition resistance and the load current, and the method is suitable for the main protection function of the power transmission line in the whole fault process after the fault. The method realizes the main protection function of the power transmission line by using 1/4-period short data windows, and can correctly and reliably act to jump off a fault phase when the power transmission line has a single-phase high-resistance earth fault.

The above description is only a preferred embodiment of the present invention, and therefore should not be taken as limiting the scope of the invention, which is defined by the appended claims and their equivalents.

Claims (1)

1. The power transmission line positive sequence current split-phase differential protection method based on the short data window is characterized in that: comprises the following steps in sequence:

(1) the protection device collects A, B, C three-phase current instantaneous values i of the power transmission line at t sampling time of m transformer substation protection installation positions in real time_mA(t)、i_mB(t)、i_mC(t), A, B, C three-phase current instantaneous values i of the power transmission line at t sampling time of n transformer substation protection installation positions are collected in real time_nA(t)、i_nB(t)、i_nC(t)；

(2) The protection device transforms m powerA, B, C three-phase current instantaneous value i at t sampling moment of station protection installation_mA(t)、i_mB(t)、i_mC(t) transition to current transient i at time t sample off axis αβ 0_mα(t)、i_mβ(t)、i_m0(t)：

$\left[\begin{array}{c}{i}_{m\mathrm{\α}}\left(t\right)\\ i_{m\mathrm{\β}}\left(t\right)\\ i_{m0}\left(t\right)\end{array}\right]=\frac{2}{3}\left[\begin{array}{ccc}1& -\frac{1}{2}& -\frac{1}{2}\\ 0& \frac{\sqrt{3}}{2}& -\frac{\sqrt{3}}{2}\\ \frac{1}{2}& \frac{1}{2}& \frac{1}{2}\end{array}\right]\left[\begin{array}{c}{i}_{mA}\left(t\right)\\ i_{mB}\left(t\right)\\ i_{mC}\left(t\right)\end{array}\right]$

(3) The protection device carries out t sampling on A, B, C three-phase current instantaneous values i at n transformer substation protection installation places_nA(t)、i_nB(t)、i_nC(t) transition to current transient i at time t sample off axis αβ 0_nα(t)、i_nβ(t)、i_n0(t)：

$\left[\begin{array}{c}{i}_{n\mathrm{\α}}\left(t\right)\\ i_{n\mathrm{\β}}\left(t\right)\\ i_{n0}\left(t\right)\end{array}\right]=\frac{2}{3}\left[\begin{array}{ccc}1& -\frac{1}{2}& -\frac{1}{2}\\ 0& \frac{\sqrt{3}}{2}& -\frac{\sqrt{3}}{2}\\ \frac{1}{2}& \frac{1}{2}& \frac{1}{2}\end{array}\right]\left[\begin{array}{c}{i}_{nA}\left(t\right)\\ i_{nB}\left(t\right)\\ i_{nC}\left(t\right)\end{array}\right]$

(4) The protection device calculates αβ 0 positive sequence current at t sampling time of m transformer substation protection installation under coordinate axis

$i_{m\mathrm{\α}}^{+}\left(t\right)=0.5i_{m\mathrm{\α}}\left(t\right)-0.5i_{m\mathrm{\β}}(t-\frac{T}{4})$

$i_{m\mathrm{\β}}^{+}\left(t\right)=0.5i_{m\mathrm{\α}}(t-\frac{T}{4})+0.5i_{m\mathrm{\β}}\left(t\right)$

$i_{m0}^{+}\left(t\right)=i_{m0}\left(t\right)$

Wherein,is β axis direction under αβ 0 coordinate axisSampling current instantaneous values of m transformer substation protection installation positions at the moment; i.e. i_mβ(t) is a current instantaneous value of the protection installation place of the m transformer substation at the sampling moment of β axis direction t under the coordinate axis of αβ 0;is α axis direction under αβ 0 coordinate axisSampling current instantaneous values of m transformer substation protection installation positions at the moment; i.e. i_mα(T) is the current instantaneous value of m transformer substation protection installation positions at α axial direction T sampling time under the coordinate axis of αβ 0, T is fundamental wave period time, i_m0(t) is a current instantaneous value of the protection installation place of the m transformer substation at the sampling moment of the 0-axis direction t under the coordinate axis of αβ 0;

(5) the protection device calculates αβ 0 positive sequence current at t sampling time of n transformer substation protection installation under coordinate axis

$i_{n\mathrm{\α}}^{+}\left(t\right)=0.5i_{n\mathrm{\α}}\left(t\right)-0.5i_{n\mathrm{\β}}(t-\frac{T}{4})$

$i_{n\mathrm{\β}}^{+}\left(t\right)=0.5i_{n\mathrm{\α}}(t-\frac{T}{4})+0.5i_{n\mathrm{\β}}\left(t\right)$

$i_{n0}^{+}\left(t\right)=i_{n0}\left(t\right)$

Wherein,is β axis direction under αβ 0 coordinate axisSampling the current instantaneous value of the n transformer substation protection installation positions at the moment; i.e. i_nβ(t) is a current instantaneous value of n transformer substation protection installation positions at the sampling time of β axis direction t under the coordinate axis of αβ 0;is α axis direction under αβ 0 coordinate axisSampling the current instantaneous value of the n transformer substation protection installation positions at the moment; i.e. i_nα(T) is the current instantaneous value of n transformer substation protection installation positions at α axial direction T sampling time under the coordinate axis of αβ 0, T is fundamental wave period time, i_n0(t) is a current instantaneous value of n transformer substation protection installation positions at the sampling time of the axis direction t of 0 under the coordinate axis of αβ 0;

(6) a, B, C phases of t sampling time of m transformer substation protection installation positions are calculated by the protection devicePositive sequence current transient

$\left[\begin{array}{c}{i}_{mA}^{+}\left(t\right)\\ i_{mB}^{+}\left(t\right)\\ i_{mC}^{+}\left(t\right)\end{array}\right]=1.5{\left[\begin{array}{ccc}1& -\frac{1}{2}& -\frac{1}{2}\\ 0& \frac{\sqrt{3}}{2}& -\frac{\sqrt{3}}{2}\\ \frac{1}{2}& \frac{1}{2}& \frac{1}{2}\end{array}\right]}^{-1}\left[\begin{array}{c}{i}_{m\mathrm{\α}}^{+}\left(t\right)\\ i_{m\mathrm{\β}}^{+}\left(t\right)\\ i_{m0}^{+}\left(t\right)\end{array}\right]$

(7) The protection device calculates A, B, C phase positive sequence current instantaneous values at t sampling time of n transformer substation protection installation positions

$\left[\begin{array}{c}{i}_{nA}^{+}\left(t\right)\\ i_{nB}^{+}\left(t\right)\\ i_{nC}^{+}\left(t\right)\end{array}\right]=1.5{\left[\begin{array}{ccc}1& -\frac{1}{2}& -\frac{1}{2}\\ 0& \frac{\sqrt{3}}{2}& -\frac{\sqrt{3}}{2}\\ \frac{1}{2}& \frac{1}{2}& \frac{1}{2}\end{array}\right]}^{-1}\left[\begin{array}{c}{i}_{n\mathrm{\α}}^{+}\left(t\right)\\ i_{n\mathrm{\β}}^{+}\left(t\right)\\ i_{n0}^{+}\left(t\right)\end{array}\right]$

(8) Protection device judgmentWhether the phase of the power transmission line is established or not is judged, if so, the protection device sends tripping signals to circuit breakers at two ends of the A-phase power transmission line; protection device judgmentWhether the phase of the power transmission line is established or not is judged, if so, the protection device sends tripping signals to circuit breakers at two ends of the B-phase power transmission line;protection device judgmentWhether the current is established or not is judged, if so, the protection device sends tripping signals to circuit breakers at two ends of the C-phase power transmission line; wherein k is₁Setting coefficient; i is_setIs a setting current threshold value.