CN104090210A - Different-phase cross-line ground fault single-terminal location method for double-circuit lines - Google Patents

Abstract

The invention discloses different-phase cross-line ground fault single-terminal location method for double-circuit lines. Firstly, the fault phase voltage, the fault phase current and the zero-sequence current at the protection installation position of the circuit line I of the double-circuit lines on the same pole are measured, the zero-sequence compensation current of the circuit line I of the double-circuit lines on the same pole is calculated according to influences of zero-sequence mutual induction between the lines, voltage of a different-phase cross-line ground fault point of the double-circuit lines is calculated, the angle of voltage drop from the protection installation position of the circuit line I of the double-circuit lines on the same pole to the different-phase cross-line ground fault point of the double-circuit lines is calculated in a one-dimension searching method after dropping of voltage from each point on the circuit line I of the double-circuit lines on the same pole to the different-phase cross-line ground fault point of the double-circuit lines, precise distance measurement of different-phase cross-line ground faults of the double-circuit lines is achieved by means of the along-line voltage drop phase characteristics, influences of zero-sequence mutual induction between the lines, transition resistance and load currents on fault distance measurement precision are eliminated, and high capacity of resisting influences of the transition resistance and load currents is achieved.

Description

The non-same famous prime minister's cross-line earth fault method of single end distance measurement of double-circuit line

Technical field

The present invention relates to Relay Protection Technology in Power System field, specifically relate to a kind of based on along the non-same famous prime minister's cross-line earth fault method of single end distance measurement of line drop phase propetry double-circuit line.

Background technology

Divide from the electric parameters used of finding range, the method for fault localization can be divided into two large classes: both-end distance measuring and single end distance measurement.Two-terminal Fault Location method is to utilize transmission line of electricity two ends electric parameters to determine the method for transmission line malfunction position, and it need to obtain opposite end electric parameters by passage, therefore strong to the dependence of passage, is also subject to the impact of both-end sampling value synchronization in actual use.Single end distance measurement method is only to utilize the electric current and voltage data of transmission line of electricity one end to determine a kind of method of transmission line malfunction position, because it only needs an end data, need not communication and data synchronizer, operating cost is low and algorithm stable, therefore in mid & low-voltage line, has obtained application widely.At present, method of single end distance measurement is mainly divided into two classes, and a class is traveling wave method, and another kind of is impedance method.Traveling wave method utilizes the transmission character of fault transient travelling wave to find range, and precision is high, not affected by the method for operation, excessive resistance etc., but very high to sampling rate requirement, needs special wave recording device, does not obtain at present substantial application.Impedance method is utilized the voltage after fault, the impedance that the magnitude of current calculates fault loop, the characteristic being directly proportional to impedance according to line length is found range, range measurement principle is simple and reliable, but while being applied to analyses for double circuits on same tower singlephase earth fault one-end fault ranging, distance accuracy is subject to zero-sequence mutual inductance between trouble spot transition resistance and line to be affected serious.Between analyses for double circuits on same tower line, have zero-sequence mutual inductance, zero-sequence mutual inductance can exert an influence to zero sequence compensation coefficient, and then causes impedance method range finding resultant error bigger than normal.If there is single-phase high resistance earthing fault in analyses for double circuits on same tower, be subject to zero-sequence mutual inductance and high transition resistance combined influence between line, impedance method range finding result usually exceeds total track length or without range finding result, abort situation information accurately cannot be provided, cause line fault line walking difficulty, be unfavorable for fault discharge and the fast quick-recovery of line powering fast.

Summary of the invention

The object of the invention is to overcome the deficiency that prior art exists, provide a kind of double-circuit line based on along line drop phase propetry non-same famous prime minister's cross-line earth fault method of single end distance measurement.The method is taken into account the impact of zero-sequence mutual inductance between line and is calculated the zero sequence compensation electric current on analyses for double circuits on same tower I loop line road, calculate the non-same famous prime minister's cross-line earth fault point voltage of double-circuit line, adopt linear search method to calculate successively every bit on analyses for double circuits on same tower I loop line road and return the angle of route protection installation place to the voltage drop of the non-same famous prime minister's cross-line earth fault of double-circuit line to the voltage drop hysteresis analyses for double circuits on same tower I of the non-same famous prime minister's cross-line earth fault of double-circuit line, utilize the precision ranging that realizes the non-same famous prime minister's cross-line earth fault of double-circuit line along line drop phase propetry, eliminate zero-sequence mutual inductance between line, the impact on fault localization precision of transition resistance and load current, there is the ability of very strong anti-transition resistance and load current impact, non-fault range finding dead band when the non-same famous prime minister's cross-line earth fault of double-circuit line occurs the outlet of protection positive dirction, there is very high one-end fault ranging precision.

For completing above-mentioned purpose, the present invention adopts following technical scheme:

The non-same famous prime minister's cross-line earth fault method of single end distance measurement of double-circuit line, comprises following sequential steps:

(1) protector measuring analyses for double circuits on same tower I returns the fault phase voltage of route protection installation place fault phase electric current and zero-sequence current wherein, φ=I loop line road A phase, I loop line road B phase, I loop line road C phase;

(2) protective device calculates the zero sequence compensation electric current on analyses for double circuits on same tower I loop line road

$\mathrm{\Δ}\stackrel{\·}{I}={\stackrel{\·}{I}}_{\mathrm{I\φ}}+\frac{Z_{I0}-Z_{I1}}{Z_{I1}}{\stackrel{\·}{I}}_{I0}+\frac{Z_m}{3Z_{I1}}{\stackrel{\·}{I}}_{I0}(-\cos (r_1+r_2-\mathrm{\β})-j\sin (r_1+r_2-\mathrm{\β}))$

Wherein, $r_1={\sin }^{-1}\left(\frac{a_3{b}_1}{\sqrt{{\left(a_3{b}_1\right)}^3+{\left(a_1{b}_3\right)}^2}}\right);r_2={\sin }^{-1}\left(\frac{a_1{b}_2-a_2{b}_1}{\sqrt{{\left(a_3{b}_1\right)}^2+{\left(a_1{b}_3\right)}^2}}\right);a_1=\mathrm{Re}\left(\frac{{\stackrel{\·}{U}}_{\mathrm{I\φ}}}{Z_{I1}}\right);$ $b_1=\mathrm{Im}\left(\frac{{\stackrel{\·}{U}}_{\mathrm{I\φ}}}{Z_{I1}}\right);a_2=\mathrm{Re}({\stackrel{\·}{I}}_{\mathrm{I\φ}}+\frac{Z_{I0}-Z_{I1}}{Z_{I1}}{\stackrel{\·}{I}}_{I0});b_2=\mathrm{Im}({\stackrel{\·}{I}}_{\mathrm{I\φ}}+\frac{Z_{I0}-Z_{I1}}{Z_{I1}}{\stackrel{\·}{I}}_{I0});a_3=b_3=\left|\frac{Z_m}{3Z_{I1}}{\stackrel{\·}{I}}_{I0}\right|;$ z _mfor the zero-sequence mutual inductance between analyses for double circuits on same tower I loop line road and analyses for double circuits on same tower II loop line road; Z _i0for the zero sequence impedance on analyses for double circuits on same tower I loop line road; Z _i1for the positive sequence impedance on analyses for double circuits on same tower I loop line road; φ=I loop line road A phase, I loop line road B phase, I loop line road C phase; $\mathrm{Re}\left(\frac{{\stackrel{\·}{U}}_{\mathrm{I\φ}}}{Z_{I1}}\right)$ For $\frac{{\stackrel{\·}{U}}_{\mathrm{I\φ}}}{Z_{I1}}$ Real part; $\mathrm{Im}\left(\frac{{\stackrel{\·}{U}}_{\mathrm{I\φ}}}{Z_{I1}}\right)$ For $\frac{{\stackrel{\·}{U}}_{\mathrm{I\φ}}}{Z_{I1}}$ Imaginary part; $\mathrm{Re}({\stackrel{\·}{I}}_{\mathrm{I\φ}}+\frac{Z_{I0}-Z_{I1}}{Z_{I1}}{\stackrel{\·}{I}}_{I0})$ For ${\stackrel{\·}{I}}_{\mathrm{I\φ}}+\frac{Z_{I0}-Z_{I1}}{Z_{I1}}{\stackrel{\·}{I}}_{I0}$ Real part; $\mathrm{Im}({\stackrel{\·}{I}}_{\mathrm{I\φ}}+\frac{Z_{I0}-Z_{I1}}{Z_{I1}}{\stackrel{\·}{I}}_{I0})$ For ${\stackrel{\·}{I}}_{\mathrm{I\φ}}+\frac{Z_{I0}-Z_{I1}}{Z_{I1}}{\stackrel{\·}{I}}_{I0}$ Imaginary part; J is complex operator;

(3) protective device calculates the non-same famous prime minister's cross-line earth fault point voltage of double-circuit line

${\stackrel{\·}{U}}_f={\stackrel{\·}{U}}_{\mathrm{I\φ}}-\frac{\mathrm{Im}\left(\frac{{\stackrel{\·}{U}}_{\mathrm{I\φ}}}{{\stackrel{\·}{I}}_{I0}+{\stackrel{\·}{I}}_{I0}(-\cos (r_1+r_2-\mathrm{\β})-j\sin (r_1+r_2-\mathrm{\β}))}\right)}{\mathrm{Im}\left(\frac{Z_{I1}\mathrm{\Δ}\stackrel{\·}{I}}{{\stackrel{\·}{I}}_{I0}+{\stackrel{\·}{I}}_{I0}(-\cos (r_1+r_2-\mathrm{\β})-j\sin (r_1+r_2-\mathrm{\β}))}\right)}{Z}_{I1}\mathrm{\Δ}\stackrel{\·}{I}$

(4) to choose fault distance initial value be l to protective device _x, calculate the l that goes back to route protection installation place apart from analyses for double circuits on same tower I _xthe fault phase voltage of point wherein, l is that analyses for double circuits on same tower I returns line length; Z _i1for the positive sequence impedance on analyses for double circuits on same tower I loop line road; for the zero sequence compensation electric current on analyses for double circuits on same tower I loop line road;

(5) protective device calculates leading angle ρ (l _x);

(6) fault distance l _xwith fixed step size Δ, l increases progressively, and returns to step (4) and calculates successively each l on analyses for double circuits on same tower I loop line road _xpoint leading angle ρ (l _x), until analyses for double circuits on same tower I returns total track length;

(7) protective device is chosen a certain l on analyses for double circuits on same tower I loop line road _xpoint leading angle ρ (l _x) drop in (90 °---90 °) scope, and its adjacent next l _x+ Δ l is ordered leading angle ρ (l _x+ Δ l) drops in (90 °---270 °) scope, and the centre position of these two points is the non-same famous prime minister's cross-line earth fault of double-circuit line; Wherein, Δ l is fixed step size, desirable Δ l=0.001l; L is that analyses for double circuits on same tower I returns line length.

Feature of the present invention and technological achievement:

The inventive method is only used single-ended single back line electric parameters; do not need to introduce another loop line road electric parameters; Protection secondary circuit is separate does not go here and there mutually; strengthen fault localization result accuracy; and fault localization precision is not subject to the impact of power system operation mode, in the time that larger change occurs power system operation mode, still there is very high distance accuracy.The inventive method is taken into account the impact of zero-sequence mutual inductance between line, has eliminated the impact of zero-sequence mutual inductance on fault localization precision between line.

The inventive method adopts linear search method to calculate successively every bit on analyses for double circuits on same tower I loop line road and returns the angle of route protection installation place to the voltage drop of the non-same famous prime minister's cross-line earth fault of double-circuit line to the voltage drop hysteresis analyses for double circuits on same tower I of the non-same famous prime minister's cross-line earth fault of double-circuit line, utilize the precision ranging that realizes the non-same famous prime minister's cross-line earth fault of double-circuit line along line drop phase propetry, eliminate zero-sequence mutual inductance between line, the impact on fault localization precision of transition resistance and load current, there is the ability of very strong anti-transition resistance and load current impact, non-fault range finding dead band when the non-same famous prime minister's cross-line earth fault of double-circuit line occurs the outlet of protection positive dirction, there is very high one-end fault ranging precision.

Brief description of the drawings

Fig. 1 is application analyses for double circuits on same tower transmission system schematic diagram of the present invention.

Embodiment

Fig. 1 is application analyses for double circuits on same tower transmission system schematic diagram of the present invention.In Fig. 1, PT is voltage transformer (VT); CT is current transformer.

The non-same famous prime minister's cross-line earth fault method of single end distance measurement of double-circuit line, comprises following sequential steps:

(1) protector measuring analyses for double circuits on same tower I returns the fault phase voltage of route protection installation place fault phase electric current and zero-sequence current wherein, φ=I loop line road A phase, I loop line road B phase, I loop line road C phase.

(2) protective device calculates the zero sequence compensation electric current on analyses for double circuits on same tower I loop line road

$\mathrm{\Δ}\stackrel{\·}{I}={\stackrel{\·}{I}}_{\mathrm{I\φ}}+\frac{Z_{I0}-Z_{I1}}{Z_{I1}}{\stackrel{\·}{I}}_{I0}+\frac{Z_m}{3Z_{I1}}{\stackrel{\·}{I}}_{I0}(-\cos (r_1+r_2-\mathrm{\β})-j\sin (r_1+r_2-\mathrm{\β}))$

Wherein, $r_1={\sin }^{-1}\left(\frac{a_3{b}_1}{\sqrt{{\left(a_3{b}_1\right)}^3+{\left(a_1{b}_3\right)}^2}}\right);r_2={\sin }^{-1}\left(\frac{a_1{b}_2-a_2{b}_1}{\sqrt{{\left(a_3{b}_1\right)}^2+{\left(a_1{b}_3\right)}^2}}\right);a_1=\mathrm{Re}\left(\frac{{\stackrel{\·}{U}}_{\mathrm{I\φ}}}{Z_{I1}}\right);$ $b_1=\mathrm{Im}\left(\frac{{\stackrel{\·}{U}}_{\mathrm{I\φ}}}{Z_{I1}}\right);a_2=\mathrm{Re}({\stackrel{\·}{I}}_{\mathrm{I\φ}}+\frac{Z_{I0}-Z_{I1}}{Z_{I1}}{\stackrel{\·}{I}}_{I0});b_2=\mathrm{Im}({\stackrel{\·}{I}}_{\mathrm{I\φ}}+\frac{Z_{I0}-Z_{I1}}{Z_{I1}}{\stackrel{\·}{I}}_{I0});a_3=b_3=\left|\frac{Z_m}{3Z_{I1}}{\stackrel{\·}{I}}_{I0}\right|;$ z _mfor the zero-sequence mutual inductance between analyses for double circuits on same tower I loop line road and analyses for double circuits on same tower II loop line road; Z _i0for the zero sequence impedance on analyses for double circuits on same tower I loop line road; Z _i1for the positive sequence impedance on analyses for double circuits on same tower I loop line road; φ=I loop line road A phase, I loop line road B phase, I loop line road C phase; $\mathrm{Re}\left(\frac{{\stackrel{\·}{U}}_{\mathrm{I\φ}}}{Z_{I1}}\right)$ For $\frac{{\stackrel{\·}{U}}_{\mathrm{I\φ}}}{Z_{I1}}$ Real part; $\mathrm{Im}\left(\frac{{\stackrel{\·}{U}}_{\mathrm{I\φ}}}{Z_{I1}}\right)$ For $\frac{{\stackrel{\·}{U}}_{\mathrm{I\φ}}}{Z_{I1}}$ Imaginary part; $\mathrm{Re}({\stackrel{\·}{I}}_{\mathrm{I\φ}}+\frac{Z_{I0}-Z_{I1}}{Z_{I1}}{\stackrel{\·}{I}}_{I0})$ For ${\stackrel{\·}{I}}_{\mathrm{I\φ}}+\frac{Z_{I0}-Z_{I1}}{Z_{I1}}{\stackrel{\·}{I}}_{I0}$ Real part; $\mathrm{Im}({\stackrel{\·}{I}}_{\mathrm{I\φ}}+\frac{Z_{I0}-Z_{I1}}{Z_{I1}}{\stackrel{\·}{I}}_{I0})$ For ${\stackrel{\·}{I}}_{\mathrm{I\φ}}+\frac{Z_{I0}-Z_{I1}}{Z_{I1}}{\stackrel{\·}{I}}_{I0}$ Imaginary part; J is complex operator.

(3) protective device calculates the non-same famous prime minister's cross-line earth fault point voltage of double-circuit line

${\stackrel{\·}{U}}_f={\stackrel{\·}{U}}_{\mathrm{I\φ}}-\frac{\mathrm{Im}\left(\frac{{\stackrel{\·}{U}}_{\mathrm{I\φ}}}{{\stackrel{\·}{I}}_{I0}+{\stackrel{\·}{I}}_{I0}(-\cos (r_1+r_2-\mathrm{\β})-j\sin (r_1+r_2-\mathrm{\β}))}\right)}{\mathrm{Im}\left(\frac{Z_{I1}\mathrm{\Δ}\stackrel{\·}{I}}{{\stackrel{\·}{I}}_{I0}+{\stackrel{\·}{I}}_{I0}(-\cos (r_1+r_2-\mathrm{\β})-j\sin (r_1+r_2-\mathrm{\β}))}\right)}{Z}_{I1}\mathrm{\Δ}\stackrel{\·}{I}$

(4) to choose fault distance initial value be l to protective device _x, calculate the l that goes back to route protection installation place apart from analyses for double circuits on same tower I _xthe fault phase voltage of point wherein, l is that analyses for double circuits on same tower I returns line length; Z _i1for the positive sequence impedance on analyses for double circuits on same tower I loop line road.

(5) protective device calculates leading angle ρ (l _x).

(6) fault distance l _xwith fixed step size Δ, l increases progressively, and calculates successively each l on analyses for double circuits on same tower I loop line road _xpoint leading angle ρ (l _x), until analyses for double circuits on same tower I returns total track length.

Work as l _xpoint goes back to route protection installation place from analyses for double circuits on same tower I and changes to the process of the non-same famous prime minister's cross-line earth fault of double-circuit line, leading angle ρ (l _x) drop in (90 ° 90 °) scope always; Work as l _xchange to analyses for double circuits on same tower I loop line road to the process of side bus from the non-same famous prime minister's cross-line earth fault of double-circuit line, leading angle ρ (l _x) drop in (90 ° 270 °) scope always.Before and after the non-same famous prime minister's cross-line earth fault of double-circuit line, leading angle ρ (l _x) can enter (90 ° 270 °) by (90 ° 90 °) sudden change, the precision ranging that utilizes this to realize the non-same famous prime minister's cross-line earth fault of double-circuit line along line drop phase propetry is as follows:

(7) protective device is chosen a certain l on analyses for double circuits on same tower I loop line road _xpoint leading angle ρ (l _x) drop in (90 °---90 °) scope, and its adjacent next l _x+ Δ l is ordered leading angle ρ (l _x+ Δ l) drops in (90 °---270 °) scope, and the centre position of these two points is the non-same famous prime minister's cross-line earth fault of double-circuit line; Wherein, Δ l is fixed step size, desirable Δ l=0.001l; L is that analyses for double circuits on same tower I returns line length.

The inventive method is only used single-ended single back line electric parameters; do not need to introduce another loop line road electric parameters; Protection secondary circuit is separate does not go here and there mutually; strengthen fault localization result accuracy; and fault localization precision is not subject to the impact of power system operation mode, in the time that larger change occurs power system operation mode, still there is very high distance accuracy.The inventive method is taken into account the impact of zero-sequence mutual inductance between line, has eliminated the impact of zero-sequence mutual inductance on fault localization precision between line.

The inventive method adopts linear search method to calculate successively every bit on analyses for double circuits on same tower I loop line road and returns the angle of route protection installation place to the voltage drop of the non-same famous prime minister's cross-line earth fault of double-circuit line to the voltage drop hysteresis analyses for double circuits on same tower I of the non-same famous prime minister's cross-line earth fault of double-circuit line, utilize the precision ranging that realizes the non-same famous prime minister's cross-line earth fault of double-circuit line along line drop phase propetry, eliminate zero-sequence mutual inductance between line, the impact on fault localization precision of transition resistance and load current, there is the ability of very strong anti-transition resistance and load current impact, non-fault range finding dead band when the non-same famous prime minister's cross-line earth fault of double-circuit line occurs the outlet of protection positive dirction, there is very high one-end fault ranging precision.

The foregoing is only preferred embodiment of the present invention; but protection scope of the present invention is not limited to this; any be familiar with those skilled in the art the present invention disclose technical scope in, the variation that can expect easily or replacement, within all should being encompassed in protection scope of the present invention.

Claims (1)

1. the non-same famous prime minister's cross-line earth fault method of single end distance measurement of double-circuit line, is characterized in that, comprises following sequential steps:

(1) protector measuring analyses for double circuits on same tower I returns the fault phase voltage of route protection installation place fault phase electric current and zero-sequence current wherein, φ=I loop line road A phase, I loop line road B phase, I loop line road C phase;

(2) protective device calculates the zero sequence compensation electric current on analyses for double circuits on same tower I loop line road

$\mathrm{\Δ}\stackrel{\·}{I}={\stackrel{\·}{I}}_{\mathrm{I\φ}}+\frac{Z_{I0}-Z_{I1}}{Z_{I1}}{\stackrel{\·}{I}}_{I0}+\frac{Z_m}{3Z_{I1}}{\stackrel{\·}{I}}_{I0}(-\cos (r_1+r_2-\mathrm{\β})-j\sin (r_1+r_2-\mathrm{\β}))$

Wherein, $r_1={\sin }^{-1}\left(\frac{a_3{b}_1}{\sqrt{{\left(a_3{b}_1\right)}^3+{\left(a_1{b}_3\right)}^2}}\right);r_2={\sin }^{-1}\left(\frac{a_1{b}_2-a_2{b}_1}{\sqrt{{\left(a_3{b}_1\right)}^2+{\left(a_1{b}_3\right)}^2}}\right);a_1=\mathrm{Re}\left(\frac{{\stackrel{\·}{U}}_{\mathrm{I\φ}}}{Z_{I1}}\right);$ $b_1=\mathrm{Im}\left(\frac{{\stackrel{\·}{U}}_{\mathrm{I\φ}}}{Z_{I1}}\right);a_2=\mathrm{Re}({\stackrel{\·}{I}}_{\mathrm{I\φ}}+\frac{Z_{I0}-Z_{I1}}{Z_{I1}}{\stackrel{\·}{I}}_{I0});b_2=\mathrm{Im}({\stackrel{\·}{I}}_{\mathrm{I\φ}}+\frac{Z_{I0}-Z_{I1}}{Z_{I1}}{\stackrel{\·}{I}}_{I0});$ z _mfor the zero-sequence mutual inductance between analyses for double circuits on same tower I loop line road and analyses for double circuits on same tower II loop line road; Z _i0for the zero sequence impedance on analyses for double circuits on same tower I loop line road; Z _i1for the positive sequence impedance on analyses for double circuits on same tower I loop line road; φ=I loop line road A phase, I loop line road B phase, I loop line road C phase; for real part; for imaginary part; $\mathrm{Re}({\stackrel{\·}{I}}_{\mathrm{I\φ}}+\frac{Z_{I0}-Z_{I1}}{Z_{I1}}{\stackrel{\·}{I}}_{I0})$ For ${\stackrel{\·}{I}}_{\mathrm{I\φ}}+\frac{Z_{I0}-Z_{I1}}{Z_{I1}}{\stackrel{\·}{I}}_{I0}$ Real part; $\mathrm{Im}({\stackrel{\·}{I}}_{\mathrm{I\φ}}+\frac{Z_{I0}-Z_{I1}}{Z_{I1}}{\stackrel{\·}{I}}_{I0})$ For imaginary part; J is complex operator;

(3) protective device calculates the non-same famous prime minister's cross-line earth fault point voltage of double-circuit line

${\stackrel{\·}{U}}_f={\stackrel{\·}{U}}_{\mathrm{I\φ}}-\frac{\mathrm{Im}\left(\frac{{\stackrel{\·}{U}}_{\mathrm{I\φ}}}{{\stackrel{\·}{I}}_{I0}+{\stackrel{\·}{I}}_{I0}(-\cos (r_1+r_2-\mathrm{\β})-j\sin (r_1+r_2-\mathrm{\β}))}\right)}{\mathrm{Im}\left(\frac{Z_{I1}\mathrm{\Δ}\stackrel{\·}{I}}{{\stackrel{\·}{I}}_{I0}+{\stackrel{\·}{I}}_{I0}(-\cos (r_1+r_2-\mathrm{\β})-j\sin (r_1+r_2-\mathrm{\β}))}\right)}{Z}_{I1}\mathrm{\Δ}\stackrel{\·}{I}$

(4) to choose fault distance initial value be l to protective device _x, calculate the l that goes back to route protection installation place apart from analyses for double circuits on same tower I _xthe fault phase voltage of point wherein, l is that analyses for double circuits on same tower I returns line length; Z _i1for the positive sequence impedance on analyses for double circuits on same tower I loop line road; for the zero sequence compensation electric current on analyses for double circuits on same tower I loop line road;

(5) protective device calculates leading angle ρ (l _x);

(6) fault distance l _xwith fixed step size Δ, l increases progressively, and returns to step (4) and calculates successively each l on analyses for double circuits on same tower I loop line road _xpoint leading angle ρ (l _x), until analyses for double circuits on same tower I returns total track length;

(7) protective device is chosen a certain l on analyses for double circuits on same tower I loop line road _xpoint leading angle ρ (l _x) drop in (90 °---90 °) scope, and its adjacent next l _x+ Δ l is ordered leading angle ρ (l _x+ Δ l) drops in (90 °---270 °) scope, and the centre position of these two points is the non-same famous prime minister's cross-line earth fault of double-circuit line; Wherein, Δ l is fixed step size, desirable Δ l=0.001l; L is that analyses for double circuits on same tower I returns line length.