CN103163424A - Line-to-ground fault distance measurement method based on instant sampling value - Google Patents

Abstract

The invention discloses a kind of line-to-ground fault distance measurement method based on instantaneous sampling value. The method of the present invention considers the influence of earth fault instantaneous voltage, to the differential equation

Difference discrete processing is carried out, fault distance is calculated using the ground fault phase voltage sampled value at three neighbouring sample moment, ground fault phase current sampling value, ground fault phase negative-sequence current sampled value and zero-sequence current sampled value. The method of the present invention realizes the precise measurement of fault distance by the ground fault phase electrical quantity instantaneous sampling value using three neighbouring sample moment; measuring speed is fast; measurement accuracy is not influenced by transition resistance and load current; measurement accuracy is better than the ground fault range measurement accuracy of traditional ground distance protection, the ground fault range measurement suitable for ground distance protection.

Description

A kind of line-to-ground fault distance measurement method based on instantaneous sampling value

Technical field

The present invention relates to the Relay Protection Technology in Power System field, particularly relate to a kind of line-to-ground fault distance measurement method based on instantaneous sampling value.

Background technology

The tradition ground distance protection thinks that earth fault is metallic earthing, to the differential equation

Carry out difference discrete, utilize instantaneous sampling value to calculate earth fault to the distance of protection installation place.In fact, even transmission line of electricity occurs through the direct earth fault of shaft tower, at the lower regional transition resistance of soil resistivity also near 10 Ω; The local transition resistance higher in resistivity can reach 30 Ω, or even higher.Transition resistance is non-vanishing make earth fault distance that traditional ground distance protection calculates with actual earth fault apart from there being larger error; if transition resistance is larger; easily cause the earth fault distance measure serious bigger than normal or less than normal; cause distance protection tripping or malfunction, having a strong impact on power network safety operation.

Summary of the invention

The object of the invention is to overcome the deficiency that prior art exists, a kind of line-to-ground fault distance measurement method based on instantaneous sampling value is provided.The inventive method utilizes three neighbouring samples earth fault phase electric parameters instantaneous value constantly to be grounded the accurate measurement of fault distance, and measuring accuracy is not subjected to the impact of transition resistance and load current, is applicable to the earth fault range observation of ground distance protection.

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

A kind of line-to-ground fault distance measurement method based on instantaneous sampling value; its step is as follows: earth fault phase voltage sampled value, earth fault phase current sampling value, earth fault phase negative-sequence current sampled value and the zero-sequence current sampled value of each sampling instant of protective device Real-time Collection line protection installation place, calculate fault distance x:

$x=\frac{u\left(t\right)i_2(t-\mathrm{\Δt})-u(t-\mathrm{\Δt})i_2\left(t\right)}{[l_1\frac{i_{\mathrm{set}1}\left(t\right)-i_{\mathrm{set}1}(t-\mathrm{\Δt})}{\mathrm{\Δt}}+r_1{i}_{\mathrm{set}2}\left(t\right)]i_2(t-\mathrm{\Δt})-[l_1\frac{i_{\mathrm{set}1}(t-\mathrm{\Δt})-i_{\mathrm{set}1}(t-2\mathrm{\Δt})}{\mathrm{\Δt}}+r_1{i}_{\mathrm{set}2}(t-\mathrm{\Δt})]i_2\left(t\right)}$

Wherein, i _Set1(t)=i (t)+k ₁i ₀(t); i _Set1(t-Δ t)=i (t-Δ t)+k ₁i ₀(t-Δ t); i _Set1(t-2 Δ t)=i (t-2 Δ t)+k ₁i ₀(t-2 Δ t); i _Set2(t)=i (t)+k ₂i ₀(t); i _Set2(t-Δ t)=i (t-Δ t)+k ₂i ₀(t-Δ t);

U (t), u (t-Δ t) are respectively the earth fault phase voltage sampled value of t, t-Δ t sampling instant; i ₂(t), i ₂(t-Δ t) is respectively the earth fault phase negative-sequence current sampled value of t, t-Δ t sampling instant; I (t), i (t-Δ t), i (t-2 Δ t) are respectively the earth fault phase current sampling value of t, t-Δ t, t-2 Δ t sampling instant; i ₀(t), i ₀(t-Δ t), i ₀(t-2 Δ t) is respectively the zero-sequence current sampled value of t, t-Δ t, t-2 Δ t sampling instant; Δ t is sampling interval; l ₁, r ₁Be respectively unit length transmission line of electricity positive sequence inductance, positive sequence resistance; l ₀, r ₀Be respectively unit length power transmission line zero-sequence inductance, zero sequence resistance.

The present invention has following positive achievement compared with prior art:

The inventive method utilizes three neighbouring samples earth fault phase electric parameters instantaneous value constantly to be grounded the accurate measurement of fault distance, measures essence

Degree is not subjected to the impact of transition resistance and load current, and measuring accuracy is better than the earth fault range measurement accuracy of traditional ground distance protection, is applicable to the earth fault distance measurement element of ground distance protection.

Description of drawings

Fig. 1 is for using circuit transmission system schematic diagram of the present invention.

Embodiment

Below comprehensive accompanying drawing technical scheme of the present invention is done further statement in detail.

The earth fault phase voltage sampled value of each sampling instant of protective device Real-time Collection line protection installation place, earth fault phase current sampling value, earth fault phase negative-sequence current sampled value and zero-sequence current sampled value.

After transmission line one-phase earth fault, t sampling instant earth fault phase electric parameters satisfies

$u\left(t\right)=u_f\left(t\right)+x{l}_1\frac{i\left(t\right)+k_1{i}_0\left(t\right)-i(t-\mathrm{\Δt})-k_1{i}_0(t-\mathrm{\Δt})}{\mathrm{\Δt}}+x{r}_1[i\left(t\right)+k_2{i}_0\left(t\right)]---\left(1\right)$

T-Δ t sampling instant earth fault phase electric parameters satisfies

$u(t-\mathrm{\Δt})=u_f(t-\mathrm{\Δt})+x{l}_1\frac{i(t-\mathrm{\Δt})+k_1{i}_0(t-\mathrm{\Δt})-i(t-2\mathrm{\Δt})-k_1{i}_0(t-2\mathrm{\Δt})}{\mathrm{\Δt}}+x{r}_1[i(t-\mathrm{\Δt})+k_2{i}_0(t-\mathrm{\Δt})]---\left(2\right)$

Wherein, u (t), u (t-Δ t) are respectively the earth fault phase voltage sampled value of t, t-Δ t sampling instant; I (t), i (t-Δ t), i (t-2 Δ t) are respectively the earth fault phase current sampling value of t, t-Δ t, t-2 Δ t sampling instant; i ₀(t), i ₀(t-Δ t), i ₀(t-2 Δ t) is respectively the zero-sequence current sampled value of t, t-Δ t, t-2 Δ t sampling instant; Δ t is sampling interval;

l ₁, r ₁Be respectively unit length transmission line of electricity positive sequence inductance, positive sequence resistance; l ₀, r ₀Be respectively unit length power transmission line zero-sequence inductance, zero sequence resistance; u _f(t), u _f(t-Δ t) is respectively the earth fault instantaneous voltage of t, t-Δ t sampling instant.

Due to the resistive ground fault, earth fault point voltage and the earth fault phase negative-sequence current same-phase of protecting the installation place, therefore, formula (1) and formula (2) can be exchanged into formula (3) and formula (4).

$u\left(t\right)={\mathrm{ki}}_2\left(t\right)+x{l}_1\frac{i\left(t\right)+k_1{i}_0\left(t\right)-i(t-\mathrm{\Δt})-k_1{i}_0(t-\mathrm{\Δt})}{\mathrm{\Δt}}+x{r}_1[i\left(t\right)+k_2{i}_0\left(t\right)]---\left(3\right)$

$u(t-\mathrm{\Δt})={\mathrm{ki}}_2(t-\mathrm{\Δt})+x{l}_1\frac{i(t-\mathrm{\Δt})+k_1{i}_0(t-\mathrm{\Δt})-i(t-2\mathrm{\Δt})-k_1{i}_0(t-2\mathrm{\Δt})}{\mathrm{\Δt}}+x{r}_1[i(t-\mathrm{\Δt})+k_2{i}_0(t-\mathrm{\Δt})]---\left(4\right)$

Wherein, i ₂(t), i ₂(t-Δ t) is respectively the earth fault phase negative-sequence current sampled value of t, t-Δ t sampling instant; K is scale-up factor.

Obtain earth fault by formula (3) and formula (4) simultaneous as follows apart from the x calculating formula to the earth fault of protecting the installation place:

$x=\frac{u\left(t\right)i_2(t-\mathrm{\Δt})-u(t-\mathrm{\Δt})i_2\left(t\right)}{[l_1\frac{i_{\mathrm{set}1}\left(t\right)-i_{\mathrm{set}1}(t-\mathrm{\Δt})}{\mathrm{\Δt}}+r_1{i}_{\mathrm{set}2}\left(t\right)]i_2(t-\mathrm{\Δt})-[l_1\frac{i_{\mathrm{set}1}(t-\mathrm{\Δt})-i_{\mathrm{set}1}(t-2\mathrm{\Δt})}{\mathrm{\Δt}}+r_1{i}_{\mathrm{set}2}(t-\mathrm{\Δt})]i_2\left(t\right)}$

Wherein, i _Set1(t)=i (t)+k ₁i ₀(t); i _Set1(t-Δ t)=i (t-Δ t)+k ₁i ₀(t-Δ t); i _Set1(t-2 Δ t)=i (t-2 Δ t)+k ₁i ₀(t-2 Δ t); i _Set2(t)=i (t)+k ₂i ₀(t); i _Set2(t-Δ t)=i (t-Δ t)+k ₂i ₀(t-Δ t).

The inventive method utilizes three neighbouring samples earth fault phase electric parameters instantaneous value constantly to be grounded the accurate measurement of fault distance, measures essence

Degree is not subjected to the impact of transition resistance and load current, and measuring accuracy is better than the earth fault range measurement accuracy of traditional ground distance protection, is applicable to the earth fault range observation of ground distance protection.

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

Claims (1)

1. line-to-ground fault distance measurement method based on instantaneous sampling value; its step is as follows: earth fault phase voltage sampled value, earth fault phase current sampling value, earth fault phase negative-sequence current sampled value and the zero-sequence current sampled value of each sampling instant of protective device Real-time Collection line protection installation place, calculate fault distance x:

$x=\frac{u\left(t\right)i_2(t-\mathrm{\Δt})-u(t-\mathrm{\Δt})i_2\left(t\right)}{[l_1\frac{i_{\mathrm{set}1}\left(t\right)-i_{\mathrm{set}1}(t-\mathrm{\Δt})}{\mathrm{\Δt}}+r_1{i}_{\mathrm{set}2}\left(t\right)]i_2(t-\mathrm{\Δt})-[l_1\frac{i_{\mathrm{set}1}(t-\mathrm{\Δt})-i_{\mathrm{set}1}(t-2\mathrm{\Δt})}{\mathrm{\Δt}}+r_1{i}_{\mathrm{set}2}(t-\mathrm{\Δt})]i_2\left(t\right)}$

Wherein, i _Set1(t)=i (t)+k ₁i ₀(t); i _Set1(t-Δ t)=i (t-Δ t)+k ₁i ₀(t-Δ t); i _Set1(t-2 Δ t)=i (t-2 Δ t)+k ₁i ₀(t-2 Δ t); i _Set2(t)=i (t)+k ₂i ₀(t); i _Set2(t-Δ t)=i (t-Δ t)+k ₂i ₀(t-Δ t);

U (t), u (t-Δ t) are respectively the earth fault phase voltage sampled value of t, t-Δ t sampling instant; i ₂(t), i ₂(t-Δ t) is respectively the earth fault phase negative-sequence current sampled value of t, t-Δ t sampling instant; I (t), i (t-Δ t), i (t-2 Δ t) are respectively the earth fault phase current sampling value of t, t-Δ t, t-2 Δ t sampling instant; i ₀(t), i ₀(t-Δ t), i ₀(t-2 Δ t) is respectively the zero-sequence current sampled value of t, t-Δ t, t-2 Δ t sampling instant; Δ t is sampling interval; l ₁, r ₁Be respectively unit length transmission line of electricity positive sequence inductance, positive sequence resistance; l ₀, r ₀Be respectively unit length power transmission line zero-sequence inductance, zero sequence resistance.