CN105403779B

CN105403779B - A kind of DC line fault recognition methods based on polar curve current gradient sum

Info

Publication number: CN105403779B
Application number: CN201510633235.9A
Authority: CN
Inventors: 束洪春; 马聪; 田鑫萃
Original assignee: Kunming University of Science and Technology
Current assignee: Kunming University of Science and Technology
Priority date: 2015-09-29
Filing date: 2015-09-29
Publication date: 2019-01-04
Anticipated expiration: 2035-09-29
Also published as: CN105403779A

Abstract

The invention relates to a direct current line fault identification method based on the sum of pole-line current gradients, and belongs to the technical field of power system relay protection. After a metallic ground fault occurs in the HVDC transmission line, the previous current value is subtracted from the next current value of the adjacent sampling points measured by the measurement terminal, and the ratio of the difference between the two and the sampling interval is defined as the current gradient. The fixed length before the current sampling point is selected as the time window length, and the current gradients of all sampling intervals are summed, and the obtained value is defined as the current gradient sum of the current sampling point. When the sum of the current gradients of five consecutive sampling points at the measuring end is greater than the set value, it is judged that an internal fault has occurred; when the sum of the current gradients of five consecutive sampling points of the measuring end is less than the set value, it is judged that an external fault has occurred. Fault. A large number of simulations show that the method is reliable and accurate for fault type identification.

Description

A kind of DC line fault recognition methods based on polar curve current gradient sum

Technical field

The present invention relates to field of relay protection in power, specifically a kind of direct current based on polar curve current gradient sum Line fault recognition methods.

Background technique

Direct current transportation is more and more widely used in power Transmission due to its peculiar advantage.DC power transmission line Distance, across area surroundings complexity, the probability to break down is big.For DC line fault, failure process and its dynamic Characteristic and DC control effect are closely related, so that DC control system is to DC line protection, especially to back-up protection Influence can not be ignored.The route protection of present engineering practice is mainly to make by the traveling-wave protection of core of electrical change rate For main protection.The protection in distal end high resistant tends to that tripping occurs.Therefore, it is necessary to study new direct current protecting calculation Method can not only identify route high resistive fault, and actuation time is much smaller than existing differential protection.Using smoothing reactor and The physical boundary that DC filter is constituted is to the attenuation of high fdrequency component, so that line-internal failure and external fault measuring end Electric current high frequency content have differences.Algorithm provided by the invention is namely based on this principle, existing 10KHz is sampled blunt Flow Line protection, fault zone can be identified by not needing lightning stroke disturbance ecology element.

Summary of the invention

The technical scheme is that after metallic earthing failure occurs on HVDC transmission line, due to flat wave electricity The electrical boundary that anti-device and filter are constituted has very strong attenuation to high-frequency signal, to line-internal failure and route outside High fdrequency component contained by the electric current that portion's failure measuring end measures is different.The fault current difference of neighbouring sample point is measured to measuring end Current gradient is constructed, the current gradient summation in window all sampling intervals when to before current sampling point.If measuring end continuous five Sampled point current gradient and both greater than setting valve, then line-internal failure has occurred in judgement；Otherwise, judgement has occurred outside route Portion's failure.Accordingly, line fault recognition methods is obtained.

It is characterized in that line-internal failure and route external fault current gradient and different specific step is as follows:

(1) it is using the gradient of polar curve electric current calculating current neighbouring sample point amplitude variation

Di (k)=(i (k)-i (k-1))/Δ t (1)

In formula: the current sampled point that k is indicated, △ t indicates the sampling interval, as unit of ms.

(2) with S (k) indicate current gradient and, i.e.,

And obtain the stepping type of (2)

S (k)=S (k-1)+(i (k)-i (k-1))/Δ t

Wherein, i (k), i (k-1) indicate the current value on sampled point k, k-1, sampling number when N is in window, S_setIt protects Protect definite value；

(3) under the sample rate of 10kHz.According to formula (2), the fault element criterion for obtaining S (k) construction is

|S(k)|≥S_set (3)

When continuous three points of starting element are both greater than setting valve, then starting is protected, after starting, first value is denoted as S (k).If having in 4 sampling intervals of broadening | S (k) |, | S (k+1) |, | S (k+2) |, | S (k+3) | and | S (k+4) | it is all larger than S_set, S_setIt is taken as 1.5pu, then is judged as line fault, it is on the contrary then be judged as route external fault.

The beneficial effects of the present invention are:

(1) this method is to realize seeking for polar curve current gradient sum based on real time data, thus to identify line-internal event Barrier and external fault, criterion are succinct.

(2) can alleviate using du/dt as the traveling-wave protection of core since transition electricity has occurred in the discreteness or route of sampling Hinder the case where slightly higher high resistive fault does not reach protection definite value and makes relay fail.

Detailed description of the invention

Fig. 1 is its measuring end fault current of electrode line road failure and its S (k).

Fig. 2 is the fault current and its S (k) of rectification side AC system singlephase earth fault anode route measuring end.

Fig. 3 is the wide ± 800KV DC transmission system structure chart of cloud.Rectification side exchanges side reactive compensation capacity with inverter side Respectively 3000 and 3040Mvar, every pole convertor unit are composed in series by 2 12 pulse inverters, and DC power transmission line overall length is 1500km.Route two sides fill the smoothing reactor of 400mH, and DC filter is 12/24/36 three-tuned filter, and rectification flanks Earth polar total track length is 109km, and inverter side ground electrode circuit overall length is 112km.

Specific embodiment

Embodiment 1: ± 800KV DC power transmission line as shown in figure 3, DC line boundary by route depending on the equivalent circuit that enters As shown in Figure 4.Metallic earthing failure, sample frequency 10kHz occur for electrode line distance M end 10km.

(1) gradient and S (k) are sought to fault current according to step (1)~(2).

(2) obtain S (k), S (k+1), S (k+2), S (k+3), S (k+4) be followed successively by 10.35 respectively, 14.81,14.96, 16.96,18.56, it is all larger than 1.5pu, is judged as line-internal failure criterion.

Embodiment 2: ± 800KV DC power transmission line as shown in figure 3, DC line boundary by route depending on the equivalent circuit that enters As shown in Figure 4.Electrode line distance M end 750km, occurs ground fault, and transition resistance is 100 Ω.

(1) gradient and S (k) are sought to fault current according to step (1)~(2).

(2) obtain S (k), S (k+1), S (k+2), S (k+3), S (k+4) be followed successively by 13.100 respectively, 3.630,4.29, 4.561,4.613, it is all larger than 1.5pu, is judged as line-internal failure criterion.

Embodiment 3: ± 800KV DC power transmission line as shown in figure 3, DC line boundary by route depending on the equivalent circuit that enters As shown in Figure 4.Side outlet failure is rectified, transition resistance is 100 Ω.

(1) gradient and S (k) are sought to fault current according to step (1)~(2).

(2) obtain S (k), S (k+1), S (k+2), S (k+3), S (k+4) be followed successively by 0.035 respectively, 0.289,0.422, 0.641,0.633, it is less than 1.5pu, is judged as route external fault criterion.

Claims

1. a DC line fault identification method based on the polar current gradient sum, it is characterized in that: after the metallic grounding fault occurs on the high-voltage direct current transmission line, because the electrical boundary that the smoothing reactor and the filter are formed has to the high-frequency signal. Therefore, the high-frequency components contained in the current measured at the measuring end are different for the internal fault of the line and the external fault of the line; the current gradient is constructed for the fault current difference between adjacent sampling points measured at the measuring end. Sum the current gradients of all sampling intervals in the time window before the current sampling point. If the sum of the current gradients of five consecutive sampling points at the measurement end is greater than the set value, then it is judged that an internal fault has occurred; otherwise, it is judged that an external fault has occurred. ;

Specific steps are as follows:

(1) Using the polar current to calculate the gradient of the amplitude change of the adjacent sampling points of the current:

di(k)=(i(k)-i(k-1))/Δt (1)

In the formula: k represents the current sampling point, △t represents the sampling interval, in ms;

(2) The current gradient sum is represented by S(k), namely:

And get the recursion of (2):

S(k)=S(k-1)+(i(k)-i(k-1))/Δt

Among them, i(k) and i(k-1) represent the current values at sampling points k and k-1, N is the number of sampling points in the time window, and S _set protects the fixed value;

(3) Under the sampling rate of 10kHz, according to formula (2), the criterion for the faulty element constructed by S(k) is:

|S(k)|≥S _set (3)

When three consecutive points of the starting element are greater than the set value, the protection starts. After starting, the first value is recorded as S(k). (k+1)|, |S(k+2)|, |S(k+3)|, and |S(k+4)| are all greater than S _set , and S _set is set to 1.5pu, then it is judged that the line is faulty , otherwise it is judged as an external fault of the line.