CN104950217A - Small-current grounding line selection method based on transient variation power direction principle - Google Patents

Abstract

The invention discloses a small-current grounding line selection method based on a transient variation power direction principle. According to the method, zero-sequence current and zero-sequence voltage variation power of high-speed sampling is utilized, the out-of-limit criterion of a 3U0 steady-state value is combined, so as to determine that a single-phase grounding fault occurs, and a grounding line is accurately selected by comparing the characteristic quantity of zero-sequence transient power of each branch when single-phase grounding occurs. The small-current grounding line selection method has the advantages of high reliability and accuracy and no limit of influence to grounding modes and compensation devices, an additional signal source is not needed, and the line selection accuracy and speed are increased.

Description

A kind of small current earthing wire-selecting method based on temporal variations amount power direction principle

Technical field

The invention belongs to relay protection of power system and technical field of automation, be specifically related to a kind of small current earthing wire-selecting method based on temporal variations amount power direction principle.

Background technology

Because small current neutral grounding system can not produce large short-circuit current when singlephase earth fault, and line voltage between phase and phase still keeps symmetrical, need not open failure circuit immediately, do not affect plurality of advantages such as the power supplies of load, therefore China 6 ~ 66kV power distribution network extensively adopts small current neutral grounding mode.But system long-play after single-phase earthing easily makes fault progression become or multipoint earthing short circuit at 2, and arc grounding also can cause total system superpotential, and then damage equipment, harm system safety operation, so must find faulty line to be excised in time.Because fault current during low current neutral grounding electric network single-phase earthing is very little; in addition distribution net work structure is complicated, and the method for operation is changeable, makes the failure line selection of power distribution network be subject to a lot of restrictions; this just causes difficulty to failure line selection protection, quick, accurately route selection of need taking measures on customs clearance.

The small current earthing wire-selecting method that current industry adopts has been summed up following three kinds: transient signal route selection method, steady-state signal route selection method and Injection Signal amount route selection method.Do not solving the accurate criterion problem of transient state with transient signal selection method wherein at present; Steady-state signal method affects seriously by system operation mode, centre-point earth mode, and route selection effect is less desirable; Injection Signal method not only needs to increase primary equipment, and can add outside extra potential faults to system, there is the reliable progress of disease of Injection Signal, the problem of acquisition process, actual effect is also not ideal enough simultaneously, is especially resembling in this special running environment of underground coal mine.The more important thing is that above three class methods all cannot accomplish the earth point location that multistage ladder is powered collaborative.

Summary of the invention

For solving prior art Problems existing; the invention provides a kind of small current earthing wire-selecting method based on temporal variations amount power direction principle, quick and precisely to determine ground connection branch road, instruct fault to remove fast; Accident prevention expands, proterctive equipment and personal safety.

The present invention is concrete by the following technical solutions.

Based on a small current earthing wire-selecting method for temporal variations amount power direction principle, it is characterized in that, described selection method comprises the following steps:

(1) mutual inductor is utilized to gather the zero-sequence current 3I of each branch road in electric substation ₀with residual voltage 3U ₀;

(2) detect whether line single phase grounding failure occurs by the out-of-limit criterion of residual voltage, the out-of-limit criterion of described residual voltage is:

3U ₀﹥ U _set, and keep setting-up time; Wherein, 3U ₀for residual voltage steady-state quantity, U _setfor the startup of setting differentiates definite value;

(3) after judging that circuit single-phase earthing occurs, extract the front 60 milliseconds of sampled datas stored of current time immediately, utilize following formulae discovery to go out each branch road transient zero-sequence power features amount and each grounding characteristic quantity Cn, Cn is preserved;

$Cn={\mathrm{\Σ}}_{x=1}^{x=P}\left(310\right(x)-310(x-1))1*\left(3U0\right(x)-3U0(x-1));$

Wherein, X represents the sequence number of the sampled data stored in 60 milliseconds, and P represents the sum of the sampled data stored in 60 milliseconds;

(4) positive and negative according to branch road transient zero-sequence power features amount Cn, each branch road is divided into two groups, and transient zero-sequence power features amount Cn is one group of negative branch road is ground connection branch road group, and transient zero-sequence power features amount Cn is positive branch road is ungrounded branch road;

(5) according to primary system topological structure, in the ground connection branch road group that step (4) obtains, find out its middle distance power end branch road be farthest judged to actual ground connection branch road.

The preferred following scheme of the present invention:

In step (2), setting-up time is 25 milliseconds, starts and differentiates that definite value is 18V.

The small current earthing wire-selecting method that the present invention is based on temporal variations amount power direction principle has very high reliability and accuracy, do not affect by earthing mode, compensation system, signal source that need not be extra, improve accuracy and the route selection speed of route selection, can accomplish that earth point is located simultaneously, significant for special power utilization environment (as underground coal mine is powered).

Accompanying drawing explanation

Fig. 1 is ground connection experimental system schematic diagram;

Fig. 2 is the small current earthing wire-selecting method process flow diagram based on temporal variations amount power direction principle of the present invention.

Embodiment

Below in conjunction with accompanying drawing and example, the present invention is described in further detail.

The present invention is concrete by the following technical solutions.

Below for the distribution network system shown in Fig. 1, introduce small current earthing wire-selecting method of the present invention.Shown in Fig. 1, power supply is the step-down transformer of a neutral by arc extinction coil grounding, and lower band three grades of buses, every grade of bus is all with load.Zero-sequence current (the 3I at every bar line outlet place is measured in real time according to Fig. 1 ₀) and bus residual voltage (3U ₀), determine singlephase earth fault occurs in conjunction with the out-of-limit criterion of 3U0 steady-state value, accurately select ground path by the zero sequence transient power characteristic quantity of each branch road during comparison generation single-phase earthing.Small current earthing wire-selecting method based on temporal variations amount power direction principle disclosed in the present application as shown in Figure 2, comprises the following steps:

Step 1, by the zero-sequence current 3I0 of branch road each in mutual inductor acquisition system (line0 ~ line3-3-2 in accompanying drawing 1, totally 17 branch roads) and residual voltage 3U0, circulate and can hold the sampling buffer of three cycle data widths stored in one.

Step 2, detect whether line single phase grounding failure occurs by the out-of-limit criterion of residual voltage, after system zero sequence voltage has gathered at every turn, zero-sequence voltage samples is extracted out at equal intervals by 1 millisecond, fourier algorithm is utilized to calculate residual voltage steady-state value 3U0, differentiate that definite value Uset compares with startup, if 3U0>Uset also keeps 25 milliseconds, in 60 milliseconds that namely think just now, just there occurs singlephase earth fault, start earthing wire-selecting logic immediately.Preferably start in the embodiment of the application and differentiate that definite value Uset is 18V.

Step 3, after judging that circuit single-phase earthing occurs, extract the front 60 milliseconds of high-speed sample data stored of current time immediately, adopt formula:

$Cn={\mathrm{\Σ}}_{x=1}^{x=P}\left(310\right(x)-310(x-1))*\left(3U0\right(x)-3U0(x-1));$

Calculate each branch road transient zero-sequence power features amount, as grounding characteristic quantity Cn, preserved by Cn, X represents the sequence number of the sampled data stored in 60 milliseconds, and P represents the sum of the sampled data stored in 60 milliseconds.

Step 4, line-selected earthing device are divided into two groups according to the positive and negative of data in Cn circuit branch road, and result is negative one group and is judged to ground path group.

During single-phase single-point grounding line fault, ground connection group membership characteristic quantity should present:

Total number of ground connection group circuit is no more than total class of track number (maximum ground connection group circuit number is no more than 4 in FIG).

Example:

When K5 point ground connection in FIG, ground path group should be line0, line2, line2-2, line2-2-4;

If during K4 point ground connection, ground path group should be line0, line3, line3-3;

Step 5, according to primary system topological structure, in the ground connection branch road group that step 4 obtains, find out its middle distance power end branch road be farthest judged to actual ground connection branch road:

K5 point ground connection in FIG, because line2-2-4 is near load side, farthest, the zero-sequence current at K5 place can flow through other several circuits in group to distance power supply, line2-2-4 can be selected as ground path according to criterion line selection apparatus;

If K4 point ground connection, in ground path group, line3-3 is near load side, and farthest, the zero-sequence current at K4 place can flow through other several circuits in group to distance power supply, line3-3 can be selected as ground path according to criterion line selection apparatus.

The case study on implementation more than provided is in order to illustrate the present invention and its practical application, not any pro forma restriction is done to the present invention, any one professional and technical personnel, not departing from the scope of technical solution of the present invention, does certain modification according to above techniques and methods and changes the Equivalent embodiments of working as and being considered as equivalent variations.

Claims (3)

1. the small current earthing wire-selecting method based on temporal variations amount power direction principle, it is characterized in that: the method utilizes zero-sequence current and the residual voltage variable quantity power of high-speed sampling, determine singlephase earth fault occurs in conjunction with the out-of-limit criterion of residual voltage 3U0 steady-state value, accurately select ground path by the zero sequence transient power characteristic quantity of each branch road during comparison generation single-phase earthing.

2. based on a small current earthing wire-selecting method for temporal variations amount power direction principle, it is characterized in that, described selection method comprises the following steps:

(1) mutual inductor is utilized to gather the zero-sequence current 3I of each branch road in electric substation ₀with residual voltage 3U ₀;

(2) detect whether line single phase grounding failure occurs by the out-of-limit criterion of residual voltage, the out-of-limit criterion of described residual voltage is:

3U ₀﹥ U _set, and keep setting-up time; Wherein, 3U ₀for residual voltage steady-state quantity, U _setfor the startup of setting differentiates definite value;

(3) after judging that circuit single-phase earthing occurs, extract the front 60 milliseconds of sampled datas stored of current time immediately, utilize following formulae discovery to go out each branch road transient zero-sequence power features amount and each grounding characteristic quantity Cn, Cn is preserved;

$Cn={\mathrm{\Σ}}_{x=1}^{x=P}(310\left(x\right)-310(x-1))*(3U0\left(x\right)-3U0(x-1));$

Wherein, X represents the sequence number of the sampled data stored in 60 milliseconds, and P represents the sum of the sampled data stored in 60 milliseconds;

(4) positive and negative according to branch road transient zero-sequence power features amount Cn, each branch road is divided into two groups, and transient zero-sequence power features amount Cn is one group of negative branch road is ground connection branch road group, and transient zero-sequence power features amount Cn is positive branch road is ungrounded branch road;

(5) according to primary system topological structure, in the ground connection branch road group that step (4) obtains, find out its middle distance power end branch road be farthest judged to actual ground connection branch road.

3. small current earthing wire-selecting method according to claim 2, is characterized in that:

In step (2), setting-up time is 25 milliseconds, starts and differentiates that definite value is 18V.