CN102004208B - Method for rapidly distinguishing CT wire break in bus protection - Google Patents

Abstract

The invention discloses a new bus protection method for realizing rapid CT wire break based on current variation and a complete of technical scheme. In the invention, the variations of the original current sampling values of connecting units of a bus are compared with a preset threshold to form the number of upward changed current units, the number of downward changed units and the number of units without change. By means of comparison between the number of three changed units and the variation direction of braking current, normal CT wire break and faults of the bus are distinguished, thus the CT wire break can be effectively judged and misoperation for bus protection can be prevented.

Description

The method of Quick CT broken string in the bus protection

Technical field

The present invention relates to the method for Quick CT broken string in a kind of bus protection, belong to the power system automation technology field.

Background technology

The CT broken string method of discrimination that is used at present bus protection is spill current greater than CT breakage lock device definite value and through after a while time-delay.The method just monitors spill current, the electric current at interval that bus protection connects is not differentiated, and can not locate the interval of CT broken string and separate.Owing to needing second time-delay of level just can judge the CT broken string, tending to cause differential protection misoperation for large current intervals CT broken string.

Summary of the invention

Technical matters to be solved by this invention provides a kind of rapid CT broken string that is applicable to bus protection and differentiates new method, can differentiate correctly, rapidly the CT broken string.

The present invention is achieved by the following technical solutions, and the method for Quick CT broken string in a kind of bus protection may further comprise the steps:

Step 1, data acquisition:

To respectively connecting the A of interval (mother, circuit, transformer etc.) on the bus, B, the C three-phase current carries out current sample with constant sample frequency;

Step 2, the variable quantity that calculates each every phase current in interval and zero-sequence current:

Calculate respectively the A that respectively connects interval (mother, circuit, transformer etc.) on the bus, B, C three-phase current variable quantity,

ΔI _nΦ＝|I _nΦ|-|I _nΦ-T|

Wherein, I _{N Φ}Be front sampled point, I _{N Φ-T}Be the last fortnight ripple sampled point, Φ is respectively A, and B, C three-phase, n represent that n on the bus connects interval, Δ I _{N Φ}Be illustrated in the difference between currents of electric current with upper two corresponding sampled points of cycle of current sampling point;

As Δ I _{N Φ}＞K*In is for upwards changing: NU _{N Φ}=1;

As Δ I _{N Φ}＜-K*In is for descending mutually direction: ND _{N Φ}=1;

When | Δ I _{N Φ}|＜K*In is unchanged: NU _{N Φ}=0, ND _{N Φ}=0;

Wherein In is the rated secondary current value; NU is that electric current upwards changes, and ND is that electric current changes downwards, the fixed coefficient of K for setting, and scope is generally at 0.01-1;

The calculating of zero-sequence current:

I _n0＝I _na+I _nb+I _nc；

Wherein, I _N0Be the current zero sequence sampled point at n interval, I _Na, I _Nc, I _NcBe n interval current sampling point;

When | I _N0| there is zero-sequence current in＞K*In n interval, its corresponding zero-sequence current sign NL _n=1;

Step 3, the poor stream of calculating and stalling current and variable quantity thereof:

Calculate the poor stream on the bus:

${\mathrm{Id}}_{\mathrm{\Φ}}=\left|\underset{n=1}{\overset{N}{\mathrm{\Σ}}}{I}_{\mathrm{n\Φ}}\right|$

${\mathrm{If}}_{\mathrm{\Φ}}=\left|\underset{n=1}{\overset{N}{\mathrm{\Σ}}}{I}_{\mathrm{n\Φ}}\right|$

Wherein, the sampled value of the current poor stream of Id, I is the current sampled value at interval,, Φ is respectively A, and B, C three-phase, N are the total unit number of bus;

The sampled value of the current braking stream of If

ΔIf _Φ＝If _Φ-If _Φ-T；

Wherein Δ If is the stalling current variable quantity, If _Φ-TFor the stalling current sampled value of the first two cycle is worked as Δ If _Φ＞Iset is that stalling current upwards changes: NFU _Φ=1;

NFU is that stalling current upwards changes, the fixed value of Iset for setting, and scope is generally 0.1In-2In;

Step 4, curent change quantitative statistics:

The current change quantity statistics:

$\mathrm{<figure-callout\; id="1"\; label="N"\; filenames="110105142331.png,110105142457.png"\; state="\{\{state\}\}">N</figure-callout>}1=\underset{n=1}{\overset{3N}{\mathrm{\&Sigma;}}}{\mathrm{NU}}_{\mathrm{n\&Phi;}};$

$N2=\underset{n=1}{\overset{3N}{\mathrm{\&Sigma;}}}{\mathrm{ND}}_{\mathrm{n\&Phi;}};$

$N3=\underset{n=1}{\overset{N}{\mathrm{\&Sigma;}}}{\mathrm{NL}}_{n0};$

$N4=\underset{n=1}{\overset{3}{\mathrm{\&Sigma;}}}{\mathrm{NFU}}_{\mathrm{n\&Phi;}};$

Wherein: N1 is the sum that current change quantity makes progress, and N2 is the downward sum of current change quantity, and N3 is the sum that zero-sequence current is arranged, and N4 is the sum that the stalling current variable quantity is arranged.

Step 5, rapid CT broken string logic are judged:

Under CT breaks the condition of not declaring:

1) not CT broken string feature if the sum that current change quantity makes progress (N1) greater than 0, is then thought, do not carry out the rapid CT broken string and differentiate;

2) not CT broken string feature if the downward sum (N2) of current change quantity greater than 1, is then thought, do not carry out the rapid CT broken string and differentiate; If the downward bus (N2) of current change quantity equals at 1 o'clock, record the interval of curent change and separate;

3) not CT broken string feature if the sum of zero-sequence current (N3) greater than 1, is then thought, do not carry out the rapid CT broken string and differentiate; If the sum of zero-sequence current (N3) equals at 1 o'clock, record the interval of zero-sequence current;

4) not CT broken string feature if the sum of stalling current variable quantity (N4) greater than 0, is then thought, do not carry out the rapid CT broken string and differentiate;

5) produce poor stream (Id _Φ) separate will with condition 2) record separate consistent, otherwise be not the CT feature that breaks;

6) interval of curent change interval (being condition 2) record) to produce the interval that interval (being condition 3) is recorded with zero sequence) consistent, otherwise be not CT broken string feature;

7) three-phase current at curent change interval relatively: vicissitudinous phase current is all less than other phase current, and the electric current of the phase that changes is less than K*In (In is the secondary rated current), and all the other biphase current amplitudes are greater than K times of this spacing current maximal phase amplitude.If this condition does not satisfy, it then not CT broken string feature;

Satisfy above condition, then think CT broken string feature, all satisfy above condition more than 4 or 4 continuously, then be judged as the CT broken string.

The invention has the beneficial effects as follows: adopt the sampled point algorithm because the rapid CT of this invention broken string is differentiated,, therefore differentiate the CT broken string time very short, can before the bus protection misoperation, effectively declare and CT broken string, lockable bus protection.Bus protection malfunction when the method can effectively prevent large electric current broken string.

Description of drawings

Fig. 1 bus-bar system figure;

Fig. 2 electric current CT figure that breaks;

Fig. 3 guard method FB(flow block) of the present invention;

Embodiment

According to Figure of description technical scheme of the present invention is elaborated.

The invention discloses a kind of current change quantity bus rapid CT thread-breakage protecting, may further comprise the steps (as shown in Figure 3):

Step 1, data acquisition:

To the A of each linkage unit on the bus, B, the C three-phase current carries out current sample with constant sample frequency.All linkage units are seen shown in the accompanying drawing 1 on the bus: take single busbar as example, linkage unit is I1, I2, and I3, I1 wherein, I2, I3 may be defined as main transformer, circuit etc.

Step 2, calculate the every phase current variable quantity in each unit and zero-sequence current:

Calculate respectively the A of each linkage unit on the bus, B, C three-phase current variable quantity, then current change quantity is compared with default definite value (K*In) and is judged the curent change direction, and remembers the change direction of every phase current.Those skilled in the art know that the current change quantity approximate data is all multiple, and preferred but be not limited to following computing method in the present invention:

ΔI _nΦ＝|I _nΦ|-|I _nΦ-T|

I is front sampled value, I _{N Φ-T}Be the last fortnight ripple sampled value, Φ is respectively A, and B, C three-phase, n represent n linkage unit on the bus, and Δ I is illustrated in the electric current of current sampled value and the difference between currents of upper two corresponding sampled values of cycle.Linkage unit as shown in Figure 1, each cell current variable quantity for take I1 C mutually as example:

Δ I _1cj=I _1c-I _1cj-T, I wherein _1cjBe current C phase current sampling value,

I _1c-TBe the corresponding sampled value of upper two cycles, the A of I1, the B phase, I2, the A of I3, B, C phase compute classes is seemingly.

The Δ I that obtains _1aj, Δ I _1bj, Δ I _1cj, Δ I _2aj, Δ I _2bj, Δ I _2cj, Δ I _3aj, Δ I _3bj, Δ I _3cjCurrent change quantity, difference representative unit 1, the A of unit 2 and unit 3, B, C phase current variable quantity.Through after the following processing, form electric current and upwards change, electric current descends change direction mutually, three kinds of curent change directions of the unchanged grade of electric current.Specifically be compared as follows (with Δ I _1cjBe example):

Δ I _1cj＞K*In, wherein In is the rated secondary current value.Then electric current upwards changes, NU _1c=1; Δ I _1cj＜-K*In then changes downwards for electric current, ND _1c=1; | Δ I _1cj|＜=K*In is that electric current is unchanged, NU _1c=0, ND _1c=0.After relatively, the change direction of electric current has all judged.

Calculate the zero-sequence current of each unit: I _N0=I _Na+ I _Nb+ I _Nc

Wherein, I _N0Be the current zero sequence sampled point of n branch road, I _Na, I _Nc, I _NcBe n branch road current sampling point;

The zero-sequence current of each unit is that Unit the 1st is example: I ₁₀=I _1a+ I _1b+ I _1c

Obtain the zero-sequence current I of unit ₁₀, I ₂₀, I ₃₀The branch road that exists through determining zero-sequence current after the following processing specifically is compared as follows (take Unit the 1st as example):

I ₁₀During＞k*In, Unit the 1st is declared and is had zero-sequence current, NL ₁=1; Otherwise declare non-zero-sequence current, NL ₁=0;

Step 3, the poor stream of calculating and stalling current and variable quantity thereof:

Calculate poor stream and the stalling current of bus:

${\mathrm{Id}}_{\mathrm{\&Phi;}}=\underset{n=1}{\overset{N}{\mathrm{\&Sigma;}}}{I}_{\mathrm{n\&Phi;}}$

${\mathrm{If}}_{\mathrm{\&Phi;}}=\underset{n=1}{\overset{N}{\mathrm{\&Sigma;}}}\left|I_{\mathrm{n\&Phi;}}\right|$

Obtain poor stream and the stalling current of the every phase of bus protection, take C mutually as example:

Id _cj＝I _1cj+I _2cj+I _3cj；

If _cj＝|I _1cj|+|I _2cj|+|I _3cj|；

Calculate the variable quantity of stalling current: Δ If _Φ=If _Φ-If _Φ-T

Δ If wherein _ΦBe stalling current variable quantity, If _Φ-TBe the stalling current of the first two cycle, If _ΦStalling current sampled value for current sampling point.

Take C mutually as example: Δ If _Cj=If _Cj-If _Cj-T

Obtain A, B, C three-phase system streaming current variable quantity, and compare with Iset (fixed value of setting is generally at 0.1In-2In) is differentiated the variation of stalling current, take C mutually as example:

As Δ If _CjDuring＞Iset, stalling current upwards changes, NFU _c=1; Otherwise the undirected upper variation of stalling current, NFU _c=0;

A by that analogy, the poor stream of B phase and the variation NFU of stalling current level stalling current _a, NFU _b

Step 4, curent change quantitative statistics:

The statistics current change quantity is mainly added up electric current upwards (N1), and the varied number of (N2), and stalling current downwards is the quantity of (N4) variation upwards, and the quantity of zero-sequence current generation unit (N3).Take 3 unit that accompanying drawing 1 is connected as example:

N1＝NU _1a+NU _1b+NU _1c+NU _2a+NU _2b+NU _2c?NU _3a+NU _3b+NU _3c；

N2＝ND _1a+ND _1b+ND _1c+ND _2a+ND _2b+ND _2c?ND _3a+ND _3b+ND _3c；

N3＝NL ₁+NL ₂+NL ₃；

N4＝NFU _a+NFU _b+NFU _c；

Step 5, rapid CT broken string logic are judged

Under CT breaks the condition of not declaring:

1) not CT broken string feature if the sum that current change quantity makes progress (N1) greater than 0, is then thought, do not carry out the rapid CT broken string and differentiate;

2) not CT broken string feature if the downward sum (N2) of current change quantity greater than 1, is then thought, do not carry out the rapid CT broken string and differentiate; If the downward bus (N2) of current change quantity equals at 1 o'clock, record the interval of curent change and separate.

3) not CT broken string feature if the sum of zero-sequence current (N3) greater than 1, is then thought, do not carry out the rapid CT broken string and differentiate; If the sum of zero-sequence current (N3) equals at 1 o'clock, record the interval of zero-sequence current.

4) not CT broken string feature if the sum of stalling current variable quantity (N4) greater than 0, is then thought, do not carry out the rapid CT broken string and differentiate;

5) produce poor stream (Id _Φ) separate will with condition 2) record separate consistent, otherwise be not the CT feature that breaks;

6) interval of curent change interval (being condition 2) record) to produce the interval that interval (being condition 3) is recorded with zero sequence) consistent, otherwise be not CT broken string feature;

7) three-phase current at curent change interval relatively: vicissitudinous phase current is all less than other phase current, and the electric current of the phase that changes is less than K*In (In is the secondary rated current), and all the other biphase current amplitudes are greater than K times of this spacing current maximal phase amplitude.If this condition does not satisfy, it then not CT broken string feature

Satisfy above condition, then think CT broken string feature, multiple spot all satisfies above condition continuously, then is judged as the CT broken string.

Record ripple schematic diagram breaks mutually for bus the 1st unit C in the diagram when being illustrated in figure 2 as the CT broken string, and C is large electric current CT broken string mutually, and the poor stream that produces during broken string is greater than the breakage lock device definite value and also greater than bus protection action definite value.

Formula above utilizing then can be calculated: N1=0, N2=1, N3=1, N4=0.Condition 1,2,3,4 satisfy.Poor the separate consistent of living separate and curent change of miscarrying, condition 5 satisfies.The unit of curent change is consistent with the unit that zero sequence exists, and condition 6 satisfies.Dropped to K*In once behind the electric current of the C phase broken string, and the amplitude of A and B phase current all the K of maximum current amplitude doubly more than, condition 7 satisfies.So criterion is very fast declares and that the 1st unit C breaks mutually and the locking bus protection.If without this criterion, bus protection can be done in malfunction.

Below announced the present invention with preferred embodiment, so it is not intended to limiting the invention, all take to be equal to replace or technical scheme that the scheme of equivalent transformation obtains, all drop in protection scope of the present invention.

Claims (1)

1. the method for Quick CT broken string in the bus protection is characterized in that, may further comprise the steps:

1) data acquisition:

To respectively connecting the A at interval on the bus, B, the C three-phase current carries out current sample with constant sample frequency;

2) calculate variable quantity and the zero-sequence current of each every phase current in interval:

Calculate respectively the A of each linkage unit on the bus, B, C three-phase current variable quantity △ I _{N Φ},

As △ I _{N Φ}K*In, for upwards changing: NU _{N Φ}=1;

As △ I _{N Φ}＜-K*In is downward variation: ND _{N Φ}=1;

When | △ I _{N Φ}|＜K*In is unchanged: NU _{N Φ}=0, ND _{N Φ}=0;

Wherein In is the rated secondary current value; NU is that electric current upwards changes, and ND is that electric current changes downwards, the fixed coefficient of K for setting, and scope is 0.01-1, Φ is respectively A, B, C three-phase;

The calculating I of zero-sequence current _N0,

When | I _N0| there is zero-sequence current in K*In n interval: NL _n=1, NL is the zero-sequence current sign;

3) calculate poor stream and stalling current and variable quantity thereof:

Calculate the poor stream on the bus:

Calculate poor stream Id and stalling current If on the bus, and calculate the variable quantity △ If of stalling current,

As △ If _ΦIset is that stalling current upwards changes: NFU _Φ=1;

NFU is that stalling current upwards changes, the fixed value of Iset for setting, and scope is 0.1In-2In;

4) curent change quantitative statistics:

The current change quantity statistics:

$N1=\underset{n=1}{\overset{3N}{\mathrm{\&Sigma;}}}{\mathrm{NU}}_{\mathrm{n\&Phi;}};$

$N2=\underset{n=1}{\overset{3N}{\mathrm{\&Sigma;}}}{\mathrm{ND}}_{\mathrm{n\&Phi;}};$

$N3=\underset{n=1}{\overset{N}{\mathrm{\&Sigma;}}}{\mathrm{NL}}_{n0};$

$N4=\underset{n=1}{\overset{3}{\mathrm{\&Sigma;}}}{\mathrm{NFU}}_{\mathrm{n\&Phi;}};$

Wherein: N1 is the sum that current change quantity makes progress, and N2 is the downward sum of current change quantity, and N3 is the sum that zero-sequence current is arranged, and N4 is the sum that the stalling current variable quantity is arranged, and N is the total unit number of bus;

5) rapid CT broken string logic is judged:

Under CT breaks the condition of not declaring:

51) not CT broken string feature if the sum that current change quantity makes progress (N1) greater than 0, is then thought, do not carry out the rapid CT broken string and differentiate;

52) not CT broken string feature if the downward sum (N2) of current change quantity greater than 1, is then thought, do not carry out the rapid CT broken string and differentiate; If the downward bus (N2) of current change quantity equals at 1 o'clock, record the interval of curent change and separate;

53) not CT broken string feature if the sum of zero-sequence current (N3) greater than 1, is then thought, do not carry out the rapid CT broken string and differentiate; If the sum of zero-sequence current (N3) equals at 1 o'clock, record the interval of zero-sequence current;

54) not CT broken string feature if the sum of stalling current variable quantity (N4) greater than 0, is then thought, do not carry out the rapid CT broken string and differentiate;

55) produce poor stream (Id _Φ) separate will with step 52) record separate consistent, otherwise be not the CT feature that breaks;

56) step 52) interval of record will with step 53) interval recorded is consistent, otherwise is not CT broken string feature;

57) three-phase current at curent change interval relatively: vicissitudinous phase current is all less than other phase current, and the electric current of the phase that changes is less than K*In, all the other biphase current amplitudes if this condition does not satisfy, then are not CT broken string feature greater than K times of this spacing current maximal phase amplitude;

Satisfy above condition, then think CT broken string feature, all satisfy above condition more than 4 or 4 continuously, then be judged as the CT broken string.

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