CN104459280A - Method for extracting resistance current of metal oxide arrester (MOA) - Google Patents

Abstract

The invention provides a method for extracting the resistance current of a metal oxide arrester (MOA). By the adoption of the method, the influence of harmonic voltages on the resistance current can be eliminated more effectively, the error of i1r and i3r is reduced ultimately, hence, the operation condition of the MOA can be reflected more accurately, and safety operation of a power electrical system is guaranteed. The principle that the capacity current and the capacitance are in proportion is used for solving the capacity current, the equivalent resistance R1 is used for eliminating the harmonic influence, hence, the resistance current (ir) can be calculated more accurately, the ir is used for calculating the i1r and the i3r through an FFT algorithm, and finally on-line monitoring of the MOA is achieved.

Description

A kind of Resistive Current of Metal Oxide Surge Arrester extracting method

Technical field:

The invention belongs to electrical equipment field tests, particularly relate to a kind of Resistive Current of Metal Oxide Surge Arrester extracting method.

Background technology:

Metal oxide arrester (metal oxide arrester; MOA) there is numerous good characteristics; it commercially instead of traditional SiC lightning arrester gradually; but its shortcoming and defect also exposed day by day simultaneously; MOA is generally and works online; affect (such as temperature, humidity etc.) by extraneous factor and aging, degradation phenomena can occur gradually, last thoroughly forfeiture protective effect even causes electrical network to occur short circuit accident.And annual MOA in electric power electric system to be carried out power-off inspection be a comparatively loaded down with trivial details job, therefore, be unfavorable for fixing a breakdown timely and effectively hidden danger, this seriously inhibits the development of China's intelligent grid, be necessary to carry out Real-Time Monitoring and anticipation to its ruuning situation.During MOA works online and runs, total leakage current can due to aging and certain increase of having made moist, but increase not obvious.Fundamental harmonic resistant leakage current (i in total leakage current _1r) and 3 current in resistance property (i _3r) great changes will take place in meeting, therefore, selects i when carrying out on-line monitoring to lightning arrester _1rand i _3rbe suitable for as main anticipation Indexes Comparison.But there is harmonic voltage interference in actual electric network, i _3rwith amplitude and the initial phase angle change of harmonic wave interference voltage, present larger fluctuation, therefore, get rid of i _1rand i _3rthe i that middle harmonic wave interference voltage produces _1rand i _3rcomposition, just can carry out on-line monitoring to MOA preferably.

More to capacity current algorithm research at present, wherein mainly contain following two kinds.Patent measures MOA current in resistance property (CN102621371A) by counterclockwise for impressed voltage phase shift 90 ° based on capacitive current compensation method, utilize the orthogonal property of capacity current and current in resistance property, get rid of the capacitive composition in total current, just can obtain current in resistance property.But when not considering to contain harmonic components in impressed voltage, the capacity current that harmonic wave interference voltage produces.A kind of Resistive Current of Metal Oxide Surge Arrester extracting method (CN101986164A), puts on respectively by identical voltage on 1F electric capacity and MOA, and its capacity current produced is the ratio of electric capacity, can obtain capacity current, and then calculates current in resistance property.But the method is not analyzed the composition of i3r, this algorithm is used to calculate i _3rcan change along with the change of harmonic voltage, therefore can produce certain error.

Summary of the invention:

For solving the deficiency that said method exists, the present invention proposes a kind of new Resistive Current of Metal Oxide Surge Arrester extracting method, and the more effective harmonic carcellation voltage of the method, on the impact of current in resistance property, finally reduces i _1rand i _3rerror, thus more accurately reflect MOA ruuning situation, ensure that the safe operation of electric power electric system.

Concrete technical scheme of the present invention is as follows:

A kind of Resistive Current of Metal Oxide Surge Arrester extracting method, the method comprises the following steps:

The inventive method can be divided and is classified as following three steps:

1) obtain by mutual inductor or capacitive divider voltage signal u (t) putting on MOA, and acted on known capacitance C ₂on.Use centre path current sensor or seal in formula current sensor and obtain the capacity current i that MOA leakage current i (t) and known capacitance C2 produces _c2, solve MOA crystal boundary electric capacity C according to capacity current and current in resistance property orthogonality principle ₁and by capacity current value ic that MOA produces ₁.

2) part producing fundamental harmonic resistant leakage current in MOA non-linear resistance is equivalent to linear resistance R1, remainder is equivalent to R2.Utilize MOA small area analysis section model, by fft algorithm, remove the fundamental harmonic resistant leakage current composition that harmonic voltage produces, thus calculate comparatively accurate equivalent resistance R ₁value.

3) use capacity current and the proportional principle of its electric capacity, solve capacity current, and utilize equivalent resistance R1 removal harmonic effects, and then accurate Calculation current in resistance property (i more _r), then to i _rby fft algorithm, calculate i _1rand i _3r, finally realize MOA on-line monitoring.

The present invention adopts above technical scheme compared with prior art, the beneficial effect had:

After this method removes the current in resistance property that produces on equivalent resistance of harmonic voltage, the fundamental harmonic resistant leakage current calculated and the aging reaction of third harmonic current in resistance property to MOA more accurate.User of service, according to to MOA performance requirement, in conjunction with result of calculation, accurately can determine the replacing construction of MOA, accomplishes to change in time aging MOA.

Within normally every 2 years, pull down lightning arrester about the fault detect of MOA in current electric system and carry out preventive trial, because lightning arrester is numerous, therefore need to expend huge human and material resources and financial resources.Use this algorithm will no longer need the monitoring in every 2 years of lightning arrester in circuit, and MOA potential faults can be got rid of timely and effectively, the work efficiency of raising, reduce the replacing number of times of MOA, saved funds.The lightening surge preventing protection of China's intelligent grid is played a significant role.

Accompanying drawing illustrates:

Fig. 1 is fundamental current phase diagram.

Fig. 2 is MOA voltage-current relationship figure.

Embodiment:

Below in conjunction with accompanying drawing, technical scheme of the present invention is described in further detail:

Resistive Current of Metal Oxide Surge Arrester extracting method of the present invention, can divide and be classified as following three steps:

The first step,

Obtain by mutual inductor or capacitive divider voltage signal u (t) be applied on MOA to be measured, voltage signal u (t) obtained is applied to known capacitance C ₂upper (note: C ₂value can be arbitrary value, convenient for measuring its capacity current signal produced, its value at 10 μ about F, as C ₂value 10 μ F); Centre path current sensor or the formula current sensor of sealing in is utilized to obtain respectively by known capacitance C ₂capacity current i _c2with by leakage current signal i (t) of MOA to be measured, according to current in resistance property with capacity current orthogonality principle is known there is formula (1) relation:

$\begin{array}{c}{\∫}_0^T{i}_{C2}\left(t\right)i\left(t\right)\mathrm{dt}={\∫}_0^T{i}_{C2}\left(t\right)[i_r\left(t\right)+\frac{C1}{C2}{i}_{C2}\left(t\right)]\mathrm{dt}\\ =\frac{C1}{C2}{\∫}_0^T{i_{C2}}^2\left(t\right)\mathrm{dt}\end{array}---\left(1\right)$

Therefore, through type (1) can derive formula (2), by known capacitance C2, capacity current i by C2 _c2and pass through leakage current i (t) of MOA, obtain MOA real crystal boundary capacitance C ₁,

$C1=\frac{C2{\∫}_0^T{i}_{C2}\left(t\right)i\left(t\right)\mathrm{dt}}{{\∫}_0^T{i_{C2}}^2\left(t\right)\mathrm{dt}}---\left(2\right)$

Ratio due to the capacity current produced by different electric capacity equals the ratio of electric capacity, therefore by the capacity current i of MOA _c1available formula (3) is expressed as follows:

$i_{C1}=\frac{C1}{C2}{i}_{C2}---\left(3\right)$

Second step,

Linear resistance R is equivalent to by producing fundamental harmonic resistant leakage current part in MOA non-linear resistance ₁, remainder is equivalent to non-linear resistance R ₂;

MOA equivalent resistance R ₁calculate by formula (4):

$R_1=u_1/(i_{r1}-\mathrm{\Σ}\frac{I_{\mathrm{MX}1}}{\sqrt{2}})---\left(4\right)$

I in formula (4) _r1for fundamental harmonic resistant leakage current, I _mx1for x subharmonic is in the amplitude of the current in resistance property at first-harmonic place, u ₁for fundamental voltage in line voltage;

Fundamental harmonic resistant leakage current i _r1solve as follows: realize fft algorithm (fft algorithm and fast fourier algorithm) by programmable array, utilize fft algorithm to decompose leakage current i (t) that MOA to be measured produces, calculate fundamental current i _x1with fundamental current phase theta; Due to fundamental current i _x1, fundamental current phase theta and fundamental harmonic resistant leakage current i _r1there is phase relation as shown in Figure 1, i in figure _r1for fundamental harmonic resistant leakage current, i _c1for first-harmonic capacity current, i _x1for fundamental current.Through type (5) can solve fundamental harmonic resistant leakage current i _r1;

i _r1＝i _x1cosθ (5)

X subharmonic is at the amplitude I of the current in resistance property at first-harmonic place _mx1solve as follows: use fft algorithm to decompose voltage u (t) putting on MOA two ends, harmonic voltage u in line voltage can be calculated _xwith fundamental voltage u ₁;

By harmonic voltage u _xbring in volt-ampere characteristic MOA valve block model as shown in Figure 2, the current in resistance property composition that in line voltage, x subharmonic voltage produces can be calculated, as shown in formula (6):

i _r(x)＝tan(u _x)/k x＝3,5,7… (6)

In formula (6), k is that lightning arrester self-characteristic determines constant, and wherein general value is within 50, if k value is 35; u _xfor harmonic voltage in line voltage, i _rx current in resistance property that () produces for x subharmonic voltage in line voltage;

To i _rx () carries out fast Flourier computing, formula (7) and formula (8) are shown in its computing:

$i_r\left(x\right)=\frac{a_0}{2}+\underset{n=1}{\overset{\∞}{\mathrm{\Σ}}}(a_n\cos \mathrm{nx}+b_n\sin \mathrm{nx})---\left(7\right)$

$\left\{\begin{array}{c}{a}_{\mathrm{xn}}=\frac{1}{\mathrm{\π}}\underset{-\mathrm{\π}}{\overset{\mathrm{\π}}{\text{\∫}}}{i}_r\left(x\right)\cos \mathrm{nxd}\left(x\right)\\ b_{\mathrm{xn}}=\frac{1}{\mathrm{\π}}\underset{-\mathrm{\π}}{\overset{\mathrm{\π}}{\∫}}{i}_r\left(x\right)\sin \mathrm{nxd}\left(x\right)\end{array}\right.---\left(8\right)$

In formula (7) and (8), n is the multiple of mains frequency, and its value is odd number, as n=1, is mains frequency, and it represents first-harmonic, as n=3, is 3 times to mains frequency, is called 3 subharmonic.Can be calculated by formula (8): x subharmonic voltage is at the current in resistance property amplitude I at first-harmonic (i.e. n=1) place _mx1, it can be expressed as formula (9):

$I_{\mathrm{MX}1}=\sqrt{{a^2}_{x1}+{b^2}_{x1}},x=\mathrm{3,5,7}...---\left(9\right)$

In formula (9), x is the number of times of harmonic voltage, can value 3,5 and above odd-times thereof;

3rd step,

MOA current in resistance property i to be measured after the current in resistance property that removal harmonic voltage produces on equivalent resistance _r" be expressed as follows:

i _r″＝i(t)-i _C1-i _r'(10)

In formula (10), i (t) is MOA leakage current, i _c1for the capacity current that MOA produces;

Harmonic voltage u _xthe current in resistance property ir ' that equivalent linear resistance R1 produces, can solve as follows by formula (11):

${\mathrm{ir}}^{\′}=\underset{x}{\mathrm{\Σ}}{u}_x/R_1,x=\mathrm{3,5,7}...---\left(11\right)$

To the current in resistance property i tried to achieve _r" carry out fft algorithm computing after, more accurate i can be obtained _1rand i _3r, thus on-line monitoring is realized to MOA.

After removing the current in resistance property that produces on equivalent resistance of harmonic voltage, the fundamental harmonic resistant leakage current calculated and the aging reaction of third harmonic current in resistance property to MOA more accurate.When aging monitoring is carried out to the MOA in building mansion, power circuit, voltage transformer (VT) and current sensor is utilized to obtain working voltage and the leakage current of MOA, and be transferred on terminal handler, terminal handler utilizes this Algorithm for Solving to go out fundamental harmonic resistant leakage current and third harmonic current in resistance property, demonstrate result of calculation in real time, the later stage can according to user of service to MOA performance requirement, and in conjunction with result of calculation, accurately can determine the replacing construction of MOA, accomplish to change in time aging MOA.

At present, normally do not have 2 years pull down lightning arrester about the fault detect of MOA in electric system and carry out preventive trial, because lightning arrester is numerous, therefore need to expend huge human and material resources and financial resources.Use this algorithm will no longer need the monitoring in every 2 years of lightning arrester in circuit, and MOA potential faults can be got rid of timely and effectively, the work efficiency of raising, reduce the replacing number of times of MOA, saved funds.

Claims (3)

1. a Resistive Current of Metal Oxide Surge Arrester extracting method, the method comprises the following steps:

The first step,

Obtain by mutual inductor or capacitive divider voltage signal u (t) be applied on MOA to be measured, voltage signal u (t) obtained is applied to known capacitance C ₂on; Centre path current sensor or the formula current sensor of sealing in is utilized to obtain respectively by known capacitance C ₂capacity current i _c2with by leakage current signal i (t) of MOA to be measured, according to current in resistance property with capacity current orthogonality principle is known there is formula (1) relation:

$\begin{array}{c}{\∫}_0^T{i}_{C2}\left(t\right)i\left(t\right)\mathrm{dt}={\∫}_0^T{i}_{C2}\left(t\right)[i_r\left(t\right)+\frac{C1}{C2}{i}_{C2}\left(t\right)]\mathrm{dt}\\ =\frac{C1}{C2}{\∫}_0^T{i_{C2}}^2\left(t\right)\mathrm{dt}\end{array}---\left(1\right)$

Therefore, through type (1) can derive formula (2), by known capacitance C2, capacity current i by C2 _c2and pass through leakage current i (t) of MOA, obtain MOA real crystal boundary capacitance C ₁,

$C1=\frac{C2{\∫}_0^T{i}_{C2}\left(t\right)i\left(t\right)\mathrm{dt}}{{\∫}_0^T{i_{C2}}^2\left(t\right)\mathrm{dt}}---\left(2\right)$

By the capacity current i of MOA _c1available formula (3) is expressed as follows:

$i_{C1}=\frac{C1}{C2}{i}_{C2}---\left(3\right)$

Second step,

Linear resistance R is equivalent to by producing fundamental harmonic resistant leakage current part in MOA non-linear resistance ₁, remainder is equivalent to non-linear resistance R ₂;

MOA equivalent resistance R ₁calculate by formula (4):

$R_1=u_1/(i_{r1}-\mathrm{\Σ}\frac{I_{\mathrm{MX}1}}{\sqrt{2}})---\left(4\right)$

I in formula (4) _r1for fundamental harmonic resistant leakage current, I _mx1for x subharmonic is in the amplitude of the current in resistance property at first-harmonic place, u ₁for fundamental voltage in line voltage;

Fundamental harmonic resistant leakage current i _r1solve as follows: realize fft algorithm by programmable array, utilize fft algorithm to decompose leakage current i (t) that MOA to be measured produces, calculate fundamental current i _x1with fundamental current phase theta; Due to fundamental current i _x1, fundamental current phase theta and fundamental harmonic resistant leakage current i _r1there is following phase relation, through type (5) can solve fundamental harmonic resistant leakage current i _r1;

i _r1＝i _x1cosθ (5)

X subharmonic is at the amplitude I of the current in resistance property at first-harmonic place _mx1solve as follows: use fft algorithm to decompose voltage u (t) putting on MOA two ends, harmonic voltage u in line voltage can be calculated _xwith fundamental voltage u ₁;

By harmonic voltage u _xbring in the MOA valve block model of volt-ampere characteristic, the current in resistance property composition that in line voltage, x subharmonic voltage produces can be calculated, as shown in formula (6):

i _r(x)＝tan(u _x)/k x＝3,5,7… (6)

In formula (6), k is that lightning arrester self-characteristic determines constant; u _xfor harmonic voltage in line voltage, i _rx current in resistance property that () produces for x subharmonic voltage in line voltage;

To i _rx () carries out fast Flourier computing, formula (7) and formula (8) are shown in its computing:

$i_r\left(x\right)=\frac{a_0}{2}+\underset{n=1}{\overset{\∞}{\mathrm{\Σ}}}(a_n\cos \mathrm{nx}+b_n\sin \mathrm{nx})---\left(7\right)$

$\left\{\begin{array}{c}{a}_{\mathrm{xn}}=\frac{1}{\mathrm{\π}}\underset{-\mathrm{\π}}{\overset{\mathrm{\π}}{\∫}}{i}_r\left(x\right)\cos \mathrm{nxd}\left(x\right)\\ b_{\mathrm{xn}}=\frac{1}{\mathrm{\π}}\underset{-\mathrm{\π}}{\overset{\mathrm{\π}}{\∫}}{i}_r\left(x\right)\sin \mathrm{nxd}\left(x\right)\end{array}\right.---\left(8\right)$

In formula (7) and (8), n is the multiple of mains frequency, can be calculated by formula (8): x subharmonic voltage is at the current in resistance property amplitude I at first-harmonic (i.e. n=1) place _mx1, it can be expressed as formula (9):

$I_{\mathrm{MX}1}=\sqrt{{a^2}_{x1}+{b^2}_{x1}},x=\mathrm{3,5,7}...\left(9\right)$

In formula (9), x is the number of times of harmonic voltage;

3rd step,

MOA current in resistance property i to be measured after the current in resistance property that removal harmonic voltage produces on equivalent resistance _r" be expressed as follows:

i _r″＝i(t)-i _C1-i _r' (10)

In formula (10), i (t) is MOA leakage current, i _c1for the capacity current that MOA produces;

Harmonic voltage u _xthe current in resistance property ir ' that equivalent linear resistance R1 produces, can solve as follows by formula (11):

${\mathrm{ir}}^{\text{'}}=\underset{x}{\mathrm{\Σ}}{u}_x/R_1,x=\mathrm{3,5,7}...\left(11\right)$

To the current in resistance property i tried to achieve _r" carry out fft algorithm computing after, can i be asked _1rand i _3r, thus on-line monitoring is realized to MOA.

2. Resistive Current of Metal Oxide Surge Arrester extracting method according to claim 1, in the method first step: described C ₂value 10 μ F.

3. Resistive Current of Metal Oxide Surge Arrester extracting method according to claim 1, in the method second step:

Described k value is 35.