CN1858954A - Method for realizing line differential protection based on long line equation - Google Patents

Abstract

The invention relates to a method for relay protection in the field of power systems. Disclosed is a method of line differential protection based on long-line equation calculation in the high-voltage transmission line of the power system, and converts the voltage and current measured at the protection installation place to a certain reference within the protection range of the line by using the vector calculation method of the long-line equation The voltage and current of point k, the _voltagem and _currentm at terminal m are converted to point k as _voltagekm and _currentkm , the voltage at terminal _n and _currentn converted to point k are _voltagekn and _currentkn , if there is a shunt reactor L in the middle of the line, it is necessary to subtract the current  ₁ on the shunt reactor to obtain ′ _km , ′ _kn , and then use the current  _km ,  _kn or ′ _km ,  at the reference point k ′ _kn performs differential calculation according to various differential formulas to judge whether an internal fault occurs.

Description

The method of the line differential protection of realizing based on long-line equation

Technical field

The present invention relates to field of power, relate more specifically to the method for relaying protection, relate to the algorithm of circuit differential current protection.

Background technology

Transmission line is the basic equipment of electric power system generating, conveying electricity etc., occupies important status in electric power system.During transmission line malfunction, then bigger if can not in time excise or mistake excision to the main system influence, cause grid disconnection easily, and major accident such as transformer overstep tripping.High-voltage line protection is undertaken the vital task of carrying electricity, is the important pivot of electric power system.Their costs are very expensive, damaged in case hinder for some reason, and the maintenance difficulty is big, the time is long, and the direct and consequential damage that national economy is caused is very huge.So just selectivity, rapidity, reliability, the sensitivity of high-voltage line protection device are had higher requirement.Based on the current differential protection of Kirchhoff's law,, be a kind of desirable protection philosophy for transmission line.Along with the development of Microcomputer Protection and mechanics of communication, current differential protection is widely used.

At present; the electric pressure of China's electrical network just develops to 1000kV from 750kV; traditional Principles of Relay Protection is to be based upon on the power frequency fault component basis; utilize lumped parameter to set up that model realizes; and in fact its distributed constant of ultra high voltage long distance transmission line is clearly; in failure process, can produce the influence of can not ignore to current differential protection by the capacitance current that distributed constant produced.Electric pressure is high more, circuit is long more, and this influence is big more.Extra high voltage line reduces the electric field strength and the corona loss of conductive line surfaces in order to improve the natural power that can transmit, and need to reduce the wave impedance of circuit, promptly reduces the inductance of circuit and increases electric capacity, therefore, makes that the capacitance current of ultra high voltage long transmission line is very big.Theoretical research shows; for 600km; the 1150kV UHV transmission line, its capacitance current reaches 76.35% of circuit natural power, so big capacitance current; must produce very big influence to the operating characteristics of ultra high voltage relaying protection; theory analysis as can be known, the various schemes of differential current protection at present comprise that condenser current compensation etc. all will be subjected to the influence of line distribution capacitance in the ultra high voltage long transmission line, can't meet the demands; therefore, can not indiscriminately imitate use.

At present, traditional differential current protection criterion algorithm is to adopt terminal voltage, end electric current directly to calculate.Computing formula is as follows:

To meet meaning described with the front for formula in the formula, increase to meet  and represent a, and b, c, promptly three-phase is done differential calculating respectively.

On superhigh pressure, ultra high voltage long transmission line, capacitance current is very big, has influenced the externally reliability the when fail safe during fault and internal fault of current differential protection greatly.With the lumped parameter is foundation, can not fundamentally solve the problem of capacitance current influence by the method for the braking criterion of lumped parameter compensation to capacitance current in the protection installation place.And,, might increase shunt reactor in the line for the compensated line capacitance current along with the increase of line length, this situation influences more serious to traditional differential protection based on the end electric current.The present invention is directed to present ultra high voltage, long transmission line and be badly in need of solving the influence of capacitance current to the differential protection criterion, proposed a kind of new algorithm, this algorithm can solve the influence of capacitance current to differential protection preferably.The result of the test surface, this algorithm can be eliminated the influence of capacitance current to differential protection preferably.New principle that this paper carries is good and bad insensitive to filtering algorithm.

Summary of the invention

For the ultra high voltage long transmission line; because the influence of line distribution capacitance electric current can not be ignored; therefore; traditional is foundation with the lumped parameter; do the algorithm of differential criterion considers can not meet the demands from sensitivity in the protection installation place; and be foundation with the lumped parameter, the algorithm at the circuit two ends based on the stable state condenser current compensation can unavoidably can prolong the operate time of protection in some cases under some failure condition.The present invention at first utilizes long-line equation that both end voltage, end electric current are converted reference point in the mode of phasor calculation; doing the differential current protection in reference point calculates; if reference point has shunt reactor; need cut the electric current on the shunt reactor earlier; be noted that two ends respectively deduct the electric current of half shunt reactor, do differential calculating again.As shown in Figure 1; if fault occurs in outside the protection range district, then owing to hold to hold to k from m and satisfy long-line equation, as can be known according to Kirchhoff's current law (KCL) to k with from n; in the differential amount of k point is zero, and the braking amount is 2 times of line currents (senses of current all be point to reference point with the protection installation place be forward).Protection can malfunction; during troubles inside the sample space; if fault occurs in n and holds between the k point; hold to the k point from m and to satisfy long-line equation; but hold to of the existence of k point from n owing to the fault point, discontented foot length line equation, but by theory analysis as can be known; at this moment, convert the operating criterion that actuating quantity that reference point k orders and braking amount satisfy differential protection by two ends protections installation place by long-line equation.

According to the present invention, a kind of method of calculating the line differential protection of realizing in the ultra-high-tension power transmission line of electric power system based on long-line equation is provided, this method comprises the steps:

In the at first selected route protection scope certain is reference point k a bit, if shunt reactor or serial compensation capacitance are arranged, the installation place of then selecting shunt reactor or serial compensation capacitance is reference point k;

Line protective devices obtain the electric current and voltage instantaneous value to the voltage current waveform sampling of instrument transformer:

Obtain the phasor form of each electric parameters by fourier algorithm:

To protect installation place survey voltage, electric current to convert reference point k by long-line equation, and, then remove shunt reactor earlier and get electric current if on the circuit shunt reactor is arranged in the mode of phasor calculation

Adopt electric current at reference point k

Or

Carry out differential calculating by multiple traditional differential equations, judge whether the generating region internal fault, formula is as follows for example:

$\left\{\begin{array}{cc}{I}_d>I_h& \\ I_d>k_1{I}_b& 0<I_d<3I_h\\ I_d>k_2{I}_b-I_h& I_d\&GreaterEqual;3I_h\end{array}\right.$

In the formula: I _dRepresent differential amount: $I_d=|{\stackrel{\&CenterDot;}{I}}_{\mathrm{km}}+{\stackrel{\&CenterDot;}{I}}_{\mathrm{kn}}|$ Or $I_d=|{\stackrel{\&CenterDot;}{I}}_{\mathrm{km}}^{\&prime;}+{\stackrel{\&CenterDot;}{I}}_{\mathrm{kn}}^{\&prime;}|,$ I _kBe the definite value of differential protection action, I _bBe the braking amount, $I_b=|{\stackrel{\&CenterDot;}{I}}_{\mathrm{km}}-{\stackrel{\&CenterDot;}{I}}_{\mathrm{kn}}|$ Or $I_b=|{\stackrel{\&CenterDot;}{I}}_{\mathrm{km}}^{\&prime;}-{\stackrel{\&CenterDot;}{I}}_{\mathrm{kn}}^{\&prime;}|,$ , k ₁, k ₂Be restraint coefficient, three-phase current needs to calculate respectively.

Description of drawings

Fig. 1 is the line fault schematic diagram that is provided with reference point k.

Specific embodiments

At first utilize long-line equation will protect installation place (is example with the m end) voltage

Electric current Convert reference point k in the mode of phasor calculation, with

Expression, n end commutation reference point with Expression, if shunt reactor is arranged, need remove earlier behind the electric current of shunt reactor

Do the required calculating of differential protection by routine formula (1) again.

$\left\{\begin{array}{cc}{I}_d>I_h& \\ I_d>k_1{I}_b& 0<I_d<3I_h\\ I_d>k_2{I}_b-I_h& I_d\&GreaterEqual;3I_h\end{array}\right.---\left(1\right)$

In the formula: I _dRepresent differential amount: $I_d=|{\stackrel{\&CenterDot;}{I}}_{\mathrm{km}}+{\stackrel{\&CenterDot;}{I}}_{\mathrm{kn}}|$ Or $I_d=|{\stackrel{\&CenterDot;}{I}}_{\mathrm{km}}^{\&prime;}+{\stackrel{\&CenterDot;}{I}}_{\mathrm{kn}}^{\&prime;}|,$ I _hBe the definite value of differential protection action, I _bBe the braking amount, $I_b=|{\stackrel{\&CenterDot;}{I}}_{\mathrm{km}}-{\stackrel{\&CenterDot;}{I}}_{\mathrm{kn}}|$ Or $I_b=|{\stackrel{\&CenterDot;}{I}}_{\mathrm{km}}^{\&prime;}-{\stackrel{\&CenterDot;}{I}}_{\mathrm{kn}}^{\&prime;}|,$ , k ₁, k ₂Be restraint coefficient, three-phase current needs to calculate respectively.

Be illustrated in figure 1 as the ultra-high-tension power transmission line that is provided with reference point k, for the circuit of shunt reactor is arranged between in the line, then reference point is chosen as the mounting points (k represents with symbol) of shunt reactor among the figure; If no shunt reactor, any k of the selection of reference point then, but protection installation place to the length of reference point can not surpass 400km, for differential protection, the selected reference point in two ends should be a point, and promptly to protect the installation place be line length to reference point apart from sum at two ends.Described method is as follows:

By long-line equation will protect install the place survey voltage (the m end with

Representative, n end with Representative), electric current (m end with Representative, n end with

Representative) convert reference point k (m end with

Representative, n end with Representative) if shunt reactor is arranged, then removes shunt reactor earlier and get electric current Doing differential protection by formula (1) again calculates.

Because long-line equation itself considered distributed constant, therefore, do not need specially capacitance current to be compensated again, theory analysis and simulation result show that all the principle of carrying eliminated the influence that the line distribution capacitance electric current is protected differential current fully.

Symbol in below discussing uses as follows: current transformer (being called for short TA, as follows) and voltage transformer (being called for short TV, as follows).

At first protect according to the TA of protection installation place and the instantaneous value that TV records electric current and voltage.Secondly obtain the phasor form of each electric parameters by fourier algorithm, utilize following formula that the two ends electric current is converted reference point (is example with the m end), the n end is done same treatment by following formula.

$\left[\begin{array}{c}{\stackrel{\&CenterDot;}{U}}_{\mathrm{km}}\\ {\stackrel{\&CenterDot;}{I}}_{\mathrm{km}}\end{array}\right]=\left[\begin{array}{cc}\mathrm{ch}\left(\mathrm{\&gamma;l}\right)& -Z_c\mathrm{sh}\left(\mathrm{\&gamma;l}\right)\\ -\mathrm{sh}\left(\mathrm{\&gamma;l}\right)/Z_c& \mathrm{ch}\left(\mathrm{\&gamma;l}\right)\end{array}\right]\left[\begin{array}{c}{\stackrel{\&CenterDot;}{U}}_m\\ {\stackrel{\&CenterDot;}{I}}_m\end{array}\right]$

In the formula:

By protection installation place (m end) the vector of survey voltage, electric current, Be voltage, the electric current of reference point k, if shunt reactor is arranged, then need deduct the electric current of shunt reactor again, two ends respectively deduct the electric current of half shunt reactor, and γ is the propagation constant of circuit, Z _cBe the wave impedance of circuit, l is that m holds to the distance of reference point k, ch (), and sh () is respectively hyperbolic cosine and SIN function; The n end is done same processing.

Because this formula is set up on modulus, therefore, needing is the mould vector with the two ends protection three-phase voltage of surveying, current conversion at first, is changing by this formula.If reference point has shunt reactor, need deduct the shunt reactor electric current earlier Do differential differentiation again.

The consideration of choosing of ordering about k; the long-line equation current differential protection goes for the superhigh pressure of random length; UHV transmission line; if series compensation capacitance is arranged in the middle of the transmission line; shunt reactor is perhaps arranged; this moment, long-line equation was false at serial compensation capacitance or shunt reactor installation place; need reference point k is selected in serial compensation capacitance or shunt reactor place; under other situations; choosing that k is ordered is not subjected to any restriction; behind the selected k point, hold the point to k for m respectively, n holds to the k point and utilizes long-line equation calculating electric current; just can realize differential relaying algorithm easily; this algorithm is for the sampling interval of Microcomputer Protection, and the transmission time of optical-fibre channel does not all have very harsh requirement, and existing Microcomputer Protection all is easy to accomplish.

Claims (3)

1. A method of line differential protection based on long-line equation calculation in the high-voltage transmission line of power system, the method may further comprise the steps: First select a certain point within the protection range of the line as the reference point k. The selection of the reference point is not more than 400km away from the protection installation. is the reference point k; The line protection device samples the voltage and current waveform of the transformer to obtain the instantaneous value of the voltage and current; Calculate the phasor form of each electric quantity by Fourier algorithm; Convert the measured voltage and current at the protection installation place to the reference point k by means of phasor calculation through the long-term equation. If there is a shunt reactor, first remove the shunt reactor to obtain the current have to Take current at reference point k

or

Carry out differential calculation according to various differential formulas to judge whether there is an internal fault, among which: $\left\{\begin{array}{cc}{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}}<span\; class="notranslate">\; ></span>{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; h</span>}}& \\ {\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}}<span\; class="notranslate">\; ></span>{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; b</span>}}& \mathrm{<span\; class="notranslate">\; 0</span>}<span\; class="notranslate">\; <</span>{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}}<span\; class="notranslate">\; <</span>{\mathrm{<span\; class="notranslate">\; 3</span>}\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; h</span>}}\\ {\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}}<span\; class="notranslate">\; ></span>{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; b</span>}}& {\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}}<span\; class="notranslate">\; \&Greater\; Equal;</span>{\mathrm{<span\; class="notranslate">\; 3</span>}\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; h</span>}}\end{array}\right.$ In the formula: I _d represents the differential amount: $I_d=|{\stackrel{\&Center\; Dot;}{I}}_{\mathrm{km}}+{\stackrel{\&CenterDot;}{I}}_{\mathrm{k\; n}}|$ or $I_d=|{\stackrel{\&CenterDot;}{I}}_{\mathrm{km}}^{\&prime;}+{\stackrel{\&Center\; Dot;}{I}}_{\mathrm{k\; n}}^{\&prime;}|,$ I _h is the fixed value of differential protection action, I _b is the braking amount, $I_b=|{\stackrel{\&CenterDot;}{I}}_{\mathrm{km}}-{\stackrel{\&CenterDot;}{I}}_{\mathrm{k\; n}}|$ or $I_b=|{\stackrel{\&Center\; Dot;}{I}}_{\mathrm{km}}^{\&prime;}-{\stackrel{\&Center\; Dot;}{I}}_{\mathrm{k\; n}}^{\&prime;}|,$ k ₁ and k ₂ are braking coefficients, and the three-phase currents need to be calculated separately. 2. The method as claimed in claim 1, at first need to convert the current at both ends to the reference point, and subtract the current of the shunt reactor, wherein when the reference point needs to subtract the shunt reactor current, each of the two ends is reduced by half 3. The method according to claim 1, wherein the voltage and current measured at the head end are converted to a reference point, and the formula is as follows: $\left[\begin{array}{c}{\stackrel{<span\; class="notranslate">\; \&Center\; Dot;</span>}{\mathrm{<span\; class="notranslate">\; u</span>}}}_{\mathrm{<span\; class="notranslate">\; km</span>}}\\ {\stackrel{<span\; class="notranslate">\; \&Center\; Dot;</span>}{\mathrm{<span\; class="notranslate">\; I</span>}}}_{\mathrm{<span\; class="notranslate">\; km</span>}}\end{array}\right]<span\; class="notranslate">\; =</span>\left[\begin{array}{cc}\mathrm{<span\; class="notranslate">\; ch</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&gamma;l</span>}<span\; class="notranslate">\; )</span>& <span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; Z</span>}}_{\mathrm{<span\; class="notranslate">\; c</span>}}\mathrm{<span\; class="notranslate">\; sh</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&gamma;l</span>}<span\; class="notranslate">\; )</span>\\ <span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; sh</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&gamma;l</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; /</span>{\mathrm{<span\; class="notranslate">\; Z</span>}}_{\mathrm{<span\; class="notranslate">\; c</span>}}& \mathrm{<span\; class="notranslate">\; ch</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&gamma;l</span>}<span\; class="notranslate">\; )</span>\end{array}\right]\left[\begin{array}{c}{\stackrel{<span\; class="notranslate">\; \&CenterDot;</span>}{\mathrm{<span\; class="notranslate">\; u</span>}}}_{\mathrm{<span\; class="notranslate">\; m</span>}}\\ {\stackrel{<span\; class="notranslate">\; \&Center\; Dot;</span>}{\mathrm{<span\; class="notranslate">\; I</span>}}}_{\mathrm{<span\; class="notranslate">\; m</span>}}\end{array}\right]$ In the formula:

In order to protect the vector of voltage and current measured at the installation site (m terminal),

is the voltage and current of the reference point k, if there is a shunt reactor on the line, the current of the shunt reactor needs to be subtracted, and half of the current of the shunt reactor is subtracted from both ends, γ is the propagation constant of the line, Zc is the line The wave impedance, l is the distance from the m terminal to the reference point k, ch(), sh() are the hyperbolic cosine and sine functions respectively; the same process is done at the n terminal.

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