CN101673941A - Zero sequence current differential protection method - Google Patents

Abstract

The invention discloses a zero sequence current differential protection method which comprises the steps of choosing a reference point in a circuit in advance; calculating out zero sequence current and zero sequence voltage at two ends of the circuit by a sequence arithmetic, adopting a long line equation to convert the zero sequence current and the zero sequence voltage at two ends of the circuitto the reference point according to a phasor form; and implementing zero sequence current differential protection judgment at the reference point and controlling the tripping of the switches at two sides of the circuit when the fault is judged to occur in the circuit. The invention provides a zero sequence current differential protection method which is used for better solving the influence of adistributed capacitance current on zero sequence current differential protection.

Description

A kind of Zero sequence current differential protection method

Technical field

The present invention relates to field of power, be specifically related to the UHV transmission line Zero sequence current differential protection method.

Background technology

Transmission line is the basic equipment of electric power system generating, conveying electricity etc., occupies important status in electric power system.When if transmission line breaks down, then very big 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.

UHV transmission line is undertaken the vital task of carrying a large amount of electric energy, is the important pivot of electric power system.Because the UHV transmission line cost is very expensive, in case the barrier time-delay is removed and damaged for some reason, the maintenance difficulty is big, the time is long, will be very huge to the direct and consequential damage that national economy causes.Therefore, selectivity, rapidity, reliability, the sensitivity of UHV transmission line protective 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 500kV; 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 the distributed constant of ultra high voltage long distance transmission line (for lumped parameter) is in failure process, and the capacitance current that is produced can produce the influence of can not ignore to current differential protection.Electric pressure is high more, circuit is long more, and this influence is big more.UHV transmission line is in order to improve the natural power of transmission, reduce the electric field strength and the corona loss on circuit surface, need to reduce the wave impedance of UHV transmission line, promptly reduce the inductance of UHV transmission line and increase electric capacity, therefore, make that the capacitance current of ultra high voltage long transmission line is very big.Theoretical research shows, for 600km, and the 1000kV UHV transmission line, its capacitance current reaches 76.35% of circuit natural power, and 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, how being badly in need of solving the influence of capacitance current to the differential protection criterion at present ultra high voltage, long power transmission line, realizing Zero sequence current differential protection, is those skilled in the art's technical issues that need to address.

Summary of the invention

The invention provides a kind of Zero sequence current differential protection method, be used for solving preferably the influence of capacitance current Zero sequence current differential protection.

The invention provides a kind of Zero sequence current differential protection method, comprising:

In circuit, select a reference point in advance;

Calculate the zero-sequence current and the residual voltage at described circuit two ends by strain sequence arithmetic;

Utilize long-line equation that the zero-sequence current and the residual voltage at described circuit two ends are converted to reference point by the phasor form;

Doing Zero sequence current differential protection in reference point judges;

When failure judgement occurs in the described circuit, control described circuit both sides switch trip.

Preferably, describedly do the step that Zero sequence current differential protection judges in reference point and be specially:

Adopt the zero-sequence current of reference point both sides to carry out the judgement of zero sequence differential protection by differential judgment formula in reference point.

Preferably, establish described circuit two ends respectively with m, n represents;

Described differential judgment formula is:

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

Work as I _d＞I _hDuring establishment, judge to have fault; As 0＜I _d＜3I _h, and I _d＞k ₁I _bDuring establishment, judge in the corresponding described circuit to have fault; Work as I _d＞k ₂I _b-I _h, and I _d〉=3I _hDuring establishment, judge in the corresponding described circuit to have fault;

In the formula: I _dRepresent differential amount;

Be reference point km side zero-sequence current, Be reference point kn side zero-sequence current, I _hDefinite value for the Zero sequence current differential protection action;

I _bBe the braking amount;

k ₁, k ₂Be restraint coefficient.

Preferably, the definite value I of described Zero sequence current differential protection action _h, be set at the secondary load current value of 0.05-0.2 transmission line doubly.

Preferably, described restraint coefficient k ₁, k ₂Be set to 0.5-0.8.

Preferably, describedly calculate the zero-sequence current of described circuit two-end-point and the step of residual voltage is specially by strain sequence arithmetic:

Utilize the current transformer of described circuit end points place installation and the instantaneous value that voltage transformer records electric current and voltage;

Obtain the phasor form of each electric parameters by fourier algorithm, utilize strain sequence arithmetic to leach the zero-sequence current and the residual voltage at two ends again.

Preferably, described strain sequence arithmetic is an example with the m end, according to following formula:

${\stackrel{\&CenterDot;}{I}}_{m0}={\stackrel{\&CenterDot;}{I}}_{\mathrm{ma}}+{\stackrel{\&CenterDot;}{I}}_{\mathrm{mb}}+{\stackrel{\&CenterDot;}{I}}_{\mathrm{mc}}$

${\stackrel{\&CenterDot;}{U}}_{m0}={\stackrel{\&CenterDot;}{U}}_{\mathrm{ma}}+{\stackrel{\&CenterDot;}{U}}_{\mathrm{mb}}+{\stackrel{\&CenterDot;}{U}}_{\mathrm{mc}}$

Calculate and obtain;

In the formula:

Hold the phasor of the residual voltage that is calculated for m; Hold the phasor of the zero-sequence current that is calculated for m;

Be respectively the phasor form of m side a, b, c three-phase current;

Be respectively the phasor form of m side a, b, c three-phase voltage.

Preferably, describedly utilize long-line equation that the zero-sequence current at described circuit two ends and residual voltage are converted to the step of reference point by the phasor form to be specially:

Utilizing following long-line equation that two ends zero-sequence current and residual voltage are converted reference point, is example with the m end of circuit,

$\left[\begin{array}{c}{\stackrel{\&CenterDot;}{U}}_{\mathrm{km}0}\\ {\stackrel{\&CenterDot;}{I}}_{\mathrm{km}0}\end{array}\right]=\left[\begin{array}{cc}\mathrm{ch}\left({\mathrm{\&gamma;}}_{0}l\right)& -Z_{c0}\mathrm{sh}\left({\mathrm{\&gamma;}}_{0}l\right)\\ -\mathrm{sh}\left({\mathrm{\&gamma;}}_{0}l\right)/Z_{c0}& \mathrm{ch}\left({\mathrm{\&gamma;}}_{0}l\right)\end{array}\right]\left[\begin{array}{c}{\stackrel{\&CenterDot;}{U}}_{m0}\\ {\stackrel{\&CenterDot;}{I}}_{m0}\end{array}\right]$

In the formula:

Hold the phasor of the residual voltage that is calculated for m;

Hold the phasor of the zero-sequence current that is calculated for m;

For the residual voltage of the m side of reference point k,

Zero-sequence current for the m side of reference point k;

γ ₀Be the zero sequence propagation constant of circuit, Z _C0Be the zero sequence wave impedance of circuit,

L is that m holds to the distance of reference point k;

Ch (), sh () is respectively hyperbolic cosine and SIN function; In the formula: r ₀Be circuit unit length zero sequence resistance; L ₀Be circuit unit length zero sequence induction reactance; g ₀For the zero sequence electricity of lead unit length is over the ground led; C ₀Be circuit unit length zero sequence electric capacity;

Another end points of described circuit n does above-mentioned same processing.

Preferably, if shunt reactor, described zero-sequence current are arranged

Deduct the zero-sequence current of shunt reactor again, two ends respectively deduct the zero-sequence current of half shunt reactor.

Preferably, in the described circuit series compensation capacitance is arranged, shunt reactor is perhaps arranged, described reference point is selected in series compensation capacitance or shunt reactor place;

Do not have series compensation capacitance in the described circuit, and do not have shunt reactor, described reference point is selected in the optional position in the described circuit.

The described Zero sequence current differential protection method of the embodiment of the invention comprises: select a reference point in advance in circuit; Calculate the zero-sequence current and the residual voltage at described circuit two ends by strain sequence arithmetic; Utilize long-line equation that the zero-sequence current and the residual voltage at two ends are converted to reference point by the phasor form; Doing Zero sequence current differential protection in reference point judges; Thereby can solve the influence of capacitance current effectively to the zero sequence differential protection.By judging that in reference point Zero sequence current differential protection judges, can judge fault and whether occur in the described circuit, when judging when occurring in the described circuit, can control described circuit both sides switch trip.

Description of drawings

Fig. 1 is the Zero sequence current differential protection method first embodiment flow chart of the present invention;

Fig. 2 is transmission line structure figure of the present invention.

Embodiment

The invention provides a kind of Zero sequence current differential protection method, be used for solving preferably the influence of capacitance current the zero sequence differential protection.

Traditional Zero sequence current differential protection criterion algorithm is that the zero-sequence current that adopts protection installation place, circuit two ends to calculate directly calculates.

On 1000kV 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, capacitance current is pressed the method for the braking criterion of lumped parameter compensation in optical fiber longitudinal differential protection device installation place, can not fundamentally solve the problem of capacitance current influence.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.

For 1000kV 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 zero-sequence current differential criterion considers can not meet the demands from sensitivity in optical fiber longitudinal differential protection device installation place; and be foundation with the lumped parameter, at the circuit two ends in some cases based on the algorithm of stable state condenser current compensation, operate time that can extended fiber longitudinal differential protection device.

Referring to Fig. 1 and Fig. 2, Fig. 1 is the Zero sequence current differential protection method first embodiment flow chart of the present invention, and Fig. 2 is transmission line structure figure of the present invention.

The described Zero sequence current differential protection method of first embodiment of the invention may further comprise the steps:

S100, in circuit, select a reference point in advance.

Be illustrated in figure 2 as the UHV transmission line that is provided with reference point k, be called for short circuit mn.For the circuit of shunt reactor L is arranged in the line, then reference point is chosen as the mounting points (k represents with symbol) of shunt reactor among Fig. 2.If no shunt reactor, then reference point can be selected arbitrfary point k, and for differential protection, the selected reference point in two ends should be a point, and promptly two ends optical fiber longitudinal differential protection device installation place is line length to reference point apart from sum.

S200, calculate the zero-sequence current and the residual voltage of described circuit two-end-point by strain sequence arithmetic.

Optical fiber longitudinal differential protection device can 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;

Leach the zero-sequence current and the residual voltage at two ends by strain sequence arithmetic;

S300, utilize long-line equation that the zero-sequence current and the residual voltage of two-end-point are converted to reference point by the phasor form.

By long-line equation zero-sequence current and residual voltage that optical fiber longitudinal differential protection device installation place calculates are converted reference point k by the phasor form; Reference point k both sides zero-sequence current is

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).

Optical fiber longitudinal differential protection device can utilize the TA of optical fiber longitudinal differential protection device installation place to record the current instantaneous value of two-end-point, and optical fiber longitudinal differential protection device can utilize the TV of optical fiber longitudinal differential protection device installation place to record the instantaneous voltage of two-end-point.

Obtain the phasor form of each electric parameters by fourier algorithm, utilize strain sequence arithmetic to leach the zero-sequence current and the residual voltage at two ends again; With the m end is example, and the strain sequence arithmetic formula is as follows:

${\stackrel{\&CenterDot;}{I}}_{m0}={\stackrel{\&CenterDot;}{I}}_{\mathrm{ma}}+{\stackrel{\&CenterDot;}{I}}_{\mathrm{mb}}+{\stackrel{\&CenterDot;}{I}}_{\mathrm{mc}}---\left(1\right)$

${\stackrel{\&CenterDot;}{U}}_{m0}={\stackrel{\&CenterDot;}{U}}_{\mathrm{ma}}+{\stackrel{\&CenterDot;}{U}}_{\mathrm{mb}}+{\stackrel{\&CenterDot;}{U}}_{\mathrm{mc}}$

In the formula:

Hold the phasor of the residual voltage that is calculated for m;

Hold the phasor of the zero-sequence current that is calculated for m;

Phasor form for m side a, b, c three-phase current;

Phasor form for m side a, b, c three-phase voltage;

Utilizing following formula is long-line equation (2), and the two ends electric current is converted reference point (is example with the m end), and the n end is done same treatment by following formula.

$\left[\begin{array}{c}{\stackrel{\&CenterDot;}{U}}_{\mathrm{km}0}\\ {\stackrel{\&CenterDot;}{I}}_{\mathrm{km}0}\end{array}\right]=\left[\begin{array}{cc}\mathrm{ch}\left({\mathrm{\&gamma;}}_{0}l\right)& -Z_{c0}\mathrm{sh}\left({\mathrm{\&gamma;}}_{0}l\right)\\ -\mathrm{sh}\left({\mathrm{\&gamma;}}_{0}l\right)/Z_{c0}& \mathrm{ch}\left({\mathrm{\&gamma;}}_{0}l\right)\end{array}\right]\left[\begin{array}{c}{\stackrel{\&CenterDot;}{U}}_{m0}\\ {\stackrel{\&CenterDot;}{I}}_{m0}\end{array}\right]---\left(2\right)$

In the formula:

Hold the phasor of the residual voltage that is calculated for m;

Hold the phasor of the zero-sequence current that is calculated for m;

Be the residual voltage of the m side of reference point k, Zero-sequence current for the m side of reference point k;

γ ₀Be the zero sequence propagation constant of circuit,

Z _C0Be the zero sequence wave impedance of circuit,

L is that m holds to the distance of reference point k;

Ch (), sh () is respectively hyperbolic cosine and SIN function; In the formula: r ₀Be circuit unit length zero sequence resistance; L ₀Be circuit unit length zero sequence induction reactance; g ₀For the zero sequence electricity of lead unit length is over the ground led; C ₀Be circuit unit length zero sequence electric capacity.

Another end points of described circuit n end points is done above-mentioned same processing.

Because long-line equation (2) itself has been considered distributed constant, therefore, do not need specially capacitance current to be compensated again, because zero-sequence current can reflect all unbalanced faults, therefore, differential can be used as of zero sequence has differential strong replenishing now; In addition, the Zero sequence current differential protection after compensation is highly sensitive, because zero-sequence current is a fault component, therefore, the differential influence that is not subjected to load component of zero sequence.

The consideration of choosing about reference point k; long-line equation (2) current differential protection goes for the UHV transmission line of random length; if series compensation capacitance is arranged in the middle of the transmission line; shunt reactor is perhaps arranged; long-line equation this moment (2) is false at series compensation capacitance or shunt reactor installation place; need reference point k is selected in the series compensation capacitance place, or the shunt reactor place.

Under other situations; choosing that reference point k is ordered is not subjected to any restriction; behind the selected reference point k point; hold point for m respectively to k; n holds to the k point and utilizes long-line equation (2) to calculate zero-sequence current, just can realize the zero sequence differential relaying algorithm easily, and this algorithm is for the sampling interval of Microcomputer Protection; the transmission time of optical-fibre channel does not all have very harsh requirement, and existing Microcomputer Protection all is easy to accomplish.

S400, do Zero sequence current differential protection at reference point k and judge; Judge whether to be described circuit internal fault, execution in step S500 in this way, otherwise determine that fault occurs in outside the described circuit.

Adopt zero-sequence current at reference point k

Carry out the differential calculating of zero sequence by multiple traditional differential equations, judge whether the generating region internal fault, promptly in the mn circuit among Fig. 2.

Zero sequence current differential protection judgment formula (3) for example:

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

In the formula: I _dRepresent differential amount;

I _Km0Be reference point km side zero-sequence current, I _Kn0Be reference point kn side zero-sequence current, I _hBe the definite value of Zero sequence current differential protection action, be set at the secondary load current value of (0.05-0.2) transmission line doubly usually.

I _bBe the braking amount;

k ₁, k ₂Be restraint coefficient.Restraint coefficient k ₁, k ₂Usually be set to 0.5-0.8.

Work as I _d＞I _hDuring establishment, judge to have fault; As 0＜I _d＜3I _h, and I _d＞k ₁I _bDuring establishment, judge in the corresponding described circuit to have fault; Work as I _d＞k ₂I _b-I _h, and I _d〉=3I _hDuring establishment, judge in the corresponding described circuit to have fault.

S500, when determining that fault occurs in the described circuit, control the both sides switch trip of described circuit.

At first with both end voltage (is example with the m end)

Electric current (subscript φ=a, b c) leach the zero-sequence current of both sides by strain sequence arithmetic And residual voltage The n end is

With

(the m end is by long-line equation the two ends zero-sequence current to be converted reference point k again

The n end is

), thereby can solve the influence of capacitance current effectively to differential protection.Whether the described Zero sequence current differential protection method of the embodiment of the invention can be judged by Zero sequence current differential protection, can judge fault and occur in the described circuit, when judging when occurring in the described circuit, can control described circuit both sides switch trip.

The described Zero sequence current differential protection method of the embodiment of the invention owing to adopted distributed constant calculating, therefore, is not subjected to the influence of distributed capacitance on the circuit, and therefore, for earth fault, especially high resistance earthing fault has good using value.

The present invention can at first calculate the zero-sequence current and the residual voltage of both sides by strain sequence arithmetic, utilize long-line equation (2) that the two ends zero-sequence current is converted to reference point k again, as shown in Figure 2, does Zero sequence current differential protection at reference point k and calculates.

If it is outward the outer or fault-free of mn circuit that fault occurs in protection range; then owing to hold to hold to k from m and satisfy long-line equation (2) to k with from n, according to Kirchhoff's current law (KCL) as can be known, when normal operation; should not having the zero sequence differential current on the circuit, is zero in the differential amount of k point zero sequence therefore.

Under the normal condition; optical fiber longitudinal differential protection device can malfunction; when in the protection range being mn circuit internal fault; 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 owing to the fault point from n; discontented foot length line equation; convert the actuating quantity of the zero-sequence current that reference point k orders and the operating criterion that the braking amount satisfies differential protection by optical fiber longitudinal differential protection device installation place, two ends by long-line equation (2) this moment but by theory analysis as can be known.

The above only is the preferred implementation of Zero sequence current differential protection method of the present invention; should be understood that; for those skilled in the art; under the prerequisite that does not break away from the principle of the invention; can also make some improvements and modifications, these improvements and modifications also should be considered as protection scope of the present invention.

Claims (10)

1, a kind of Zero sequence current differential protection method is characterized in that, described method comprises:

In circuit, select a reference point in advance;

Calculate the zero-sequence current and the residual voltage at described circuit two ends by strain sequence arithmetic;

Utilize long-line equation that the zero-sequence current and the residual voltage at described circuit two ends are converted to reference point by the phasor form;

Doing Zero sequence current differential protection in reference point judges;

When failure judgement occurs in the described circuit, control described circuit both sides switch trip.

2, Zero sequence current differential protection method according to claim 1 is characterized in that, describedly does the step that Zero sequence current differential protection judges in reference point and is specially:

Adopt the zero-sequence current of reference point both sides to carry out the judgement of zero sequence differential protection by differential judgment formula in reference point.

3, Zero sequence current differential protection method according to claim 2 is characterized in that, establishes described circuit two ends respectively with m, and n represents;

Described differential judgment formula is:

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

Work as I _d＞I _hDuring establishment, judge to have fault; As 0＜I _d＜3I _h, and I _d＞k ₁I _bDuring establishment, judge in the corresponding described circuit to have fault; Work as I _d＞k ₂I _b-I _h, and I _d〉=3I _hDuring establishment, judge in the corresponding described circuit to have fault;

In the formula: I _dRepresent differential amount;

Be reference point km side zero-sequence current,

Be reference point kn side zero-sequence current, I _hDefinite value for the Zero sequence current differential protection action;

I _bBe the braking amount;

$I_b=|{\stackrel{.}{I}}_{\mathrm{km}0}-{\stackrel{.}{I}}_{\mathrm{kn}0}|,$ k ₁, k ₂Be restraint coefficient.

4, Zero sequence current differential protection method according to claim 3 is characterized in that,

The definite value I of described Zero sequence current differential protection action _h, be set at the secondary load current value of 0.05-0.2 transmission line doubly.

5, Zero sequence current differential protection method according to claim 3 is characterized in that,

Described restraint coefficient k ₁, k ₂Be set to 0.5-0.8.

6, Zero sequence current differential protection method according to claim 1 is characterized in that,

Describedly calculate the zero-sequence current of described circuit two-end-point and the step of residual voltage is specially by strain sequence arithmetic:

Utilize the current transformer of described circuit end points place installation and the instantaneous value that voltage transformer records electric current and voltage;

Obtain the phasor form of each electric parameters by fourier algorithm, utilize strain sequence arithmetic to leach the zero-sequence current and the residual voltage at two ends again.

7, Zero sequence current differential protection method according to claim 6 is characterized in that,

Described strain sequence arithmetic is an example with the m end, according to following formula: $\begin{array}{c}{\stackrel{.}{I}}_{m0}={\stackrel{.}{I}}_{\mathrm{ma}}+{\stackrel{.}{I}}_{\mathrm{mb}}+{\stackrel{.}{I}}_{\mathrm{mc}}\\ {\stackrel{.}{U}}_{m0}={\stackrel{.}{U}}_{\mathrm{ma}}+{\stackrel{.}{U}}_{\mathrm{mb}}+{\stackrel{.}{U}}_{\mathrm{mc}}\end{array}$

Calculate and obtain;

In the formula:

Hold the phasor of the residual voltage that is calculated for m;

Hold the phasor of the zero-sequence current that is calculated for m;

Be respectively the phasor form of m side a, b, c three-phase current;

Be respectively the phasor form of m side a, b, c three-phase voltage.

8, Zero sequence current differential protection method according to claim 7 is characterized in that,

Describedly utilize long-line equation that the zero-sequence current at described circuit two ends and residual voltage are converted to the step of reference point by the phasor form to be specially:

Utilizing following long-line equation that two ends zero-sequence current and residual voltage are converted reference point, is example with the m end of circuit,

$\left[\begin{array}{c}{\stackrel{.}{U}}_{\mathrm{km}0}\\ {\stackrel{.}{I}}_{\mathrm{km}0}\end{array}\right]=\left[\begin{array}{cc}\mathrm{ch}\left({\mathrm{\&gamma;}}_{0}l\right)& -Z_{c0}\mathrm{sh}\left({\mathrm{\&gamma;}}_{0}l\right)\\ -\mathrm{sh}\left({\mathrm{\&gamma;}}_{0}l\right)/Z_{c0}& \mathrm{ch}\left({\mathrm{\&gamma;}}_{0}l\right)\end{array}\right]\left[\begin{array}{c}{\stackrel{.}{U}}_{m0}\\ {\stackrel{.}{I}}_{m0}\end{array}\right]$

In the formula: Hold the phasor of the residual voltage that is calculated for m;

Hold the phasor of the zero-sequence current that is calculated for m;

For the residual voltage of the m side of reference point k, Zero-sequence current for the m side of reference point k;

γ ₀Be the zero sequence propagation constant of circuit, Z _C0Be the zero sequence wave impedance of circuit,

L is that m holds to the distance of reference point k;

Ch (), sh () is respectively hyperbolic cosine and SIN function; In the formula: r ₀Be circuit unit length zero sequence resistance; L ₀Be circuit unit length zero sequence induction reactance; g ₀For the zero sequence electricity of lead unit length is over the ground led; C ₀Be circuit unit length zero sequence electric capacity;

Another end points of described circuit n does above-mentioned same processing.

9, Zero sequence current differential protection method according to claim 8 is characterized in that,

If shunt reactor, described zero-sequence current are arranged

Deduct the zero-sequence current of shunt reactor again, two ends respectively deduct the zero-sequence current of half shunt reactor.

10, Zero sequence current differential protection method according to claim 1 is characterized in that,

In the described circuit series compensation capacitance is arranged, shunt reactor is perhaps arranged, described reference point is selected in series compensation capacitance or shunt reactor place;

Do not have series compensation capacitance in the described circuit, and do not have shunt reactor, described reference point is selected in the optional position in the described circuit.

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