CN105044543A - Electric reactor fault determination method after PT disconnection - Google Patents

Abstract

The invention provides an electric reactor fault determination method after PT disconnection, comprising steps of (1) calculating zero sequence impedance Zm0 of the electric reactor after the PT disconnection, measuring fault front end current II and fault rear end current I2, if zero sequence impedance Zm0<2.5ZL, current variable Delta I1>0, Delta I2>0, and I1=I2, determining the fault is an inter-turn fault, and if zero sequence impedance Zm0<2.5ZL, current variable Delta I1<0, Delta I2<0, and I1=I2, determining the fault is an external fault. The invention provides a criteria to a fault protection action after the PT disconnection, and the criteria can reliably distinguish the open phase and the inter-turn fault, which improves the reliability of the protection action and improves the adaptability and action performance of the protection device.

Description

Reactor Fault method of discrimination after a kind of PT broken string

Technical field

The present invention relates to a kind of power system fault analysis method, be specifically related to the rear Reactor Fault method of discrimination of a kind of PT broken string.

Background technology

The capacitive earth current of remote extra high voltage network is very large, for absorbing this capacitive reactive power, the power-frequency overvoltage of restriction system and switching overvoltage, for the circuit using single phase autoreclosing, for restriction secondary arc current, the success ratio improving reclosing, all three-phase shunt reactor over the ground should be installed in the electric substation of power transmission line both ends or one end.

UHV (ultra-high voltage) shunt reactor runs power system stability and plays vital effect, and therefore, the research of UHV (ultra-high voltage) shunt reactor protection comes into one's own day by day.Large-scale reactor many employings split-phase type structure; its major failure is reactor single-phase earthing and turn-to-turn short circuit; therefore interturn short circuit protection is also the main protection of reactor; but longitudinal difference protection can not react shorted-turn fault, the zero sequence impedance relay be made up of reactor residual voltage, zero-sequence current constitutes reactor interturn protection.During inductor turn-to-turn fault, zero sequence source is inner at reactor, the advanced residual voltage of zero-sequence current, and what reactor head end measured is system zero sequence impedance; And when reactor external earth-fault; zero sequence source is outside at reactor; the delayed residual voltage of zero-sequence current; the zero sequence impedance of what reactor head end measured is reactor; because system zero sequence impedance is much smaller than reactor zero sequence impedance; therefore the size by comparing zero-sequence current direction and head end measurement zero sequence impedance can judge abort situation easily, improves the sensitivity of interturn protection simultaneously.

During reactor generation turn-to-turn fault rear due to PT broken string; reactor head end measures the zero sequence impedance less than reality; therefore each reactor protection producer meeting locking interturn protection when PT breaks; and the turn-to-turn short circuit of reactor is more common a kind of internal fault form; for improving the performance of interturn short circuit protection; improve sensitivity, in the urgent need to studying novel shunt reactor interturn short circuit protection principle.

Summary of the invention

For overcoming above-mentioned the deficiencies in the prior art, the invention provides the rear Reactor Fault method of discrimination of a kind of PT broken string, voltage characteristic after utilizing PT to break, calculates residual voltage when breaking rear and turn-to-turn fault; Utilize system normally to run and zero-sequence current size after fault, calculate the resistance value in two kinds of situations respectively; According to the difference of resistance value, propose the fault distinguishing method based on zero sequence impedance; When utilizing turn-to-turn fault, fault current feature, judges reactor internal fault external fault, proposes the criterion of turn-to-turn fault protection act after PT broken string.

Realizing the solution that above-mentioned purpose adopts is:

Reactor Fault method of discrimination after a kind of PT broken string, wherein, the method comprises the following steps:

(1) calculating reactance device zero sequence impedance Zm0 after PT broken string, measures fault phase head end electric current I 1 and fault phase end current I2;

(2) if zero sequence impedance Zm0 < is 2.5Z _l, current change quantity Δ I1 > 0, Δ I2 > 0, I1=I2, be then judged to turn-to-turn fault simultaneously;

(3) if zero sequence impedance Zm0 < is 2.5Z _l, current change quantity Δ I1 < 0, Δ I2 < 0, I1=I2, be then judged to external area error simultaneously.

First judge that PT breaks by reactor head end zero negative sequence voltage, due to the impact of protective device circuit connection mode, after PT broken string, broken string still has voltage mutually.And criterion derivation is above zero based on broken string phase voltage, therefore judge that broken string this phase voltage mutually rearmounted is zero.Then the zero sequence impedance value of half cycle (10ms) is calculated by reactor head end residual voltage, zero-sequence current sampled value: Z0 (i+1), Z0 (i+2) ..., Z0 (i+N/2).

Wherein, N is the sampling number in 1 cycle.Adopt the Parameter Identification based on least square, namely choose half-wave data window, if there is certain m to make Z0 (i+m) < 2.5Z _l, m=1,2,3 ..., N/2, can judge to break down.

Then the difference of phase currents of half cycle (10ms) is calculated by reactor head end current sampling data and end current sampled value: △ Is (i+1), △ Is (i+2) ..., △ Is (i+N/2); △ Im (i+1), △ Im (i+2) ..., △ Im (i+N/2).

Wherein, N is the sampling number in 1 cycle.Adopt the Parameter Identification based on least square, namely choose half-wave data window, if there is certain m to make △ Is (i+m) > 0, △ Im (i+m) > 0, m=1,2 simultaneously, 3 ..., N/2, can judge turn-to-turn fault occurs.Otherwise be then judged to external area error.

Preferably, in described step (1), described reactor comprises A phase, B phase and C phase;

Described zero sequence impedance, measures residual voltage by head end PT and measures zero-sequence current acquisition divided by head end CT;

Described fault phase head end electric current I 1, for electric current measured by head end current transformer;

Described fault phase end current I2, for electric current measured by end current mutual inductor.

Preferably, in described step (2), during any phase broken string, calculate zero sequence impedance Z _m0all be less than Z _l+ Z _n; When systems are functioning properly, zero-sequence current I _a0≈ 0, if now there is PT broken string, calculates zero sequence impedance Z _m0approach infinity, considers normal fluctuation and the error of calculation, gets calculating zero sequence impedance value and is less than 2.5Z _lbe judged as breaking down time (reactor resistance value).

Z _lfor reactor impedance; Z _nfor small reactor on neutral point

Described turn-to-turn fault is between reactor circle and circle because the short trouble that insulation damages causes;

Described current change quantity Δ I1 is head end current transformer current change quantity;

Described current change quantity Δ I2 is end current transformer current variable quantity.

Preferably, in described step (3), extra-high voltage reactor generally adopts the Y type mode of connection to be connected in parallel on the one or both ends of transmission line of electricity, and for suppressing the problem such as secondary arc current and resonance overvoltage, shunt reactor is often with small reactor on neutral point.When metallic earthing fault occurs A phase, with A phase for special phase boundray condition be

$\left\{\begin{array}{c}{U}_{A1}+U_{A2}+U_{A0}=0\\ I_{A1}=I_{A2}=I_{A0}=\frac{1}{3}{I}_A\end{array}\right.$

Consider small reactor on neutral point Z _n, protection installation place is measured zero sequence impedance and is:

$\begin{array}{c}{Z}_{m0}=\frac{3U_0}{3I_0}=\frac{U_A+U_B+U_C+3U_N}{3I_{A0}}\\ =\frac{U_{B1}+U_{B2}+U_{B0}+U_{C1}+U_{C2}+U_{C0}+3I_{A0}\&times;3Z_N}{3I_{A0}}\\ =\frac{a^2{U}_{A1}+{\mathrm{aU}}_{A2}+U_{A0}+{\mathrm{aU}}_{A1}+a^2{U}_{A2}+U_{A0}+3I_{A0}\&times;3Z_N}{3I_{A0}}\\ =\frac{\left(-U_{A1}-U_{A2}\right)+2U_{A0}+3I_{A0}\&times;3Z_N}{3I_{A0}}\\ =Z_L+3Z_N\end{array}$

In formula, U ₀for residual voltage, I ₀for zero-sequence current, U _a, U _b, U _cfor each phase voltage, U _nfor small reactor on neutral point voltage, Z _nfor neutral reactor impedance, I _a0for A phase zero-sequence current; Z _lfor reactor impedance, if now there is A phase PT broken string, U _a=0, it is still Z that zero sequence impedance is measured in protection installation place _l+ 3Z _n; If now there is B phase PT broken string, U _b=0, protection installation place is measured zero sequence impedance and is:

$\begin{array}{c}{Z}_{m0}=\frac{{\mathrm{aU}}_{A1}{a}^2{U}_{A2}+U_{A0}+3I_{A0}\&times;3Z_N}{3I_{A0}}\\ =\frac{\left(a-a^2\right)U_{A1}+\left(a-a^2\right)U_{A0}+3I_{A0}\&times;3Z_N}{3I_{A0}}\\ =-j\sqrt{3}\frac{Z_{2\mathrm{\&Sigma;}}+2Z_{0\mathrm{\&Sigma;}}}{3}+3Z_N\end{array}$

Work as Z _{2 Σ}=Z _{0 Σ}time, $Z_{m0}=-j\sqrt{3}{Z}_L+3Z_N$

In formula, U _a1for A phase positive sequence voltage, U _a2for A phase negative sequence voltage, U _a0for A phase residual voltage, a=e ^{j120 °}, j is the imaginary part of plural number, Z _{2 Σ}for equivalent negative sequence impedance, Z _{0 Σ}for equivalent zero sequence impedance;

In like manner, when there is C phase PT broken string, U _c=0, protection installation place is measured zero sequence impedance and is

$\begin{array}{c}{Z}_{m0}=\frac{a^2{U}_{A1}+{\mathrm{aU}}_{A2}+U_{A0}+3I_{A0}\&times;3Z_N}{3I_{A0}}\\ =\frac{\left(a^2-a\right)U_{A1}-\left(a-1\right)U_{A0}+3I_{A0}3Z_N}{3I_{A0}}\\ =\frac{-j\sqrt{3}{Z}_{2\mathrm{\&Sigma;}}-\left(j\frac{\sqrt{3}}{2}+\frac{3}{2}\right)Z_{0\mathrm{\&Sigma;}}}{3}+3Z_N\end{array}$

Work as Z _{2 Σ}=Z _{0 Σ}time, Z _m0=-Z _l+ 3Z _n

As seen from the above analysis, the singlephase earth fault outside rear generating region if reactor PT breaks, protection installation place calculates zero sequence impedance and is to the maximum for modulus value, Z _nfor small reactor on neutral point; Consider the error existed in measuring process, protect at whole timing considerations adequate allowance, with Zm0<2.5Z _lfor criterion; When systems are functioning properly, zero-sequence current I _a0≈ 0, if now there is PT broken string, calculates zero sequence impedance Z _m0approach infinity.

Described external area error is reactor place bus-bar fault or line fault.

During reactor generation turn-to-turn fault, fault phase head end I1 all increases with end current I2 and sized phases is identical;

During reactor generation near-end external area error, fault phase head end electric current I 1 all reduces with end current I2 and sized phases is identical;

During reactor generation far-end external area error, first end current is almost unchanged;

During reactor open-phase operation, first end current reduces to zero.

Compared with prior art, the present invention has following beneficial effect:

The present invention sentences turn-to-turn fault during PT broken string, without locking, can reliably distinguish non-three phase and turn-to-turn fault, thus can improve raising protection act reliability, improves adaptability and the performance of protective device.

Accompanying drawing explanation

Fig. 1 is the rear interturn protection logical diagram of PT broken string in the present invention;

Shunt reactor and system equivalent circuit diagram when Fig. 2 is turn-to-turn fault in the present invention;

Compound sequence network figure when Fig. 3 is reactor interturn short circuit of the present invention.

Embodiment

Below in conjunction with accompanying drawing, the specific embodiment of the present invention is described in further detail.

In reactor generating region, during turn-to-turn fault, fault signature is slight, for A phase, if equivalent impedance is Z after fault _f, shunt reactor and system equivalent circuit are as shown in Figure 2.

Be special phase with A phase, port F, F ' there is asymmetric three-phase voltage U A, UB, UC, can find out that boundary condition is

$\left\{\begin{array}{c}{U}_A=I_A(Z_F-Z_L)\\ U_B=0\\ U_C=0\end{array}\right.$

According to symmetrical component method, port F, F can be obtained ' the compound sequence network figure at place is as shown in Figure 3.

The each order components in port can be tried to achieve by compound sequence network figure:

$I_{A0}=-\frac{U_{A0}}{Z_{0\mathrm{\&Sigma;}}+(Z_L+3Z_N)}$

$I_{A2}=-\frac{U_{A0}}{Z_{2\mathrm{\&Sigma;}}+Z_L}$

$I_{A1}=-\frac{U_{A0}}{\frac{1}{3}(Z_F-Z_L)}-(I_{A0}+I_{A2})$

If protection installation place electric current is I _mA, I _mB, I _mC, then installation place voltage is protected to be shown below.

$\left\{\begin{array}{c}{U}_{mA}=I_{mA}\&times;Z_F+U_N\\ U_{mB}=I_{mB}\&times;Z_L+U_N\\ U_{mC}=I_{mC}\&times;Z_L+U_N\end{array}\right.$

Protection installation place measurement impedance Z _m0for

$\begin{array}{c}{Z}_{m0}=\frac{U_A+U_B+U_C+3U_N}{3I_{A0}}\\ =\frac{I_{mA}\&times;Z_F+I_{mB}\&times;Z_L+I_{mC}\&times;Z_L+3U_N}{3I_{A0}}\\ =\frac{I_{mA}\&times;\left(Z_F-Z_L\right)+3I_{A0}\&times;Z_L+3U_N}{3I_{A0}}=-Z_{0\mathrm{\&Sigma;}}\end{array}$

If now there is B phase PT broken string, because faulted phase voltage reduces less, residual voltage amplitude still close to phase voltage, 3U ₀≈ U _b.

$\begin{array}{c}\left|Z_{m0}\right|=\left|\frac{I_{mB}\&times;Z_L+U_N}{3I_{A0}}\right|\\ =\left|\frac{I_{mB}\&times;Z_L}{3I_{A0}}+Z_N\right|\&le;\left|\frac{I_{mB}\&times;Z_L}{3I_{A0}}\right|+Z_N\end{array}$

Based on experience value, during reactor 2% turn-to-turn fault, fault current is greater than for healthy phase current.So | Z _m0|≤Z _l+ Z _n.When in like manner A, C phase breaks, measurement impedance is all less than Z _l+ Z _n.

Finally should be noted that: above embodiment is only for illustration of the technical scheme of the application but not the restriction to its protection domain; although with reference to above-described embodiment to present application has been detailed description; those of ordinary skill in the field are to be understood that: those skilled in the art still can carry out all changes, amendment or equivalent replacement to the embodiment of application after reading the application; but these change, revise or be equal to replacement, all applying within the claims awaited the reply.

Claims (4)

1. a Reactor Fault method of discrimination after PT broken string, it is characterized in that, the method comprises the following steps:

(1) calculating reactance device zero sequence impedance Zm0 after PT broken string, measures fault phase head end electric current I 1 and fault phase end current I2;

(2) if zero sequence impedance Zm0 < is 2.5Z _l, current change quantity Δ I1 > 0, Δ I2 > 0, I1=I2, be then judged to turn-to-turn fault, wherein Z simultaneously _lfor reactor impedance;

(3) if zero sequence impedance Zm0 < is 2.5Z _l, current change quantity Δ I1 < 0, Δ I2 < 0, I1=I2, be then judged to external area error, wherein Z simultaneously _lfor reactor impedance.

2. method of discrimination as claimed in claim 1, it is characterized in that, in described step (1), described reactor comprises A phase, B phase and C phase;

Described zero sequence impedance, measures residual voltage by head end PT and measures zero-sequence current acquisition divided by head end CT;

Described fault phase head end electric current I 1, for current transformer head end measures electric current;

Described fault phase end current I2, for current transformer end measures electric current.

3. method of discrimination as claimed in claim 1, is characterized in that, in described step (2):

Described turn-to-turn fault is between reactor circle and circle because the short trouble that insulation damages causes;

Described current change quantity Δ I1 is current transformer head end current change quantity;

Described current change quantity Δ I2 is current transformer end current variable quantity.

4. method of discrimination as claimed in claim 1, is characterized in that, in described step (3), when external area error A phase PT broken string occurs A phase, calculates zero sequence impedance $Z_{m0}=\frac{3U_0}{3I_0}=\frac{U_A+U_B+U_C+3U_N}{3I_{A0}}=Z_L+3Z_N;$

U in formula ₀for residual voltage, I ₀for zero-sequence current, U _a, U _b, U _cfor each phase voltage, U _nfor small reactor on neutral point voltage, Z _nfor neutral reactor impedance, I _a0for A phase zero-sequence current;

When there is external area error B phase PT broken string in B phase,

$Z_{m0}=\frac{3U_0}{3I_0}=\frac{{\mathrm{aU}}_{A1}+a^2{U}_{A2}+U_{A0}+3I_{A0}\&times;3Z_N}{3I_{A0}}=-j\sqrt{3}\frac{Z_{2\mathrm{\&Sigma;}}+2Z_{0\mathrm{\&Sigma;}}}{3}+3Z_N;$

Work as Z _{2 Σ}=Z _{0 Σ}time, $Z_{m0}=-j\sqrt{3}{Z}_L+3Z_N;$

When there is external area error C phase PT broken string in C phase,

$Z_{m0}=\frac{3U_0}{3I_0}=\frac{a^2{U}_{A1}+{\mathrm{aU}}_{A2}+U_{A0}+3I_{A0}\&times;3Z_N}{3I_{A0}}=\frac{-j\sqrt{3}{Z}_{2\mathrm{\&Sigma;}}-(j\frac{\sqrt{3}}{2}+\frac{3}{2})Z_0\mathrm{\&Sigma;}}{3}+3Z_N;$

In formula, U _a1for A phase positive sequence voltage, U _a2for A phase negative sequence voltage, U _a0for A phase residual voltage, a=e ^{j120 °}, j is the imaginary part of plural number, Z _{2 Σ}for equivalent negative sequence impedance, Z _{0 Σ}for equivalent zero sequence impedance;

Work as Z _{2 Σ}=Z _{0 Σ}time, $Z_{m0}=-Z_L+3Z_N;$

If i.e. singlephase earth fault outside the rear generating region of reactor PT broken string, protection installation place calculates zero sequence impedance Zm0 and is to the maximum consider the error existed in measuring process, protect at whole timing considerations adequate allowance, with Zm0<2.5Z _lfor criterion;

Described external area error is reactor place bus-bar fault or line fault.