CN105207186A - Distance protection method for power transmission line containing unified power flow controller - Google Patents

Abstract

The invention discloses a distance protection method for a power transmission line containing a unified power flow controller. According to the method, a complex neural network algorithm or synchronous measurement phasor information on the two sides of the line is not required to be adopted, the voltage and current on the same side are used only, in cooperation with an R-L differential equation algorithm, the distance from a fault point to a mounting position of a relay protection device can be obtained through calculation, faults inside and outside regions can be recognized according to fault distance calculation results and fluctuation degree thereof, and influences of UPFC operation modes and control parameters are avoided, so that the accuracy of protection action behaviors is guaranteed, high convenience and reliability are realized, implementation is easy and a good application prospect is realized.

Description

A kind of distance protecting method for the transmission line containing THE UPFC

Technical field

The invention belongs to Relay Protection Technology in Power System field, be specifically related to a kind of distance protecting method for the transmission line containing THE UPFC.

Background technology

THE UPFC (unifiedpowerflowcontroller, UPFC) be jointly made up of series connection converter and parallel inverter, series connection converter injects an amplitude and all adjustable series voltage of phase place by series transformer to electrical network, with the meritorious of control circuit and reactive power flow; Parallel inverter is then absorbed by shunt transformer or provides active power constant to maintain DC voltage, simultaneously stability or provide reactive power with the voltage of the ac bus regulating UPFC and access.Therefore, UPFC can change ac bus voltage, line parameter circuit value and trend, thus increases substantially Transmission Lines capacity, reduction line loss and improve system stability level.

Although the control ability that UPFC is powerful brings great benefit to the operation of electric power system, its access proposes many new problems also to the protective relaying device in electrical network, performance greatly deterioration due to the access of UPFC of especially traditional distance protection.The general principle of traditional distance protection utilizes fundamental component in measuring voltage, electric current to calculate apparent impedance from protection installation place to fault point, and compared with setting value, thus judge whether to there occurs protection zone internal fault.But the electrical network of access UPFC, between age at failure, the operation characteristic of UPFC will change measuring voltage, steady-state component in electric current and transient state component, thus impacts the measurement impedance of traditional distance protection and performance.

At present; power transmission line distance protection improvement project containing UPFC mainly can be divided into two large classes: the first kind is the adaptive distance protection scheme based on neural network algorithm, and another kind of is the distance protection improvement project of synchro measure phasor based on transmission line both sides voltage, electric current.In general, UPFC has three kinds of different operational modes such as three kinds of STATCOM patterns, Static Series Synchronous Compensator pattern and complete UPFC pattern.And the controling parameters of UPFC requires to adjust by according to different operations of power networks under different operational mode.In addition, time different according to electric network fault type, the order of severity and duration, after fault also will there is larger difference in the output voltage of UPFC, electric current.Therefore, in Steady state and transient state situation, the operation conditions of UPFC is very complicated, causes the adaptive distance protection scheme based on neural network algorithm to need to carry out a large amount of tests and study.On the other hand, the requirement of distance protection improvement project to communication system based on the synchro measure phasor of transmission line both sides voltage, electric current is higher, and protective device is comparatively complicated, and therefore its engineer applied faces certain difficulty.

Therefore, how studying and to propose a kind of distance protection scheme being applicable to the transmission line containing UPFC, to guarantee the correctness of protection act behavior, running significant for guarantee power system safety and stability, is current urgent problem.

Summary of the invention

Technical problem solved by the invention is the electrical network overcoming existing access UPFC; between age at failure, the operation characteristic of UPFC is by the steady-state component in change measuring voltage, electric current and transient state component, thus to the problem that measurement impedance and the performance of traditional distance protection impact.Distance protecting method for the transmission line containing THE UPFC of the present invention; utilize this side voltage, Current calculation fault point to the distance of protective relaying device installation place; and according in the degree of fluctuation cog region of fault distance result of calculation and external area error; to guarantee the correctness of protection act behavior; convenient and reliable; easy realization, has a good application prospect.

Achieve the above object to solve, the technical solution adopted in the present invention is:

For a distance protecting method for the transmission line containing THE UPFC, it is characterized in that: comprise the following steps,

Step (1), arranges fault distance l _iterinitial value, make l _iter=0.5l _whole, wherein l _iterfor fault distance, for from protective relaying device installation place to the distance of fault point, l _wholefor the total length of transmission line, if transmission line breaks down, the moment occurs record trouble is t ₀;

Step (2), obtain the sampled value of protective relaying device at current sampling point, the sampling instant that current sampling point is corresponding is t _cal;

Step (3), carries out preliminary treatment to the sampled value obtained, and obtains the fault point voltage of the measuring voltage after the process of second order Butterworth LPF, electric current and reconstruct;

Step (4), if t _cal-t ₀>=5ms, then enter step (5); Otherwise, return step (2);

Step (5), by t _cal-5ms the moment is to t _calsampled data between moment, substitutes into the R-L Differential Equation Model of transmission line, obtains formula (1),

$\begin{array}{c}{u}_a\left(t\right)=\{L_{line\left(1\right)}\frac{d\[i_a\left(t\right)-i_{a\left(0\right)}\left(t\right)\]}{dt}+R_{line\left(1\right)}\[i_a\left(t\right)-i_{a\left(0\right)}\left(t\right)\]\\ +L_{line\left(0\right)}\frac{{\mathrm{di}}_{a\left(0\right)}\left(t\right)}{dt}+R_{line\left(0\right)}\·i_{a\left(0\right)}\left(t\right)\}\·l+u_{fr}\left(t\right)\end{array}---\left(1\right)$

Wherein, u _a(t) and i _at () is respectively the phase voltage and electric current that protective relaying device measurement obtains, u _frt () is the fault point voltage of reconstruct, i _{a (0)}t zero-sequence current that () obtains for protective relaying device measurement; R _{line (1)}and L _{line (1)}be respectively transmission line unit length positive sequence resistance and reactance, R _{line (0)}and L _{line (0)}be respectively transmission line unit length zero sequence resistance and reactance; L is the result of calculation that protective relaying device installation place is arrived in fault point;

Step (6), utilizes the differential equation group of least-squares algorithm to formula (1) to solve, obtains the result of calculation l of fault point to protective relaying device installation place distance, and make l _iter=l;

Step (7), if t _cal-t ₀<30ms, then move to next sampled point, and repeat step (2) ~ step (6), calculates the distance of fault point to protection protective relaying device installation place of next sampled point; Otherwise, enter step (8);

Step (8), according to step (7), obtains, in fault, moment t occurs ₀the fault distance that rear 5ms to 30ms time period each sampled point calculates, because moment t occurs fault ₀the fault distance result of calculation of rear 5ms to 10ms time period is unstable, therefore utilizes fault that moment t occurs ₀the fault distance result of calculation of rear 10ms to 30ms time period describes its degree of fluctuation, according to formula (2), obtains coefficient of variation σ,

$\mathrm{\&sigma;}=\left|\frac{l_{max}-l_{min}}{(l_{max}+1_{\min })/2}\right|---\left(2\right)$

Wherein, l _maxand l _minbe respectively maximum and the minimum value of fault distance result of calculation;

Step (9), the criterion according to formula (3),

It is troubles inside the sample space or external area error that identification obtains fault, guarantees the correctness of the protection act behavior of protective relaying device.

The aforesaid distance protecting method for the transmission line containing THE UPFC; it is characterized in that: the described second order Butterworth LPF of step (3) is used for the high fdrequency component in filtering measuring voltage, electric current, ensure that each electric parameters measured in formula (1) in step (5) meets the initial parameter model of transmission line.

The aforesaid distance protecting method for the transmission line containing THE UPFC, is characterized in that: the amplitude-frequency response characteristic of described second order Butterworth LPF, as shown in formula (4),

$|H\left(\mathrm{\&omega;}\right){|}^2=\frac{1}{1+{(\mathrm{\&omega;}/{\mathrm{\&omega;}}_c)}^4}---\left(4\right)$

Wherein, ω _cfor cut-off angular frequency.

The invention has the beneficial effects as follows: the distance protecting method for the transmission line containing THE UPFC of the present invention; without the need to adopting complicated neural network algorithm or the synchro measure phasor information of circuit both sides; only utilize this side voltage, Current calculation fault point to the distance of protective relaying device installation place; and according in the degree of fluctuation cog region of fault distance result of calculation and external area error; to guarantee the correctness of protection act behavior; convenient and reliable; easy realization, has a good application prospect.

Accompanying drawing explanation

Fig. 1 is the flow chart of the distance protecting method for the transmission line containing THE UPFC of the present invention.

Embodiment

Below in conjunction with Figure of description, the present invention is further illustrated.

As shown in Figure 1, the distance protecting method for the transmission line containing THE UPFC of the present invention, comprises the following steps,

Step (1), arranges fault distance l _iterinitial value, make l _iter=0.5l _whole, wherein l _iterfor fault distance, be the distance from protective relaying device installation place to fault point, l _wholefor the total length of transmission line, if transmission line breaks down, the moment occurs record trouble is t ₀;

Step (2), obtain the sampled value of protective relaying device at current sampling point, the sampling instant that current sampling point is corresponding is t _cal;

Step (3), preliminary treatment is carried out to the sampled value obtained, obtain measuring voltage, the electric current after the process of second order Butterworth LPF, and reconstruct fault point voltage, second order Butterworth LPF is used for the high fdrequency component in filtering measuring voltage, electric current, ensures that each electric parameters of subsequent calculations use meets the initial parameter model of transmission line, the amplitude-frequency response characteristic of second order Butterworth LPF, as shown in formula (4)

$|H\left(\mathrm{\&omega;}\right){|}^2=\frac{1}{1+{(\mathrm{\&omega;}/{\mathrm{\&omega;}}_c)}^4}---\left(4\right)$

Wherein, ω _cfor cut-off angular frequency, in the present invention, get ω _c=942.48rad/s;

The distance protection being arranged on transmission line first and end cannot know the voltage of fault point, can only utilize the measuring voltage after the process of second order Butterworth LPF, electric current is reconstructed fault point voltage, as shown in formula (5),

Wherein, u _frfor the fault point voltage of reconstruct, R _frfor the transition resistance of reconstruct, u _fr1component before the fault of the fault point voltage of reconstruct, i _{a (0)}for the zero-sequence current that protective relaying device measurement obtains, i _afor the faulted phase current that protective relaying device measurement obtains, according to formula (6), obtain reconstruct fault point voltage fault before component u _fr1,

u _fr1＝u _a-(L _line(1)di _a/dt+R _line(1)i _a)l _iter(6)

Wherein, u _afor the faulted phase voltage that protective relaying device measurement obtains, R _{line (1)}and L _{line (1)}be respectively transmission line unit length positive sequence resistance and reactance.Meanwhile, before breaking down, in formula (5), on the right of equal sign, Section 2 is zero, i.e. R _fri _{a (0)}=0, R _fri _a=0; After breaking down, in formula (5), on the right of equal sign, Section 1 is zero, i.e. u _fr1=0, i _{a (0)}or i _ait is then the actual measurement electric current of protective relaying device;

Step (4), if t _cal-t ₀>=5ms, then enter step (5); Otherwise, return step (2);

Step (5), by t _cal-5ms the moment is to t _calsampled data between moment, substitutes into the R-L Differential Equation Model of transmission line, obtains formula (1),

$\begin{array}{c}{u}_a\left(t\right)=\{L_{line\left(1\right)}\frac{d\&lsqb;i_a\left(t\right)-i_{a\left(0\right)}\left(t\right)\&rsqb;}{dt}+R_{line\left(1\right)}\&lsqb;i_a\left(t\right)-i_{a\left(0\right)}\left(t\right)\&rsqb;\\ +L_{line\left(0\right)}\frac{{\mathrm{di}}_{a\left(0\right)}\left(t\right)}{dt}+R_{line\left(0\right)}\&CenterDot;i_{a\left(0\right)}\left(t\right)\}\&CenterDot;l+u_{fr}\left(t\right)\end{array}---\left(1\right)$

Wherein, u _a(t) and i _at () is respectively the phase voltage and electric current that protective relaying device measurement obtains, u _frt () is the fault point voltage of reconstruct, i _{a (0)}t zero-sequence current that () obtains for protective relaying device measurement; R _{line (1)}and L _{line (1)}be respectively transmission line unit length positive sequence resistance and reactance, R _{line (0)}and L _{line (0)}be respectively transmission line unit length zero sequence resistance and reactance; L is the result of calculation that protective relaying device installation place is arrived in fault point;

Step (6), utilizes the differential equation group of least-squares algorithm to formula (1) to solve, obtains the result of calculation l of fault point to protective relaying device installation place distance, and make l _iter=l;

Step (7), if t _cal-t ₀<30ms, then move to next sampled point, and repeat step (2) ~ step (6), calculates the distance of fault point to protective relaying device installation place of next sampled point; Otherwise, enter step (8);

Step (8), according to step (7), obtains, in fault, moment t occurs ₀the fault distance that rear 5ms to 30ms time period each sampled point calculates.Because moment t occurs fault ₀the fault distance result of calculation of rear 5ms to 10ms time period is unstable, therefore utilizes fault that moment t occurs ₀the fault distance result of calculation of rear 10ms to 30ms time period describes its degree of fluctuation, according to formula (2), obtains coefficient of variation σ,

$\mathrm{\&sigma;}=\left|\frac{l_{max}-l_{min}}{(l_{max}+1_{\min })/2}\right|---\left(2\right)$

Wherein, l _maxand l _minbe respectively maximum and the minimum value of fault distance result of calculation;

Step (9), the criterion according to formula (6),

It is troubles inside the sample space or external area error that identification obtains fault, guarantees the correctness of the protection act behavior of protective relaying device.

More than show and describe general principle of the present invention, principal character and advantage.The technical staff of the industry should understand; the present invention is not restricted to the described embodiments; what describe in above-described embodiment and specification just illustrates principle of the present invention; without departing from the spirit and scope of the present invention; the present invention also has various changes and modifications, and these changes and improvements all fall in the claimed scope of the invention.Application claims protection range is defined by appending claims and equivalent thereof.

Claims (3)

1., for a distance protecting method for the transmission line containing THE UPFC, it is characterized in that: comprise the following steps,

Step (1), arranges fault distance l _iterinitial value, make l _iter=0.5l _whole, wherein l _iterfor fault distance, for from protective relaying device installation place to the distance of fault point, l _wholefor the total length of transmission line, if transmission line breaks down, the moment occurs record trouble is t ₀;

Step (2), obtain the sampled value of protective relaying device at current sampling point, the sampling instant that current sampling point is corresponding is t _cal;

Step (3), carries out preliminary treatment to the sampled value obtained, and obtains the fault point voltage of the measuring voltage after the process of second order Butterworth LPF, electric current and reconstruct;

Step (4), if t _cal-t ₀>=5ms, then enter step (5); Otherwise, return step (2);

Step (5), by t _cal-5ms the moment is to t _calsampled data between moment, substitutes into the R-L Differential Equation Model of transmission line, obtains formula (1),

$\begin{array}{c}{u}_a\left(t\right)=\{L_{line\left(1\right)}\frac{d\&lsqb;i_a\left(t\right)-i_{a\left(0\right)}\left(t\right)\&rsqb;}{dt}+R_{line\left(1\right)}\&lsqb;i_a\left(t\right)-i_{a\left(0\right)}\left(t\right)\&rsqb;\\ +L_{line\left(0\right)}\frac{{\mathrm{di}}_{a\left(0\right)}\left(t\right)}{dt}+R_{line\left(0\right)}\&CenterDot;i_{a\left(0\right)}\left(t\right)\}\&CenterDot;l+u_{fr}\left(t\right)\end{array}---\left(1\right)$

Wherein, u _a(t) and i _at () is respectively the phase voltage and electric current that protective relaying device measurement obtains, u _frt () is the fault point voltage of reconstruct, i _{a (0)}t zero-sequence current that () obtains for protective relaying device measurement; R _{line (1)}and L _{line (1)}be respectively transmission line unit length positive sequence resistance and reactance, R _{line (0)}and L _{line (0)}be respectively transmission line unit length zero sequence resistance and reactance; L is the result of calculation that protective relaying device installation place is arrived in fault point;

Step (6), utilizes the differential equation group of least-squares algorithm to formula (1) to solve, obtains the result of calculation l of fault point to protective relaying device installation place distance, and make l _iter=l;

Step (7), if t _cal-t ₀<30ms, then move to next sampled point, and repeat step (2) ~ step (6), calculates the distance of fault point to protection protective relaying device installation place of next sampled point; Otherwise, enter step (8);

Step (8), according to step (7), obtains, in fault, moment t occurs ₀the fault distance that rear 5ms to 30ms time period each sampled point calculates, because moment t occurs fault ₀the fault distance result of calculation of rear 5ms to 10ms time period is unstable, therefore utilizes fault that moment t occurs ₀the fault distance result of calculation of rear 10ms to 30ms time period describes its degree of fluctuation, according to formula (2), obtains coefficient of variation σ,

$\mathrm{\&sigma;}=\left|\frac{l_{max}-l_{min}}{(l_{max}+l_{\min })/2}\right|---\left(2\right)$

Wherein, l _maxand l _minbe respectively maximum and the minimum value of fault distance result of calculation;

Step (9), the criterion according to formula (3),

It is troubles inside the sample space or external area error that identification obtains fault, guarantees the correctness of the protection act behavior of protective relaying device.

2. the distance protecting method for the transmission line containing THE UPFC according to claim 1; it is characterized in that: the described second order Butterworth LPF of step (3) is used for the high fdrequency component in filtering measuring voltage, electric current, ensure that each electric parameters measured in formula (1) in step (5) meets the initial parameter model of transmission line.

3. the distance protecting method for the transmission line containing THE UPFC according to claim 1 and 2, is characterized in that: the amplitude-frequency response characteristic of described second order Butterworth LPF, as shown in formula (4),

$|H\left(\mathrm{\&omega;}\right){|}^2=\frac{1}{1+{(\mathrm{\&omega;}/{\mathrm{\&omega;}}_c)}^4}---\left(4\right)$

Wherein, ω _cfor cut-off angular frequency.