CN1180272C - Small-current earth fault switch-selecting and sectioning method for power system - Google Patents

Abstract

The present invention relates to line selecting and sectioning method for low-current ground faults of an electric power system, particularly to a protective method for single-phase grounding of a low-current grounding system with self characteristics. The present invention uses various on-line monitoring devices to select fault lines and determine fault sections. The present invention is characterized in that relevant information of transient zero-sequence voltage and transient zero-sequence current generated by faults are simultaneously used as references for fault line selection and sectioning, and components with compatibility constraint relation in the transient zero-sequence voltage and the transient zero-sequence current generated by the faults are used as judging references. Fault lines are fault sections are determined according to wattless power and directions in transient signals. The method of the present invention can be suitable for neutral-point ungrounded systems, arc-suppression coil grounding systems and high-resistance grounding systems without the influence of flash-arc faults. Moreover, other kinds of line fault information are not needed during fault line selection, and the present invention has self characteristics.

Description

Electric system low-current ground fault line selection, segmentation method

Technical field

Electric system low-current ground fault line selection, segmentation method; relate to a kind of isolated neutral, grounding through arc or high resistance ground system medium voltage distribution network single-phase earth fault line selection, split fix method, relate in particular to a kind of single-phase earthing protection method for small current earthing system that has from the tool characteristics.

Background technology

China's distribution system adopts isolated neutral or resonance grounding (grounding through arc) processing mode mostly.The reasons such as ground connection process instability little owing to fault current, that arc light causes, singlephase earth fault detect and are difficult to thorough solution always.

In the isolated neutral electrical network, fault wire power frequency zero-sequence current equals all and perfects line mutual-ground capacitor electric current sum during single-phase earthing, and direction is pointed to bus from circuit.Equal self capacitive earth current and perfect the circuit zero-sequence current, direction is pointed to circuit from bus.But above-mentioned rule is no longer set up in arc suppression coil earthing system.

In arc suppression coil earthing system, because the induction reactance increase of arc suppression coil is its compensating action descends, and the distributed capacitance capacitive reactance descends over the ground for higher hamonic wave.Therefore, can ignore the effect of arc suppression coil, think that promptly faulty line is bigger and direction is opposite than non-fault line amplitude for the harmonic wave composition more than 5 times in the zero-sequence current.But harmonic content is very little in the fault zero-sequence current, and detection acquires a certain degree of difficulty.

System's negative phase-sequence equivalent electrical circuit is different from the zero sequence equivalent electrical circuit during fault, and the negative-sequence current that is produced by fault is flowed through and directly injected high-pressure system by transformer behind the faulty line, and it is very little to perfect circuit negative-sequence current amplitude.The method of utilizing this principle as: " Chinese patent communique " on September 6th, 2000 is disclosed; application number: 00114452.9; denomination of invention: earthing protection method for small current earthing system; this method step is 1; the monitoring system residual voltage; each feeder line negative-sequence current; select each phase voltage of monitoring and each feeder line zero-sequence current; 2; residual voltage is greater than setting valve decision-making system fault then; 3; calculate fault each feeder line negative-sequence current variable quantity of back takes place; 4; certain feeder line negative-sequence current variable quantity respectively can be according to the negative-sequence current size during greater than accurate working current; direction or energy function are judged this line fault.Though this method also can realize failure line selection and segmentation, it is bigger influenced by load variations.

Utilize above-mentioned feature to carry out the method for failure line selection, the steady-state current signal that has produced when having utilized fault mostly respectively has relative merits.Because the steady-state current amplitude is little, and physical fault many be as Fig. 1, Fig. 2, flashing fault shown in Figure 3, fault takes place during near maximal value and disappears behind voltage over zero at voltage, so does not have stable steady-state process basically in the ground current.Brought limitation based on the method for stable state for all.

Constantly perfect along with the development of distribution automation and fault management capability, how singlephase earth fault is realized that quick location, isolation and the recovery of fault section perfect the power supply of circuit, and not only be confined to traditional failure line selection, become the major subjects of those skilled in the art research.The present invention is for addressing this problem, and is self-closing as railway, connect circuit etc. particularly for singly going out the line length system of distance, will produce positive effect.

Summary of the invention

The technical problem to be solved in the present invention is, provides a kind of and can be suitable for all small current neutral grounding systems, is not subjected to the flashing fault effects, the reliability height, has the low-current ground fault line selection method from the tool characteristics, and can utilize this method to realize the fault segmentation.When singlephase earth fault appears in system, can determine faulty line or fault section fast, further automatic or manual instruction respective circuit breakers, switching manipulation excision faulty line or isolated fault section.Utilize this method can realize the defencive function of singlephase earth fault.

The technical scheme that technical solution problem of the present invention is taked is: carry out failure line selection and determine fault section by various on-line measuring devices, implementation procedure is:

A is with the variation of residual voltage or the zero-sequence current entry condition as fault;

B determines the initial moment of fault and transient signal time-delay length;

C carries out the two-way tape pass filter to transient state residual voltage, transient zero-sequence current;

D calculates failure line selection, the required failure message of segmentation: determine filter parameter and extract corresponding component u in transient state residual voltage, the electric current according to the transient zero-sequence current main resonatnt frequency ₀' (t) and i ₀' (t), make it keep the capacitive restriction relation, $u_0^{\′}\left(t\right)=R*i_0^{\′}\left(t\right)+\frac{1}{c}{\∫}_{-\∞}^t{i}_0^{\′}\left(\mathrm{\τ}\right)\mathrm{d\τ},$ Wherein R is the circuit equiva lent impedance, and C is the line-to-ground equivalent capacity, again according to the component u with capacitive restriction relation ₀' (t) and i ₀' (t) calculate the size and the direction of reactive power in the transient signal: $Q={\∫}_0^T{i}_0^{\′}\left(t\right)\×\frac{{\mathrm{du}}_0^{\′}\left(t\right)}{\mathrm{dt}}\mathrm{dt}={\∫}_0^T{i}_0^{\′}\left(t\right){\mathrm{du}}_0^{\′}\left(t\right),$ Wherein T is a power frequency period;

E determines faulty line according to the size and the direction of reactive power in the transient signal;

F determines fault section for faulty line according to the size and the direction of reactive power in the transient signal.

This method is to utilize the transient state residual voltage of fault generation, transient zero-sequence current as basis for estimation simultaneously, by press the on-Line Monitor Device that section is installed on outlet outlet or circuit, realizes single-phase grounded malfunction in grounded system of low current route selection, segmentation.

Transient state residual voltage, transient zero-sequence current signal are carried out the two-way tape pass filter to be handled as follows: adopt the related function method to estimate the main resonatnt frequency ω 1 of transient zero-sequence current, determine that the wave filter high pass cut off frequency is 3 ω 0, low-pass cut-off frequencies is ω 1+ ω r, wherein ω 0 is the power frequency angular frequency, ω r is a safe clearance, utilizes IIR filter IIR that transient state residual voltage, transient zero-sequence current are made the two-way tape pass filter.

In step e according to transient signal in the size and the method that direction is determined faulty line of reactive power as follows: for the check point of the different outlets outlets of same bus, if the transient state reactive power is less than zero, this circuit is a faulty line, otherwise the transient state reactive power is greater than zero, and it is for perfecting circuit.

The method of determining fault section in step f is as follows: for faulty line, determine fault section by main website according to the failure message that each pick-up unit on the circuit reports, if settle a plurality of pick-up units by section thereon, then fault is positioned at the opposite section of both sides reactive power direction, if the transient state reactive power of all check points is all greater than zero, then the trouble spot is between bus and first check point, if all less than zero, then the trouble spot is between last check point and line end for the transient state reactive power of all check points.

Compared with prior art the invention has the beneficial effects as follows:

During single-phase earthing, transient state process mainly by fault relatively the capacitor discharge process constitute with non-fault charging process mutually.The ratio of maximum transient electric current and stable state capacitance current is approximately equal to the ratio of resonance frequency and work frequency, and promptly its amplitude may be bigger several times to tens times than steady-state value.

In resonant earthed system, because the electric current in the arc suppression coil can not suddenly change, the transient current pace of change of the arc suppression coil of flowing through is far smaller than the variation of transient state capacitance current.Simultaneously, the induction reactance of arc suppression coil increases along with increasing of frequency, and the capacitive reactance of electric capacity descends simultaneously.Therefore, when adopting transient zero-sequence current, can not consider the influence of arc suppression coil.

The zero sequence transient current generally is made up of a plurality of sinusoidal signals by exponential damping, and wherein the resonance signal of total system perfects in fault wire and all and all accounts for principal ingredient in the line, is called the dominant frequency signal.Can prove that on any check point of any system, the dominant frequency component of transient state residual voltage, electric current must be the capacitive relation.Utilize this relation can determine faulty line and fault section.This method only needs residual voltage, the zero sequence current signal of check point when route selection, can be used as the protection philosophy of one-phase ground protection relay.

In sum, when utilizing method of the present invention to carry out single-phase earth fault line selection or segmentation, transient signal is bigger than steady-state signal amplitude, be easy to detect; Not influenced by the system neutral earthing mode; Insulating during the flashing fault to puncture again each time all can produce transient state process, and transient signal is abundant, widely applicable more; During failure line selection, do not need other line information, have from the tool characteristics.

Description of drawings

Fig. 1 perfects line zero-sequence current waveform for the singlephase earth fault of physical record;

Fig. 2 is the fault wire zero-sequence current waveform with the same fault of Fig. 1;

Fig. 3 is the residual voltage waveform with the same fault of Fig. 1;

Fig. 4 is that transient state residual voltage, electric current capacitive component concern synoptic diagram;

Fig. 5 is two ends, trouble spot transient state reactive power and direction synoptic diagram;

Fig. 6 is special-purpose line selection apparatus structural drawing;

Fig. 7 is a fault segmentation implement device synoptic diagram.

Among the figure: R circuit equiva lent impedance C line-to-ground distributed capacitance i ₀' (t) zero-sequence current u ₀' (t) residual voltage D1-D5 is that check point f trouble spot DAU1-DAUn data acquisition unit CB outlet isolating switch S1-S6 on-pole switch FTU1-FTU6 is that feeder line on-line measuring device RTU is transformer station's on-line measuring device.

Embodiment

The present invention can realize failure line selection and fragmentation feature respectively with several different methods, can be the specialized equipment with single-minded function, also can install with other, as distribution automation system, the shared hardware and software platform of feeder line outlet protection equipment.

Narration respectively below:

1, power station fault line selection method for single-phase-to-ground fault:

Utilize the present invention can as classic method, compare each bar outlet failure message and realize failure line selection.Accompanying drawing 6 is depicted as its apparatus structure synoptic diagram, and wherein dotted portion is optional part.Each data acquisition unit DAU is responsible for detecting different circuits, and will detect the data upload CPU element and focus on, and result can show or upload remote dispatching in a variety of forms in the locality.The specific implementation step is as follows:

1) with the variation of residual voltage, zero-sequence current entry condition as fault:

In small current neutral grounding system, when the metallicity singlephase earth fault took place, the ground connection phase voltage was reduced to 0, and two perfect phase voltage raise for line voltage be phase voltage

Doubly.Simultaneously, residual voltage on the circuit and zero-sequence current all can increase, the phase voltage when wherein the residual voltage amplitude equals operate as normal.Therefore, can utilize residual voltage or zero-sequence current to surmount the entry condition of certain threshold as singlephase earth fault:

S ₀＞S _0d

Used residual voltage, zero-sequence current can be that the result who directly measures calculates by three-phase voltage or electric current:

$S_0\left(t\right)=\frac{1}{3}(S_A\left(t\right)+S_B\left(t\right)+S_C\left(t\right))$

S has represented voltage or electric current in above-mentioned two formulas.

When there was transition resistance in earth point, residual voltage reduced along with the increase of transition resistance.The influence of unbalance voltage when overcoming operate as normal simultaneously, the threshold of residual voltage generally is taken as 30% of phase voltage.

The power frequency effective value of residual voltage electric current or instantaneous value can be as the foundations of fault initiating condition.

2) determine the initial moment of fault according to the variation of transient zero-sequence current signal:

Because transient signal is only shorter in initial moment appearance of fault and duration in the quiet earth fault.In order to utilize all failure messages fully, exactly, must search the initial moment of fault exactly, promptly represent first measurement point of this transient state process.

After singlephase earth fault starts, start previous power frequency cycle in the time range that starts a back power frequency cycle, seeking the moment that transient zero-sequence current sudden change flow control once surmounts a set threshold, can think the initial moment of fault.Threshold can be measured instantaneous maximal value according to transient zero-sequence current sudden change in this scope and determines, as its 20%.

3) according to the autocorrelation function estimating system main resonatnt frequency of transient zero-sequence current:

Method based on the fourier transform analysis signal spectrum must could estimate the signal wave spectrum reliably by a large amount of samplings, and must suppose that signal is static.Because instantaneous value has transient state and non-static characteristics, the wave spectrum that calculates may be not accurate enough.To also making the wave spectrum distortion of calculating after the weighting of FFT employing window function.What analyze attenuated sinusoidal signal is the Prony method than good model, but it is subjected to the influence of noise bigger.

The calculating of instantaneous frequency can adopt related function to realize that it can estimate the dynamic change in the measuring-signal.

$r\left(\mathrm{\τ}\right)={\∫}_0^{T}x\left(t\right)x(t+\mathrm{\τ})\mathrm{dt}$

The related function of discrete data-signal is as shown in the formula expression:

$r\left[k\right]=\underset{n=1}{\overset{N-k}{\mathrm{\Σ}}}x\left[n\right]x[n+k]$

Wherein: N is a data length, and k is time-delay.Participate in computing data should from zero hour of this transient process to the finish time.The related function time value that related function reaches the minimum value place equals the half cycle length by the sinusoidal signal of exponential damping.Can obtain the main resonatnt frequency of transient state process in view of the above.

4) according to system's main resonatnt frequency determine bandpass filter by frequency:

Because the big transient voltage current component of frequency ratio system dominant frequency not exclusively satisfies capacitive relation, the amplitude that promptly not exclusively satisfies fault wire on this frequency perfects circuit greater than all and polarity is opposite.Therefore, before calculating fault direction, must carry out low-pass filtering to transient state residual voltage, current signal.The effect of low-pass filtering mainly is: the unwanted transient signal of filtering, filtering high-frequency interferencing signal.

Simultaneously, for the faulty line of neutral point resonant earthed system, it is emotional resistance near power frequency, therefore should the elimination low frequency component.

Therefore, should make bandpass filtering to transient state residual voltage electric current.Wherein low pass determines according to main resonatnt frequency by frequency.Because the actual wave digital lowpass filter that uses can not have the passband of zero width.Therefore, on the predominant frequency that calculates, must add certain safe clearance ω _r, specifically determine by following formula:

ω _r＝max(200，0.1ω _h)

Wherein: ω _rBe main resonatnt frequency.And the cutoff frequency of high pass can be elected 3 times work frequency as.The cutoff frequency that is bandpass filter is: (3 ω ₀, ω ₁+ ω _r)

5) transient state residual voltage, electric current are implemented the two-way tape pass filter:

In order not influence the phase relation between dominant frequency signal voltage, electric current, require digital band-pass filter to have linear phase.If use the wave filter (as the infinite impulse response iir filter) of nonlinear phase, then must use the bidirectional filtering technology to avoid phase distortion.Promptly earlier begin to carry out low-pass filtering sampled point to the last, the result of the filtering first time is begun inverse filtering up to first data from last data again from first sampled point of transient signal.

6) determine duration of transient state process:

The duration difference of transient signal under the different faults condition is for operational failure data more accurately must determine that the concluding time of fault is the delay time of fault.Because most transient state process duration mostly less than a power frequency cycle, are therefore carried out bandpass filtering to the transient zero-sequence current data of a complete power frequency period after the fault, choose the maximum amplitude of signal in the transient zero-sequence current component that keeps.Compare one by one to top from the tail end of sample sequence, up to reaching a ultimate value (for example peaked 10%).With the finish time of this moment as transient signal.

7) calculate transient state reactive power size and Orientation:

The method of calculating transient state residual voltage electric current reactive power has multiple.As with all radio-frequency components of transient zero-sequence current signal displacement 90 degree all:

$i_0^{\′\′}\left(t\right)=\underset{k=0}{\overset{N}{\mathrm{\Σ}}}{I}_0^{\′}\sin (w_k+{\mathrm{\θ}}_k+\mathrm{\π}/2)$

Calculate reactive power again:

$Q={\∫}_0^T{u}_0\left(t\right)i_0^{\′\′}\left(t\right)\mathrm{dt}$

Because under the frequency of transient signal, therefore the effect of line impedance can utilize formula less than distributed capacitance $Q={\∫}_0^T{i}_0^{\′}\left(t\right)\×\frac{{\mathrm{du}}_0^{\′}\left(t\right)}{\mathrm{dt}}\mathrm{dt}={\∫}_0^T{i}_0^{\′}\left(t\right){\mathrm{du}}_0^{\′}\left(t\right)$ Simplify and calculate the transient state reactive power.

8) relatively each bar outlet transient state reactive power direction is determined faulty line:

The transient state reactive power of faulty line for the negative circuit that perfects for just.Owing to be subject to noise when more weak when perfecting line current signal, therefore can select some bigger outlets of transient current amplitude or transient state reactive power in its polarity of comparison.

This kind equipment has more single-minded function, needs by many of equipment monitors even all outlets.Equipment set mainly is made of a plurality of collecting unit DAU and a CPU element.

Among Fig. 6: a responsible monitor voltage signal in the collecting unit, all the other every collecting unit is responsible for monitoring the zero-sequence current of some outlets, whole device can be selected different collecting unit numbers for use according to power station outlet number.After breaking down, start all collecting units simultaneously by residual voltage or zero-sequence current, data before and after the fault of collecting unit record certain-length, and pass to CPU element.

CPU element is responsible for the management and the co-ordination of package unit, accepts the definite value that the user is provided with, and stores, analyzes the fault data of each collecting unit record, utilizes this method to determine to provide route selection result and alerting signal with different forms behind the faulty line.And can as required fault data or analysis result be uploaded higher level main website or distant place system.

2, fault segmentation method:

Realize fragmentation feature, whole system should be made up of three parts: be distributed in the on-line measuring device on each check point of circuit, the CPU (central processing unit) that is positioned at transformer station and communication system.Accompanying drawing 7 is depicted as an exemplary systems structure, utilizes the existing hardware device of feeder automation,, as CPU (central processing unit), only need increase corresponding software again and get final product with main website as on-line measuring device with FTU, RTU.Be compared to the method for only utilizing transient zero-sequence current, this method must need residual voltage, zero sequence current signal simultaneously.

On-line measuring device is responsible for the variation of real-time Monitoring Line residual voltage, zero-sequence current, calculates the size and Orientation of transient state reactive power in the back of breaking down, and result of calculation is reported CPU (central processing unit).CPU (central processing unit) is determined fault section and is sent alerting signal after receiving the information that each on-line measuring device reports.By artificial or automatic remote control respective switch fault isolation and recovery are perfected the power supply of circuit again.

The specific implementation step is as follows:

The circuit on-line measuring device:

1) with the variation of residual voltage, zero-sequence current entry condition as fault,

2) determine the initial moment of fault according to the variation of transient zero-sequence current signal,

3) according to the autocorrelation function estimating system main resonatnt frequency of transient zero-sequence current,

4) according to system's main resonatnt frequency determine bandpass filter by frequency,

5) transient state residual voltage, electric current are implemented the two-way tape pass filter,

6) determine duration of transient state process,

7) calculate transient state reactive power size and Orientation.

Main website:

Determine fault section according to different check point failure messages on the faulty line,

Fault is positioned at the opposite section of both sides reactive power direction.If all greater than zero, then the trouble spot is between bus and first check point for the transient state reactive power direction of all check points.On the contrary, if the transient state reactive power direction of all check points all less than zero, then the trouble spot is between last check point and line end.

3, singlephase earth fault outlet guard method:

Utilize the present invention to realize that failure line selection only needs residual voltage and this circuit zero sequence current signal, do not need the failure message of other circuit, have from the tool characteristics.Therefore, can utilize this method to realize the singlephase earth fault defencive function.The specific implementation step is as follows:

1) with the variation of residual voltage, zero-sequence current entry condition as fault,

2) determine the initial moment of fault according to the variation of transient zero-sequence current signal,

3) according to the autocorrelation function estimating system main resonatnt frequency of transient zero-sequence current,

4) according to system's main resonatnt frequency determine bandpass filter by frequency,

5) transient state residual voltage, electric current are implemented the two-way tape pass filter,

6) determine duration of transient state process,

7) calculate transient state reactive power size and Orientation,

8) utilize outlet outlet failure message to determine whether detected circuit is faulty line:

To being positioned at the check point of j bar outlet outlet, if the reactive power Q of this circuit transient signal filtering _j＜0, then j bar circuit is a faulty line, otherwise Q _j＞0 its for perfecting circuit.In perfecting circuit transient current hour, the reactive power of calculating and direction may be wrong, therefore, should to the transient current amplitude certain threshold be set before the failure judgement circuit.

As development trend, various outlet defencive functions can close as a whole in power distribution network, promptly save investment, simplify line and device space, are convenient to management again.In existing outlet protection equipment, increase the singlephase earth fault defencive function, can make full use of existing resource, only need corresponding software of increase and a small amount of hardware to get final product.

As the singlephase earth fault defencive function,, can export trip command isolated fault circuit immediately if determine that detected circuit is a faulty line.Also can send warning message earlier, and continue operation a period of time according to the rules regulation, machine sends trip command again by manual intervention when appropriate.

Claims (4)

1, electric system low-current ground fault line selection, segmentation method carry out failure line selection and determine fault section by on-line measuring device, it is characterized in that implementation procedure is:

A is with the variation of residual voltage or the zero-sequence current entry condition as fault;

B determines the initial moment of fault and transient signal time-delay length;

C carries out the two-way tape pass filter to transient state residual voltage, transient zero-sequence current;

D calculates failure line selection, the required failure message of segmentation: determine filter parameter and extract corresponding component u in transient state residual voltage, the electric current according to the transient zero-sequence current main resonatnt frequency ₀' (t) and i ₀' (t), make it keep the capacitive restriction relation, $u_0^{\′}\left(t\right)=R*i_0^{\′}\left(t\right)+\frac{1}{c}{\∫}_{-\∞}^t{i}_0^{\′}\left(\mathrm{\τ}\right)\mathrm{d\τ},$ Wherein R is the circuit equiva lent impedance, and C is the line-to-ground equivalent capacity, again according to the component u with capacitive restriction relation ₀' (t) and i ₀' (t) calculate the size and the direction of reactive power in the transient signal: $Q={\∫}_0^T{i}_0^{\′}\left(t\right)\×\frac{d{u}_0^{\′}\left(t\right)}{\mathrm{dt}}\mathrm{dt}={\∫}_0^T{i}_0^{\′}\left(t\right){\mathrm{du}}_0^{\′}\left(t\right),$ Wherein T is a power frequency period;

E determines faulty line according to the size and the direction of reactive power in the transient signal;

F determines fault section for faulty line according to the size and the direction of reactive power in the transient signal.

2. method according to claim 1, it is characterized in that, transient state residual voltage, transient zero-sequence current signal are carried out the two-way tape pass filter to be handled as follows: adopt the related function method to estimate the main resonatnt frequency ω 1 of transient zero-sequence current, determine that the wave filter high pass cut off frequency is 3 ω 0, low-pass cut-off frequencies is ω 1+ ω r, wherein ω 0 is the power frequency angular frequency, ω r is a safe clearance, utilizes IIR filter IIR that transient state residual voltage, transient zero-sequence current are made the two-way tape pass filter.

3. method according to claim 1, it is characterized in that, in step e according to transient signal in the size and the method that direction is determined faulty line of reactive power as follows: for the check point of the different outlets outlets of same bus, if the transient state reactive power is less than zero, this circuit is a faulty line, otherwise the transient state reactive power is greater than zero, and it is for perfecting circuit.

4. method according to claim 1, it is characterized in that, the method of determining fault section in step f is as follows: for faulty line, determine fault section by main website according to the failure message that each pick-up unit on the circuit reports, if settle a plurality of pick-up units by section thereon, then fault is positioned at the opposite section of both sides reactive power direction, if the transient state reactive power of all check points is all greater than zero, then the trouble spot is between bus and first check point, if all less than zero, then the trouble spot is between last check point and line end for the transient state reactive power of all check points.

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