CN101814731A - Distribution network fault line selection method using non-power frequency transient state component - Google Patents

Abstract

The invention discloses a new method for performing fault line selection by using the characteristic of a non-power frequency transient state fault component for extracting single-phase fault zero-sequence current by using Hilbert-Huang transform (HHT). The method comprises the following steps: performing EMD decomposition on fault zero-sequence current of each feeder line by using the HHT to acquire an IMF component of the zero-sequence current of each feeder line; constructing a resolving signal according to Hilbert transform, solving instantaneous amplitude and frequency of the zero-sequence current of each feeder line, and eliminating a power frequency component in the instantaneous frequency of the zero-sequence current of each feeder line to acquire a non-power frequency fault component; and forming a line selection criterion according to the characteristics that the amplitude of the non-power frequency fault component of the fault line is greater than that of the non-fault line and the polarity of the fault line is opposite to that of the non-fault line. The line selection method is not affected by an arc suppression coil, and is applicable to non-grounded, arc suppression coil grounded and high-resistor grounded systems, overhead lines or cable lines and cable overhead mixed lines; and the line selection result shows that the method applied to low-current single-phase grounding fault line selection is accurate and reliable.

Description

A kind of distribution network fault line selection method of using non-power frequency transient state component

Technical field

The present invention relates to a kind of distribution network fault line selection method, particularly use Hilbert-Huang conversion (HHT) and extract the method that non-power frequency transient state fault zero-sequence current component is carried out failure line selection.

Background technology

For a long time, low current grounding detection problem is a great problem in the electric power system always.The selection method of traditional small current neutral grounding system has amplitude comparison method, polarity comparison method, colony than width of cloth phase comparing method, zero-sequence current reactive power direction method etc., these methods can only satisfy the route selection requirement of little electric current isolated neutral system substantially, and inapplicable resonant earthed system.

The selection method that is applied to resonant earthed system at present mainly contains real component comparison method and harmonic ratio than two kinds of methods.The real component comparison method mainly comprises the amplitude of fault current active current component and polarity comparison method, active current direction comparison method, active power direction comparison method, but because the real component little (being generally less than 1A) of earth current, and it is bigger to be subjected to voltage transformer summation current transformer phase angle to spread all over error effect, cause this method reliability low, can not satisfy of the requirement of present power supply grid reliability.It is bigger that the harmonic wave comparison method is influenced by the content of harmonic source in the system and abort situation, and the method reliability is lower, does not reach practical requirement equally.

Summary of the invention

Purpose of the present invention is intended to overcome the deficiency of above-mentioned existing low current neutral grounding system fault route selecting method, the evident characteristic that has transient state component according to the single-phase grounded malfunction in grounded system of low current initial stage, a kind of selection method that HHT extracts the non-power frequency transient state of single-phase fault zero-sequence current fault component feature of using is proposed, this selection method is not influenced by arc suppression coil, applicable to earth-free, through arc suppression coil (resonance) ground connection with through the high resistance ground system; Applicable overhead transmission line or cable line, also applicable cable aerial mixed line is to reach the requirement of satisfying present power supply reliability.The transient current amplitude is big, and antijamming capability is strong, crosses zero failure and still has tangible transient signal, has rejected the component of not supporting the route selection requirement in the transient signal, and principle is more advanced.Not influenced by unstable arc, and detect when arc grounding and intermittent ground connection more reliable.

The technical scheme that the present invention is taked for its purpose of realization is: utilize the non-power frequency transient state fault signature component after HHT extracts the zero-sequence current fault, non-power frequency transient state component according to faulty line after the fault is opposite with non-fault line non-power frequency transient state component polarity, faulty line non-power frequency transient state component amplitude is obviously greater than the fault signature of non-fault line, single-phase grounded malfunction in grounded system of low current is carried out fast line selection, realizes as follows:

(1) when bus residual voltage instantaneous value u (t) greater than KU, fault line selection device starts immediately, 1 each feeder line zero-sequence current x (t) of periodic waveform behind the record trouble, wherein the K value 0.15, U represents the bus rated voltage;

(2) use HHT to each feeder fault after in 1/10 cycle zero-sequence current x (t) carry out empirical modal and decompose (Empirical Mode Decomposition is called for short EMD), decomposite eigen mode state function (Intrinsic ModeFunction is called for short IMF).Concrete decomposable process is as follows:

1) the mean value m that obtains its coenvelope line and lower envelope line according to local maximum and the local minimum of zero sequence current signal x (t) ₁

2) can obtain a new data sequence h who removes low frequency after former data sequence being deducted average envelope ₁=x (t)-m ₁Judge h ₁Whether be the IMF condition, if do not satisfy, with h ₁Regard new x (t) as, repeat above-mentioned processing procedure, up to h ₁When satisfying the IMF condition, note c ₁=h ₁, be considered as IMF1.

3) with r=x (t)-h ₁Regard new x (t) as, repeat above (1) and (2) step, can obtain IMF2 successively, IMF3 ..., up to c _nOr r satisfies given end condition, and time screening finishes; At last, original data sequence x (t) can be represented by these IMF components and average or trend term r.

$x\left(t\right)=\underset{i=1}{\overset{n}{\mathrm{\Σ}}}{c}_i+r---\left(1\right)$

(3) IMF that the fault zero-sequence current is decomposited carries out the Hilbert conversion and asks for various instantaneous frequency compositions for arbitrary continuous time signal X (t), and its Hilbert transform definition is:

$Y\left(t\right)=\frac{1}{\mathrm{\π}}{\∫}_{-\∞}^{+\∞}\frac{X\left(\mathrm{\τ}\right)}{t-\mathrm{\τ}}\mathrm{d\τ}---\left(2\right)$

It is right that X (t) and Y (t) form complex conjugate, by its analytic signal that constitutes is:

Z(t)＝X(t)+jY(t)＝a(t)e ^jθ(t)

$a\left(t\right)=\sqrt{X^2\left(t\right)+Y^2\left(t\right)}---\left(3\right)$

θ(t)＝arctan[Y(t)/X(t)]

In the formula: a (t) is an instantaneous amplitude; θ (t) is a phase place.According to

Ask for instantaneous frequency.

(4) reject power frequency component according to the various instantaneous frequency compositions of gained, zero-sequence current non-power frequency transient state component in 1/10 cycle behind each feeder fault.

Inventive principle:

1, uses HHT and extract non-power frequency fault component

HHT is a kind of brand-new non-linear, non-stationary data analysing method, comprises EMD and Hilbert conversion two parts composition, and its core is empirical mode decomposition (EMD).According to available research achievements, EMD can directly adopt.HHT is several eigen mode state functions (IMF) by EMD with signal decomposition, and the characteristics of IMF are to have rational instantaneous frequency definition, then IMF are carried out the Hilbert conversion and obtain time dependent instantaneous frequency of each IMF and instantaneous amplitude.The low current grounding current signal comprises abundant instantaneous frequency composition, is fit to use HHT zero sequence current signal is carried out the fault signature that decomposition transform gets zero-sequence current.

2, non-power frequency fault component transient state signature analysis:

Power distribution network zero-sequence current fault signature is subjected to the influence of several factors, as the size of the size of fault switching angle, abort situation (fault point is apart from the position of bus), earth resistance, arc suppression coil compensation degree etc.The zero sequence transient current of faulty line is made up of the capacitive transient state inductive current of whole non-fault lines and the transient state inductive current of arc suppression coil.The transient current amplitude has bigger than stable state amplitude, is convenient to detect, and comprises abundant failure-frequency composition, is fit to and carries out route selection research.

The inventive method at different faults switching angle, abort situation, earth resistance, arc suppression coil compensation degree, is carried out a large amount of emulation at first respectively, and each circuit zero-sequence current of emulation gained is carried out HHT analyze, and obtains the non-power frequency transient state current component of each circuit.Find by analysis and summary: in 1/10 cycle after short circuit (0～20 sampled point), the non-power frequency transient current characteristic of faulty line and non-fault line is significantly different, the non-power frequency transient current polarity of faulty line and non-fault line is opposite, and the non-power frequency transient state current component of faulty line amplitude is obviously greater than non-fault line, and this is route selection criterion basis.

Based on above-mentioned analysis, realize that the route selection step is:

1,,, starts line selection apparatus automatically when residual voltage during greater than set point according to record bus residual voltage instantaneous value situation.

2, utilize HHT that each feeder fault zero-sequence current is carried out EMD and decompose, obtain the IMF component of each feeder line zero-sequence current.

3, according to Hilbert transform structure analytic signal, ask for each feeder line zero-sequence current instantaneous amplitude and frequency.

4, reject power frequency component in each feeder line zero-sequence current instantaneous frequency, obtain non-power frequency fault component.

5, according to the non-power frequency fault component of faulty line amplitude greater than non-fault line, the polarity feature opposite with non-fault line forms the route selection criterion.

Hilbert-Huang conversion (HHT) is a kind of brand-new complete adaptive Time Frequency Analysis method that Huang proposes, and it has good local time-frequency characteristic, therefore more can reflect the characteristic of original signal exactly.HHT carries out EMD from the scale feature of signal itself to signal and decomposes and obtain intrinsic mode function (intrinsic mode function, IMF), by IMF is carried out the Hilbert conversion, obtain analytic signal, ask for instantaneous frequency with real physical meaning.

The present invention compared with prior art has following advantage:

1, this method is utilized non-power frequency transient current, and amplitude is big, and antijamming capability is strong, and zero failure still has tangible transient signal, route selection success rate height excessively.

2, rejected the power frequency component that each feeder line all comprises in the transient signal, obtained being fit to the component of route selection requirement, faulty line and the difference of non-fault line feature are more obvious, and principle is more advanced.

3, not influenced by unstable arc, and detect when arc grounding and intermittent ground connection more reliable

4, by different models are carried out emulation, this selection method is not influenced by arc suppression coil, applicable to earth-free, through grounding through arc with through the high resistance ground system; Applicable overhead transmission line or cable line, also applicable cable aerial mixed line.

5, utilize HHT to extract non-power frequency transient state fault component and carry out route selection, lower to the requirement of hardware, have certain economy.

6, this method is not subjected to paraphase of faulty line zero-sequence current and the saturated influence of CT, and the failure line selection precision is higher.

Description of drawings

Fig. 1, Fig. 2 are contrast different faults non-power frequency fault component oscillogram constantly

Fig. 3, Fig. 4 are the non-power frequency fault component oscillogram of contrast different faults distance

Fig. 5, Fig. 6 are the non-power frequency fault component oscillogram of the different compensativities of contrast

Fig. 7, Fig. 8 are the non-power frequency fault component oscillogram of contrast different grounding resistance

Fig. 9 is a fault-line selecting method flow chart of the present invention

Figure 10 is radial resonant earthed system

Embodiment

During small current neutral grounding system generation single phase ground fault, utilize the foregoing invention method can realize perfect failure line selection.Concrete implementing procedure figure as shown in the figure.

Concrete implementation step is as follows:

1, when bus residual voltage instantaneous value u (t) greater than KU, fault line selection device starts automatically, notes each feeder line zero-sequence current of cycle after the fault, K value 0.15, U represents the bus rated voltage;

2, utilize HHT that zero-sequence current in each feeder line 1/10 cycle is carried out EMD and decompose, obtain the IMF component of each circuit zero-sequence current respectively.

3,, ask for the analytic signal of each IMF, and then calculate the amplitude and the instantaneous frequency composition of each feeder fault zero-sequence current according to Hilbert transform.

4, according to calculating each feeder line instantaneous frequency signal of gained, reject wherein power frequency component, obtain each feeder line zero-sequence current non-power frequency transient state component.

5, during single phase ground fault, in 1/10 cycle after short circuit (0～20 sampled point), faulty line non-power frequency transient state component amplitude is obviously greater than non-fault line, and the non-power frequency transient current polarity of faulty line and non-fault line is opposite, therefore forms the route selection criterion.

Specific embodiment 1:

Fig. 8 is radial resonant earthed system, and G is a power supply, and T is a transformer, and no-load voltage ratio is 110Kv/11kV, and the connection group is YN/d11, and wherein neutral point adopts overcompensation 10% through arc suppression coil series resistance ground connection; R is an arc suppression coil damped resistor, and Rf is an earth resistance; Arc suppression coil is by isolating switch K switching; Circuit is the cable joint line.

System's generation single phase ground fault, sampling apparatus sample frequency are 10000Hz, record circuit zero-sequence current and bus residual voltage.

Zero-sequence current behind each feeder fault is carried out the HHT conversion obtain non-power frequency transient state fault component, result such as Fig. 1.

To carrying out amplitude and polarity as each feeder line non-power frequency transient state component among Fig. 1 relatively, result such as table 1:

Table 1: resonance grounding cable hybrid system emulation conversion route selection result

The route selection result is consistent with emulation setting faulty line.

Claims (1)

1. the distribution network fault line selection method of a using non-power frequency transient state component, utilize the non-power frequency transient state fault signature component after Hilbert Huang (HHT) extracts the zero-sequence current fault, non-power frequency transient state component according to faulty line after the fault is opposite with non-fault line non-power frequency transient state component polarity, faulty line non-power frequency transient state component amplitude is obviously greater than the fault signature of non-fault line, single-phase grounded malfunction in grounded system of low current is carried out fast line selection, realizes as follows:

(1) when bus residual voltage instantaneous value u (t) greater than KU, fault line selection device starts immediately, 1 each feeder line zero-sequence current x (t) of periodic waveform behind the record trouble, wherein the K value 0.15, U represents the bus rated voltage;

(2) use HHT to each feeder fault after in 1/10 cycle zero-sequence current x (t) carry out empirical modal and decompose (Empirical Mode Decomposition is called for short EMD), decomposite eigen mode state function (Intrinsic ModeFunction is called for short IMF).Concrete decomposable process is as follows:

A. the mean value m that obtains its coenvelope line and lower envelope line according to local maximum and the local minimum of zero sequence current signal x (t) ₁

B. can obtain a new data sequence h who removes low frequency after former data sequence being deducted average envelope ₁=x (t)-m ₁Judge h ₁Whether be the IMF condition, if do not satisfy, with h ₁Regard new x (t) as, repeat above-mentioned processing procedure, up to h ₁When satisfying the IMF condition, note c ₁=h ₁, be considered as IMF1;

C. with r=x (t)-h ₁Regard new x (t) as, repeat above (1) and (2) step, can obtain IMF2 successively, IMF3 ..., up to c _nOr r satisfies given end condition, and time screening finishes; At last, original data sequence x (t) can be represented by these IMF components and average or trend term r;

$x\left(t\right)=\underset{i=1}{\overset{n}{\mathrm{\Σ}}}{c}_i+r$

(3) IMF that the fault zero-sequence current is decomposited carries out the Hilbert conversion and asks for various instantaneous frequency compositions for arbitrary continuous time signal X (t), and its Hilbert transform definition is:

$Y\left(t\right)=\frac{1}{\mathrm{\π}}{\∫}_{-\∞}^{+\∞}\frac{X\left(\mathrm{\τ}\right)}{t-\mathrm{\τ}}\mathrm{d\τ}$

It is right that X (t) and Y (t) form complex conjugate, by its analytic signal that constitutes is:

Z(t)＝X(t)+jY(t)＝a(t)e ^jθ(t)

$a\left(t\right)=\sqrt{X^2\left(t\right)+Y^2\left(t\right)}$

θ(t)＝arctan[Y(t)/X(t)]

In the formula: a (t) is an instantaneous amplitude; θ (t) is a phase place, according to Ask for instantaneous frequency;

(4) reject power frequency component according to the various instantaneous frequency compositions of gained, zero-sequence current non-power frequency transient state component in 1/10 cycle behind each feeder fault.

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