CN103050942A - Current transformer (CT) saturation detection method based on Hilbert-Huang transformation (HHT) - Google Patents

Abstract

The invention discloses a current transformer (CT) saturation detection method based on Hilbert-Huang transformation (HHT), and the method comprises the followings steps that instantaneous frequency spectrum, Hilbert spectrum and Hilbert marginal spectrum are obtained through EMD decomposition and Hilbert diversion by collecting differential current signals on both sides of a transformer; the detection of saturation faults and CT saturation outside a transformer area is completed respectively arranged to the three types of spectrum so as to realize the quick action and the reliable action of differential protection under CT saturation; the method serves as a preferential improvement to a traditional CT saturation detection method and combines instantaneous frequency criteria, Hilbert spectrum criteria and Hilbert marginal spectrum criteria in the forms of 'and' and 'or'; when a judgment result has errors, another method can correctly judge, so that the reliability of differential protection is improved; and in addition, fault current outside the transformer area, fault current in the area, conversion fault current and the like under the two circumstances of CT saturation and unsaturation are fully considered, and the CT saturation detection method based on HHT has the advantages of stronger functions, higher efficiency, higher reliability and the like.

Description

A kind of CT saturation detection method based on HHT

Technical field

The invention belongs to field of relay protection in power, be specifically related to a kind of CT saturation detection method based on HHT.

Background technology

In the intelligent grid process of construction of China take extra-high voltage grid as key rack, the expansion of electric power system scale and the raising of electric pressure, objectively the requirement larger capacity of configuration and the more power equipment of voltage levels.Putting into operation of high-power transformer proposes higher requirement to relaying protection.The recent statistics data show, the average action accuracy of 2001～2011 years 220kV and above transformer is 79.794%, is lower than about 20 percentage points of generator and route protection.At present, differential protection is as one of main protection of power transformer interior fault, and its reliability is subjected to the saturated impact of CT.Under the CT saturated conditions, when external area error occured, the differential current of transformer both sides current transformer was very large, can cause the misoperation of differential protection.

At present, the general ratio braking method that adopts is differentiated in the engineering reality, but this kind method can not guarantee the reliability of differential protection under CT extreme saturated conditions, must be aided with other and differentiate the saturated measure of CT.The domestic and international recognition methods that proposes also has time difference method, harmonic restraint method, Wavelet Singularity detection method, second order or three order derivative methods etc. in addition; these methods can guarantee the fail safe of transformer differential protection when the experience fault substantially; but also have some problems on the rapid property of time or accuracy, above-mentioned some method is too complicated and be not suitable for practical application.

Hilbert-Huang transform (Hilbert-Huang Transform), it is the HHT conversion, emerging intelligent algorithm as proposition in a kind of 1998, application in field of power just begins, analyze to read on the basis of lot of documents this algorithm application in the CT saturation detection, a kind of simple, efficient new approaches not only can be provided for CT is saturated, widen to a certain extent the application of this algorithm simultaneously, have very high theory value and Research Significance.

Summary of the invention

The purpose of the embodiment of the invention is to propose a kind of CT saturation detection method based on HHT; can be under the CT saturated conditions by HHT; easily with transformer external area error, troubles inside the sample space and and the district is outer turns to the evolved fault in the district correctly to differentiate, be beneficial to the misoperation problem that solves differential protection.

To achieve these goals, the present invention adopts following technical scheme:

A kind of CT saturation detection method based on HHT comprises the steps:

A, collection transformer both sides differential current signal obtain the intrinsic mode function that several satisfy the IMF condition after process EMD decomposes, i.e. the IMF component;

B, above-mentioned IMF component is carried out the Hilbert conversion, obtain instantaneous frequency, obtain Hilbert spectrum and Hilbert marginal spectrum, detailed process is as follows:

The IMF component is designated as X (t), it is carried out Hilbert conversion Y (t) is:

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

Then the analytic signal Z (t) of X (t) is

Z(t)=X(t)+jY(t)=a(t)e ^jθ(t) （2）

In the formula

Be instantaneous amplitude, θ (t)=arctan (Y (t)/X (t)) is phase place, according to phase value θ (t)

Further can obtain instantaneous frequency:

ω(t)=d(θ(t))/dt (3）

Can express clearly amplitude and the phase place of instantaneous frequency by formula (3), and then reflect the instantaneity of data;

Further can draw according to formula (3):

$f\left(t\right)=\frac{1}{2\mathrm{\π}}\mathrm{\ω}\left(t\right)=\frac{1}{2\mathrm{\π}}\×\frac{d\left(\mathrm{\θ}\left(t\right)\right)}{\mathrm{dt}}---\left(4\right)$

Can obtain like this:

$X\left(t\right)=\mathrm{RP}\underset{i=1}{\overset{n}{\mathrm{\Σ}}}{a}_i\left(t\right)e^{j{\mathrm{\θ}}_i\left(t\right)}=\mathrm{RP}\underset{i=1}{\overset{n}{\mathrm{\Σ}}}{a}_i\left(t\right)e^{j{\∫\mathrm{\ω}}_i\mathrm{dt}}---\left(5\right)$

Top expansion is called the Hilbert spectrum, is denoted as:

$H(\mathrm{\ω},t)=\mathrm{RP}\underset{i=1}{\overset{n}{\mathrm{\Σ}}}{a}_i\left(t\right)e^{j\∫{\mathrm{\ω}}_i\mathrm{dt}}---\left(6\right)$

Define again marginal spectrum:

$h\left(\mathrm{\ω}\right)={\∫}_0^{T}H(\mathrm{\ω},t)\mathrm{dt}---\left(7\right)$

In the formula (7), T is the length of signal, this shows, what marginal spectrum characterized is [0, T] in the time each frequency content energy accumulation and, the amplitude that H (ω, t) can accurately describe signal on whole frequency band in time with the rule of conversion of frequency, the amplitude that h (ω) then reflects signal on whole frequency band with the situation of change of frequency;

Wherein,

Utilize the instantaneous frequency time-frequency spectrum, differentiate the saturated generation of CT constantly, so saturated fault outside the identification transformer district, when the generation external area error causes that CT is saturated, Output rusults " 0 ", when the generating region internal fault, Output rusults " 1 ", and start differential protection;

According to the instantaneous frequency fluctuation situation that Hilbert spectrum reflects, whether the outer saturated fault of cog region detects CT and occurs saturatedly, occurs when saturated when detecting CT, and Output rusults " 0 " when detecting CT Output rusults " 1 " does not occur when saturated;

By the Hilbert marginal spectrum that Hilbert obtains time integral, whether the outer saturated fault of cog region detects CT and occurs saturatedly, occurs when saturated when detecting CT, and Output rusults " 0 " when detecting CT Output rusults " 1 " does not occur when saturated.

Preferably, after described step b, also comprise step c:

The result that c, the result who first the Hilbert spectrum is judged and Hilbert marginal spectrum are judged carries out exclusive disjunction; to carry out and computing through the result that the result behind the exclusive disjunction and instantaneous frequency time-frequency spectrum are judged again, then according to computing after the result judge whether to start differential protection:

When through with computing after the result be " 0 ", Blocking Differential Protection, when through with computing after the result be " 1 ", the startup differential protection.

Preferably, the hardware configuration of realizing described CT saturation detection method based on HHT comprises CPU module, analogue collection module, control output module, communication module and MMI module.

Preferably, described CPU module adopts 32 high-performance digital signal processors.

Advantage of the present invention is:

A kind of CT saturation detection method based on HHT that the present invention addresses; by gathering transformer both sides differential current signal; and successively through obtaining instantaneous frequency time-frequency spectrum ω (t), Hilbert spectrum H (ω after EMD decomposition, the Hilbert conversion; t), Hilbert marginal spectrum h (ω); finish respectively the detection of saturated fault and CT saturation outside the transformer district according to above three kinds of frequency spectrums, and then realize quick-action and the reliability action of differential protection under the CT saturated conditions.

As a kind of advantageous embodiment of the present invention; with instantaneous frequency criterion, Hilbert spectrum criterion and Hilbert marginal spectrum criterion with " with ", the "or" form combines; when a kind of judged result is made a fault; another kind can correctly be judged; improved the reliability of differential protection; and take into full account the multiple situations such as transformer external area error electric current, troubles inside the sample space electric current and evolved fault electric current in the saturated and unsaturated two kinds of situations of CT, that the method has is with better function, efficient is higher and reliability advantages of higher more.

Description of drawings

Fig. 1 is the FB(flow block) of a kind of CT saturation detection method based on HHT in the embodiment of the invention;

Fig. 2 is the method flow diagram that EMD decomposes among Fig. 1;

Fig. 3 a is the oscillogram of embodiment of the invention fault current outside CT saturated conditions inferior segment;

Fig. 3 b is the instantaneous frequency time-frequency spectrum that the external area error electric current is corresponding among Fig. 3 a;

Fig. 3 c is the oscillogram of embodiment of the invention troubles inside the sample space electric current under the CT saturated conditions;

Fig. 3 d is the instantaneous frequency time-frequency spectrum that the troubles inside the sample space electric current is corresponding among Fig. 3 c;

Fig. 4 a is Hilbert spectrum corresponding to external area error electric current that the embodiment of the invention utilizes the Hilbert spectrum to detect under the CT saturated conditions;

Fig. 4 b is frequency change figure corresponding to Hilbert spectrum among Fig. 4 a;

Fig. 4 c is Hilbert spectrum corresponding to troubles inside the sample space electric current that the embodiment of the invention utilizes the Hilbert spectrum to detect under the CT saturated conditions;

Fig. 4 d is frequency change figure corresponding to Hilbert spectrum among Fig. 4 c;

Fig. 5 a is embodiment of the invention Hilbert marginal spectrum corresponding to fault current outside CT saturated conditions inferior segment;

Fig. 5 b is the embodiment of the invention Hilbert marginal spectrum that the troubles inside the sample space electric current is corresponding under the CT saturated conditions;

Fig. 6 is a kind of further decision flow chart of CT saturation detection method on Fig. 1 FB(flow block) basis based on HHT in the embodiment of the invention;

Fig. 7 is a kind of hardware block diagram that adopts based on the CT saturation detection method of HHT in the embodiment of the invention.

Embodiment

In conjunction with Fig. 1, shown in Figure 2, the HHT algorithm comprises empirical mode decomposition (being called for short EMD) and Hilbert analysis of spectrum (being called for short HAS) two parts.Gather and to obtain several intrinsic mode functions that satisfy certain condition (being called for short the IMF component) and a surplus after transformer both sides differential current signal decomposes through EMD.Subsequently these IMF components are carried out the Hilbert conversion, obtain instantaneous frequency, obtain Hilbert spectrum and Hilbert marginal spectrum.

Detailed process is as follows:

The IMF component is designated as X (t), it is carried out Hilbert conversion Y (t) is:

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

Then the analytic signal Z (t) of X (t) is

Z(t)=X(t)+jY(t)=a(t)e ^jθ(t) （2）

In the formula

Be instantaneous amplitude, θ (t)=arctan (Y (t)/X (t)) is phase place, according to phase value θ (t)

Further can obtain instantaneous frequency:

ω(t)=d(θ(t))/dt (3）

Can express clearly amplitude and the phase place of instantaneous frequency by formula (3), and then reflect the instantaneity of data;

Further can draw according to formula (3):

$f\left(t\right)=\frac{1}{2\mathrm{\π}}\mathrm{\ω}\left(t\right)=\frac{1}{2\mathrm{\π}}\×\frac{d\left(\mathrm{\θ}\left(t\right)\right)}{\mathrm{dt}}---\left(4\right)$

Can obtain like this:

$X\left(t\right)=\mathrm{RP}\underset{i=1}{\overset{n}{\mathrm{\Σ}}}{a}_i\left(t\right)e^{j{\mathrm{\θ}}_i\left(t\right)}=\mathrm{RP}\underset{i=1}{\overset{n}{\mathrm{\Σ}}}{a}_i\left(t\right)e^{j{\∫\mathrm{\ω}}_i\mathrm{dt}}---\left(5\right)$

Top expansion is called the Hilbert spectrum, is denoted as:

$H(\mathrm{\ω},t)=\mathrm{RP}\underset{i=1}{\overset{n}{\mathrm{\Σ}}}{a}_i\left(t\right)e^{j\∫{\mathrm{\ω}}_i\mathrm{dt}}---\left(6\right)$

Define again marginal spectrum:

$h\left(\mathrm{\ω}\right)={\∫}_0^{T}H(\mathrm{\ω},t)\mathrm{dt}---\left(7\right)$

In the formula (7), T is the length of signal, this shows, what marginal spectrum characterized is [0, T] in the time each frequency content energy accumulation and, the amplitude that H (ω, t) can accurately describe signal on whole frequency band in time with the rule of conversion of frequency, the amplitude that h (ω) then reflects signal on whole frequency band with the situation of change of frequency.

In the once-through operation process of above-mentioned HHT, can finish three judgements:

(1) owing in the outer saturated fault current in district obvious catastrophe point is arranged, and not significantly sudden change in the troubles inside the sample space electric current, thereby utilize the instantaneous frequency time-frequency spectrum, can differentiate the saturated generation of CT constantly, and then identify saturated fault outside the transformer district, when the generation external area error causes that CT is saturated, Output rusults " 0 ", Blocking Differential Protection is when the generating region internal fault, Output rusults " 1 ", and start differential protection;

(2) owing to saturated fault current harmonic component decay outside the transformer district is very fast, instantaneous frequency fluctuates obviously in time, and the troubles inside the sample space electric current keeps fundamental frequency constant substantially, thereby according to the instantaneous frequency fluctuation situation that the Hilbert spectrum reflects, can identify the outer saturated fault in district, detect CT and whether occur saturated, occur when saturated when detecting CT, Output rusults " 1 " does not occur when saturated when detecting CT in Output rusults " 0 ";

(3) owing to contain a large amount of high order harmonic components in the saturated fault current outside the transformer district, and the troubles inside the sample space electric current is close to sine wave, thereby the Hilbert marginal spectrum that time integral is obtained by Hilbert, can cog region outer saturated fault, detect CT and whether occur saturatedly, when detecting CT Output rusults " 0 " occurs when saturated, Output rusults " 1 " does not occur when saturated when detecting CT.

Fig. 3 a to Fig. 3 d shows and utilize instantaneous frequency time-frequency spectrum identification transformer fault under the CT saturated conditions, by Fig. 3 a, Fig. 3 b as can be known, in the saturated situation of CT, when external area error occurs when, corresponding 4 the instantaneous frequency catastrophe points (minimum point) of the differential current in each cycle; And by Fig. 3 c, Fig. 3 d as can be known, corresponding 1 the instantaneous frequency catastrophe point of the troubles inside the sample space electric current in each cycle can realize the reliable recognition of external area error and troubles inside the sample space thus.

Fig. 4 a to Fig. 4 d shows and utilize Hilbert spectrum discrimination transformer fault under the CT saturated conditions, by Fig. 4 a, Fig. 4 b as can be known, under the CT saturated conditions, when external area error occurs when, in the differential current owing to contain a large amount of higher harmonic components, be reflected to the larger frequency fluctuation of appearance in the Hilbert spectrum, frequency change rate is larger; And by Fig. 4 c, Fig. 4 d as can be known, when the generating region internal fault, differential current is approximately a sine wave, and frequency content is single, so Hilbert spectrum medium frequency is basicly stable at 50Hz, and frequency change rate is less, can realize thus the identification of external area error and troubles inside the sample space.

Fig. 5 a, Fig. 5 b show and utilize Hilbert marginal spectrum identification transformer fault under the CT saturated conditions, by Fig. 5 a as can be known, under the CT saturated conditions, when external area error occurs, owing to contain a large amount of higher harmonic content in the differential current waveform, thus fundamental frequency to account for the percentage of current signal lower; And by Fig. 5 b as can be known, the troubles inside the sample space electric current only contains a small amount of harmonic wave, and the percentage that fundamental frequency accounts for current signal is higher, can realize thus the identification of troubles inside the sample space and external area error.

In conjunction with shown in Figure 6; as a kind of advantageous embodiment of the present invention; with instantaneous frequency criterion, Hilbert spectrum criterion and Hilbert marginal spectrum criterion with " with ", the "or" form combines; be exactly specifically; the result that the result who first the Hilbert spectrum is judged and Hilbert marginal spectrum are judged carries out exclusive disjunction; to carry out and computing through the result that the result behind the exclusive disjunction and instantaneous frequency time-frequency spectrum are judged again, then according to computing after the result judge whether to start differential protection.

When the generation external area error causes that CT is saturated, instantaneous frequency criterion output " 0 ", and through Hilbert spectrum and Hilbert marginal spectrum, it is saturated all to detect CT, Output rusults also is " 0 ", through or behind the door output " 0 ", differentiate for twice the result through and be output as behind the door " 0 ", so differential protection execution action not; Otherwise; when the generating region internal fault, (comprise the saturated and unsaturated two kinds of situations of CT of CT); instantaneous frequency can correctly detect troubles inside the sample space; Output rusults " 1 "; and Hilbert spectrum and Hilbert marginal spectrum also can correctly identify troubles inside the sample space; Output rusults " 1 ", twice differentiation process and behind the door output " 1 " start differential protection.

If because the impact of other factors such as harmonic wave; mistake appears in the differentiation of Hilbert spectrum or Hilbert marginal spectrum; namely external area error is identified as troubles inside the sample space and exports " 1 " by mistake; Output rusults " 1 " after then process or door are differentiated; and the instantaneous frequency criterion can correctly detect external area error; Output rusults " 0 " is through exporting afterwards " 0 ", Blocking Differential Protection with door.

Therefore; three kinds of criterions can form a complementary relationship; when a kind of differentiation result makes a fault; another kind can correctly be judged; can not affect the Reliability of Microprocessor of differential protection; and take into full account the multiple situations such as transformer external area error electric current, troubles inside the sample space electric current and evolved fault electric current in the saturated and unsaturated two kinds of situations of CT, that this determination methods has is with better function, efficient is higher and reliability advantages of higher more.

In conjunction with shown in Figure 7; the present invention uses the HHT algorithm and carries out CT saturation detection and evolved fault identification; amount of calculation is larger; especially in the situation of high yardstick, and various theory during concrete the application, needs the various situation more complicated of considering in engineering; logic judgment unit is more; in order to satisfy the requirement of protection quick-action, accuracy, cooperate simultaneously the renewal of hardware, this hardware core adopts 32 high-performance digital signal processor TMS320F2812 of TI to finish.

Whole hardware configuration comprises that CPU module, analogue collection module, control output module, communication module and MMI module five parts form, and wherein the MMI module comprises keyboard input submodule and liquid crystal display submodule.

Claims (4)

1. the CT saturation detection method based on HHT is characterized in that comprising the steps:

A, collection transformer both sides differential current signal obtain the intrinsic mode function that several satisfy the IMF condition after process EMD decomposes, i.e. the IMF component;

B, above-mentioned IMF component is carried out the Hilbert conversion, obtain instantaneous frequency, obtain Hilbert spectrum and Hilbert marginal spectrum, detailed process is as follows:

The IMF component is designated as X (t), it is carried out Hilbert conversion Y (t) is:

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

Then the analytic signal Z (t) of X (t) is

Z(t)=X(t)+jY(t)=a(t)e ^jθ(t) （2）

In the formula

Be instantaneous amplitude, θ (t)=arctan (Y (t)/X (t)) is phase place, further can obtain instantaneous frequency according to phase value θ (t):

ω(t)=d(θ(t))/dt (3）

Can express clearly amplitude and the phase place of instantaneous frequency by formula (3), and then reflect the instantaneity of data;

Further can draw according to formula (3):

$f\left(t\right)=\frac{1}{2\mathrm{\π}}\mathrm{\ω}\left(t\right)=\frac{1}{2\mathrm{\π}}\×\frac{d\left(\mathrm{\θ}\left(t\right)\right)}{\mathrm{dt}}---\left(4\right)$

Can obtain like this:

$X\left(t\right)=\mathrm{RP}\underset{i=1}{\overset{n}{\mathrm{\Σ}}}{a}_i\left(t\right)e^{j{\mathrm{\θ}}_i\left(t\right)}=\mathrm{RP}\underset{i=1}{\overset{n}{\mathrm{\Σ}}}{a}_i\left(t\right)e^{j{\∫\mathrm{\ω}}_i\mathrm{dt}}---\left(5\right)$

Top expansion is called the Hilbert spectrum, is denoted as:

$H(\mathrm{\ω},t)=\mathrm{RP}\underset{i=1}{\overset{n}{\mathrm{\Σ}}}{a}_i\left(t\right)e^{j\∫{\mathrm{\ω}}_i\mathrm{dt}}---\left(6\right)$

Define again marginal spectrum:

$h\left(\mathrm{\ω}\right)={\∫}_0^{T}H(\mathrm{\ω},t)\mathrm{dt}---\left(7\right)$

In the formula (7), T is the length of signal, this shows, what marginal spectrum characterized is [0, T] in the time each frequency content energy accumulation and, the amplitude that H (ω, t) can accurately describe signal on whole frequency band in time with the rule of conversion of frequency, the amplitude that h (ω) then reflects signal on whole frequency band with the situation of change of frequency;

Wherein,

Utilize the instantaneous frequency time-frequency spectrum, differentiate the saturated generation of CT constantly, so saturated fault outside the identification transformer district, when the generation external area error causes that CT is saturated, Output rusults " 0 ", when the generating region internal fault, Output rusults " 1 ", and start differential protection;

According to the instantaneous frequency fluctuation situation that Hilbert spectrum reflects, whether the outer saturated fault of cog region detects CT and occurs saturatedly, occurs when saturated when detecting CT, and Output rusults " 0 " when detecting CT Output rusults " 1 " does not occur when saturated;

By the Hilbert marginal spectrum that Hilbert obtains time integral, whether the outer saturated fault of cog region detects CT and occurs saturatedly, occurs when saturated when detecting CT, and Output rusults " 0 " when detecting CT Output rusults " 1 " does not occur when saturated.

2. a kind of CT saturation detection method based on HHT according to claim 1 is characterized in that, after described step b, also comprises step c:

The result that c, the result who first the Hilbert spectrum is judged and Hilbert marginal spectrum are judged carries out exclusive disjunction; to carry out and computing through the result that the result behind the exclusive disjunction and instantaneous frequency time-frequency spectrum are judged again, then according to computing after the result judge whether to start differential protection:

When through with computing after the result be " 0 ", Blocking Differential Protection, when through with computing after the result be " 1 ", the startup differential protection.

3. a kind of CT saturation detection method based on HHT according to claim 1 and 2, it is characterized in that, realize that the hardware configuration of described CT saturation detection method based on HHT comprises CPU module, analogue collection module, control output module, communication module and MMI module.

4. a kind of CT saturation detection method based on HHT according to claim 3 is characterized in that, described CPU module adopts 32 high-performance digital signal processors.

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