CN105319447A - Dielectric loss Tan delta test method and tester - Google Patents

Abstract

The invention discloses a dielectric loss Tan delta test method and tester. The test method comprises the steps of: first, current and voltage signal collection: detecting the work current and work voltage of an electrical device to be tested in real time, and collecting data through a signal collection circuit; and second, signal processing: processing current values and voltage values collected at each sampling time according to a sampling sequence, wherein the current value and voltage value processing comprises the steps of: 201, signal receiving and synchronous storage; and 202: calculation of dielectric loss Tan delta at a current time: data group creation and analysis and processing of signals of a next sampling time. The tester comprises a current detection unit, a voltage detection unit, a signal collection circuit and a data processor. The test method has the characteristics of reasonable design, easy realization, sound use effect, great instantaneity and high test precision, and can conveniently and rapidly test the dielectric loss Tan delta of an electrical device to be tested.

Description

A kind of dielectric loss angle tangent method of testing and tester

Technical field

The invention belongs to power equipment on-line testing technique field, especially relate to a kind of dielectric loss angle tangent on-line testing method and tester.

Background technology

Dielectric loss angle, leakage current and insulating medium electric capacity Cx are three characteristic quantities weighing insulation of electrical installation degree.Because dielectric loss angle tangent (i.e. tan δ) only depends on properties of materials and has nothing to do with the size and dimension of material, therefore be very effective using tan δ as the parameter of Whole Equipment insulation status.

In recent years, along with the development of state inspection, dielectric loss (hereinafter referred to as dielectric loss) online measuring technique also comes into one's own day by day, and develop multiple detection method gradually, Liang great branch below main formation: the first is mainly by the detection method that " hardware " realizes, and with bridge method, zero crossing phase-comparison method for representative, the method relies on hardware unit to realize, impact by hardware itself is comparatively large, and accuracy is difficult to ensure; It two is main methods realized by " software ", mainly contain correlation function algorithm, higher modes influence, discrete fourier transform algorithm etc., usually measure working voltage respectively by sensor device and flow through the electric current of test product, again the simulating signal measured is converted into digital signal, then adopt correlation analysis method to extract the fundamental phase difference information of voltage and current, thus estimate Dielectric loss angle.Software Method, with its good anti-interference and stability, becomes detection method ideal at present.

When adopting traditional Fourier transform converter technique to carry out dielectric loss test, subtracted each other can be obtained dielectric loss angle by two fundamental phase, and then can dielectric loss angle tangent be calculated.But there is the problems such as real-time is poor, measuring accuracy is lower in traditional Fourier transform converter technique.

Summary of the invention

Technical matters to be solved by this invention is for above-mentioned deficiency of the prior art, a kind of dielectric loss angle tangent method of testing is provided, its method step is simple, reasonable in design and realization is convenient, result of use is good, can easy, fast the dielectric loss angle tangent of tested electrical equipment is tested, and real-time is good, and measuring accuracy is high.

For solving the problems of the technologies described above, the technical solution used in the present invention is: a kind of dielectric loss angle tangent method of testing, is characterized in that: the method comprises the following steps:

Step one, electric current and voltage signal acquisition: adopt current detecting unit and voltage detection unit to detect in real time respectively the working current of tested electrical equipment and operating voltage, and by signal acquisition circuit and according to the sample frequency f preset _sthe current signal that current detecting unit detects is gathered respectively with the voltage signal detected, and the current value each sampling instant collected and the equal synchronous driving of magnitude of voltage are to data processor;

Step 2, signal transacting: described data processor, according to sampling sequencing, processes respectively to the current value of signal acquisition circuit collection described in each sampling instant and magnitude of voltage; The current value that each sampling instant gathers is all identical with the disposal route of magnitude of voltage, when the current value gather and magnitude of voltage process, comprises the following steps any one sampling instant:

Step 201, Signal reception and stores synchronized: after described data processor receives the current value and magnitude of voltage that signal acquisition circuit described in current time gathers, stores synchronized is carried out to the current value received and magnitude of voltage, and total sampling number of signal acquisition circuit described in current time is judged: as total sampling number > N of signal acquisition circuit described in current time, enter step 202; Otherwise, enter step 203; Wherein, N is positive integer and N=f _s/ f (1-22), in formula (1-22), f is the line frequency of tested electrical equipment, f _sfor the sample frequency designed in advance;

Step 202, current time dielectric loss angle tangent calculate: described data processor calls the dielectric loss angle tangent of dielectric loss angle tangent computing module to the tested electrical equipment of current time and calculates, and process is as follows:

Step 2021, data group build: the current value of signal acquisition circuit collection described in the current value of signal acquisition circuit collection described in current time and a front N' sampling instant is formed a current data group, and sort from front to back to current value described in the N'+1 in described current data group according to sampling sequencing; Simultaneously, the magnitude of voltage of signal acquisition circuit collection described in the magnitude of voltage of signal acquisition circuit collection described in current time and a front N' sampling instant is formed a voltage data group, and according to sampling sequencing, magnitude of voltage described in the N'+1 in described voltage data group is sorted from front to back;

Wherein, N' is positive integer and N'=N or N-1;

As N'=N, current value described in N'+1 in described current data group be denoted as respectively from front to back i (0), i (1), i (2) ..., i (N), magnitude of voltage described in the N'+1 in described voltage data group be denoted as respectively from front to back u (0), u (1), u (2) ..., u (N);

As N'=N-1, current value described in N'+1 in described current data group be denoted as respectively from front to back i (1), i (2) ..., i (N), magnitude of voltage described in the N'+1 in described voltage data group is denoted as from front to back respectively, u (1), u (2) ..., u (N);

Wherein, i (N) and u (N) is respectively current value and the magnitude of voltage of signal acquisition circuit collection described in current time;

Step 2022, dielectric loss angle tangent calculate: according to formula and current data group described in integrating step 2021 and described voltage data group, calculate the dielectric loss angle tangent tan δ of the tested electrical equipment of current time;

Wherein, as N'=N, a in formula (1-21) _i1and b _i1according to formula calculate; Further, a _u1and b _u1according to formula calculate;

As N'=N-1, a _i1and b _i1according to formula calculate; Further, a _u1and b _u1according to formula calculate;

Step 203, next sampling instant signal analysis and processing: according to the method described in step 201 to step 202, described data processor processes the current value of signal acquisition circuit collection described in next sampling instant and magnitude of voltage.

Said method, is characterized in that: N=16 ~ 100 described in step 201.

Simultaneously, the invention discloses a kind of structure simple, reasonable in design and use easy and simple to handle, the dielectric loss angle tangent tester that result of use is good, it is characterized in that: comprise the current detecting unit working current of tested electrical equipment being carried out to detection in real time, the operating voltage of tested electrical equipment is carried out to the voltage detection unit detected in real time, the signal acquisition circuit that the current detecting unit current signal detected and the voltage signal that voltage detection unit detects are gathered respectively and carry out processing to signal acquisition circuit is signal collected and synchronously draws the data processor of the dielectric loss angle tangent of current tested electrical equipment, described current detecting unit and voltage detection unit all connect with signal acquisition circuit, the working current of described tested electrical equipment is three-phase current, and described current detecting unit is three-phase current detection unit, the operating voltage of described tested electrical equipment is three-phase voltage, and described voltage detection unit is detecting voltage by three phase unit.

Above-mentioned tester, is characterized in that: also comprise the host computer connected with data processor.

Above-mentioned tester, is characterized in that: described signal acquisition circuit is A/D converter, and described data processor is dsp chip.

Above-mentioned tester, it is characterized in that: described current detecting unit comprises three current transformers carrying out respectively detecting in real time to the three-phase working current of described tested electrical equipment respectively, described voltage detection unit comprises three voltage transformer (VT) carrying out respectively detecting in real time to the three-phase operating voltage of described tested electrical equipment respectively.

Above-mentioned tester, it is characterized in that: described current detecting unit also comprises three the first signal conditioning circuits connected with three described current transformers respectively and three the first low-pass filter circuit of connecting of first signal conditioning circuit described with three respectively, and three described first low-pass filter circuits all connect with signal acquisition circuit; Described voltage detection unit also comprises three secondary signal modulate circuits connected with three described voltage transformer (VT) respectively and three the second low-pass filter circuit of connecting of secondary signal modulate circuit described with three respectively, and three described second low-pass filter circuits all connect with signal acquisition circuit; Three described first low-pass filter circuits and three described second low-pass filter circuits are second-order low-pass filter circuit, and described second-order low-pass filter circuit and signal Acquisition Circuit connects.

Above-mentioned tester, is characterized in that: described second-order low-pass filter circuit comprises chip U3 and chip U4, and described chip U3 and chip U4 is operational amplifier;

The normal phase input end of described chip U3 divides two-way, and a road is ground connection after electric capacity C2, and another road connects with its inverting input after resistance R8, electric capacity C1 and resistance R10, and the wiring point between resistance R8 and electric capacity C1 is the input end of described second-order low-pass filter circuit; Inverting input ground connection after resistance R9 of described chip U3;

The normal phase input end of described chip U4 divides two-way, one tunnel is ground connection after electric capacity C4, another road connects with its inverting input after resistance R12, electric capacity C3 and resistance R14, and the wiring point between resistance R12 with electric capacity C3 connects with the output terminal of described chip U3 after resistance R11; Inverting input ground connection after resistance R13 of described chip U4, the output terminal of described chip U4 is the output terminal of described second-order low-pass filter circuit and it connects with signal acquisition circuit.

Above-mentioned tester, it is characterized in that: three described first signal conditioning circuits and three described secondary signal modulate circuits are analog signal conditioner circuit, the scaling circuit that described analog signal conditioner circuit comprises biasing circuit and connects with described biasing circuit, described scaling circuit connects with described second-order low-pass filter circuit;

Described biasing circuit comprises chip U1, and described chip U1 is operational amplifier and its normal phase input end ground connection after resistance R4; The inverting input of described chip U1 divides three tunnels, and a road connects with its output terminal after resistance R3, and another road meets bias voltage Vin after resistance R2, and the 3rd tunnel connects with the output terminal of current transformer or voltage transformer (VT) after resistance R1;

Described scaling circuit comprises chip U2, and described chip U2 is operational amplifier and its positive input end grounding; The inverting input of described chip U2 divides two-way, and a road connects with its output terminal after resistance R6, and another road connects with the output terminal of chip U1 after resistance R5; The output terminal of described chip U2 connects with the input end of described second-order low-pass filter circuit after resistance R7.

Above-mentioned tester, is characterized in that: described chip U1, chip U2, chip U3 and chip U4 are chip OP07.

The present invention compared with prior art has the following advantages:

1, the dielectric loss angle tangent method of testing step adopted is simple, reasonable in design and realization is convenient, and input cost is low.

2, the dielectric loss angle tangent method of testing data handling procedure adopted is simple and data processing amount is little, just can convert according to Fourier coefficient and draw the dielectric loss angle tangent of current time electrical equipment to be tested, and without the need to carrying out Fourier expansion to detected voltage and current signal, Fourier coefficient just can convert reckoning according to detected curtage value and draw; Meanwhile, the signal value of the signal collected value of current time and front multiple sampling instant collection is utilized just can to complete dielectric loss angle tangent computation process and based on queuing theory.

3, the dielectric loss angle tangent method of testing adopted is a kind of real time fourier processing algorithm, and compared with conventional Fourier transform algorithm, real-time is good, can realize dielectric loss angle on-line monitoring truly.

4, the dielectric loss angle tangent method of testing adopted is a kind of dielectric loss angle tangent on-line monitoring method based on instantaneous active and reactive current, avoids measuring power-factor angle, and then reduces the measuring error that hardware zero point drift brings.

5, the dielectric loss angle tangent method of testing result of use adopted is good, and the dielectric loss angle tangent calculated is accurate, and measuring accuracy is high, achieves real real-time in-line testing dielectric loss angle tangent.Adopt dynamic reactive current detecting theoretical, the relation between dielectric loss angle tangent tan δ and instantaneous voltage, electric current is determined by trigonometric function mathematical relation, and application queue theory carries out the real-time Fourier algorithm of improvement formation to Fourier Transform Algorithm, avoid conventional Fourier and calculate primitive period renewal defect once, ensure the real-time of data.Thus, adopt the present invention to efficiently solve the problem that dielectric loss angle on-line monitoring exists specified poor real, poor accuracy, real-time is good and highly sensitive.

6, simple, the reasonable in design and easy-to-connect of the dielectric loss angle tangent tester structure adopted, use is easy and simple to handle, result of use good, can complete real-time, accurate test and the simultaneous display process of dielectric loss angle tangent.And, the second-order low-pass filter circuit adopted is simple, reasonable in design and input cost is low, result of use is good, effective filtering process can be carried out to detected electric current and voltage signal, realize effectively detecting faint electric current and voltage signal, thus can effectively solve existing electric current and voltage detecting circuit exists signal interference problem, thus ensure the accuracy of institute's calculation medium loss tangent.

In sum, the present invention is reasonable in design, realization is convenient and result of use is good, can easy, fast the dielectric loss angle tangent of tested electrical equipment is tested, and real-time is good, and measuring accuracy is high.

Below by drawings and Examples, technical scheme of the present invention is described in further detail.

Accompanying drawing explanation

Fig. 1 is the method flow block diagram of the present invention when processing the current value of a sampling instant collection and magnitude of voltage.

Fig. 1-1 is the phasor graph of tested electrical equipment working current and operating voltage.

Fig. 2 is the schematic block circuit diagram of dielectric loss angle tangent tester of the present invention.

Fig. 3 is the circuit theory diagrams of analog signal conditioner circuit of the present invention.

Fig. 4 is the result of calculation comparison diagram of " real-time FFT " and " traditional FFT " that the present invention adopts.Description of reference numerals:

1-current detecting unit; 1-1-current transformer; 1-2-the first signal conditioning circuit;

1-3-the first low-pass filter circuit; 2-voltage detection unit;

2-1-voltage transformer (VT); 2-2-secondary signal modulate circuit;

2-3-the second low-pass filter circuit; 3-signal acquisition circuit.

4-data processor; 5-host computer.

Embodiment

A kind of dielectric loss angle tangent method of testing as shown in Figure 1, comprises the following steps:

Step one, electric current and voltage signal acquisition: adopt current detecting unit 1 and voltage detection unit 2 to detect in real time respectively the working current of tested electrical equipment and operating voltage, and by signal acquisition circuit 3 and according to the sample frequency f preset _sthe current signal that current detecting unit 1 detects is gathered respectively with the voltage signal detected, and the current value each sampling instant collected and the equal synchronous driving of magnitude of voltage are to data processor 4;

Step 2, signal transacting: described data processor 4 is according to sampling sequencing, and the current value gather signal acquisition circuit 3 described in each sampling instant and magnitude of voltage process respectively; The current value that each sampling instant gathers is all identical with the disposal route of magnitude of voltage, when the current value gather and magnitude of voltage process, comprises the following steps any one sampling instant:

Step 201, Signal reception and stores synchronized: after described data processor 4 receives the current value and magnitude of voltage that signal acquisition circuit 3 described in current time gathers, stores synchronized is carried out to the current value received and magnitude of voltage, and total sampling number of signal acquisition circuit described in current time 3 is judged: as total sampling number > N of signal acquisition circuit described in current time 3, enter step 202; Otherwise, enter step 203; Wherein, N is positive integer and N=f _s/ f (1-22), in formula (1-22), f is the line frequency of tested electrical equipment, f _sfor the sample frequency designed in advance;

Step 202, current time dielectric loss angle tangent calculate: described data processor 4 calls the dielectric loss angle tangent of dielectric loss angle tangent computing module to the tested electrical equipment of current time and calculates, and process is as follows:

Step 2021, data group build: the current value that described in the current value gather signal acquisition circuit described in current time 3 and a front N' sampling instant, signal acquisition circuit 3 gathers forms a current data group, and sort from front to back to current value described in the N'+1 in described current data group according to sequencing of sampling; Simultaneously, the magnitude of voltage that described in the magnitude of voltage gather signal acquisition circuit described in current time 3 and a front N' sampling instant, signal acquisition circuit 3 gathers forms a voltage data group, and sorts from front to back to magnitude of voltage described in the N'+1 in described voltage data group according to sampling sequencing;

Wherein, N' is positive integer and N'=N or N-1;

As N'=N, current value described in N'+1 in described current data group be denoted as respectively from front to back i (0), i (1), i (2) ..., i (N), magnitude of voltage described in the N'+1 in described voltage data group be denoted as respectively from front to back u (0), u (1), u (2) ..., u (N);

As N'=N-1, current value described in N'+1 in described current data group be denoted as respectively from front to back i (1), i (2) ..., i (N), magnitude of voltage described in the N'+1 in described voltage data group is denoted as from front to back respectively, u (1), u (2) ..., u (N);

Wherein, i (N) and u (N) is respectively current value and the magnitude of voltage of signal acquisition circuit 3 collection described in current time;

Step 2022, dielectric loss angle tangent calculate: according to formula and current data group described in integrating step 2021 and described voltage data group, calculate the dielectric loss angle tangent tan δ of the tested electrical equipment of current time;

Wherein, as N'=N, a in formula (1-21) _i1and b _i1according to formula calculate; Further, a _u1and b _u1according to formula calculate;

As N'=N-1, a _i1and b _i1according to formula calculate; Further, a _u1and b _u1according to formula calculate;

Step 203, next sampling instant signal analysis and processing: according to the method described in step 201 to step 202, described data processor 4 processes the current value of signal acquisition circuit 3 collection described in next sampling instant and magnitude of voltage.

In the present embodiment, N=16 ~ 100 described in step 201.

Further, N=20.In actual use procedure, can according to specific needs, the value size of N be adjusted accordingly.

In the present embodiment, f=50Hz.

Wherein, line frequency is the frequency to the alternating current that tested electrical equipment is powered.

When adopting traditional Fourier transform converter technique to carry out dielectric loss test to electrical equipment, first extract fundamental current and the fundamental voltage of tested electrical equipment according to Fourier transform, then calculate the dielectric loss angle tangent (i.e. tan δ) of tested electrical equipment according to the angle relationship of fundamental voltage and fundamental current.

According to Fourier Transform Algorithm, one-period signal can be decomposed into the linear superposition of the sinusoidal signal of DC component c0 (i.e. 0 frequency) and different frequency by Fourier transform, refer to formula: c in formula (1-1) _mfor the amplitude of m subharmonic obtained after Fourier transform, to be the initial phase of m ω, m subharmonic be for the angular frequency of m subharmonic and its effective value is m is positive integer and m=1,2,3,

Meanwhile, formula (1-1) also can be expressed as: wherein, a _mand b _mbe Fourier coefficient and ω=2 π f, f are fundamental frequency;

As m=1, the expression formula of fundametal compoment is in formula (1-3) for obtaining the initial phase of fundamental signal after Fourier transform, the angular frequency of fundamental signal is ω and first-harmonic effective value is

When adopting the traditional dielectric loss angle tangent of Fourier Transform Algorithm to tested electrical equipment to calculate, first periodic sampling is carried out to the working current of tested electrical equipment, obtain current sampling signal (i.e. current sample sequence); Again discrete Fourier transformation is carried out to obtained current sampling signal, obtains the frequency spectrum of this signal, and try to achieve fundamental current signal (also referred to as current first harmonics component), be denoted as: θ in formula (1-4) ₂for the initial phase of fundamental signal obtained after carrying out Fourier transform to the working current sampling tested electrical equipment, the angular frequency of fundamental signal is ω _iand I is first-harmonic effective value; Herein, the electric current when working current of tested electrical equipment is the operation of tested electrical equipment bringing onto load;

In like manner, periodic sampling is carried out to the operating voltage of tested electrical equipment, obtain voltage sampling signal (i.e. voltage sample sequence); Again discrete Fourier transformation is carried out to obtained voltage sampling signal, obtains the frequency spectrum of this signal, and try to achieve fundamental voltage signal (also referred to as voltage fundamental component), be denoted as: θ in formula (1-5) ₁for the initial phase of fundamental signal obtained after carrying out Fourier transform to the working current sampling tested electrical equipment, the angular frequency of fundamental signal is ω _uand U is first-harmonic effective value; Herein, the voltage when operating voltage of tested electrical equipment is the operation of tested electrical equipment bringing onto load.Wherein, ω _u=ω _i=ω.

Adopt traditional Fourier Transform Algorithm to carry out dielectric loss angle tangent when calculating, the phase place of two fundamental signals (i.e. fundamental current signal and fundamental voltage signal) is subtracted each other and obtains dielectric loss angle δ, namely

After respectively Fourier transform is carried out to the working current of tested electrical equipment and operating voltage, obtain phasor graph as Figure 1-1.

In step 2022, the derivation of formula (1-27) and (1-28) is as follows: can be found out by Fig. 1-1: the idle component I of working current _q=Isin Φ (1-7), the real component I of working current _p=Icos Φ (1-8); Wherein, Φ=θ ₁-θ ₂=(ω t+ θ ₁)-(ω t+ θ ₂) (1-9);

By trigonometric function relation sin (alpha-beta)=sin α cos β-cos α sin β, can obtain:

Can draw thus: the dielectric loss angle tangent of tested electrical equipment:

In formula (1-12), Ucos θ ₁, Usin θ ₁, Icos θ ₂with Isin θ ₂, Fourier algorithm all can be utilized to carry out decomposition to the working current of the tested electrical equipment collected and operating voltage and to draw.

Wherein, according to formula (1-2), the working current of the tested electrical equipment collected is discrete signal and obtains after carrying out real time fourier processing to it: in formula (1-13), n is positive integer and n=1,2,3, b _inand a _inbe Fourier coefficient, i ₀for DC component;

In like manner, the operating voltage of the tested electrical equipment collected is discrete signal and obtains after carrying out real time fourier processing to it: in formula (1-14), b _unand a _unbe Fourier coefficient, u ₀for DC component;

Wherein, after carrying out real time fourier processing respectively to the working current of the tested electrical equipment collected and operating voltage, obtaining fundamental current signal is i ₁(t)=b _i1cos (ω t)+a _i1sin (ω t) (1-15), and fundamental voltage signal is u ₁(t)=b _u1cos (ω t)+a _u1sin (ω t) (1-16);

Meanwhile, according to formula with and ω _u=ω _i=ω, draws

According to formula (1-17) and (1-18), can draw with

Thus, formula (1-12) can be transformed into:

a in formula (1-21) _i1and b _i1be the Fourier coefficient of the fundamental current signal obtained after Fourier transform is carried out to the tested electrical equipment working current collected, a _u1and b _u1be the Fourier coefficient of the fundamental voltage signal obtained after Fourier transform is carried out to the tested electrical equipment operating voltage collected.

When supposing to sample to the working current of tested electrical equipment and operating voltage, sample frequency is f _s, then the sampling number N=f of each primitive period _s/ f (1-22), wherein f is fundamental frequency,

Formula in, a _mand b _mbe Fourier coefficient;

Wherein,

In formula (1-23) and (1-24), k is positive integer and it represents the sequence number of sampled point in a primitive period, k=1,2,3 ..., N; F (k) is the signal value that in the primitive period, a kth sampled point collects, and u (k) is the magnitude of voltage that in the primitive period, a kth sampled point collects;

According to formula (1-23) and (1-24), draw:

According to formula (1-25) and (1-26), draw:

In formula (1-27), i (k) is the current value that in the primitive period, a kth sampled point collects; In formula (1-28), u (k) is the magnitude of voltage that in the primitive period, a kth sampled point collects.

In addition, a _i1and b _i1also can according to formula $(1-29),$ Calculate; In formula (1-29), k' is positive integer and it represents the sequence number of sampled point in a primitive period, k'=1,2,3 ..., N-1; I (k') be kth in the primitive period ' the current value that collects of individual sampled point, i (N) is the current value that in the primitive period, last sampled point (i.e. N number of sampled point) collects, and i (0) is the current value that in the primitive period, on front side of first sampled point, a sampled point collects;

In like manner, a _u1and b _u1also can according to formula $(1-30),$ Calculate; In formula (1-30), k' is positive integer and it represents the sequence number of sampled point in a primitive period, k'=1,2,3 ..., N-1; U (k') be kth in the primitive period ' the magnitude of voltage that collects of individual sampled point, u (N) is the magnitude of voltage that in the primitive period, last sampled point (i.e. N number of sampled point) collects, and u (0) is the magnitude of voltage that in the primitive period, on front side of first sampled point, a sampled point collects.

Thus, the dielectric loss angle tangent computing method adopted in step 202 of the present invention, for the dielectric loss angle tangent on-line monitoring method based on instantaneous active and reactive current, can avoid measuring power-factor angle, and then the measuring error that the zero point drift of reduction hardware brings.

In addition, when adopting traditional Fourier algorithm to carry out dielectric loss angle tangent calculating, can only calculate once at a primitive period (i.e. 20ms, corresponding fundamental frequency is 50Hz).And when adopting the present invention to carry out dielectric loss angle tangent calculating, just can calculate once in each sampling instant.Thus the calculated rate of dielectric loss angle tangent is increased to the N of conventional Fourier algorithm calculated rate doubly, namely calculate a dielectric loss angle tangent a sampling period (i.e. 20ms/N), effectively can solve the problem that traditional Fourier algorithm carries out the poor real existed when dielectric loss angle tangent calculates like this.Thus, dielectric loss angle tangent method of testing disclosed by the invention, also can be described as real-time Fourier algorithm, and the data basis avoiding conventional Fourier transform must ensure that sampled data is the problem of complete primitive period, and real-time is good.

Further, when adopting the present invention to carry out dielectric loss angle tangent calculating, current data group and voltage data group need first be built.During actual implementation, to build based on queuing theory, and according to the sequencing in sampling time, magnitude of voltage described in the N'+1 in current value described in the N'+1 of current data group and voltage data group is sorted, and forms current value queue and magnitude of voltage queue.Like this, there is one group of periodic quantity all the time in the current value queue of arbitrary sampling instant and magnitude of voltage queue, and real-time update, and then the real-time measured can be realized, achieve instantaneity truly.Thus, the dielectric loss angle tangent computing method that the present invention adopts are carry out integrating the real time fourier processing method formed to queuing theory and Fourier transform principle.The Data Update time of the present invention only has conventional Fourier transform algorithm update time and consider the current value of each sampling instant and the renewal of magnitude of voltage based on queuing theory, thus instantaneous result of calculation is more accurate, and sensitivity is higher.

A kind of dielectric loss angle tangent tester as shown in Figure 2, comprise the current detecting unit 1 working current of tested electrical equipment being carried out to detection in real time, the operating voltage of tested electrical equipment is carried out to the voltage detection unit 2 detected in real time, the signal acquisition circuit 3 that current detecting unit 1 current signal detected and the voltage signal that voltage detection unit 2 detects are gathered respectively and carry out processing to signal acquisition circuit 3 is signal collected and synchronously draws the data processor 4 of the dielectric loss angle tangent of current tested electrical equipment, described current detecting unit 1 and voltage detection unit 2 all connect with signal acquisition circuit 3, the working current of described tested electrical equipment is three-phase current, and described current detecting unit 1 is three-phase current detection unit, the operating voltage of described tested electrical equipment is three-phase voltage, and described voltage detection unit 2 is detecting voltage by three phase unit.

In the present embodiment, dielectric loss angle tangent tester of the present invention, also comprises the host computer 5 connected with data processor 4.

In the present embodiment, described signal acquisition circuit 3 is A/D converter.

Further, described data processor 4 is dsp chip.

During actual use, described data processor 4 also can adopt the data processing chip of other type, is ARM chip etc.

In the present embodiment, described current detecting unit 1 comprises three current transformer 1-1 carrying out respectively detecting in real time to the three-phase working current of described tested electrical equipment respectively, and described voltage detection unit 2 comprises three voltage transformer (VT) 2-1 carrying out respectively detecting in real time to the three-phase operating voltage of described tested electrical equipment respectively.

Simultaneously, described current detecting unit 1 also comprises three current transformer 1-1 described with three connect the first signal conditioning circuit 1-2 and three the first low-pass filter circuit 1-3 of connecting of first signal conditioning circuit 1-2 described with three respectively respectively, and three described first low-pass filter circuit 1-3 all connect with signal acquisition circuit 3; Described voltage detection unit 2 also comprises three voltage transformer (VT) 2-1 described with three connect secondary signal modulate circuit 2-2 and three the second low-pass filter circuit 2-3 of connecting of secondary signal modulate circuit 2-2 described with three respectively respectively, and three described second low-pass filter circuit 2-3 all connect with signal acquisition circuit 3; Three described first low-pass filter circuit 1-3 and three described second low-pass filter circuit 2-3 are second-order low-pass filter circuit, and described second-order low-pass filter circuit and signal Acquisition Circuit 3 connects.

As shown in Figure 3, in the present embodiment, described second-order low-pass filter circuit comprises chip U3 and chip U4, and described chip U3 and chip U4 is operational amplifier.

The normal phase input end of described chip U3 divides two-way, and a road is ground connection after electric capacity C2, and another road connects with its inverting input after resistance R8, electric capacity C1 and resistance R10, and the wiring point between resistance R8 and electric capacity C1 is the input end of described second-order low-pass filter circuit; Inverting input ground connection after resistance R9 of described chip U3.

The normal phase input end of described chip U4 divides two-way, one tunnel is ground connection after electric capacity C4, another road connects with its inverting input after resistance R12, electric capacity C3 and resistance R14, and the wiring point between resistance R12 with electric capacity C3 connects with the output terminal of described chip U3 after resistance R11; Inverting input ground connection after resistance R13 of described chip U4, the output terminal of described chip U4 is the output terminal of described second-order low-pass filter circuit and it connects with signal acquisition circuit 3.

In the present embodiment, three described first signal conditioning circuit 1-2 and three described secondary signal modulate circuit 2-2 are analog signal conditioner circuit, the scaling circuit that described analog signal conditioner circuit comprises biasing circuit and connects with described biasing circuit, described scaling circuit connects with described second-order low-pass filter circuit.

Described biasing circuit comprises chip U1, and described chip U1 is operational amplifier and its normal phase input end ground connection after resistance R4; The inverting input of described chip U1 divides three tunnels, and a road connects with its output terminal after resistance R3, and another road meets bias voltage Vin after resistance R2, and the 3rd tunnel connects with the output terminal of current transformer 1-1 or voltage transformer (VT) 2-1 after resistance R1.

Described scaling circuit comprises chip U2, and described chip U2 is operational amplifier and its positive input end grounding; The inverting input of described chip U2 divides two-way, and a road connects with its output terminal after resistance R6, and another road connects with the output terminal of chip U1 after resistance R5; The output terminal of described chip U2 connects with the input end of described second-order low-pass filter circuit after resistance R7.

During physical cabling, the output terminal of described voltage transformer (VT) 2-1 is denoted as Uin, and the output terminal of described current transformer 1-1 is denoted as Iin.

In the present embodiment, described chip U1, chip U2, chip U3 and chip U4 are chip OP07.

In the present embodiment, the resistance of resistance R9, R10, R13 and R14 is r, and the resistance of resistance R8 and R12 is r ₂, the resistance of resistance R7 and R11 is r ₁, the capacitance (i.e. reactance) of electric capacity C1 and C3 is C ₁, the capacitance (i.e. reactance) of electric capacity C2 and C4 is C ₂.

In the present embodiment, because described data processor 4 is dsp chip, thus by described analog signal conditioner circuit, the voltage signal that detected current signal or voltage signal are all adjusted to 0V ~ 3V (being specially 0.5V ~ 2.5V) is inputed to data processor 4, undertaken processing by data processor 4 and calculate the dielectric loss angle tangent of the tested electrical equipment of current time, and by host computer 5 for the dielectric loss angle tangent calculated carries out simultaneous display.

When dielectric loss angle tangent is calculated, signal interference problem is the key factor affecting on-line insulation inspection system safe and reliable operation always, in the electromagnetic interference environment of especially some complexity, the detection difficulty of feeble signal is larger, and common way is design simulation filter circuit or adopts filtering algorithm to carry out digital filtering.

As shown in Figure 3, in the present embodiment, the low-pass filter circuit adopted is second-order low-pass filter circuit, and this filtering circuit is two-stage voltage controlled voltage source filtering circuit is in series, and every one-level filtering circuit both introduced negative feedback, introduced positive feedback again; When the frequency of institute's detection signal is tending towards 0, the reactance of electric capacity C1 and C3 is tending towards infinite; When the frequency of institute's detection signal is tending towards infinite, the reactance of electric capacity C2 and C4 is tending towards 0.

The transport function of described second-order low-pass filter circuit is:

In the present embodiment, the voltage peak-to-peak value produced by signal generator SDG1020 (also claims peak-to-peak value, refer to the difference between signal mxm. and minimum in one-period) for 4V and frequency is respectively the ac voltage signal of 50Hz, 150Hz and 250Hz, the circuit performance of described second-order low-pass filter circuit is tested.Drawing after tested, is the ac voltage signal of 50Hz for frequency, and the output voltage of described second-order low-pass filter circuit is substantially undamped; Be the ac voltage signal of 150Hz for frequency, the output voltage peak-to-peak value of described second-order low-pass filter circuit is 54mV, attenuation ratio 54/4000=1.35%; Be the ac voltage signal of 250Hz for frequency, the output voltage peak-to-peak value of described second-order low-pass filter circuit is within 20mV, and attenuation ratio is less than 20/4000=0.5%.Therefore, described second-order low-pass filter circuit to the inhibition of electrical network more than three times and three times harmonic waves clearly.

Below the method for testing (i.e. real time fourier processing algorithm, hereinafter referred to as " real-time FFT ") that conventional Fourier transform algorithm (hereinafter referred to as " traditional FFT ") and the present invention adopt is contrasted.The present invention gathers current value and the magnitude of voltage of 20 sampled points within each primitive period (i.e. 20ms), starts input signal and is that peak-to-peak value is 4V and frequency is the voltage signal of 50Hz, suddenly peak-to-peak value is become 2V in operational process.The dielectric loss angle tangent that " traditional FFT " and " real-time FFT " this two kinds of methods calculate, refers to table 1; Further, the two dielectric loss angle tangent comparing result calculated refers to Fig. 4.

The dielectric loss angle tangent contrast table that table 1 " traditional FFT " and " real-time FFT " calculate

As shown in Figure 4, the voltage signal inputted during the 52nd sampled point changes (peak-to-peak value becomes 2V from 4V), the trend now adopting " real-time FFT " just can follow voltage signal presents downtrending, and " traditional FFT " still keeps the calculated value of a cycle (i.e. primitive period).Therefore, compared with " real-time FFT ", " traditional FFT ", due to intrinsic defect, can have the time delay of one-period (primitive period) at least when signal is undergone mutation, and period data and signal actual difference very large.In Fig. 4, horizontal ordinate is sampling number, and the ordinate of the Voltage Peak peak value of input signal is voltage and its unit is V, and the ordinate of " traditional FFT " and " real-time FFT " is the dielectric loss angle tangent calculated.

Below to the present invention adopt the dielectric loss angle tangent result of calculation of " real-time FFT " method to analyze, and the phase angle difference of given institute's input current and voltage is respectively 90 °-85 °, 90 °-80 °, 90 °-75 °, 90 °-70 °, 90 °-65 ° and 90 °-60 °, namely when δ is respectively 5 °, 10 °, 15 °, 20 °, 25 ° and 30 °, " real-time FFT " method of employing calculates dielectric loss angle tangent, and result of calculation refers to table 2:

Table 2 " real-time FFT " dielectric loss angle tangent result of calculation table

As shown in Figure 2, " real-time FFT " disclosed by the invention method is adopted to calculate the maximum error of dielectric loss angle tangent very little, specific as follows: when °-85 °=5 °, δ=90, maximum error e1=(0.097702-0.0874)/0.0874=11.4%; When δ=10 °, maximum error e2=(0.182562-0.1763)/0.1763=3.5%; When δ=15 °, maximum error e3=(0.273428-0.2679)/0.2679=2.0%; When δ=20 °, maximum error e4=(0.367488-0.3639)/0.3639=0.0098%; When δ=25 °, maximum error e5=(0.445992-0.4663)/0.4663=-4.2%; When δ=30 °, maximum error e3=(0.550209-0.5773)/0.5773=-4.6%; Can find out thus: adopt the full accuracy of " real-time FFT " disclosed by the invention method can ensure thousand effectiveness of classifications, normality precision can reach within 5%.

The above; it is only preferred embodiment of the present invention; not the present invention is imposed any restrictions, every above embodiment is done according to the technology of the present invention essence any simple modification, change and equivalent structure change, all still belong in the protection domain of technical solution of the present invention.

Claims (10)

1. a dielectric loss angle tangent method of testing, is characterized in that: the method comprises the following steps:

Step one, electric current and voltage signal acquisition: adopt current detecting unit (1) and voltage detection unit (2) to detect in real time respectively the working current of tested electrical equipment and operating voltage, and by signal acquisition circuit (3) and according to the sample frequency f preset _sthe current signal that current detecting unit (1) detects is gathered respectively with the voltage signal detected, and the current value each sampling instant collected and the equal synchronous driving of magnitude of voltage are to data processor (4);

Step 2, signal transacting: described data processor (4) is according to sampling sequencing, and the current value gather signal acquisition circuit (3) described in each sampling instant and magnitude of voltage process respectively; The current value that each sampling instant gathers is all identical with the disposal route of magnitude of voltage, when the current value gather and magnitude of voltage process, comprises the following steps any one sampling instant:

Step 201, Signal reception and stores synchronized: after described data processor (4) receives the current value and magnitude of voltage that signal acquisition circuit described in current time (3) gathers, stores synchronized is carried out to the current value received and magnitude of voltage, and total sampling number of signal acquisition circuit described in current time (3) is judged: as total sampling number > N of signal acquisition circuit described in current time (3), enter step 202; Otherwise, enter step 203; Wherein, N is positive integer and N=f _s/ f (1-22), in formula (1-22), f is the line frequency of tested electrical equipment, f _sfor the sample frequency designed in advance;

Step 202, current time dielectric loss angle tangent calculate: described data processor (4) calls the dielectric loss angle tangent of dielectric loss angle tangent computing module to the tested electrical equipment of current time and calculates, and process is as follows:

Step 2021, data group build: the current value that described in the current value gather signal acquisition circuit described in current time (3) and a front N' sampling instant, signal acquisition circuit (3) gathers forms a current data group, and sort from front to back to current value described in the N'+1 in described current data group according to sequencing of sampling; Simultaneously, the magnitude of voltage that described in the magnitude of voltage gather signal acquisition circuit described in current time (3) and a front N' sampling instant, signal acquisition circuit (3) gathers forms a voltage data group, and sorts from front to back to magnitude of voltage described in the N'+1 in described voltage data group according to sampling sequencing;

Wherein, N' is positive integer and N'=N or N-1;

As N'=N, current value described in N'+1 in described current data group be denoted as respectively from front to back i (0), i (1), i (2) ..., i (N), magnitude of voltage described in the N'+1 in described voltage data group be denoted as respectively from front to back u (0), u (1), u (2) ..., u (N);

As N'=N-1, current value described in N'+1 in described current data group be denoted as respectively from front to back i (1), i (2) ..., i (N), magnitude of voltage described in the N'+1 in described voltage data group is denoted as from front to back respectively, u (1), u (2) ..., u (N);

Wherein, i (N) and u (N) is respectively the current value and magnitude of voltage that signal acquisition circuit described in current time (3) gathers;

Step 2022, dielectric loss angle tangent calculate: according to formula (1-21), and current data group described in integrating step 2021 and described voltage data group, calculate the dielectric loss angle tangent tan δ of the tested electrical equipment of current time;

Wherein, as N'=N, a in formula (1-21) _i1and b _i1according to formula $\left\{\begin{array}{c}{a}_{i1}=\frac{2}{N}\underset{k^{\′}=1}{\overset{N-1}{\Σ}}i\left(k^{\′}\right)\sin \frac{2k^{\′}\mathrm{\π}\·f_s}{N}\\ b_{i1}=\frac{1}{N}\[i\left(0\right)+2\underset{k^{\′}=1}{\overset{N-1}{\Σ}}i\left(k^{\′}\right)\cos \frac{2k^{\′}\mathrm{\π}\·f_s}{N}+i\left(N\right)\]\end{array}\right.---\left(1-29\right),$ Calculate; Further, a _u1and b _u1according to formula $\left\{\begin{array}{c}{a}_{u1}=\frac{2}{N}\underset{k^{\′}=1}{\overset{N-1}{\Σ}}u\left(k^{\′}\right)\sin \frac{2k^{\′}\mathrm{\π}\·f_s}{N}\\ b_{u1}=\frac{1}{N}\[u\left(0\right)+2\underset{k^{\′}=1}{\overset{N-1}{\Σ}}u\left(k^{\′}\right)\cos \frac{2k^{\′}\mathrm{\π}\·f_s}{N}+u\left(N\right)\]\end{array}\right.---\left(1-30\right),$ Calculate;

As N'=N-1, a _i1and b _i1according to formula $\left\{\begin{array}{c}{a}_{i1}=\frac{2}{N}\underset{k=1}{\overset{N}{\Σ}}i\left(k\right)\sin \frac{2k\mathrm{\π}\·f_s}{N}\\ b_{i1}=\frac{2}{N}\underset{k=1}{\overset{N}{\Σ}}i\left(k\right)\cos \frac{2k\mathrm{\π}\·f_s}{N}\end{array}\right.---\left(1-27\right),$ Calculate; Further, a _u1and b _u1according to formula $\left\{\begin{array}{c}{a}_{u1}=\frac{2}{N}\underset{k=1}{\overset{N}{\Σ}}u\left(k\right)\sin \frac{2k\mathrm{\π}\·f_s}{N}\\ b_{u1}=\frac{2}{N}\underset{k=1}{\overset{N}{\Σ}}u\left(k\right)\cos \frac{2k\mathrm{\π}\·f_s}{N}\end{array}\right.---\left(1-28\right),$ Calculate;

Step 203, next sampling instant signal analysis and processing: according to the method described in step 201 to step 202, the current value that described data processor (4) gathers signal acquisition circuit (3) described in next sampling instant and magnitude of voltage process.

2., according to a kind of dielectric loss angle tangent method of testing according to claim 1, it is characterized in that: N=16 ~ 100 described in step 201.

3. one kind realizes the tester of dielectric loss angle tangent method of testing as claimed in claim 1, it is characterized in that: comprise the current detecting unit (1) working current of tested electrical equipment being carried out to detection in real time, the operating voltage of tested electrical equipment is carried out to the voltage detection unit (2) detected in real time, the signal acquisition circuit (3) that current detecting unit (1) current signal detected and the voltage signal that voltage detection unit (2) detects are gathered respectively and carry out processing to signal acquisition circuit (3) is signal collected and synchronously draws the data processor (4) of the dielectric loss angle tangent of current tested electrical equipment, described current detecting unit (1) and voltage detection unit (2) all connect with signal acquisition circuit (3), the working current of described tested electrical equipment is three-phase current, and described current detecting unit (1) is three-phase current detection unit, the operating voltage of described tested electrical equipment is three-phase voltage, and described voltage detection unit (2) is detecting voltage by three phase unit.

4. according to tester according to claim 3, it is characterized in that: also comprise the host computer (5) connected with data processor (4).

5. according to the tester described in claim 3 or 4, it is characterized in that: described signal acquisition circuit (3) is A/D converter, described data processor (4) is dsp chip.

6. according to the tester described in claim 3 or 4, it is characterized in that: described current detecting unit (1) comprises three current transformers (1-1) carrying out respectively detecting in real time to the three-phase working current of described tested electrical equipment respectively, described voltage detection unit (2) comprises three voltage transformer (VT) (2-1) carrying out respectively detecting in real time to the three-phase operating voltage of described tested electrical equipment respectively.

7. according to tester according to claim 6, it is characterized in that: described current detecting unit (1) also comprises three the first signal conditioning circuits (1-2) connected with three described current transformers (1-1) respectively and three the first low-pass filter circuit (1-3) of connecting of first signal conditioning circuit (1-2) described with three respectively, and three described first low-pass filter circuits (1-3) all connect with signal acquisition circuit (3); Described voltage detection unit (2) also comprises three secondary signal modulate circuits (2-2) connected with three described voltage transformer (VT) (2-1) respectively and three the second low-pass filter circuit (2-3) of connecting of secondary signal modulate circuit (2-2) described with three respectively, and three described second low-pass filter circuits (2-3) all connect with signal acquisition circuit (3); Three described first low-pass filter circuits (1-3) and three described second low-pass filter circuits (2-3) are second-order low-pass filter circuit, and described second-order low-pass filter circuit and signal Acquisition Circuit (3) connects.

8. according to tester according to claim 7, it is characterized in that: described second-order low-pass filter circuit comprises chip U3 and chip U4, described chip U3 and chip U4 is operational amplifier;

The normal phase input end of described chip U3 divides two-way, and a road is ground connection after electric capacity C2, and another road connects with its inverting input after resistance R8, electric capacity C1 and resistance R10, and the wiring point between resistance R8 and electric capacity C1 is the input end of described second-order low-pass filter circuit; Inverting input ground connection after resistance R9 of described chip U3;

The normal phase input end of described chip U4 divides two-way, one tunnel is ground connection after electric capacity C4, another road connects with its inverting input after resistance R12, electric capacity C3 and resistance R14, and the wiring point between resistance R12 with electric capacity C3 connects with the output terminal of described chip U3 after resistance R11; Inverting input ground connection after resistance R13 of described chip U4, the output terminal of described chip U4 is the output terminal of described second-order low-pass filter circuit and it connects with signal acquisition circuit (3).

9. according to tester according to claim 8, it is characterized in that: three described first signal conditioning circuits (1-2) and three described secondary signal modulate circuits (2-2) are analog signal conditioner circuit, the scaling circuit that described analog signal conditioner circuit comprises biasing circuit and connects with described biasing circuit, described scaling circuit connects with described second-order low-pass filter circuit;

Described biasing circuit comprises chip U1, and described chip U1 is operational amplifier and its normal phase input end ground connection after resistance R4; The inverting input of described chip U1 divides three tunnels, one tunnel connects with its output terminal after resistance R3, another road meets bias voltage Vin after resistance R2, and the 3rd tunnel connects with the output terminal of current transformer (1-1) or voltage transformer (VT) (2-1) after resistance R1;

Described scaling circuit comprises chip U2, and described chip U2 is operational amplifier and its positive input end grounding; The inverting input of described chip U2 divides two-way, and a road connects with its output terminal after resistance R6, and another road connects with the output terminal of chip U1 after resistance R5; The output terminal of described chip U2 connects with the input end of described second-order low-pass filter circuit after resistance R7.

10. according to tester according to claim 9, it is characterized in that: described chip U1, chip U2, chip U3 and chip U4 are chip OP07.