CN102565542B - Capacitive equipment medium loss online monitoring method based on IEC61850-9-2 standard - Google Patents

Abstract

The invention discloses a capacitive equipment medium loss online monitoring method based on an IEC61850-9-2 sampling standard in an intelligent substation. According to the invention, medium loss measurement based on the IEC61850-9-2 sampling standard in the intelligent substation can be realized. Through fiber B code timing, synchronization acquisition of a reference voltage and a leakage current can be realized. Through a high-precision zero-flux mutual inductor and a 16 bit AD, the acquisition of the leakage current can be realized. Through a resampling algorithm and a software frequency tracking algorithm, rejection of an interference signal and full period sampling can be realized. And high-precision online monitoring of the capacitive equipment medium loss can be realized. By using the method of the invention, a medium loss measurement problem based on the digital sampling in the intelligent substation can be solved.

Description

On-line monitoring method of dielectric loss of capacitive equipment based on IEC61850-9-2 standard

technical field

The invention belongs to the technical field of on-line monitoring of electric power equipment. More precisely, the invention relates to an on-line monitoring method for dielectric loss of capacitive equipment based on the IEC61850-9-2 sampling standard in an intelligent substation.

Background technique

Since 2010, the construction of smart substations has gradually become the mainstream of new substations, and will lead to explosive growth in the future. In the construction of smart substations, it is emphasized that through online monitoring of the status of primary equipment, the condition maintenance of primary equipment and timely early warning of failures will be gradually realized, so as to achieve less maintenance and maintenance-free, and avoid power outages and casualties caused by equipment failures. Capacitive power equipment occupies a large proportion in the power transmission and transformation system, such as transformer bushings, lightning arresters, etc. These power equipment are affected by factors such as electricity, heat, and harsh environments during operation, and their insulation performance decreases. become an accident hazard. Dielectric loss is an important insulation index that reflects the insulation status of capacitive power equipment, and plays a very important role in the stable operation of power equipment. Enhancing online monitoring of capacitive devices has enormous social and economic benefits.

The principle of dielectric loss measurement of capacitive equipment is shown in Figure 1. The dielectric loss measurement collects the voltage signal Un of the bus PT and transforms it into a low-voltage AC voltage signal U1 through a voltage transformer, and the U2 signal generated by a high-precision micro-current sensor (CT) from the final screen current signal of the capacitive device Cx under test. U1 and U2 are connected to the conditioning circuit and AD sampling circuit of the dielectric loss measurement unit through cables. Under the control of the CPU, the signal acquisition systems of U1 and U2 start at the same time, and the analog voltage signal output by the sensor is synchronously sampled, and then the capacitance is calculated. The phase difference Ph of the terminal current signal Ix of the type equipment relative to the bus voltage Un, so as to obtain parameters such as dielectric loss tanδ and capacitance Cx. The synchronous sampling control technology of the measurement unit, the sampling accuracy of micro-current, frequency tracking and the elimination of harmonics and interference signals are the keys to ensure the accuracy of dielectric loss measurement.

Document 1 "On-line Monitoring Method and Device for Dielectric Loss of Capacitive Power Equipment" (Chinese Patent Application No. 200410026133.2) discloses a method and device for on-line monitoring of dielectric loss of capacitive power equipment. The method connects the voltage transformer signal of the substation bus voltage and the high-precision micro-current sensor signal installed on the equipment grounding line to the computer PCI acquisition card in the monitoring room through the cable for calculation. This method has the following problems: First, the power grid frequency is not tracked, and the entire cycle sampling cannot be guaranteed. There are fence effects and leakage effects, which bring large errors to the calculated spectrum, especially the phase; second, the voltage signal and the final screen current The signal cannot be collected locally, but is pulled to the computer in the monitoring room for processing through the cable. Since the output of the transformer is a weak signal, it is not suitable for long-distance transmission and is easily interfered by external signals; the third is AD conversion. The 8-bit resolution of the chip cannot meet the measurement accuracy requirements of weak signals of leakage current; fourth, it does not meet the requirements of digital sampling in smart substations, and the measurement of bus voltage cannot meet the sampling requirements through merging units, which is not suitable for the design requirements of smart substations.

In the smart substation, for the measurement of voltage and current signals, the merging unit has been widely used to digitize the signal on the spot, and the original sampled value of the measurement is transmitted to the measurement, protection, recording through the IEC61850-9-2 standard and the optical fiber as the communication medium. wave, dynamic vector and other functional units. The method of laying cables is no longer used to connect analog signals such as voltage and current to the measurement protection unit. In the design of smart substation, based on unified consideration, no cable will be laid separately for the dielectric loss measurement unit to collect voltage signals. The dielectric loss measurement unit needs the voltage signal of the bus PT, which brings problems to the application of the traditional dielectric loss on-line measurement unit. It is necessary to develop a new generation of on-line monitoring unit for dielectric loss of capacitive equipment based on IEC61850-9-2 standard.

Document 2 "On-line monitoring method for dielectric loss factor of capacitive equipment based on DSP" (Power System Automation, October 2004, Volume 28, No. 19, Page 71) discloses a DSP-based online monitoring method for dielectric loss of capacitive equipment . This method takes into account factors such as signal interference, harmonics, and grid frequency fluctuations that affect measurement accuracy. However, its sampling is traditional analog sampling, and the frequency tracking algorithm it introduces is not suitable for digital sampling requirements based on the IEC-61850-9-2 standard.

Document 3 "Analysis of Dielectric Loss Angle Measurement Based on Harmonic Analysis Method with Hanning Window Interpolation" (Power System Automation, January 2006, Volume 30, Issue 2, Page 81) discloses a Hanning window The interpolated harmonic analysis method can alleviate the influence of non-synchronous sampling on the dielectric loss angle measurement. First of all, this method is also based on analog quantity acquisition and is not suitable for smart substations based on digital sampling. Secondly, frequency tracking is not carried out. The harmonic analysis method based on adding Hanning window interpolation is only to reduce the influence of non-period sampling on the measurement of dielectric loss angle, and does not realize full-period sampling through frequency tracking.

Contents of the invention

The purpose of the invention of the present invention is:

1. In the smart substation, the bus PT voltage is collected locally through the merging unit, which cannot meet the current requirements of the dielectric loss measurement unit to access the analog signal through a cable. This invention needs to solve the problem of sampling based on the IEC61850-9-2 standard in the smart substation. Dielectric loss measurement method;

2. The merging unit for collecting the bus PT voltage and collecting the leakage current is not the same merging unit. How to ensure the synchronous acquisition of the two signals is the key to accurately measure the dielectric loss;

3. How to suppress the DC drift in the signal and the influence of the 3rd, 5th, and 7th harmonics of the power grid on the measurement accuracy of the dielectric loss angle;

4. In the case of power grid frequency fluctuations, how does the dielectric loss measurement unit based on IEC61850-9-2 standard sampling realize frequency tracking and prevent spectrum leakage and fence effects.

In order to achieve the above object, the present invention is achieved by taking the following technical solutions:

A kind of capacitive equipment dielectric loss on-line monitoring method based on IEC61850-9-2 standard, it is characterized in that, comprises the following steps:

1) Connect a high-precision zero-flux leakage current transformer on the grounding wire of the capacitive equipment, connect the voltage signal output by the transformer to the dielectric loss measurement unit installed on site, and start the leakage current according to the sub-pulse signal output by the B code The AD sampling;

2) The busbar or line reference voltage is measured on-site through the merging unit, and the dielectric loss measurement unit is connected to the IEC61850-9-2 standard reference voltage sampling value information collected by the merging unit through an optical fiber; the sampling value is re-sampled and Fu Liye transform, calculate the amplitude, phase angle and frequency, adjust the resampling frequency, and perform frequency tracking;

3) Perform Fourier transform on the leakage current sampling signal collected in step 1), calculate the phase and amplitude of the leakage current, and calculate the dielectric loss value in combination with the amplitude and phase of the reference voltage at the same time calculated in step 2).

The aforementioned capacitive equipment dielectric loss online monitoring method based on the IEC61850-9-2 standard is characterized in that: the algorithm of resampling in the step 2) is: let fs be the sampling frequency of the merging unit, and Ts be the corresponding sampling period, fs' is the resampling frequency of the dielectric loss measurement unit, Ts' is the corresponding resampling period, then

${\mathrm{<span\; class="notranslate">\; Ts</span>}}^{<span\; class="notranslate">\; \&prime;</span>}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; fs</span>}}{{\mathrm{<span\; class="notranslate">\; fs</span>}}^{<span\; class="notranslate">\; \&prime;</span>}}\mathrm{<span\; class="notranslate">\; Ts</span>}$

T(n)=T(n-1)+Ts'

T(n) is the position of the interpolation point, the floating point number T(n-1) is the position of the previous point interpolation point, let m be the largest integer smaller than T(n), and set the floating point number u=T(n), then linear interpolation The formula is as follows:

x'(n)=x(m)*(m+1-u)+x(m+1)*(u-m)

In the formula, x'(n) is the nth point in the resampling sequence, x(m) is the value of the mth point in the original sampling sequence, and x(m+1) is the m+1th point in the original sampling sequence value.

Aforesaid capacitive equipment dielectric loss on-line monitoring method based on IEC61850-9-2 standard, it is characterized in that: in described step 2), the step of frequency tracking is as follows:

21) Carrying out Fourier transform of the whole cycle to the reference voltage signal Ux;

22) Filtering the Fourier transform result;

23) Use the filtered fundamental wave vector to calculate the phase difference of adjacent cycles

24) Using phase difference Calculate frequency change

25) Calculate the original signal frequency f=f _s -Δf;

26) Adjust the resampling interval according to the calculated latest frequency value, and return to step 21).

The aforementioned online monitoring method for dielectric loss of capacitive equipment based on the IEC61850-9-2 standard is characterized in that: the amplitude and phase of the reference voltage at the same moment are acquired through the clock timing unit in the station through 2 optical fiber B code timing signals The merging unit and the dielectric loss measurement unit are respectively connected to realize the information collection of the same time section of the reference voltage and leakage current information.

Beneficial effects achieved by the present invention: In the present invention, a dielectric loss measurement method based on digital signal sampling is disclosed, which adopts B code time synchronization based on GPS time synchronization of the whole station to realize synchronous sampling, and utilizes high-precision zero magnetic flux Leakage current transformers and high-resolution AD ensure high-precision sampling, and use Fourier transform and frequency tracking algorithms to ensure measurement accuracy. The method of the invention can solve the problem of measuring the dielectric loss of capacitive power equipment based on the digital sampling of the whole station in the construction of the current intelligent substation. And put forward a kind of key technical solutions such as synchronous sampling and frequency tracking brought about by digital sampling. In this scheme, the time synchronization error based on the optical fiber B code is less than 1 μs, and the frequency measurement accuracy reaches 0.003 Hz, which fully meets the measurement requirements of dielectric loss. The accuracy and stability of the measurement are guaranteed by the localized collection of leakage current, the use of high-precision transformers and high-resolution AD chips. The more traditional measurement method avoids problems such as signal attenuation and susceptibility to external interference caused by long-distance transmission of small signals. In addition, on-site digital collection and the use of optical fiber instead of cables can save the cost of substation construction and improve information sharing, which is in line with the concept of energy saving and environmental protection of smart substations.

Description of drawings

Figure 1 is a schematic diagram of the dielectric loss measurement of traditional capacitive power equipment;

Fig. 2 is the composition and structural block diagram of the capacitive equipment dielectric loss measurement system based on the IEC61850-9-2 standard implemented by the present invention;

Fig. 3 is a diagram illustrating the hardware structure of the core board for realizing the dielectric loss measuring device of the present invention;

Fig. 4 is a flow chart illustrating the algorithm for realizing the dielectric loss measuring method of the present invention by using a program.

Detailed ways

Based on the IEC61850-9-2 standard on-line monitoring method for the dielectric loss of capacitive equipment, the dielectric loss measurement unit collects the reference voltage signal through IEC61850-9-2 standard communication with the merging unit, and realizes the reference voltage and leakage through the optical fiber B code time synchronization Synchronous collection of current, through high-precision zero-flux transformer and 16-bit AD to realize the collection of leakage current, through the resampling algorithm and software frequency tracking algorithm to realize the elimination of interference signals and the sampling of the whole cycle, to realize the dielectric loss of capacitive equipment High-precision online monitoring, including the following steps:

1) Connect a high-precision zero-flux leakage current transformer on the grounding wire of the equipment, and connect the voltage signal output by the transformer to the locally installed dielectric loss measurement unit (U1) to measure the leakage current signal of the capacitive equipment , U1 has a B code time synchronization interface, and uses the divided pulse signal output by the B code to start AD sampling;

2) The AC sampling (SV) interface (optical fiber port) of U1 is connected to the output interface of the merging unit for collecting reference voltages or the corresponding AC sampling network (SV network) through an optical fiber, and the sampled value information collected by it has a time stamp;

3) In U1, the leakage current signal and the reference voltage signal are aligned based on the time scale information. Since the current merging unit uses a sampling frequency of 80 points/cycle, resampling is required, and signal processing methods such as spectrum analysis are performed based on the resampled data. Out-of-angle difference, leakage current, frequency, capacitance and other parameters, and finally adjust the resampling interval according to the calculated frequency to achieve full-cycle sampling and improve measurement accuracy and stability. The specific algorithm is as follows:

31) Resample the raw data of the merging unit:

Suppose fs is the sampling frequency of the merging unit, Ts is the corresponding sampling period, fs' is the resampling frequency of the dielectric loss measurement unit, and Ts' is the corresponding resampling period, then

${\mathrm{<span\; class="notranslate">\; Ts</span>}}^{<span\; class="notranslate">\; \&prime;</span>}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; fs</span>}}{{\mathrm{<span\; class="notranslate">\; fs</span>}}^{<span\; class="notranslate">\; \&prime;</span>}}\mathrm{<span\; class="notranslate">\; Ts</span>}$

T(n)=T(n-1)+Ts'

T(n) is the position of the interpolation point, generally a floating point number, let m be the largest integer smaller than T(n), and set the floating point number u=T(n), then the linear interpolation formula is as follows:

x'(n)=x(m)*(m+1-u)+x(m+1)*(u-m)

32) Perform Fourier transform after resampling to calculate the amplitude and phase angle,

The Fourier transform result can be expressed as:

${\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; x</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; o</span>}}<span\; class="notranslate">\; +</span>\underset{\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\overset{\mathrm{<span\; class="notranslate">\; N</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; km</span>}}\mathrm{<span\; class="notranslate">\; sin</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; k\&omega;t</span>}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; \&alpha;</span>}}_{\mathrm{<span\; class="notranslate">\; k</span>}}<span\; class="notranslate">\; )</span>$

${\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; x</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; o</span>}}<span\; class="notranslate">\; +</span>\underset{\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\overset{\mathrm{<span\; class="notranslate">\; N</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; km</span>}}\mathrm{<span\; class="notranslate">\; sin</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; k\&omega;t</span>}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; \&beta;</span>}}_{\mathrm{<span\; class="notranslate">\; k</span>}}<span\; class="notranslate">\; )</span>$

In the formula, Ux is the measured reference voltage, U _o is its DC component, U _km is the amplitude of each harmonic, and α _k is the phase angle of each harmonic. I _x is the measured leakage current, I _o is its DC component, I _km is the amplitude of each harmonic, β _k is the phase angle of each harmonic, k is the harmonic order, and N is the maximum harmonic order , t is the time, ω is the angular frequency of the signal.

After calculating the voltage and current fundamental wave phase angles α ₁ and β ₁ , the dielectric loss angle can be obtained:

tanδ＝tan[90°-(β ₁ -α ₁ )]

33) Carry out frequency tracking, the steps are as follows:

331) performing full-cycle Fourier transform on the reference voltage signal Ux;

332) Filtering the Fourier transform result;

333) Use the filtered fundamental wave vector to calculate the phase difference of adjacent cycles

334) exploit Calculate frequency change

335) Calculate the original signal frequency f=f _s -Δf;

4) Adjust the resampling interval according to the calculated latest frequency value, and return to step 1).

The following is a preferred embodiment of the present invention, including a specific dielectric loss measurement unit based on the 61850-9-2 standard realized by the method of the present invention. Other characteristics, objects and advantages of the present invention can also be seen from the description of the embodiments and the drawings.

It can be seen from Figure 2 that the dielectric loss measurement system for capacitive equipment includes a transformer, a clock unit, a merging unit, a dielectric loss measurement unit, a comprehensive monitoring unit or a station-side monitoring unit. The clock unit receives time synchronization information through a wireless time reference or a wired time reference signal. The generated optical fiber B code time synchronization signal is transmitted to the merging unit, the dielectric loss measurement unit and other devices that need time synchronization through the optical fiber. The merging unit is installed in the outdoor cabinet on site, and converts the reference voltage signal into a digital signal and sends it to the dielectric loss measurement unit and the measurement protection device. The dielectric loss measurement unit receives the B code time synchronization signal, collects the leakage current signal and completes the synchronization with the reference voltage signal and the calculation of the dielectric loss. The dielectric loss unit sends the calculation results and data to the station control level monitoring system or the comprehensive monitoring unit.

Accompanying drawing 3 is the hardware architecture diagram of the core board of the dielectric loss measuring device. In the figure, the high-performance embedded processor PowerPC is responsible for 2 serial interfaces, one of which is the RS232 debugging port, and the other is the communication interface of the station control layer system using RS485 communication. Optical fiber Ethernet communication port 1 is used to communicate with the main intelligent electronic equipment of the transformer intelligent component or the analysis system of the station control layer. Optical fiber Ethernet communication port 2 is used to communicate with the IEC61850-9-2 standard of the merging unit. The PowerPC processor also completes the calculation of the dielectric loss algorithm and the communication program with the outside. The FPGA realizes the time synchronization system of the device and the synchronous sampling of the AD signal. External FLASH is used for program storage.

Accompanying drawing 4 is the flowchart of the application program in the embedded processor of the dielectric loss measurement unit. It is divided into two modules in the flow chart. One is the vector angle, amplitude and frequency calculation module of the reference voltage. Another module is the phase angle, amplitude and dielectric loss calculation module of the leakage current.

The communication subroutine between the dielectric loss measurement unit and the merging unit in the first module stores the received reference voltage of the IEC61850-9-2 standard into the buffer area ①, and analyzes the IEC61850-9-2 data in the buffer area to extract the integral time The original sampling data ②, re-sampling the original value ③ and performing spectrum analysis and filtering on the re-sampling data, and calculating the amplitude and phase angle of the fundamental wave vector at the integral time ④. Calculate the phase angle difference according to the phase angle information of the previous cycle, calculate the difference between the current calculation frequency and the actual frequency according to the phase angle difference, and correct the current calculation frequency according to the frequency difference ⑤. Adjust the resampling frequency of the voltage signal and the sampling period of the leakage current according to the current calculation frequency ⑥.

The second module starts the sampling of the leakage current at the full minute according to the sampling frequency calculated in step ⑥ of module 1 and the time synchronization information of the B code ⑦. Perform Fourier transform on the sampled data to calculate the amplitude and phase angle of the fundamental wave vector⑧. Wait for the calculation result of step ④, obtain the phase information of the reference voltage at the same time, and calculate the dielectric loss.

The present invention has been described according to the preferred embodiments, it should be understood that the above embodiments do not limit the present invention in any form, and all technical solutions obtained in the form of equivalent replacement or equivalent transformation all fall within the protection scope of the present invention Inside.

Claims (2)

1. the capacitive apparatus medium loss on-line monitoring method based on IEC61850-9-2 standard, is characterized in that, comprises the following steps:

1) on capacitive apparatus ground wire, be socketed high precision zero flux leakage current transformer, the voltage signal of mutual inductor output is accessed to local mounted dielectric loss measurement unit, and dielectric loss measurement unit is according to the AD sampling of minute pulse signal starting leakage current of B code output;

2) bus or circuit reference voltage are measured on the spot by merge cells, dielectric loss measurement unit accesses the reference voltage sampled value information of the IEC61850-9-2 standard of merge cells collection by optical fiber; Sampled value resampled and carries out Fourier transform, calculate amplitude, phase angle and frequency, adjusting resampling frequency, carrying out frequency-tracking;

3) according to step 1) the leakage current sampled signal that gathers carries out Fourier transform, calculates phase place and the amplitude of leakage current, integrating step 2) amplitude and the phase place of the reference voltage of the synchronization of calculating calculate dielectric loss value,

Described step 2) algorithm resampling in is: establishing fs is merge cells sample frequency, and Ts is the corresponding sampling period, and fs ' is dielectric loss measurement unit resampling frequency, and Ts ' is the corresponding resampling cycle,

${\mathrm{Ts}}^{\&prime;}=\frac{\mathrm{fs}}{{\mathrm{fs}}^{\&prime;}}\mathrm{Ts}$

T(n)＝T(n-1)+Ts'

Floating number T (n) is current interpolation point position, and floating number T (n-1) is upper interpolation point position, and establishing m is the maximum integer that is less than T (n), and establishes floating number u=T (n), and linear interpolation formula is as follows:

x'(n)＝x(m)*(m+1-u)+x(m+1)*(u-m)

In formula, the n point value of x'(n) attaching most importance in sample sequence, x (m) is the m point value in former sample sequence, x (m+1) is the m+1 point value in former sample sequence;

In described step 2) in, the step of frequency-tracking is as follows:

21) reference voltage signal Ux is carried out to the Fourier transform of complete cycle ripple;

22) Fourier transform result is carried out to filtering processing;

23) utilize the phase differential of the adjacent cycle of filtered first-harmonic vector calculation

24) utilize phase differential calculated rate changes

25) calculate original signal frequency f=fs-Δ f;

26) according to the up-to-date frequency values calculating, adjust resampling interval, return to step 21).

2. the capacitive apparatus medium loss on-line monitoring method based on IEC61850-9-2 standard according to claim 1, is characterized in that: the amplitude of the reference voltage of synchronization and phase place obtain be by internal clock time service unit, station by 2 road optical fiber B codes to time signal discontinuity surface when accessing respectively merge cells and dielectric loss measurement unit and realizing reference voltage and leakage current information same information acquisition.