CN111273140A - Transformer partial discharge monitoring and positioning system and method adopting multiple composite sensors - Google Patents

Abstract

The invention relates to a partial discharge monitoring and positioning system and a partial discharge monitoring and positioning method for a transformer by adopting a multi-composite sensor. Compared with the prior art, the invention solves the problem that whether the PD signal comes from the interior of the transformer is judged only by a single-property signal source at present.

Description

Transformer partial discharge monitoring and positioning system and method adopting multiple composite sensors

Technical Field

The invention relates to a system and a method for monitoring and positioning partial discharge of a transformer, in particular to a system and a method for monitoring and positioning partial discharge of a transformer by adopting a multi-composite sensor.

Background

When Partial Discharge (PD) occurs in the presence of defects in the transformer oil paper insulation, electric pulses, electromagnetic radiation, ultrasonic waves, light and some new products are generated, and physical and chemical reactions such as local overheating are caused. Therefore, in principle, these phenomena, if detectable, can be used as indications of PD defects. Methods for locating transformers under applied voltage have been developed including electrical, ultrasonic (AE), electromagnetic Ultra High Frequency (UHF), optical and thermal locating. This is also a positioning method if the PD is subjected to external stimuli, such as X-or gamma-ray irradiation, in addition to the applied voltage.

Ultrasonic (AE) positioning measures the time delay of signals measured by different sensors through a plurality of AE sensors, sets up an equation set according to the position of the AE sensor, equivalent sound velocity and time delay, and then solves a nonlinear equation set, so that the position of a PD source can be determined. According to the difference of the reference signals, the AE detection positioning can be divided into an electro-acoustic detection positioning method and an acoustic-acoustic detection positioning method, wherein the electro-acoustic detection positioning method uses the electric pulse of the PD as a trigger reference signal, and the acoustic-acoustic detection positioning method selects one AE sensor as a reference probe to measure the relative time difference of the same PD ultrasonic signal when the same PD ultrasonic signal is transmitted to other sensors. The ultrahigh frequency (UHF) method positioning is PD positioning using UHF electromagnetic wave signals, and is based on the fmax shortest optical path principle followed by electromagnetic wave diffraction, i.e., electromagnetic wave propagates along a ray, and it is considered that signals received by a UHF sensor are wave front reflection of a wavelet that the PD signals first arrive along the shortest optical path and with the minimum propagation time. The UHF positioning method and the AE positioning method are based on the principle of signal arrival time difference, namely, signal time delay is estimated, a time delay equation set is arranged in parallel, and then the space position of a PD source is solved.

At present, there are many researches and application reports on a UHF and AE combined transformer PD monitoring and positioning method, in which a sensor for respectively detecting UHF and AE signals generated by a PD is used, and a PD electromagnetic wave signal detected by the UHF sensor is used as a time reference, so as to obtain a time delay of the received AE signal, and further calculate a distance between a discharge point and the sensor, as shown in fig. 1. The system and the method are based on UHF and AE sensors which work independently, generally 1 UHF sensor and 3-4 external AE sensors are added, signal acquisition is carried out simultaneously, 3-4 time delays are calculated by taking an electromagnetic wave signal as a reference, an equation set is listed according to the position, the equivalent sound velocity and the time delay of the AE sensor, and a nonlinear equation set is solved, so that the position of a PD source is determined. The monitoring system and the method thereof use an external AE sensor: when the transformer works under the actual operation condition, the problems of external signal interference of a transformer substation, AE signal attenuation caused by a shell of transformer equipment, transmission multipath caused by AE signals in different medium acoustic impedances of transformer equipment materials (insulating oil, steel plates and the like) and the like exist, and the defects of poor system anti-interference performance, incapability of working under the weak discharge condition, large deviation of PD source positioning and the actual position and the like exist as shown in FIG. 2.

Disclosure of Invention

The invention aims to overcome the defects of the prior art and provide a system and a method for monitoring and positioning partial discharge of a transformer by using a multi-composite sensor.

The purpose of the invention can be realized by the following technical scheme:

a transformer partial discharge monitoring and positioning system adopting a multi-composite sensor comprises a composite sensor integrated by a piezoelectric AE sensor and a UHF electromagnetic wave sensor, a multi-channel pilot frequency data synchronous acquisition device, a transmission network, a data server, an application server and a user terminal, wherein the composite sensor is connected with the transmission network through the multi-channel pilot frequency data synchronous acquisition device, and the transmission network is respectively connected with the data server, the application server and the user terminal.

Preferably, the composite sensor is connected with the multi-channel pilot frequency data synchronous acquisition device through two coaxial cables, and outputs mutually independent AE and UHF signals.

Preferably, the composite sensor is arranged on the transformer shell in two modes of a preset built-in mode and an oil drain valve invasion built-in mode;

the composite sensor is directly contacted with the transformer insulating oil, wherein the AE sensor receives direct ultrasonic signals of PD ultrasonic waves.

Preferably, the multichannel pilot frequency data synchronous acquisition device is stored in an outdoor terminal box, 4 paths of electromagnetic waves UHF and 4 paths of ultrasonic waves AE of 4 composite sensors are collected to total 8 paths of signals, and the acquired data are transmitted to a data server through a transmission network.

Preferably, the transmission network is an optical fiber ethernet network, and the optical fiber ethernet network forms a local area network with the multi-channel pilot frequency data synchronous acquisition device, the data server, the application server and the user terminal.

Preferably, the data server is provided with a storage array for storing 8 paths of original data of signals, which are obtained by the multi-channel pilot frequency data synchronous acquisition device and are counted by 4 paths of electromagnetic waves UHF and 4 paths of ultrasonic waves AE of 4 composite sensors.

Preferably, the application server accesses the latest monitoring data in the database server in real time to perform positioning solution, and the solution result data is obtained and returned to the data server.

Preferably, the user terminal is a server, a PC or a mobile notebook computer capable of deploying Web page software, and the terminal checks real-time or historical monitoring data and a positioning solving result thereof in the data server and sets working parameters of the multi-channel pilot frequency data synchronous acquisition device based on the developed Web page software.

Preferably, the system further comprises other terminal cabinets connected with the transmission network and used for collecting load current and operation voltage signals of the transformer.

A method for the partial discharge monitoring and positioning system of the transformer adopting the multi-compound sensor comprises the following steps:

1) any one ultrahigh frequency UHF channel of the 8-channel multi-channel pilot frequency data synchronous acquisition device is set as a trigger channel, and 7 signals of other 3 ultrahigh frequency UHF channels and 4 ultrasonic AE channels are acquired simultaneously to obtain 4 groups of signals output by 4 composite sensors: sensor 1(UHF1, AE1, T1), sensor 2(UHF2, AE2, T2), sensor 3(UHF3, AE3, T3) and sensor 4(UHF4, AE4, T4), wherein the UHF, AE and T are all one-dimensional array sequences, and the data units in the sequences are mV, mV and μ s respectively;

2) criterion 1: presence of UHF1_peak<＝UHF_bj1Or UHF2_peak<＝UHF_bj2Or UHF3_peak＝<UHF_bj3Or UHF4_peak<＝UHF_bj4、AE1_peak<＝AE_bj1Or AE2_peak<＝AE_bj2Or AE3_peak＝<AE_bj3Or AE4_peak<＝AE_bj4If the current 4 groups of signal data are invalid data, 4 time delay equation sets cannot be established, and the requirements are not met;

if UHF1 is not present_peak<＝UHF_bj1Or UHF2_peak<＝UHF_bj2Or UHF3_peak＝<UHF_bj3Or UHF4_peak<＝UHF_bj4、AE1_peak<＝AE_bj1Or AE2_peak<＝AE_bj2Or AE3_peak＝<AE_bj3Or AE4_peak<＝AE_bj4If yes, the currently acquired 4 groups of signal data meet the requirements; of which UHF1_peak、UHF2_peak、UHF3_peakAnd, UHF4_peakPeak value of 4 groups of signal electromagnetic wave signals, UHF_bj1、UHF_bj2、UHF_bj3And UHF_bj4Background noise, AE1, for each of the 4 composite sensor output electromagnetic wave signal paths_peak、AE2_peak、AE3_peakAnd, AE4_peakPeak values, AE, of the ultrasonic signals of the 4 groups of signals, respectively_bj1、AE_bj2、AE_bj3And AE_bj4Background noise of the ultrasonic signal channels output by the 4 composite sensors, the UHF_peakAnd AE_bjUpdating the dynamic threshold UHF for 1 time every 2 hours for the average peak value of the 20mS time period of the collected signals under the condition of no trigger of each channel_bj1、UHF_bj2、UHF_bj3And UHF_bj4And AE_bj1、AE_bj2、AE_bj3And AE_bj4；

3) Computing UHF1_peakAnd AE1_peakTime delay Δ T1, UHF2_peakAnd AE2_peakTime delay Δ T2, UHF3_peakAnd AE3_peakTime delay Δ T3 and UHF4_peakAnd AE4_peakTime delay Δ T4; criterion 2: presence of Δ T1>ΔT_maxOr Δ T2>ΔT_maxOr Δ T3>ΔT_maxOr Δ T4>ΔT_maxThen the currently acquired 4 sets of signal data are invalid data, if there is no Δ T1>ΔT_maxOr Δ T2>ΔT_maxOr Δ T3>ΔT_maxOr Δ T4>ΔT_maxIf yes, the currently acquired 4 groups of signal data meet the requirements; wherein Δ T_maxThe maximum time value (mus) of electromagnetic wave propagation under the maximum diagonal distance of the tested transformer shell is obtained, and the time of ultrasonic wave propagation is ignored;

4)5 positioning solving: solving 1 utilization data (UHF1, AE1, T1, AE2, T2, AE3, T3 and AE4, T4), solving 2 utilization data (UHF2, AE1, T1, AE1, T1 and AE1, T1), solving 3 utilization data (UHF1, AE1, T1 and AE1, T1), solving 4 utilization data (UHF1, AE1, T1, AE1, T1 and AE1, T1), and solving 5 utilization data (UHF1, T1, UHF1 and UHF1, T1); solving 1 to solving 4 respectively obtain 4 time delay values by using ultrahigh frequency UHF1, UHF2, UHF3 and UHF4 electromagnetic waves as reference signals, and obtaining PD source space position results (X1, Y1 and Z1), (X2, Y2 and Z2), (X3, Y3 and Z3) and (X4, Y4 and Z4); the equivalent propagation velocity V in the solution 5 is chosen to be 2/3C₀，C₀Obtaining PD source space position results (X5, Y5, Z5) for the speed of light;

5) according to the 5-time positioning solving results, giving display and storing, and recommending a weighted average positioning result (X)_mean，Y_mean，Z_mean)，X_mean＝(X1+X2+X3+X4+X5)/5，Y_mean＝(Y1+Y2+Y3+Y4+Y5)/5，Z_mean＝(Z1+Z2+Z3+Z4+Z5)/5。

Compared with the prior art, the invention has the following advantages:

1. the invention adopts the composite sensor which can simultaneously output the UHF and ultrasonic AE signals, constructs the PD monitoring and positioning system of the transformer, can mutually support and prove effective data signals which are synchronously monitored and output by the UHF and the ultrasonic AE, and solves the problem that whether the PD signals come from the interior of the transformer is judged only by a single-property signal source at present.

2. The built-in composite sensor based on ultrasonic AE detection avoids the problems of external signal interference of a transformer substation, AE signal attenuation caused by a transformer equipment shell, transmission multipath caused by AE signals in different medium acoustic impedances of transformer equipment materials (insulating oil, steel plates and the like) and the like when the transformer works under the actual operation working condition, and solves the defects that the existing monitoring system is poor in anti-interference performance, cannot work under the weak discharge working condition, and is large in PD source positioning and actual position deviation.

3. The adopted comprehensive positioning method can eliminate invalid data, only carries out positioning solution on the monitoring data signals with accurate time delay delta t and effective amplitude values, can simultaneously give 5 positioning solution results, and recommends a weighted average positioning result for decision making of maintainers.

Drawings

FIG. 1 is a schematic diagram of a prior art ultrahigh frequency and ultrasonic wave combination-based transformer PD detection system and a positioning method;

FIG. 2 is a schematic diagram of external and internal ultrasonic AE sensors for monitoring PD of a transformer;

FIG. 3 is a block diagram of a partial discharge monitoring and positioning system for a transformer based on multiple composite sensors according to the present invention;

FIG. 4 is a schematic view of a composite sensor module of the present invention;

FIG. 5 illustrates three mounting configurations of the composite sensor of the present invention on a transformer housing;

FIG. 6 is a data flow diagram of the system of the present invention;

fig. 7 is a flowchart of a comprehensive positioning method designed by the present invention.

Detailed Description

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are some, not all, embodiments of the present invention. All other embodiments, which can be obtained by a person skilled in the art without any inventive step based on the embodiments of the present invention, shall fall within the scope of protection of the present invention.

As shown in figure 3, the transformer partial discharge monitoring and positioning system adopting the multi-composite sensor comprises a composite sensor formed by integrally integrating a piezoelectric AE sensor and a UHF electromagnetic wave sensor, a multi-channel pilot frequency data synchronous acquisition device 4, other terminal cabinets 5, a transmission network 6, a data server 7, an application server 8 and a user terminal 9, wherein the composite sensor is installed on a shell of a transformer 1 and is connected with the transmission network 6 through the multi-channel pilot frequency data synchronous acquisition device 4, the transmission network 6 is respectively connected with the other terminal cabinets 5, the data server 7, the application server 8 and the user terminal 9, and the composite sensor comprises a preset built-in composite sensor 2 and an oil drain valve invasion built-in composite sensor 3.

The composite sensor comprises: the piezoelectric AE sensor and the UHF electromagnetic wave sensor are integrally designed, mutually independent AE and UHF signals are output through two coaxial cables, a signal output schematic diagram of a composite sensor module and a PD (potential of Hydrogen) test in transformer oil is shown in figure 4, and the signal output has the remarkable characteristic that the AE lags the time delay of a UHF signal delta t; two built-in installation forms of the composite sensor on the transformer shell are shown in fig. 5 and are a preset built-in form and a drain valve invasion built-in form, namely the composite sensor is directly contacted with the transformer insulating oil, wherein an AE sensor receives direct ultrasonic signals of PD ultrasonic waves, A is the drain valve invasion built-in form, and B is the preset built-in form.

The outdoor terminal box: the multi-channel pilot frequency data synchronous acquisition device is stored, 4 paths of electromagnetic waves UHF and 4 paths of ultrasonic waves AE of 4 composite sensors are collected to count 8 paths of signals, and the acquired data are transmitted to the data server through the optical fiber Ethernet.

The optical fiber Ethernet network comprises: a data flow diagram in the system is shown in fig. 6, wherein the system is formed by combining a multichannel pilot frequency data synchronous acquisition device, other terminal cabinet signals (mainly load current and running voltage signals of a transformer), a data server, an application server and a user (Web) terminal in an outdoor terminal box into a local area network by using optical fibers.

The data server: the original data of the signals of the 4 paths of electromagnetic waves UHF and the 4 paths of ultrasonic waves AE of the 4 composite sensors obtained by the multi-channel pilot frequency data synchronous acquisition device are stored, and the application server calls positioning solving result data obtained by data processing software compiled according to a flow chart of the comprehensive positioning method shown in the figure 7.

The application server: and storing data processing algorithm software compiled according to the flow chart of the comprehensive positioning method designed as shown in fig. 7, accessing the latest monitoring data in the database server in real time to perform positioning solution, and returning solution result data to the data server.

The user (Web) terminal: based on the developed Web page software, checking real-time (historical) monitoring data and a positioning solving result thereof in a data server, and setting working parameters of a multi-channel pilot frequency data synchronous acquisition device; the terminal can be a server, a PC or a mobile notebook computer which can deploy Web page software.

The integrated positioning method flowchart shown in fig. 7 is explained as follows:

1) any one ultrahigh frequency (UHF) channel of the 8-channel pilot frequency data synchronous acquisition device in the outdoor terminal box is set as a trigger channel, and other 7 channels of signals (3 channels of UHF +4 channels of ultrasonic AE) are acquired simultaneously to obtain 4 groups of signals output by 4 composite sensors: sensor 1(UHF1, AE1, T1), sensor 2(UHF2, AE2, T2), sensor 3(UHF3, AE3, T3) and sensor 4(UHF4, AE4, T4), wherein the UHF, AE and T are all one-dimensional array sequences, and the data units in the sequences are mV, mV and μ s respectively;

2) criterion 1: presence of UHF1_peak<＝UHF_bj1Or UHF2_peak<＝UHF_bj2Or UHF3_peak＝<UHF_bj3Or UHF4_peak<＝UHF_bj4、AE1_peak<＝AE_bj1Or AE2_peak<＝AE_bj2Or AE3_peak＝<AE_bj3Or AE4_peak<＝AE_bj4If the current 4 groups of signal data are invalid data, 4 time delay equation sets cannot be established, and the requirements are not met; if UHF1 is not present_peak<＝UHF_bj1Or UHF2_peak<＝UHF_bj2Or UHF3_peak＝<UHF_bj3Or UHF4_peak<＝UHF_bj4、AE1_peak<＝AE_bj1Or AE2_peak<＝AE_bj2Or AE3_peak＝<AE_bj3Or AE4_peak<＝AE_bj4Then the number of 4 groups of signals currently acquiredAccording to the requirements; of which UHF1_peak、UHF2_peak、UHF3_peakAnd, UHF4_peakPeak value (mV), UHF of 4 groups of signal electromagnetic wave signals_bj1、UHF_bj2、UHF_bj3And UHF_bj4Background noise, AE1, for each of the 4 composite sensor output electromagnetic wave signal paths_peak、AE2_peak、AE3_peakAnd, AE4_peakPeak value (mV), AE of ultrasonic signals of 4 groups of signals_bj1、AE_bj2、AE_bj3And AE_bj4Background noise of the ultrasonic signal channels output by the 4 composite sensors, the UHF_peakAnd AE_bjUpdating the dynamic threshold UHF1 time every 2 hours for the average peak value (mV) of the 20mS time period of the collected signals under the non-trigger working condition of each channel_bj1、UHF_bj2、UHF_bj3And UHF_bj4And AE_bj1、AE_bj2、AE_bj3And AE_bj4；

3) Computing UHF1_peakAnd AE1_peakTime delay Δ T1, UHF2_peakAnd AE2_peakTime delay Δ T2, UHF3_peakAnd AE3_peakTime delay Δ T3 and UHF4_peakAnd AE4_peakTime delay Δ T4; criterion 2: presence of Δ T1>ΔT_maxOr Δ T2>ΔT_maxOr Δ T3>ΔT_maxOr Δ T4>ΔT_maxThen the currently acquired 4 sets of signal data are invalid data, if there is no Δ T1>ΔT_maxOr Δ T2>ΔT_maxOr Δ T3>ΔT_maxOr Δ T4>ΔT_maxIf yes, the currently acquired 4 groups of signal data meet the requirements; wherein Δ T_maxThe maximum time value (μ s) of electromagnetic wave propagation at the maximum diagonal distance of the tested transformer shell is ignored here, note that: delta T>ΔT_maxIndicating that the ultrahigh frequency UHF signal or the ultrasonic AE signal is generated by external interference of the shell of the current transformer instead of the internal PD, and is invalid data;

4)5 positioning solving: solution 1 utilization data (UHF1, AE1, T1, AE2, T2, AE3, T3, AE4 and T4), solution 2 utilization data (UHF2, AE1, T1, AE2, T2, AE3, T3 and AE4, T4)4) Solving 3 utilization data (UHF3, AE1, T1, AE2, T2, AE3, T3, AE4 and T4), solving 4 utilization data (UHF4, AE1, T1, AE2, T2, AE3, T3, AE4 and T4) and solving 5 utilization data (UHF1, T1, UHF2, T2, UHF3, T3, UHF4 and T4); solving 1 to solving 4 respectively obtain 4 time delay values by using ultrahigh frequency UHF1, UHF2, UHF3 and UHF4 electromagnetic waves as reference signals, and obtaining PD source space position results (X1, Y1 and Z1), (X2, Y2 and Z2), (X3, Y3 and Z3) and (X4, Y4 and Z4); the equivalent propagation velocity V in the solution 5 is chosen to be 2/3C₀，C₀The PD source spatial position results (X5, Y5, Z5) are obtained for the speed of light.

5) According to the 5-time positioning solving results, giving display and storing, and recommending a weighted average positioning result (X)_mean，Y_mean，Z_mean)，X_mean＝(X1+X2+X3+X4+X5)/5，Y_mean＝(Y1+Y2+Y3+Y4+Y5)/5，Z_mean＝(Z1+Z2+Z3+Z4+Z5)/5。

6) The positioning solution calculation method is as follows:

the time delay solution method is that n (4 in the invention) sensors of the same type are arranged on the outer wall of the transformer oil tank, 1 of the sensors is used as a trigger reference, and n signals are recorded and compared at the same time; taking the time delay of the measured signals of the reference sensor and other sensors as t_iPropagation time from the source point of the PD to each sensor; multiplying the equivalent propagation velocity V (electromagnetic or ultrasonic) by the time delay t_iTo obtain the space distance Vt from the discharge point to each sensor_i. This yields the spherical equation:

in the formula: x is the number of_PD,y_PD,z_PD-three-dimensional rectangular coordinates of the PD source point; xi, y_i,z_i-the arrangement position coordinates of the ith sensor; t is t_i-the time delay value of the waveform signal received by the ith sensor relative to the reference sensor; i is 1,2,3, …, n-the number of sensors.

The solution of the non-linear equation (1) is the position coordinates of the PD source point and the equivalent propagation velocity V. Therefore, at least 4 sensors are needed to determine the position coordinates of the PD source point and its equivalent propagation velocity.

Let the real distance from the PD source point to the ith sensor be d_i＝Vt_iThe delay value is t_iAnd if the propagation velocity is equal to V, the measured distance is as follows:

d_i＝[(x_PD-x_i)²+(y_PD-y_i)²+(z_PD-z_i)²]^0.5(2)

selecting a distance error psi_iTesting distance D for ith sensor_iAnd the true distance d_iThe difference of (a):

ψ_i＝Vt_i-[(x_PD-x_i)²+(y_PD-y_i)²+(z_PD-z_i)²]^0.5(3)

the objective function psi (x)_PD,y_PD,z_PDAnd V) is the sum of the squares of the errors:

since the least square solution of equation (4) is x with ψ as the minimum value_PD,y_PD,z_PDV value, so if ψ takes the minimum value, x is respectively given to ψ_PD,y_PD,z_PDV partial derivatives are calculated and made equal to zero, respectively, to obtain a set of normal equations:

and (3) converting the formula (1) into the formula (5) to obtain a nonlinear equation system, and solving by using a Newton iteration method. When the PD source sphere has 4 unknown parameters to be solved, let:

f_i(x₁,x₂,x₃,x₄)＝(x₁-x_1i)²+(x₂-x_2i)²+(x₃-x_3i)²-(x₄t_4i)²＝0 (6)

let f_i(x₁,x₂,x₃,x₄) Is n 4-degree binary continuous differentiable functions defined on a four-dimensional space domain, and the value domain of the functions is also contained in the four-dimensional space domain. At the solution of f_i(x₁,x₂,x₃,x₄) 0 (ξ)₁,ξ₂,ξ₃,ξ₄) When resolving, will f_iAt its solution (ξ)₁,ξ₂,ξ₃,ξ₄) And when a nearby point is expanded according to the Taylor series and the residual term is ignored, a linear equation set can be obtained:

the coefficients of the unknown parameters in the formula are Jacobian matrices:

J＝J(x₁,x₂,x₃,x₄) (8)

let f be (f)₁,f₂,…,f_n)^T、x＝(x₁,x₂,x₃,x₄)^T、

Equation (8) can be expressed as:

f(x⁰)+J(x⁰)(x-x⁰)＝0 (9)

the solution is as follows:

x¹＝x⁰-J^-1(x⁰)f(x⁰) (10)

the newton iteration formula is thus obtained:

x^k+1＝x^k-J^-1(x^k)f(x^k),k＝0,1,2,…,n (11)

properly selecting an initial value x⁰Setting control error according to a certain calculation, and making the modulus of error between two adjacent iterations be less than set value

When is at time

The iteration is ended and the obtained result is the positioning solution, i.e. the PD source point coordinates and the equivalent propagation velocity:

while the invention has been described with reference to specific embodiments, the invention is not limited thereto, and various equivalent modifications and substitutions can be easily made by those skilled in the art within the technical scope of the invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the claims.

Claims (10)

1. A transformer partial discharge monitoring and positioning system adopting a multi-composite sensor is characterized by comprising a composite sensor, a multi-channel pilot frequency data synchronous acquisition device, a transmission network, a data server, an application server and a user terminal, wherein the composite sensor is formed by integrally integrating a piezoelectric AE sensor and a UHF electromagnetic wave sensor, the composite sensor is connected with the transmission network through the multi-channel pilot frequency data synchronous acquisition device, and the transmission network is respectively connected with the data server, the application server and the user terminal.

2. The partial discharge monitoring and positioning system for transformer using multiple composite sensors as claimed in claim 1, wherein the composite sensors are connected to the multi-channel pilot frequency data synchronous acquisition device through two coaxial cables, and output mutually independent AE and UHF signals.

3. The partial discharge monitoring and positioning system for the transformer adopting the multiple composite sensors as claimed in claim 1, wherein the composite sensors are installed on the transformer shell in two modes of a preset built-in mode and an oil drain valve intrusion built-in mode;

the composite sensor is directly contacted with the transformer insulating oil, wherein the AE sensor receives direct ultrasonic signals of PD ultrasonic waves.

4. The partial discharge monitoring and positioning system of transformer using multiple composite sensors as claimed in claim 1, wherein said multi-channel pilot frequency data synchronous acquisition device is stored in an outdoor terminal box, 4 paths of electromagnetic wave UHF and 4 paths of ultrasonic wave AE of 4 composite sensors are collected to total 8 paths of signals, and the acquired data is transmitted to a data server through a transmission network.

5. The partial discharge monitoring and positioning system of transformer using multiple composite sensors as claimed in claim 1, wherein the transmission network is an optical fiber ethernet network, and the optical fiber ethernet network forms a local area network with the multi-channel pilot frequency data synchronous acquisition device, the data server, the application server and the user terminal.

6. The partial discharge monitoring and positioning system for the transformer using the multiple composite sensors as claimed in claim 1, wherein the data server is provided with a storage array for storing 8 paths of original data of signals, which are obtained by the multi-channel pilot frequency data synchronous acquisition device, of 4 paths of electromagnetic waves UHF and 4 paths of ultrasonic waves AE of 4 composite sensors.

7. The transformer partial discharge monitoring and positioning system adopting multiple composite sensors as claimed in claim 1, wherein the application server accesses the latest monitoring data in the database server in real time to perform positioning solution, and the solution result data is returned to the data server.

8. The system according to claim 1, wherein the user terminal is a server, a PC or a mobile notebook computer capable of deploying Web page software, and the terminal checks real-time or historical monitoring data and positioning solution results thereof in the data server and sets working parameters of the multi-channel pilot frequency data synchronous acquisition device based on the developed Web page software.

9. The transformer partial discharge monitoring and positioning system adopting the multi-compound sensor as claimed in claim 1, wherein the system further comprises other terminal cabinets connected with a transmission network for collecting load current and operation voltage signals of the transformer.

10. A method for the transformer partial discharge monitoring and positioning system using the multi-composite sensor as claimed in claim 1, comprising the steps of:

1) any one ultrahigh frequency UHF channel of the 8-channel multi-channel pilot frequency data synchronous acquisition device is set as a trigger channel, and 7 signals of other 3 ultrahigh frequency UHF channels and 4 ultrasonic AE channels are acquired simultaneously to obtain 4 groups of signals output by 4 composite sensors: sensor 1(UHF1, AE1, T1), sensor 2(UHF2, AE2, T2), sensor 3(UHF3, AE3, T3) and sensor 4(UHF4, AE4, T4), wherein the UHF, AE and T are all one-dimensional array sequences, and the data units in the sequences are mV, mV and μ s respectively;

2) criterion 1: presence of UHF1_peak<＝UHF_bj1Or UHF2_peak<＝UHF_bj2Or UHF3_peak＝<UHF_bj3Or UHF4_peak<＝UHF_bj4、AE1_peak<＝AE_bj1Or AE2_peak<＝AE_bj2Or AE3_peak＝<AE_bj3Or AE4_peak<＝AE_bj4If the current 4 groups of signal data are invalid data, 4 time delay equation sets cannot be established, and the requirements are not met;

if UHF1 is not present_peak<＝UHF_bj1Or UHF2_peak<＝UHF_bj2Or UHF3_peak＝<UHF_bj3Or UHF4_peak<＝UHF_bj4、AE1_peak<＝AE_bj1Or AE2_peak<＝AE_bj2Or AE3_peak＝<AE_bj3Or AE4_peak<＝AE_bj4If yes, the currently acquired 4 groups of signal data meet the requirements; of which UHF1_peak、UHF2_peak、UHF3_peakAnd, UHF4_peakPeak value of 4 groups of signal electromagnetic wave signals, UHF_bj1、UHF_bj2、UHF_bj3And UHF_bj4Background noise, AE1, for each of the 4 composite sensor output electromagnetic wave signal paths_peak、AE2_peak、AE3_peakAnd, AE4_peakPeak values, AE, of the ultrasonic signals of the 4 groups of signals, respectively_bj1、AE_bj2、AE_bj3And AE_bj4Background noise of the ultrasonic signal channels output by the 4 composite sensors, the UHF_peakAnd AE_bjUpdating the dynamic threshold UHF for 1 time every 2 hours for the average peak value of the 20mS time period of the collected signals under the condition of no trigger of each channel_bj1、UHF_bj2、UHF_bj3And UHF_bj4And AE_bj1、AE_bj2、AE_bj3And AE_bj4；

3) Computing UHF1_peakAnd AE1_peakTime delay Δ T1, UHF2_peakAnd AE2_peakTime delay Δ T2, UHF3_peakAnd AE3_peakTime delay Δ T3 and UHF4_peakAnd AE4_peakTime delay Δ T4; criterion 2: presence of Δ T1>ΔT_maxOr Δ T2>ΔT_maxOr Δ T3>ΔT_maxOr Δ T4>ΔT_maxThen the currently acquired 4 sets of signal data are invalid data, if there is no Δ T1>ΔT_maxOr Δ T2>ΔT_maxOr Δ T3>ΔT_maxOr Δ T4>ΔT_maxIf yes, the currently acquired 4 groups of signal data meet the requirements; wherein Δ T_maxThe maximum time value (mus) of electromagnetic wave propagation under the maximum diagonal distance of the tested transformer shell is obtained, and the time of ultrasonic wave propagation is ignored;

4)5 positioning solving: solution 1 utilization data (UHF1, AE1, T1, AE2, T2)AE3, T3 and AE4, T4), solve for 2 utilization data (UHF2, AE1, T1, AE2, T2, AE3, T3 and AE4, T4), solve for 3 utilization data (UHF3, AE1, T1, AE2, T2, AE3, T3 and AE4, T4), solve for 4 utilization data (UHF4, AE1, T1, AE2, T2, AE3, T3 and AE4, T4) and solve for 5 utilization data (UHF1, T1, UHF2, T2, UHF3, T3 and UHF4, T4); solving 1 to solving 4 respectively obtain 4 time delay values by using ultrahigh frequency UHF1, UHF2, UHF3 and UHF4 electromagnetic waves as reference signals, and obtaining PD source space position results (X1, Y1 and Z1), (X2, Y2 and Z2), (X3, Y3 and Z3) and (X4, Y4 and Z4); the equivalent propagation velocity V in the solution 5 is chosen to be 2/3C₀，C₀Obtaining PD source space position results (X5, Y5, Z5) for the speed of light;

5) according to the 5-time positioning solving results, giving display and storing, and recommending a weighted average positioning result (X)_mean，Y_mean，Z_mean)，X_mean＝(X1+X2+X3+X4+X5)/5，Y_mean＝(Y1+Y2+Y3+Y4+Y5)/5，Z_mean＝(Z1+Z2+Z3+Z4+Z5)/5。

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