Detection circuit and calculation method for insulation resistance in strong induced electricity environment

Abstract

The invention discloses a detection circuit and a calculation method for insulation resistance in a strong induced electricity environment, and relates to the technical field of insulation resistance measurement. The detection circuit for the insulation resistance in the strong induced electricity environment comprises a current sampling module, an induced electricity processing module and a data calculation module, the induced electricity processing module is used for removing interference of induced electricity, and the current sampling module is used for sampling a dynamic current value of the insulation resistance of a direct current system. According to the detection circuit and the calculation method for the insulation resistance in the strong induced electricity environment, the detection speed and accuracy of the insulation resistance of a direct-current system for a transformer substation in the induced electricity environment are superior to those of a traditional test technology. According to the method, the insulation resistance of the direct current system for the transformer substation in the induced electricity environment can be quickly calculated on the premise of accuracy, and the method has the characteristics of short response time, high robustness and relatively strong anti-interference capability to external induced electricity.

Description

Technical Field

[0001] The present invention relates to the technical field of insulation resistance measurement, and particularly to a detection circuit and calculation method for insulation resistance in a strong induced electric environment. Background Art

[0002] With the development of power utilization technology, in various large-scale electrical equipment today, in order to improve power utilization efficiency, the system voltage is usually much higher than the human body safety voltage threshold. Therefore, the requirements for accurately testing insulation resistance are becoming increasingly strict. In substations, large equipment is often in harsh environments including vibration, shock, high temperature, etc. The aging problem of insulating materials or insulating media is more prominent, resulting in a decrease in insulation resistance value and an increase in leakage current, seriously endangering insulation safety and even causing accidents such as electronic device failure, fire, and explosion, threatening personal and property safety. In addition, in a high-voltage and strong electromagnetic environment, due to the coupling effect of induced electric interference and system distributed capacitance in the DC system used in substations, the insulation resistance test signal is distorted, affecting the accuracy of the test result.

[0003] At present, the insulation resistance test methods in an induced electric field are as follows:

[0004] DC high-voltage generator pressure test method (direct high method). A DC test voltage as high as 100 kV is applied across the measured insulating medium by a DC high-voltage generator. Since the amplitude of the equipment interference voltage is relatively small and can be ignored. After the DC high-voltage generator boosts the voltage, a DC microammeter is used to measure the leakage current in the circuit, and the insulation resistance value is calculated based on Ohm's law. The measurement range of the insulation resistance by this method is limited by the output characteristics of the DC high-voltage generator, and the humidity of the test environment needs to meet the preset conditions to ensure the measurement accuracy; at the same time, high-voltage isolation and protection devices need to be configured during the test process to ensure the safety of the operator.

[0005] Parallel capacitor step-down test method. By connecting a large capacitor in parallel across the measured insulating material or insulating medium, the interference voltage is guided to the ground loop, thereby suppressing the influence of the interference voltage on the test result. At this time, the measured resistance value is the equivalent parallel resistance of the parallel capacitor and the measured insulating material or medium. However, the leakage current of the parallel capacitor will introduce measurement errors, and due to the large capacitance value, the test system needs to go through a long transient process to reach a stable state, resulting in an extended test time.

[0006] In the prior art, for example, CN118311457A does not apply suppression measures against high-frequency electromagnetic interference. It only relies on the switching branch and voltage division principle to measure the battery insulation resistance and does not have an electromagnetic interference resistance design. After introducing additional signal noise in a strong induced electric environment, it will cause voltage fluctuations, which in turn will cause the sampling value to be distorted and affect the accuracy of the insulation resistance calculation. However, this patent is specifically designed with a processing module for filtering out the induced voltage in the induced electric environment, which can directly and significantly reduce the influence of the induced electric through the parallel capacitor and the algorithm processing of the dynamic current. This dual design of hardware filtering and algorithm optimization proposed in this patent can ensure high-precision measurement of the insulation resistance in a strong induced electric environment. Summary of the Invention

[0007] (1) Technical problems to be solved

[0008] In view of the deficiencies of the prior art, the present invention provides a detection circuit and calculation method for insulation resistance in a strong induced electric environment, which solves the technical problems mentioned in the background art.

[0009] (2) Technical solutions

[0010] To achieve the above objectives, the present invention is realized through the following technical solutions: A detection circuit for insulation resistance in a strong induced electric environment includes a current sampling module, an induced electric processing module, and a data calculation module. The induced electric processing module is used to remove the interference of the induced electric. The current sampling module is used to sample the dynamic current value of the insulation resistance of the DC system. The data calculation module is used to calculate the dynamic sampling current value, obtain the steady-state current value, and calculate the accurate resistance value of the insulation resistance of the DC system through Ohm's law. The current sampling module includes the positive terminal of the current sampling module, the grounding terminal of the current sampling module, and the negative terminal of the current sampling module. A resistor R2 is connected in parallel between the positive terminal of the current sampling module and the grounding terminal of the current sampling module. A resistor R5 and a resistor R4 are connected in parallel between the grounding terminal of the current sampling module and the negative terminal of the current sampling module. A switch T1 is connected in series on the resistor R2. A switch T2 is connected in series on the resistor R5. A resistor R6 is connected in parallel between the positive terminal of the current sampling module and the negative terminal of the current sampling module. R2 = R5. R4 and R6 are used together as voltage dividing resistors, and they work together to achieve accurate voltage division and sampling of the current signal.

[0011] Preferably, the induced electric processing module includes a first loop composed of two capacitors C1 and C2 connected in series, and the middle terminal of the two capacitors C1 and C2 connected in series is grounded.

[0012] A calculation method for a detection circuit of insulation resistance in a strong induced electric environment includes the following steps:

[0013] Turn on switch T1 and close switch T2;

[0014] Ud1 is represented as the lower bridge arm voltage, Uu1 is represented as the upper bridge arm voltage, U is represented as the system voltage, U+ is the positive terminal voltage of the system, and U- is the negative terminal voltage of the system. According to Kirchhoff's law, we can obtain:

[0015] I 1 +I 3 =I 2 +I 5

[0016] R 1 I 1 =R 2 I 2

[0017] R 1 I 1 =U u1

[0018] R 3 I 3 =R 4 I 4

[0019] R 3 I 3 =U d1

[0020] U=U d1 +U u1

[0021] From the above equations, the voltage ratio of the upper and lower bridge arms can be deduced as

[0022]

[0023] When the switch T1 is closed and the switch T2 is opened, the voltage ratio at this time is

[0024]

[0025] Take ka and kb as

[0026]

[0027] Thus, the insulation resistance is calculated

[0028]

[0029]

[0030] Preferably, the calculation method uses the steady-state current L-M algorithm to estimate the insulation resistance. The specific operation method for measuring the steady-state currents I1 and I3 is as follows:

[0031] The induced current processing module is connected to the DC system used in the substation. The current sampling module samples to obtain the test dynamic sampling current value of the insulation resistance of the DC system used in the substation, calculates the stable current value from the test dynamic sampling current value of the insulation resistance of the measured DC system used in the substation, and calculates the insulation resistance of the DC system used in the substation through Ohm's law. For the dynamic sampling current, there are several generally accepted analytical functions that can be used to approximate the decay curve of the current, which are composed of an exponential or the sum of several exponentials with different time constants. Since after connecting the measurement voltage source for a period of time, the ammeter cannot measure a large current exceeding the measurement limit;

[0032] And there is a current-limiting resistor R6, and the measurement voltage will not be established immediately;

[0033] Therefore, the current curve should include an exponential component. Thus, the analytical expression of the steady-state current curve is designed as follows

[0034]

[0035] Where is the exponential component, t′ 0 is the supplementary variable, I(t′) is the insulation resistance dynamic sampling current values I1′ and I3′, t′ is the time, n is the exponent, n ∈ [0.1...1.7], S 1 、S 2 are specific coefficients depending on the dielectric type of the insulation resistance of the DC system used in the substation and the voltage applied thereto, S 0 is the insulation resistance steady-state current values I1 and I3;

[0036] Based on the above steady-state current calculation formula, the numerical calculation of the current of this analytical formula is realized using the L-M algorithm. Set the dynamic sampling current data as

[0037] [(t 1 , i 1 ), (t 2 , i 2 ),..., (t i , i i ),..., (t n , i n )] Here t i represents the sampling time series, i i represents the dynamic sampling current value I(t′), and set the parameter x as

[0038] x = [h 1 , h 2 , h 3 T

[0039] ​The calculation of the parameter vector x is positioned as a non - linear least - squares problem, which is about how to handle minimizing the difference between the final value of the model and the sampled data;

[0040]

[0041] The function I(t i , x) represents the output of the feedback current model, and the parameter vector x needs to be iteratively updated to minimize the difference between the model output and the sampled data;

[0042] f i (x) represents the residual, f(x) represents the residual vector, and F(x) is the sum of the squares of the residuals;

[0043] The goal of the L - M algorithm is to minimize the sum of the squares of the residuals F(x) and solve for the parameter vector, using the following iterative method:

[0044] x k+1 = x k + Δx k

[0045] The specific expression is

[0046] Δx k = -[H(x)+μI] -1 J(x) T f(x)

[0047]

[0048] H(x) = J(x) T J(x)

[0049] Based on the combination of the L - M algorithm and the steady - state current calculation formula, after the test voltage is connected, the dynamic sampled current will be calculated, and the steady - state current calculation formula for S0 will be quickly solved. S0 is the steady - state current value I1 and I3 of the insulation resistance of the DC system for substation use when t approaches infinity. From this steady - state current value S0, the insulation resistance value of the DC system for substation use is calculated through Ohm's law.

[0050] (III) Beneficial effects

[0051] The present invention provides a detection circuit and calculation method for insulation resistance in a strong induced - electricity environment. It has the following beneficial effects:

[0052] The detection circuit and calculation method of insulation resistance in a strong induced electric environment are superior to traditional testing techniques in terms of the detection speed and accuracy of the insulation resistance of the DC system used in substations under an induced electric environment. It can quickly calculate the insulation resistance of the DC system used in substations under an induced electric environment on the premise of accuracy. Its characteristics are fast response time, high robustness, and strong anti-interference ability to external induced electricity.

[0053] In the present invention, the switching of T1T2 is used for initial dynamic current sampling. And multiple groups of dynamic current data are obtained by changing the voltage-dividing resistor configuration. Further eliminate the induced electric interference and deduce the accurate value of the insulation resistance.

[0054] In the present invention, finally, the L-M algorithm iteratively optimizes the parameters S according to the analytical formula of the steady-state current curve and the obtained dynamic current data 0 、S 1 、τ and quickly estimates S 0 (i.e., I 1 and I 3 ), improving the anti-interference ability and accuracy of insulation resistance calculation. BRIEF DESCRIPTION OF THE DRAWINGS

[0055] Figure 1 is the flowchart of measuring resistance by the steady-state current L-M algorithm.

[0056] Figure 2 is the schematic diagram of the induced electric processing module circuit.

[0057] Figure 3 is the schematic diagram of the current sampling module circuit.

[0058] Figure 4 is the schematic diagram of the insulation resistance test process. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0059] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0060] Induced electric processing module: It is used to remove the induced electric interference in the process of testing the insulation resistance of the DC system used in the substation to be measured;

[0061] Current sampling module: It is used to sample the dynamic current value of the insulation resistance of the DC system used in the substation;

[0062] Data calculation module: It is used to calculate the dynamic sampling current value, obtain the steady-state current value, and calculate the accurate resistance value of the insulation resistance of the DC system for substations through Ohm's law;

[0063] The induced electricity processing module includes a first loop composed of two large capacitors C1 and C2 connected in series. The middle end is grounded to remove induced electricity interference. In the first loop, a first branch is added; both ends of the first branch are respectively connected to the positive and negative poles of the DC system for substations, thus forming a direct electrical connection with the DC system for substations; further, in the connection of this first branch, the insulation resistance to ground of the positive terminal of the DC system for substations is defined as R1, and the resistance to ground of the negative terminal of the insulation resistance of the DC system for substations is defined as R3;

[0064] The current sampling module has the following structural connection relationships: The upper positive pole and the lower negative pole of the current sampling module are respectively connected to the upper positive pole and the lower negative pole of the induced electricity processing module, and the middle end of the current sampling module is grounded; further, two branches are arranged inside the current sampling module. The first branch is composed of resistor R2 and resistor R5. The two are used as bridge arm resistors and are connected in series between the positive and negative poles of the current sampling module, and the resistance value of resistor R2 is equal to the resistance value of resistor R5, that is, R2 = R5 = R. This setting ensures the balance of the bridge arm; the second branch includes resistor R6, and together with resistor R4 on the other branch path except resistor R2 in the first branch, they are used as voltage dividing resistors, and the two work together to achieve precise voltage division and sampling of the current signal.

[0065] The specific implementation of the current sampling module processing method is achieved by controlling different combination methods of two switches T1 and T2, including the following two operation modes: The first operation mode: In this mode, switch T2 is closed, that is, in the conductive state, and at the same time switch T1 is opened, that is, in the non-conductive state. This combination method enables the current sampling module to perform current sampling and processing according to the preset first path; The second operation mode: In this mode, switch T1 is opened, that is, in the non-conductive state, and at the same time switch T2 is closed, that is, in the conductive state. This combination method enables the current sampling module to perform current sampling and processing according to a second path different from the first mode.

[0066] After the insulation resistance detection method forms a circuit loop, there are the following equations: Ud1 represents the lower bridge arm voltage, Uu1 represents the upper bridge arm voltage, U represents the system voltage, U+ is the system positive terminal voltage, U- is the system negative terminal voltage, ka and kb: the upper and lower bridge arm voltage ratios in two operation modes. According to Kirchhoff's law, we can get:

[0067] I 1 +I 2 =I 2+I 5

[0068] R 1 I 1 =R 2 I 2

[0069] R 1 I 1 =U u1

[0070] R 3 I 3 =R 4 I 4

[0071] R 3 I 3 =U d1

[0072] U=U d1 +U u1

[0073] From the above equations, the voltage ratio of the upper and lower bridge arms can be deduced as

[0074]

[0075] Similarly, in Embodiment 2, switch T1 is closed and switch T2 is opened. At this time, the voltage ratio is

[0076]

[0077] Let ka and kb be

[0078]

[0079] Thus, the insulation resistance can be calculated as

[0080]

[0081] The steady-state current L-M algorithm adopted by the present invention is used to estimate the insulation resistance. The specific operation methods for measuring the steady-state currents I1 and I3 are as follows:

[0082] The induction electricity processing module is connected to the DC system used in the substation. The current sampling module samples to obtain the test dynamic sampling current value of the insulation resistance of the DC system used in the substation, calculates the stable current value from the test dynamic sampling current value of the insulation resistance of the measured DC system used in the substation, and calculates the insulation resistance of the DC system used in the substation through Ohm's law. For the dynamic sampling current, there are several generally accepted analytical functions that can be used to approximate the decay curve of the current, which are composed of an exponential or the sum of several exponentials with different time constants. Since the ammeter cannot measure a large current exceeding the measurement limit after connecting the measurement voltage source for a period of time. And there is a current-limiting resistor R6, and the measurement voltage is not established immediately. Therefore, the current curve should include an exponential component. Thus, the analytical expression of the steady-state current curve is designed as follows

[0083]

[0084] Where is the exponential component, τ is the time constant, describing the current dynamic characteristics, t′ 0 is the supplementary variable, I(t′) is the insulation resistance dynamic sampling current values I1′ and I3′, t′ is the time, n is the exponent, n ∈ [0.1...1.7], S 1 、S 2 are specific coefficients depending on the dielectric type of the insulation resistance of the DC system used in the substation and the voltage applied thereto, S 0 is the insulation resistance steady-state current values I1 and I3.

[0085] Based on the above steady-state current calculation formula, the numerical calculation of the current of this analytical formula is further realized using the L-M algorithm, which is a method widely used to solve the nonlinear least squares problem. Set the dynamic sampling current data as

[0086] [(t 1 , i 1 ), (t 2 , i 2 ),..., (t i , i i ),..., (t n , i n )]

[0087] Here t i represents the sampling time series, i i represents the dynamic sampling current value I(t′), and set the parameter x as

[0088] x = [h 1 , h 2 , h 3 T

[0089] x = [h​1 ,h 2 ,h 3 T is the parameter vector of the L-M algorithm, corresponding to S 0 、S 1 、τ.

[0090] The calculation of the parameter vector x is positioned as a non-linear least squares problem, which is how to handle minimizing the difference between the final value of the model and the sampled data.

[0091]

[0092] The function I(t i , x) represents the output of the feedback current model, and the parameter vector x needs to be iteratively updated to minimize the difference between the model output and the sampled data. f i (x) represents the residual, f(x) represents the residual vector, and F(x) is the sum of the squares of the residuals. The goal of the L-M algorithm is to minimize the sum of the squares of the residuals F(x) and solve for the parameter vector, using the following iterative method:

[0093] x k+1 = x k + Δx k

[0094] The specific expression is

[0095] Δx k = -[H(x) + μI] -1 J(x) T f(x)

[0096] H(x) = J(x) T J(x)

[0097] μ is the damping factor used to adjust the algorithm convergence, and I is the identity matrix used to adjust the algorithm convergence

[0098] Based on the combination of the L-M algorithm and the steady-state current calculation formula, after turning on the test voltage, the dynamic sampled current will be calculated, and the steady-state current calculation formula for S0 will be quickly solved. S0 is the steady-state current value I1 and I3 of the insulation resistance of the DC system for substation use when t approaches infinity. From this steady-state current value S0, the insulation resistance value of the DC system for substation use is calculated through Ohm's law.

[0099] ​It should be noted that in the description of the invention, the orientation or positional relationship indicated by terms such as "upper", "lower", "left", "right", "front", "rear", etc. is the description of the structure of the present invention based on the figures shown, and is only for the convenience of describing the present invention simply, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation. Therefore, it should not be construed as a limitation to the present invention.

[0100] For the "first" and "second" in this technical solution, they are only used to distinguish the names of the same or similar structures, or corresponding structures with similar functions, rather than arranging the importance of these structures, nor having an order, or comparing sizes, or other meanings.

[0101] In addition, unless otherwise clearly specified and limited, the terms "installation" and "connection" should be understood in a broad sense. For example, the connection can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium, and it can be the communication inside two structures. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to the general idea of the present invention and in connection with the specific circumstances of this solution.

Claims

1. A detection circuit for insulation resistance in a strong inductive electrical environment, comprising a current sampling module, an inductive electrical processing module, and a data calculation module, wherein the inductive electrical processing module is used to remove the interference of the inductive electrical, the current sampling module is used to sample the dynamic current value of the insulation resistance of the DC system, and the data calculation module is used to calculate the dynamic sampling current value and obtain the steady-state current value and calculate the accurate resistance value of the insulation resistance of the DC system by Ohm's law, characterized in that: The current sampling module includes a positive terminal connected to the current sampling module, a ground terminal connected to the current sampling module, and a negative terminal connected to the current sampling module. A resistor R2 is connected in parallel between the positive terminal of the current sampling module and the ground terminal of the current sampling module. A resistor R5 and a resistor R4 are connected in parallel between the ground terminal of the current sampling module and the negative terminal of the current sampling module. A switch T1 is connected in series with the resistor R2, and a switch T2 is connected in series with the resistor R5. A resistor R6 is connected in parallel between the positive terminal of the current sampling module and the negative terminal of the current sampling module. R2=R5. R4 and R6 are used together as voltage dividing resistors, and the two work together to achieve accurate voltage division and sampling of current signals.

2. The detection circuit of insulation resistance in a strong inductive electrical environment according to claim 1, characterized in that: The inductive power processing module includes a first loop consisting of two capacitors C1 and C2 connected in series, and the middle ends of the two capacitors C1 and C2 are grounded.

3. A method for calculating the insulation resistance detection circuit in a strong inductive electrical environment as claimed in claim 2, characterized in that: The steps include: Open switch T1 and close switch T2; Ud1 represents the voltage of the lower bridge arm, Uu1 represents the voltage of the upper bridge arm, U represents the system voltage, U+ represents the positive terminal voltage of the system, and U- represents the negative terminal voltage of the system. According to Kirchhoff's law, we can get: I1+I2=I2+I5 R1I1=R2I2 R1I1=U u1 R3I3=R4I4 R3I3=U d1 U=U d1 +U u1 From the above formula, the voltage ratio of the upper and lower bridge arms can be deduced as Close switch T1 and open switch T2. The voltage ratio is Take ka and kb as The insulation resistance is calculated 4. The method for calculating the insulation resistance detection circuit in a strong inductive electrical environment according to claim 3 is characterized in that: The calculation method uses the steady-state current LM algorithm to estimate the insulation resistance. The specific operation method for measuring the steady-state currents of I1 and I3 is as follows: The induction power processing module is connected to the DC system for the substation, and the current sampling module samples and obtains the dynamic sampling current value of the insulation resistance test of the DC system for the substation, calculates the stable current value of the dynamic sampling current value of the insulation resistance test of the DC system for the substation, and calculates the insulation resistance of the DC system for the substation through Ohm's law. For the dynamic sampling current, there are several generally accepted analytical functions that can be used to approximate the decay curve of the current, which are composed of an exponential or the sum of several exponentials with different time constants. After the measuring voltage source is connected for a period of time, the ammeter cannot measure large currents exceeding the measurement limit; And there is a current limiting resistor R6, the measured voltage will not be established immediately; Therefore, the current curve should contain an exponential component. Therefore, the analytical expression of the designed steady-state current curve is as follows: in is the exponential component, t′0 is the supplementary variable, I(t′) is the dynamic sampling current value I1′ and I3′ of the insulation resistance, t′ is the time, n is the exponent, n∈[0.1...1.7], S1 and S2 are specific coefficients depending on the dielectric type of the DC system insulation resistance of the substation and the voltage applied thereto, and S0 is the steady-state current value I1 and I3 of the insulation resistance; Based on the above steady-state current calculation formula, the LM algorithm is used to realize the numerical calculation of the current of this analytical formula, and the dynamic sampling current data is set to [(t1,i1),(t2,i2),...,(t i ,i i ),...,(t n ,i n )] Here i represents the time series of sampling, i i Represents the dynamic sampling current value I(t′), and sets the parameter x to x=[h1,h2,h3] T The calculation of the parameter vector x is positioned as a nonlinear least squares problem, which is how to minimize the difference between the final value of the model and the sampled data; Function I(t i , x) represents the output of the feedback current model, and the parameter vector x needs to be updated iteratively to minimize the difference between the model output and the sampled data; f i (x) represents the residual, f(x) represents the residual vector, and F(x) is the sum of squares of the residuals; The goal of the LM algorithm is to minimize the sum of squares of the residuals F(x) and solve for the parameter vector using the following iterative method: x k+1 =x k +Δx k The specific expression is Δx k =-[H(x)+μI] -1 J(x) T f(x) H(x)=J(x) T J(x) Based on the combination of LM algorithm and steady-state current calculation formula, after the test voltage is turned on, the dynamic sampling current will be calculated, and S0 in the steady-state current calculation formula will be quickly solved. S0 is the steady-state current value I1 and I3 of the insulation resistance of the DC system for substation when t approaches infinity. The steady-state current value S0 is further calculated through Ohm's law to obtain the insulation resistance value of the DC system for substation.

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