A method for early warning of loose cable joints in power distribution cabinets based on real-time data acquisition

Abstract

The present invention relates to a method for early warning of loose cable joints in a power distribution cabinet based on real-time data acquisition. By comprehensively analyzing the accident data of loose cable joints and the correspondence between online monitoring data and joint failure data in a high-voltage power distribution cabinet, a comprehensive evaluation expression for early warning of loose cable joints is established. First, the electrical parameters and external environmental parameters that affect the stability of the cable joints are collected, calculated, and stored to form a complete characteristic model of the accident data of loose cable joints. Then, the correspondence between the online monitoring data in the power distribution cabinet and the joint failure data is analyzed to make a more accurate judgment on the loose state of the cable joints and realize fault identification.

Description

Technical Field

[0001] The invention belongs to the field of electric power systems and relates to a method for predicting loose cable joints, and in particular to an early warning method for loose cable joints in a power distribution cabinet based on real-time data collection. Background Art

[0002] During the production and maintenance process, the cable joints are often in a loose operating state due to incorrect joint manufacturing process, loose crimping, loose welding, mechanical vibration, electric repulsion, thermal expansion, corrosion and oxidation of the cable joints, etc., which will lead to high-resistance connection faults in the power supply line, reduce power supply reliability, voltage imbalance, reduce the working efficiency of electrical equipment, and affect power transmission. If the fault is not controlled in time, long-term overheating will produce gas discharge phenomena such as spark discharge, glow discharge, fault arc discharge, etc., and eventually cause cable fire accidents.

[0003] At present, the existing technical solutions for detecting and preventing loose cable joint failures have many shortcomings, such as inaccurate fault detection, poor real-time performance, complex operation, high cost, and high risk. Summary of the invention

[0004] In view of the deficiencies in the above-mentioned prior art, the present invention establishes a comprehensive evaluation expression for cable joint loosening warning by comprehensively analyzing the accident data of cable joint loosening and the correspondence between the online monitoring data and the joint failure data in the high-voltage distribution cabinet, and proposes a cable joint loosening warning method. The method can accurately warn of loose cable joints in distribution cabinets under different conditions, detect faults in a timely and rapid manner, and cut off the faulty lines.

[0005] A method for early warning of loose cable joints in a power distribution cabinet based on real-time data collection, comprising the following steps:

[0006] Step 1: Use a variety of sensors to collect electrical parameters and external environmental parameters that affect the loose state of the cable;

[0007] Step 2: After data screening and calculation of the collected electrical parameters and external environmental parameters, the correlation coefficients obtained form a complete cable joint loosening accident data feature model, which is used to determine the degree of cable joint loosening;

[0008] Step 3: According to the coefficients obtained in step 2, assign corresponding weights to each coefficient, calculate the root mean square, consider the correction coefficient of the service life of the cable joint, and obtain the comprehensive evaluation value A of the loose state of the cable joint.

[0009]

[0010] r is the service life of the cable joint; m is the estimated service life of the cable joint;

[0011] If the A value is less than 1, it means that the cable joint is in a tightened state. If the A value is between 1 and 10, it means that the cable joint is in a semi-loose state. If it is greater than 10, it means that the cable joint grid is in a completely loose state.

[0012] In step 1, the electrical parameter collection includes collecting the contact voltage U1 of the cable connector, the kth harmonic component U K , the maximum contact current I of the cable connector max , minimum contact current I of cable connector min , the voltage amplitude of the cable joint arc U m , short circuit current I S , line overload time t Ls , line light load time t Lq , load rated output power P'; external environmental parameters collected include cable connector skin temperature T F , the current ambient temperature near the cable connector T S , air humidity λ, cable external temperature T V ; Temperature T of the inner surface of the distribution cabinet.

[0013] The correlation coefficients in step 2 include the cable joint temperature change rate coefficient, the contact current distortion rate coefficient, the arc energy coefficient and the load risk coefficient.

[0014] The temperature change rate coefficient of the cable joint refers to the ability of the cable joint of the power distribution cabinet to withstand temperature. Harmonics can cause the cable joint to overheat, shorten its life, and even cause fire. Therefore, harmonic-related indicators are added to the temperature change rate coefficient of the cable joint.

[0015] Consider the deviation value T between the cable connector skin temperature and the ambient temperature F -T S , using its inverse tangent relationship Take Get the surface composite heat transfer coefficient parameters, and then refer to the calculation method of temperature change qualification rate:

[0016]

[0017] Get reference value Combined with the Fourier series decomposition of the contact voltage of the cable joint, the fundamental component with the same frequency as the power frequency and the kth harmonic component with an integer multiple of the power frequency are obtained. Perform weighted processing to derive the cable joint temperature change rate coefficient A T ,

[0018] The cable joint temperature change rate coefficient A that forms a complete cable joint loosening accident data characteristic model T calculate:

[0019]

[0020] Where: γ is the skin effect factor; U1 is the contact voltage of the cable connector; U K is the kth harmonic voltage RMS value; k = 2, 3, 4, 5, 6; T F is the cable connector skin temperature; T S is the current ambient temperature near the cable connector.

[0021] The contact current distortion coefficient refers to the ability of the contact current amplitude difference to exceed the specified range; loose cable joints will lead to increased additional line losses and malfunctions of various protection and automatic devices. The maximum contact current I of the cable joint is summarized within the data collection time range. max and minimum contact current value I min , considering the difference between the maximum and minimum contact currents and the peak change rate Combined with the cosine ratio of the maximum and minimum contact currents, the integration is performed within the data collection time range to calculate the influence relationship between the contact current distortion rate and the looseness of the cable joint, and the contact current distortion rate coefficient A is derived. I ,

[0022] The contact current distortion coefficient A that forms a complete cable joint loosening accident data characteristic model I :

[0023]

[0024] Where: I max is the maximum contact current of the cable connector; I min is the minimum contact current of the cable joint; t Ls is the line overload time; t Lq is the line light load time; η I is the peak rate of change.

[0025] The arc energy coefficient reflects the degree of energy change before and after the loosening of the cable joint. The loosening of the cable joint is predicted by analyzing the changes in arc light, arc sound amplitude and short-circuit current before and after the characteristic sub-band of the arc sound signal. Since the instantaneous energy changes of the arc and current are different at different temperatures, the corresponding functional relationship between the looseness of the cable and the arc energy coefficient is obtained based on this difference. The arc energy coefficient Ap is:

[0026]

[0027] Among them U m is the voltage amplitude of the arc at the cable joint, T is the temperature of the inner surface of the distribution cabinet, η max is the maximum peak change rate of short-circuit current; η minis the minimum peak change rate of the short-circuit current; U is the effective value of the arc voltage of the cable joint, and k is the Boltzmann constant.

[0028] The load risk factor is a factor that reflects the effect of loose cable joints on the load power factor, taking into account the comprehensive load effect factor of the lines in the system and the sum of the hth harmonic components whose frequency is an integer multiple of the power frequency ∑U h And, derive the load risk factor A F ,

[0029] The load risk coefficient A of the complete cable joint loosening accident data characteristic model is formed F calculate:

[0030]

[0031] Where: T1 is the temperature of the cable connector, τ = 0.17 is the influence coefficient of the sensor's own error on power transmission, P' is the rated output power of the load; T V is the external temperature of the cable; λ is the air humidity.

[0032] The advantages and effects of the present invention are as follows:

[0033] The present invention aims at the electrical parameters and external environmental parameters that affect the looseness of the cable joints in the distribution cabinet, constructs a functional relationship through the electrical parameters and the external environmental parameters, calculates the correlation coefficient, and finally obtains a comprehensive value for evaluating the looseness of the cable joints. The state of the joint is judged by the comprehensive evaluation value of the loose state of the cable joint, and corresponding maintenance arrangements are made when the loose state of the cable joints in the distribution cabinet is evaluated in a relatively timely manner, which is conducive to reducing economic costs and the probability of accidents. The looseness of the cable joints in the high-voltage cabinet is predicted, and timely judgment is made according to the corresponding relationship between the online monitoring data in the high-voltage distribution cabinet and the joint failure data, so as to obtain a more accurate early warning method for loose cable joints.

[0034] According to the analysis of the corresponding relationship between the comprehensive information sensor data in the high-voltage distribution cabinet and the weakening of the mechanical strength of the cable joints, an effective method for accurately detecting loose faults based on online monitoring data is proposed to realize fault identification. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 It is a flow chart of the early warning method of the present invention.

[0036] Figure 2 This is a schematic block diagram of the characteristic model structure of the present invention. DETAILED DESCRIPTION

[0037] Example

[0038] Step 1: Use a variety of sensors to collect electrical parameters and external environmental parameters that affect the loose state of the cable; the electrical parameters collected mainly include the contact voltage U1 of the cable connector, the kth harmonic component U K , the maximum contact current I of the cable connector max , minimum contact current I of cable connector min , the voltage amplitude of the cable joint arc U m , short circuit current I S , line overload time t Ls , line light load time t Lq , load rated output power P'; external environmental parameters collected include cable connector skin temperature T F , the current ambient temperature near the cable connector T S , air humidity λ, cable external temperature T V ; Temperature T of the inner surface of the distribution cabinet.

[0039] Step 2: After data screening and calculation, the collected contact voltage, harmonic voltage root mean square value, maximum contact current value, minimum contact current value, arc voltage amplitude, short-circuit current, line overload time, line light load time, transformer overload time, load rated output power, current ambient temperature near the cable joint and cable external temperature are used to obtain the correlation coefficient to form a complete cable joint loose accident data feature model for judging the degree of cable joint looseness.

[0040] Step 2.1: The cable joint temperature change coefficient refers to the temperature resistance of the distribution cabinet cable joint. Harmonics can cause the cable joint to overheat, shorten its life, and even cause fire, so harmonic-related indicators are added to the cable joint temperature change coefficient.

[0041] Consider the deviation value T between the cable connector skin temperature and the ambient temperature F -T S , using its inverse tangent relationship Take Get the surface composite heat transfer coefficient parameters, and then refer to the calculation method of temperature change qualification rate:

[0042]

[0043] Get reference value Combined with the Fourier series decomposition of the contact voltage of the cable joint, the fundamental component with the same frequency as the power frequency and the kth harmonic component with an integer multiple of the power frequency are obtained. Perform weighted processing to derive the cable joint temperature change rate coefficient A T :

[0044] The cable joint temperature change rate coefficient A that forms a complete cable joint loosening accident data characteristic model T calculate:

[0045]

[0046] Where: γ is the skin effect factor; U1 is the contact voltage of the cable connector; U K is the kth harmonic voltage RMS value; k = 2, 3, 4, 5, 6; T F is the cable connector skin temperature; T S is the current ambient temperature near the cable connector.

[0047] Step 2.2: The contact current distortion coefficient refers to the ability of the contact current amplitude difference to exceed the specified range. Loose cable joints will lead to increased additional line losses and malfunction of various protection and automatic devices. Summarize the maximum contact current I of the cable joint within the data collection time range. max and minimum contact current value I min , considering the difference between the maximum and minimum contact currents and the peak change rate Combined with the cosine ratio of the maximum and minimum contact currents, the integration is performed within the data collection time range to calculate the influence relationship between the contact current distortion rate and the looseness of the cable joint, and the contact current distortion rate coefficient A is derived. I :

[0048] The voltage quality coefficient A that forms a complete cable joint loosening accident data characteristic model I calculate:

[0049]

[0050] Where: I max is the maximum contact current of the cable connector; I min is the minimum contact current of the cable joint; t Ls is the line overload time; t Lq is the line light load time; η I is the peak rate of change.

[0051] Step 2.3: The arc energy coefficient can reflect the degree of energy change before and after the cable joint is loosened. The looseness of the cable joint can be predicted by analyzing the changes in arc light, arc sound amplitude and short-circuit current before and after the characteristic sub-band of the arc sound signal. Since the instantaneous energy changes of the arc and current are different at different temperatures, the corresponding functional relationship between the degree of cable looseness and the arc energy coefficient is obtained based on this difference:

[0052]

[0053] Among them U mis the voltage amplitude of the arc at the cable joint, T is the temperature of the inner surface of the distribution cabinet, η max is the maximum peak change rate of short-circuit current; η min is the minimum peak change rate of the short-circuit current; U is the effective value of the arc voltage of the cable joint, and k is the Boltzmann constant.

[0054] Step 2.4: The load risk factor reflects the influence of loose cable joints on the load power factor. Consider the comprehensive load influence factor of the lines in the system and the sum of the hth harmonic components whose frequency is an integer multiple of the power frequency ∑U h And, derive the load utilization factor A F :

[0055] The load risk coefficient A of the complete cable joint loosening accident data characteristic model is formed F calculate:

[0056]

[0057] Where: T1 is the temperature of the cable connector, τ = 0.17 is the influence coefficient of the sensor's own error on power transmission, P' is the rated output power of the load; T V is the external temperature of the cable; λ is the air humidity.

[0058] Step 3: According to the 4 coefficients obtained, assign corresponding weights to each coefficient, calculate the root mean square, consider the cable joint service life correction coefficient, and obtain the comprehensive evaluation value of the loose state of the cable joint.

[0059]

[0060] r is the service life of the cable connector; m is the estimated service life of the cable connector.

[0061] If the A value is less than 1, it means that the cable joint is in a tightened state. If the A value is between 1 and 10, it means that the cable joint is in a semi-loose state. If it is greater than 10, it means that the cable joint grid is in a completely loose state.

[0062] Application Examples

[0063] The contact voltage U1 of the cable joint is 380V, and the kth harmonic voltage components are U2=10.5V, U3=8.5, U4=6.1, U5=4.3, U6=1.6 respectively. The maximum contact current I max The minimum contact current of the cable connector is 24.5A. min is 22.4A, the skin effect factor γ = 1.11, and the voltage amplitude of the cable joint arc is U m =16V, short circuit current I S =345A, line overload time tLs is 9.8h, and the line light load time t Lq The load rated output power P′ is 445 kW, and the external environmental parameters collected include the cable connector skin temperature T F The current ambient temperature near the cable connector is 26 degrees Celsius. S The temperature is 38 degrees Celsius, the air humidity is 50%, and the cable external temperature is T V The temperature of the inner surface of the distribution cabinet is 27 degrees Celsius; the temperature T of the inner surface of the distribution cabinet is 35 degrees, r=5, m=7.

[0064] 1. Calculation of the temperature change rate coefficient of the cable joint: U1 is the root mean square value of the fundamental voltage, U1 = 380V, T F =26℃, T S =38℃, γ=1.11 Substitute into the formula Solve for A T =6.37.

[0065] 2. Calculation of contact current distortion coefficient: I max =24.5A, I min =22.4A, t Ls =9.8h,t Lq =18.5h substituted into the formula Solve for A I =1.698.

[0066] 3. Calculation of arc energy coefficient: m =16V, U=79, T=35℃, η max =0.685,η min =0.155 T S =38℃Substitute into the formula Solve for A P =4.089.

[0067] 4. Calculation of load risk factor: Set P′=445W, I s =345A, T V =27℃, T Lq =12.9h, substitute into the formula Solve for A F =3.989.

[0068] 5. A T =2.95, A I =1.612, A P =2.62, A F =3.989, substitute into the formula The comprehensive evaluation value of the grid operation status is A=3.542. A value between 1 and 10 represents that the cable joint is in a semi-loose state.

[0069] The above are merely examples of the present invention and are not intended to limit the present invention. Therefore, any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of the claims of the present invention.

Claims

1. A method for early warning of loose cable joints in a power distribution cabinet based on real-time data acquisition, characterized in that The steps include: Step 1: Use a variety of sensors to collect electrical parameters and external environmental parameters that affect the loose state of the cable; Step 2: After data screening and calculation of the collected electrical parameters and external environmental parameters, the correlation coefficients obtained form a complete cable joint loosening accident data feature model, which is used to determine the degree of cable joint loosening; Step 3: According to the coefficients obtained in step 2, assign corresponding weights to each coefficient, calculate the root mean square, consider the correction coefficient of the service life of the cable joint, and obtain the comprehensive evaluation value A of the loose state of the cable joint. r is the service life of the cable joint; m is the estimated service life of the cable joint; If the A value is less than 1, it means that the cable joint is in a tightened state. If the A value is between 1 and 10, it means that the cable joint is in a semi-loose state. If it is greater than 10, it means that the cable joint network is in a completely loose state. In step 1, the electrical parameter collection includes collecting the contact voltage U1 of the cable connector, the kth harmonic component U K , the maximum contact current I of the cable connector max , minimum contact current I of cable connector min , the voltage amplitude of the cable joint arc U m , short circuit current I S , line overload time t Ls , line light load time t Lq , load rated output power P'; external environmental parameters collected include cable connector skin temperature T F , the current ambient temperature near the cable connector T S , air humidity λ, cable external temperature T V ; Temperature T of the inner surface of the power distribution cabinet; The correlation coefficients in step 2 include the cable joint temperature change rate coefficient, the contact current distortion rate coefficient, the arc energy coefficient and the load risk coefficient; The temperature change rate coefficient of the cable joint refers to the ability of the cable joint of the power distribution cabinet to withstand temperature. Harmonics can cause the cable joint to overheat, shorten its life, and even cause fire. Therefore, harmonic-related indicators are added to the temperature change rate coefficient of the cable joint. Consider the deviation value T between the cable connector skin temperature and the ambient temperature F -T S , using its inverse tangent relationship Take Get the surface composite heat transfer coefficient parameters, and then refer to the calculation method of temperature change qualification rate: Get reference value Combined with the Fourier series decomposition of the contact voltage of the cable joint, the fundamental component with the same frequency as the power frequency and the kth harmonic component with an integer multiple of the power frequency are obtained. Perform weighted processing to derive the cable joint temperature change rate coefficient A T , The cable joint temperature change rate coefficient A that forms a complete cable joint loosening accident data characteristic model T calculate: Where: γ is the skin effect factor; U1 is the contact voltage of the cable connector; U K is the kth harmonic voltage RMS value; k = 2, 3, 4, 5, 6; T F is the cable connector skin temperature; T S is the current ambient temperature near the cable connector; The contact current distortion coefficient refers to the ability of the contact current amplitude difference to exceed the specified range; loose cable joints will lead to increased additional line losses and malfunctions of various protection and automatic devices. The maximum contact current I of the cable joint is summarized within the data collection time range. max and minimum contact current value I min , considering the difference between the maximum and minimum contact currents and the peak change rate Combined with the cosine ratio of the maximum and minimum contact currents, the integration is performed within the data collection time range to calculate the influence relationship between the contact current distortion rate and the looseness of the cable joint, and the contact current distortion rate coefficient A is derived. I , The contact current distortion coefficient A that forms a complete cable joint loosening accident data characteristic model I : Where: I max is the maximum contact current of the cable connector; I min is the minimum contact current of the cable joint; t Ls is the line overload time; t Lq It is the line light load time; η I is the peak rate of change; The arc energy coefficient reflects the degree of energy change before and after the loosening of the cable joint. The loosening of the cable joint is predicted by analyzing the changes in arc light, arc sound amplitude and short-circuit current before and after the characteristic sub-band of the arc sound signal. Since the instantaneous energy changes of the arc and current are different at different temperatures, the corresponding functional relationship between the looseness of the cable and the arc energy coefficient is obtained based on this difference. The arc energy coefficient Ap is: Among them U m is the voltage amplitude of the arc at the cable joint, T is the temperature of the inner surface of the distribution cabinet, η max is the maximum peak change rate of short-circuit current; η min is the minimum peak change rate of short-circuit current; U is the effective value of the arc voltage at the cable joint, and k is the Boltzmann constant; The load risk factor is a factor that reflects the effect of loose cable joints on the load power factor, taking into account the comprehensive load effect factor of the lines in the system and the sum of the hth harmonic components whose frequency is an integer multiple of the power frequency ∑U h And, derive the load risk factor A F , The load risk coefficient A of the complete cable joint loosening accident data characteristic model is formed F calculate: Where: T1 is the temperature of the cable connector, τ = 0.17 is the influence coefficient of the sensor's own error on power transmission, P' is the rated output power of the load; T V is the external temperature of the cable; λ is the air humidity.

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