A method for diagnosing cable joint aging based on temperature reflection

Abstract

The present invention discloses a method for diagnosing the aging of a cable joint based on temperature reflection. The detection device is installed on the surface of the cable joint plug, the temperature of the cable joint is monitored in real time, and the collected temperature signal is converted into a voltage signal, which is then compared with the set voltage threshold; when the detection value is greater than the threshold, an alarm is issued. The present invention uses a thermistor and combines it with a 555 oscillation circuit to first convert the temperature signal into a frequency signal, and then uses an LM331 frequency-to-voltage converter to convert the frequency signal into a voltage signal, thereby realizing a device for measuring and judging the degree of aging of the cable joint plug, avoiding voltage loss in the transmission line when the temperature signal is directly converted into a voltage signal; at the same time, it ensures that the device works reliably in a strong magnetic field and a strong electric field environment, greatly improving its anti-interference ability. The ultrasonic reflection method is used to set the threshold voltage during the alarm, so that the threshold is more accurate and reasonable, which conforms to the voltage condition when the actual cable joint is just burned.

Description

Technical Field

[0001] The invention belongs to the technical field of cable joint diagnosis, and in particular relates to a cable joint aging diagnosis method based on temperature reflection. Background Art

[0002] As a medium-voltage transformer load switch cabinet, the ring main unit is flexible in use, good in scalability, safe in operation, low in manufacturing cost, compact and simple in structure, and easy to maintain. It is widely used in office buildings, residential areas, factories, and substations, and is an important node in the urban distribution network. Cable joints are commonly found in ring main units.

[0003] The intermediate joint refers to the joint in the middle of the cable line; its main function is to make the line unobstructed and the cable sealed, so that it can run safely and reliably. The intermediate joint insulation can ensure the normal and stable operation of the intermediate joint. However, the plug of the cable joint will inevitably age and be corroded by external factors (such as insect bites) after long-term use, which will cause the plug surface to be damaged, reduce the sealing, and allow external humid air to enter the cavity to form an automatic breathing phenomenon, resulting in local discharge and causing the cable joint to burn. How to judge the aging of the plug part has become a research difficulty. The existing temperature or ultrasonic monitoring technology cannot directly characterize the intrinsic properties such as the aging degree of the plug part of the cable joint. At the same time, there are defects such as poor anti-interference ability, low measurement accuracy, and delayed warning. Summary of the invention

[0004] The invention provides a cable joint aging diagnosis method based on temperature reflection, which solves the problems existing in the prior art.

[0005] In order to solve the above technical problems, the present invention adopts the following solutions:

[0006] A cable joint aging diagnosis method based on temperature reflection, wherein a detection device is installed on the surface of the cable joint plug, the temperature of the cable joint is monitored in real time, and the collected temperature signal is converted into a voltage signal, which is then compared with a set voltage threshold; when the detection value is greater than the threshold, an alarm is issued.

[0007] Further optimization, the detection device includes a signal acquisition module, an STM32 data processing module, a wireless radio frequency communication module and an online monitoring platform; the acquisition module and the wireless radio frequency communication module are electrically connected to the STM32 data processing module. By setting the wireless radio frequency communication module, the detection device and the online monitoring platform can perform real-time wireless communication, so that the monitoring platform can receive the signal sent by the processing module in time, such as sending an alarm signal to remind the staff to carry out maintenance in time.

[0008] Further optimization, the acquisition module includes a thermistor and a NE555 timer, and the thermistor and the NE555 timer form a multivibrator circuit to convert the temperature signal on the surface of the cable plug into a frequency signal.

[0009] Commonly used temperature sensors include digital temperature sensors and thermistors. However, digital temperature sensors have weak anti-interference capabilities in strong magnetic and electric field environments and are not suitable for use in the working environment of this project. In order to ensure that the temperature sensor can work reliably in strong magnetic and electric field environments, the present invention utilizes thermistors in combination with 555 oscillation circuits to convert temperature information into frequency signals, greatly improving its anti-interference capabilities.

[0010] Further optimization, the input capture function of the timer in the STM32 data processing module is used to count at a frequency of 1.5 MHz. D The frequency f output by the multivibrator is collected, and two falling edges are captured continuously by the microprocessor. The time difference Δt between the two falling edges is calculated. After obtaining the output frequency f, the output end of the temperature measurement circuit is connected to the input end of the frequency-voltage converter to obtain the output voltage V of the voltage conversion circuit. O1 .

[0011] Further optimization, the voltage threshold is pre-set by ultrasonic reflection method, specifically: an ultrasonic probe is installed at the plug position of a cable connector where a plug has cracks and has just burned, and the probe emits an ultrasonic signal to the bottom wave reflected back. B After normalization, Fourier transform is performed to obtain its spectrum waveform. The peak A based on this spectrum is f peak , and then the frequency is f peak The signal is used as the input of the voltage converter to obtain the threshold voltage V REF .

[0012] Compared with the prior art, the present invention has the following beneficial effects:

[0013] 1. In view of the fact that current technology cannot directly characterize the aging of the middle joint of the cable joint, the present invention adopts thermistor and combines it with 555 oscillation circuit to first convert the temperature signal into a frequency signal, and then use LM331 frequency-voltage converter to convert the frequency signal into a voltage signal, thereby realizing a device for measuring and judging the aging degree of the cable joint plug, avoiding the voltage loss in the transmission line when the temperature signal is directly converted into a voltage signal; at the same time, it ensures that the device can work reliably in a strong magnetic field and a strong electric field environment, greatly improving its anti-interference ability. The ultrasonic reflection method is used to set the threshold voltage during the alarm, so that the threshold is more accurate and reasonable, which conforms to the voltage condition when the actual cable joint is just burned.

[0014] 2. In the present invention, the thermistor and the temperature acquisition and data transmission end obtain electrical energy through electromagnetic induction. The temperature acquisition circuit converts the temperature analog signal of the thermistor into a frequency-type digital signal. The frequency-to-voltage conversion circuit converts the frequency signal into a voltage signal, which is processed by the STM32 microprocessor and sent to the data receiving end through wireless radio frequency communication. REF Compare and determine whether to issue an alarm signal. If an alarm signal is issued, the data center will be informed of the degree of danger. It has strong anti-interference ability, high measurement accuracy and timely warning. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 It is a schematic diagram of the process of the cable joint aging diagnosis method based on temperature reflection according to the present invention;

[0016] Figure 2 This is a schematic diagram of the internal structure of NE555 described in the present invention;

[0017] Figure 3 This is a schematic diagram of the temperature measurement circuit of the present invention;

[0018] Figure 4 This is a schematic diagram of the LM331 frequency-to-voltage converter circuit of the present invention;

[0019] Figure 5 Schematic diagram of the voltage comparator of the present invention. DETAILED DESCRIPTION

[0020] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution of the present invention will be clearly and completely described below in conjunction with the accompanying drawings. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0021] like Figure 1 As shown, a cable joint aging diagnosis method based on temperature reflection is shown, in which a detection device is installed on the surface of the cable joint plug, the temperature of the cable joint is monitored in real time, and the collected temperature signal is converted into a voltage signal, which is then compared with the set voltage threshold; when the detection value is greater than the threshold, an alarm is issued.

[0022] In this embodiment, the detection device includes a signal acquisition module, an STM32 data processing module, a wireless radio frequency communication module and an online monitoring platform; the acquisition module and the wireless radio frequency communication module are both electrically connected to the STM32 data processing module, and the wireless radio frequency communication module is set to enable the detection device to perform real-time wireless communication with the online monitoring platform.

[0023] In this embodiment, the acquisition module includes a thermistor and a NE555 timer. The thermistor and the NE555 timer form a multivibrator circuit to convert the temperature signal on the surface of the cable plug into a frequency signal.

[0024] The present invention uses a thermistor as a temperature measuring element and a 555 time base integrated circuit to form a multivibrator circuit to convert the temperature value into a frequency value, that is, to convert the temperature analog signal into a frequency type digital signal, thereby improving the accuracy of the temperature sensor in a strong electric field or a strong magnetic field. In this embodiment, the high stability and high precision NE555 produced by FAIRCHILD is selected as the oscillator control chip, and the internal structure is as follows: Figure 2 As shown, the multivibrator circuit is Figure 3 shown.

[0025] like Figure 2 As shown in the figure, the internal structure of NE555 consists of two comparators C1 and C2, a basic RS trigger, a discharge transistor and a buffer inverter. The comparison voltages of comparators C1 and C2 are 2VCC / 3 and VCC / 3 respectively. Assume that the voltage on C21 is U c , then the relationship between the output of comparators C1, C2, Q, discharge tube state and OUT is shown in Table 1.

[0026] Table 1: 555 internal state relationship table

[0027]

[0028] After the device is powered on, the 5V power supply is used to charge the capacitor C21 through the resistors R24 and R10. When the voltage on C21 is less than 5 / 3V, the states of the comparators C1 and C2 are 1, 0, Q is 1, the discharge tube is cut off, and the output OUT is high level; when the voltage on C21 is greater than or equal to 5 / 3V and less than 10 / 3V, the states of the comparators C1 and C2 are 1, 1, Q remains 1, the discharge tube is cut off, and the output OUT is high level; when the voltage on C21 is greater than or equal to 10 / 3V, the states of the comparators C1 and C2 are 0, 1, Q becomes 0, and the output OUT is low level, the discharge tube is turned on, C21 discharges through R10 and the discharge tube, and the voltage at C21 decreases according to an exponential curve; when the voltage of C21 is between 5 / 3V:10 / 3V, the states of comparators C1 and C2 are 1,1, Q remains 0, and the output OUT maintains a low level; when the voltage of C21 is less than 5 / 3V, the states of comparators C1 and C2 become 1,0 again, Q is 1, the output OUT becomes high level, the discharge tube is cut off, and C21 starts to charge again; this oscillation repeats over and over again, and continuous rectangular pulses are output. In order to enable the processor to effectively capture the high and low levels of the rectangular pulse, the output end of the oscillation circuit is connected to the transistor Q1. When OUT is high level, Q1 is turned on, and the processor IO port is pulled high. When OUT is low level, Q1 is turned off, and the processor IO port is pulled low, so that the level state captured by the processor is consistent with the level state output by the oscillation circuit.

[0029] In this embodiment, the input capture function of the timer in the STM32F407VGT6 data processing module is used to count at a frequency of 1.5 MHz. D Collect the frequency f output by the multivibrator, capture two falling edges continuously through the microprocessor, calculate the time difference Δt between the two falling edges, and combine Figure 3 In the temperature measurement and acquisition circuit shown, the calculation formula of the multivibrator output frequency f is as follows:

[0030]

[0031] After obtaining the output frequency f, connect the output end of the temperature measurement circuit to the input end of the frequency-voltage converter LM331 to obtain the output voltage V of the voltage conversion circuit. O1 :

[0032]

[0033] In this embodiment, the voltage threshold V REF Preset by ultrasonic reflection method, V REF The method for obtaining the value of is as follows: an ultrasonic probe is installed at the plug position of a cable connector that has cracks and has just burned out. The probe emits an ultrasonic signal and the reflected bottom wave T BAfter normalization, Fourier transform is performed to obtain its spectrum waveform. The peak A based on this spectrum is f peak , and then the frequency is f peak The signal is used as the input of LM331 to get the threshold voltage V REF The expression is

[0034]

[0035] In actual early warning, the temperature signal is converted into a voltage V through a temperature measurement circuit and a frequency voltage converter. O1 , V O1 Through the voltage comparator and the set threshold voltage V REF Automatically compare, the voltage comparator circuit such as Figure 5 As shown. If V O1 >V REF , then the output V O =V O1 , an alarm aging signal is issued, indicating that the cable plug position has been severely damaged and needs to be repaired and replaced in time, otherwise it is very easy to burn out.

[0036] Based on the above ideal embodiments of the present invention, the relevant staff can make various changes and modifications without departing from the technical concept of the present invention through the above description. The technical scope of the present invention is not limited to the contents of the specification, and its technical scope must be determined according to the scope of the claims.

Claims

1. A cable joint aging diagnosis method based on temperature reflection, characterized in that: The detection device is installed on the surface of the cable joint plug to monitor the temperature of the cable joint in real time, and the collected temperature signal is converted into a voltage signal, which is then compared with the set voltage threshold; when the detection value is greater than the threshold, an alarm is issued; The detection device includes a signal acquisition module, an STM32 data processing module, a wireless radio frequency communication module and an online monitoring platform; the acquisition module and the wireless radio frequency communication module are both electrically connected to the STM32 data processing module, and the detection device and the online monitoring platform are enabled to perform real-time wireless communication by setting the wireless radio frequency communication module; The acquisition module includes a thermistor and a NE555 timer, which form a multi-vibrator circuit to convert the temperature signal on the surface of the cable plug into a frequency signal; The input capture function of the timer in the STM32 data processing module uses a counting frequency of 1.5MHz. D The frequency f output by the multivibrator is collected, and two falling edges are captured continuously by the microprocessor. The time difference Δt between the two falling edges is calculated. After obtaining the output frequency f, the output end of the temperature measurement circuit is connected to the input end of the frequency-voltage converter to obtain the output voltage V of the voltage conversion circuit. O1 ; The voltage threshold is preset by an ultrasonic reflection method, specifically, an ultrasonic probe is installed at the plug position of a cable connector where a plug has cracks and has just burned, and the probe emits an ultrasonic signal to reflect the back wave. B After normalization, Fourier transform is performed to obtain its spectrum waveform. The peak A based on this spectrum is f peak , and then the frequency is f peak The signal is used as the input of the voltage converter to obtain the threshold voltage V REF .

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