Contact resistance evaluation method and system based on temperature rise

Abstract

The invention discloses a contact resistance assessment method and system based on temperature rise, and belongs to the technical field of electrical contact monitoring. A contact temperature sensor is installed on a to-be-assessed electrical contact, an environment temperature sensor is additionally arranged to detect the environment temperature, and temperature values obtained by the contact temperature sensor and the environment temperature sensor are transmitted to a host; and the host obtains temperature rise through the temperature difference value of the contact temperature sensor and the environment temperature sensor, calculates the contact resistance corresponding to the electrical contact to be evaluated through the temperature rise, and evaluates the safety risk of the contact based on the change of the contact resistance. According to the method, the safety risk and the change trend of the electrical contact are pre-judged through the contact resistance value, compared with an existing evaluation method according to the temperature value, the temperature development trend and the potential risk of the contact resistance can be pre-judged in advance, and risk misjudgment caused by the influence of the environment temperature on the temperature is avoided.

Description

Technical Field

[0001] The present invention belongs to the technical field of electrical contact monitoring, and particularly relates to a method and system for evaluating contact resistance based on temperature rise. Background Art

[0002] In the power system, there are a large number of electrical contacts, including static contacts fixed by screws and dynamic contacts of switches. Due to the existence of contact resistance (the resistance presented between mutually contacting conductors), when passing through load current, the electrical contacts will generate heat. As time goes by, the contacts of the electrical contacts will oxidize, resulting in an increase in the contact resistance value. The increase in the contact resistance will cause a sharp rise in the temperature rise (the difference between the temperature of the electrical component and the ambient temperature of the electrical component), posing a great safety hazard to the equipment. At the same time, when alternating current flows through, electrodynamic force will also be generated, causing the fixing screws of the contacts to become loose. Therefore, the evaluation of contact resistance is an important means to prevent risks. At present, the commonly used method is to measure the contact temperature and set a high-temperature alarm threshold to achieve risk prevention. However, this method can only detect risks when the temperature is relatively high and the risk is already relatively large, and it is prone to false alarms. Because when the line load is large, the current is also large, and the temperature rises, but at this time, the high temperature rise is a normal situation. Summary of the Invention

[0003] In order to solve the deficiencies of the prior art and achieve the purpose of predicting the risk of contact resistance temperature rise and reducing the probability of false alarms, the present invention adopts the following technical solutions: A contact resistance evaluation system based on temperature rise, including a host and a contact temperature sensor and an ambient temperature sensor respectively connected to the host. The contact temperature sensor is arranged on the electrical contact to obtain the temperature of the electrical contact. The host calculates the temperature rise through the difference between the temperature of the electrical contact and the ambient temperature obtained by the ambient temperature sensor, calculates the contact resistance corresponding to the electrical contact to be evaluated through the temperature rise, and evaluates the safety risk of the contact according to the change of the contact resistance.

[0004] Further, by taking the second derivative of the temperature rise, twice the contact resistance value is obtained, and the safety risk of the contact is evaluated according to the change of the contact resistance value.

[0005] Further, the system further includes a current transformer arranged on the electrical circuit on one side of the electrical contact to obtain the current value. By dividing the temperature rise by the square of the current value, the contact resistance value of the contact is obtained, and the safety risk of the contact is evaluated according to the change of the contact resistance value.

[0006] A contact resistance evaluation method based on temperature rise includes the following steps: Step 1: Install a contact temperature sensor on the electrical contact to be evaluated, add an ambient temperature sensor to detect the ambient air temperature, and transmit the temperature values obtained by the contact temperature sensor and the ambient temperature sensor to the host through wired or wireless means; Step 2: The host obtains the temperature rise through the temperature difference between the contact temperature sensor and the ambient temperature sensor, and calculates the contact resistance corresponding to the electrical contact to be evaluated through the temperature rise; Step 3: Evaluate the safety risk of the contact based on the change in contact resistance.

[0007] Further, in Step 2, take the second derivative of the temperature rise to obtain twice the contact resistance value.

[0008] Further, install a current transformer on the electrical circuit on one side of the electrical contact to obtain the current value. In Step 3, divide the temperature rise by the square of the current value to obtain the contact resistance value of the contact.

[0009] The contact resistance evaluation method based on temperature rise is applied to the host side: Obtain the temperature of the electrical contact to be evaluated and its corresponding ambient temperature, and obtain the temperature rise according to the difference between the two; Calculate the contact resistance corresponding to the electrical contact to be evaluated through the temperature rise; Evaluate the safety risk of the contact based on the change in contact resistance.

[0010] Further, take the second derivative of the temperature rise to obtain twice the contact resistance value.

[0011] Further, obtain the current value of the electrical circuit on one side of the electrical contact, and divide the temperature rise by the square of the current value to obtain the contact resistance value of the contact.

[0012] The advantages and beneficial effects of the present invention are as follows: The contact resistance evaluation method and system based on temperature rise of the present invention perform risk assessment on the contacts of high and low voltage electrical circuits. By taking the derivative of the temperature rise or directly calculating by introducing the load current value to obtain the contact resistance value, and judging the safety risk and change trend existing in the electrical contact through the contact resistance value. Compared with the existing evaluation method according to the temperature value, the evaluation scheme according to the contact resistance value of the present invention can predict in advance the temperature development trend and potential risk of the contact resistance, and avoid the risk misjudgment caused by the influence of the ambient temperature on the temperature. Description of the Drawings

[0013] Figure 1 is a schematic diagram of contact resistance temperature rise evaluation for alarm through a temperature sensor in the prior art.

[0014] Figure 2 is a schematic diagram of the system structure of an embodiment of the present invention.

[0015] Figure 3 is the flowchart of the method according to an embodiment of the present invention.

[0016] Figure 4 is a schematic diagram of the contact temperature value in an embodiment of the present invention.

[0017] Figure 5 is a schematic diagram of the contact temperature rise in an embodiment of the present invention.

[0018] Figure 6 is a schematic diagram of the system structure with a current transformer added in an embodiment of the present invention. Specific Embodiments

[0019] The following will describe in detail the specific embodiments of the present invention with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are only for the purpose of illustrating and explaining the present invention, and are not intended to limit the present invention.

[0020] As Figure 1 shown, in the prior art, the contact temperature is obtained through a wired (optical fiber) or wireless temperature sensor, and a high-temperature alarm threshold is set to output an alarm signal to prevent risks from occurring.

[0021] This method can only detect risks when the temperature is relatively high and the risk is relatively large, and it is prone to misjudgment. Because when the line load is relatively large, the current is large, the temperature rise is high, and at this time, the high temperature rise is a normal situation. At the same time, the influence of the ambient temperature on the contact temperature is not excluded. Especially in winter, when the ambient temperature is relatively low, although the contact temperature here is not high, the actual temperature rise is already very high, reaching the standard of potential safety hazards.

[0022] As Figure 2 shown, the present invention proposes a contact resistance evaluation system based on temperature rise, including a host and a contact temperature sensor and an ambient temperature sensor respectively connected to the host. The contact temperature sensor is arranged at the electrical contact for obtaining the temperature of the electrical contact. The host calculates the temperature rise through the difference between the temperature of the electrical contact and the ambient temperature obtained by the ambient temperature sensor, calculates the contact resistance corresponding to the electrical contact to be evaluated through the temperature rise, and evaluates the safety risk of the contact according to the change of the contact resistance.

[0023] As Figure 3 shown, the present invention also proposes a contact resistance evaluation method based on temperature rise. Based on the contact resistance evaluation system based on temperature rise, the change of the actual contact resistance is evaluated through the temperature rise to predict the risk of the power system in advance and reduce the probability of false alarms. The specific steps are as follows: Step 1: Install a contact temperature sensor on the electrical contact to be evaluated, add an ambient temperature sensor to detect the ambient air temperature, and transmit the temperature values obtained by the contact temperature sensor and the ambient temperature sensor to the host respectively through wired or wireless means.

[0024] Step 2: The host obtains the temperature rise through the temperature difference between the contact temperature sensor and the ambient temperature sensor, and calculates the contact resistance corresponding to the electrical contact to be evaluated based on the temperature rise.

[0025] As Figure 4 , Figure 5 shown, the temperature rise is a constant value, indicating that the current is constant. Temperature rise = heating power / contact thermal resistance. Since the thermal resistance is a constant value, the temperature rise is closely related to the heating power. Heating power = I * I * R, where I represents the current and R represents the contact resistance plus the conductor resistance. Since the conductor resistance is very small compared with the contact resistance and can be ignored, the contact resistance is approximated as R. When the current changes (for example, the load changes greatly during normal factory work and off-work hours, which will cause a large change in the current and lead to a change in the temperature rise), the typical temperature rise is proportional to the square of the current I. The value of the contact resistance remains basically unchanged within a period of time and is a constant value. Therefore, by taking the second derivative of the temperature rise, a value of 2R can be obtained, and thus the contact resistance value R of the contact to be evaluated can be obtained.

[0026] Step 3: Based on the change of the contact resistance, evaluate the safety risk of the contact.

[0027] Specifically, by analyzing and tracking the change of the contact resistance R value in real time, it is possible to predict in advance whether there are safety risks such as contact loosening and oxidation of the contact.

[0028] In another embodiment, as Figure 6 shown, on the basis of the contact resistance evaluation system based on the temperature rise, a current transformer is added to the electrical circuit on one side of the contact. It is not necessary to take the second derivative of the contact temperature rise data. Just divide it directly by the square value of the current to obtain the contact resistance value of the contact, and the real-time monitoring and risk assessment of the contact resistance of the electrical contact can also be realized.

[0029] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A contact resistance evaluation system based on temperature rise, comprising a host and a contact temperature sensor and an ambient temperature sensor respectively connected to the host, characterized in that: The contact temperature sensor is arranged at the electrical contact to obtain the temperature of the electrical contact. The host calculates the temperature rise by the difference between the temperature of the electrical contact and the ambient temperature obtained by the ambient temperature sensor, calculates the contact resistance corresponding to the electrical contact to be evaluated by the temperature rise, and evaluates the safety risk of the contact based on the change of the contact resistance.

2. The contact resistance evaluation system based on temperature rise according to claim 1, characterized in that: By taking the second-order derivative of the temperature rise, twice the contact resistance value is obtained, and the safety risk of the contact is evaluated based on the change in the contact resistance value.

3. The contact resistance evaluation system based on temperature rise according to claim 1, characterized in that: The system also includes a current transformer arranged on the electrical circuit on one side of the electrical contact to obtain the current value, and obtain the contact resistance value of the contact by dividing the temperature rise by the square of the current value, and evaluate the safety risk of the contact according to the change of the contact resistance value.

4. The contact resistance evaluation method based on temperature rise is characterized by The steps include: Step 1: Install a contact temperature sensor on the electrical contact to be evaluated, add an ambient temperature sensor to detect the ambient temperature, and transmit the temperature values ​​obtained by the contact temperature sensor and the ambient temperature sensor to the host respectively; Step 2: The host obtains the temperature rise through the temperature difference between the contact temperature sensor and the ambient temperature sensor, and calculates the contact resistance corresponding to the electrical contact to be evaluated through the temperature rise; Step 3: Evaluate the safety risk of the contacts based on the change in contact resistance.

5. The contact resistance evaluation method based on temperature rise according to claim 4, characterized in that: In the step 2, the second-order derivative of the temperature rise is calculated to obtain twice the contact resistance value.

6. The contact resistance evaluation method based on temperature rise according to claim 4, characterized in that: A current transformer is provided on the electrical circuit on one side of the electrical contact to obtain the current value. In the step three, the contact resistance value of the contact is obtained by dividing the temperature rise by the square of the current value.

7. The contact resistance evaluation method based on temperature rise is applied to the host side, characterized in that: Obtain the temperature of the electrical contact to be evaluated and its corresponding ambient temperature, and obtain the temperature rise based on the difference between the two; Calculate the contact resistance corresponding to the electrical contact to be evaluated through temperature rise; Assess the safety risk of contacts based on changes in contact resistance.

8. The contact resistance evaluation method based on temperature rise according to claim 7, characterized in that: Taking the second derivative of the temperature rise yields twice the contact resistance value.

9. The contact resistance evaluation method based on temperature rise according to claim 7, characterized in that: The current value of the electrical circuit on one side of the electrical contact is obtained, and the contact resistance value of the contact is obtained by dividing the temperature rise by the square of the current value.

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