Pulse-based cable insulation temperature measuring device and method

Abstract

The invention discloses a pulse-based cable insulation temperature measuring device and method, and relates to the technical field of electrician detection, and the device comprises a pulse injection device which is used for transmitting an original pulse signal to a to-be-measured cable; the measuring device is connected with the pulse injection device, and the measuring device is used for receiving a reflected pulse signal passing through the cable to be measured; the processing terminal is connected with the measuring device and the pulse injection device, and is used for calculating according to the original pulse signal and the reflected pulse signal to obtain the insulation temperature of the cable to be measured; the insulation temperature of the insulation material is reversely deduced through the electromagnetic wave velocity based on the quantitative relation.

Description

Technical Field

[0001] The present invention relates to the field of electrical detection technology, and more particularly to a pulse-based cable insulation temperature measurement device and method. Background Art

[0002] At present, power cables are important equipment in modern power systems, among which cross-linked polyethylene is the most commonly used insulation material for cables. The insulation temperature of cables is a key factor affecting the insulation state and service life of cables. To prevent cable insulation failure, the cable conductor temperature is usually limited to below 90°C. Therefore, real-time monitoring of cable insulation temperature is of great significance.

[0003] However, there are two main methods for measuring cable insulation temperature in the prior art. One is the thermocouple temperature measurement method, but this method can only be arranged on the surface of the cable, using a single sensor to measure the temperature of a single point, and cannot display the temperature characteristics of the long line. The other is the optical fiber temperature measurement method. In this method, the optical fiber can be arranged inside the cable or attached to the surface of the cable. Both arrangements require the optical fiber to be laid along the entire cable and equipped with a set of terminal equipment to realize the temperature measurement function. This temperature measurement method requires independent construction, is extremely costly, and has low monitoring efficiency.

[0004] Therefore, how to provide a cable insulation temperature measurement device and method that can solve the above problems is an issue that technical personnel in this field urgently need to solve. Summary of the invention

[0005] In view of this, the present invention provides a pulse-based cable insulation temperature measurement device and method, which reversely infers the dielectric properties of the insulating material through the electromagnetic wave velocity based on a quantitative relationship, and then maps the cable insulation temperature according to the correlation between the dielectric parameters and the cable insulation temperature. It does not require any equipment or components to be installed along the line, reduces the construction difficulty, and improves the economy of the system.

[0006] In order to achieve the above object, the present invention adopts the following technical solution:

[0007] A pulse-based cable insulation temperature measurement device, comprising:

[0008] A pulse injection device, used for sending an original pulse signal to the cable to be tested;

[0009] A measuring device, the measuring device is connected to the pulse injection device, and the measuring device is used to receive a reflected pulse signal passing through the cable to be tested;

[0010] A processing terminal is connected to the measuring device and the pulse injection device, and is used to calculate according to the original pulse signal and the reflected pulse signal to obtain the insulation temperature of the cable to be measured.

[0011] Preferably, the pulse injection device comprises:

[0012] A pulse generator, used for generating an original pulse signal;

[0013] A coupling coil is arranged on the cable to be tested and connected to the pulse generator, and is used to transmit the original pulse signal on the cable to be tested.

[0014] Preferably, the measuring device comprises:

[0015] A sensor unit, the sensor unit is connected to the coupling coil and is used to receive a reflected pulse passing through the cable to be tested;

[0016] A signal transmission unit is connected to the sensor unit and is used to transmit the reflected pulse signal.

[0017] Preferably, the processing terminal includes:

[0018] A receiving unit, the receiving unit is connected to the signal transmission unit and the pulse generator, and is used to receive the original pulse signal and the reflected pulse signal;

[0019] A calculation unit, used to determine the insulation temperature of the cable to be tested by determining an expression of the original pulse signal, the reflected pulse signal and a signal attenuation coefficient;

[0020] A display unit is connected to the receiving unit and the calculating unit, and is used to display the original pulse signal, the reflected pulse signal and the insulation temperature.

[0021] Preferably, the calculation unit further includes:

[0022] When determining the insulation temperature of the cable to be tested, the calculation unit is also used to determine a capacitance relationship based on the correlation between the capacitance and relative dielectric constant of the cable to be tested, and then substitute the expressions of the relative dielectric constant and insulation temperature of the cable to be tested into the relationship and the expression to obtain the insulation temperature of the cable to be tested.

[0023] The present invention also provides a pulse-based cable insulation temperature measurement method, comprising the following steps:

[0024] Sending an original pulse signal to the cable under test based on a pulse injection device;

[0025] Receiving, by a measuring device, a reflected pulse signal passing through the cable to be tested;

[0026] The insulation temperature of the cable to be tested is determined according to an expression of the original pulse signal and the reflected pulse signal.

[0027] Preferably, the specific process of determining the insulation temperature of the cable to be tested includes:

[0028] Determine the signal expression of the cable transmission under test according to the correlation between the original pulse signal, the reflected pulse signal and the signal attenuation coefficient;

[0029] Determine a capacitance expression of the cable to be tested based on the capacitance of the cable to be tested, the signal attenuation coefficient, and a correlation between a relative dielectric constant of the cable to be tested;

[0030] Determining a relative dielectric constant expression based on the correlation between the relative dielectric constant and the insulation temperature of the cable to be tested;

[0031] Substituting the relative dielectric constant expression into the capacitance expression to obtain a corresponding calculation result;

[0032] Finally, the calculation result is substituted into the signal expression to obtain the final insulation temperature calculation result.

[0033] It can be known from the above technical scheme that compared with the prior art, the present invention discloses a pulse-based cable insulation temperature measurement device and method, which studies the electromagnetic wave velocity of the cross-linked polyethylene insulated cable, inversely infers the dielectric properties of the insulating material, and obtains the insulation temperature of the cable insulation to be measured according to the correlation between the dielectric parameter and the insulation temperature. Compared with the traditional thermocouple temperature measurement method, it can display the temperature characteristics of the entire cable line. Compared with the optical fiber temperature measurement method, it does not require the optical fiber to be laid along the cable throughout the entire process. This method is more economical and greatly reduces the cost of cable temperature measurement. At the same time, the present invention can quickly measure the cable insulation temperature and perform status evaluation according to the cable insulation temperature. Not only is the result more reliable, but the temperature measurement process is simpler and faster, which has certain significance in terms of safety, efficiency and economy. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying creative work.

[0035] Figure 1 A schematic diagram of an overall device of a pulse-based cable insulation temperature measurement device provided by the present invention;

[0036] Figure 2 A structural principle block diagram of a pulse-based cable insulation temperature measurement device provided by the present invention;

[0037] Figure 3 A comparison diagram of the electromagnetic wave velocity versus insulation temperature provided in Example 1 of the present invention;

[0038] Figure 4 A graph showing the relationship between the relative dielectric constant and the insulation temperature provided in Example 1 of the present invention;

[0039] Figure 5 This is a pulse waveform diagram provided for Example 2 of the present invention. DETAILED DESCRIPTION

[0040] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only 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.

[0041] Example 1

[0042] See also Figure 1-2 As shown, Embodiment 1 of the present invention discloses a pulse-based cable insulation temperature measurement device, comprising:

[0043] A pulse injection device, used for sending an original pulse signal to the cable to be tested;

[0044] A measuring device, the measuring device is connected to the pulse injection device, and the measuring device is used to receive a reflected pulse signal passing through the cable to be tested;

[0045] The processing terminal is connected to the measuring device and the pulse injection device, and is used to calculate according to the original pulse signal and the reflected pulse signal to obtain the insulation temperature of the cable to be measured.

[0046] In a specific embodiment, the pulse injection device comprises:

[0047] A pulse generator is used to generate the original pulse signal. The pulse generated by the pulse injection device will propagate in the cable. When the pulse encounters an impedance change along the transmission line, such as the end of a cable with non-characteristic impedance, it will be reflected back in the opposite direction;

[0048] The coupling coil is arranged on the cable to be tested and connected to the pulse generator, and is used to transmit the original pulse signal on the cable to be tested.

[0049] In a specific embodiment, the measuring device comprises:

[0050] The sensor unit is connected to the coupling coil and is used to receive the reflected pulse passing through the cable to be tested. The sensor unit can be implemented by an electromagnetic coupling sensor. The sensor of the sensor unit will detect the reflected pulse from different impedance changes, and the signal transmission unit will transmit it to the processing terminal through the signal transmission line to observe the reflected waveform, so as to calculate the wave speed;

[0051] The signal transmission unit is connected to the sensor unit and is used for transmitting the reflected pulse signal.

[0052] In a specific embodiment, the processing terminal includes:

[0053] A receiving unit, the receiving unit is connected to the signal transmission unit and the pulse generator, and is used to receive the original pulse signal and the reflected pulse signal;

[0054] A calculation unit, used for determining the insulation temperature of the cable to be tested by determining the expression of the original pulse signal, the reflected pulse signal and the signal attenuation coefficient;

[0055] The display unit is connected with the receiving unit and the calculating unit and is used for displaying the original pulse signal, the reflected pulse signal and the insulation temperature.

[0056] In a specific embodiment, the computing unit further includes:

[0057] When determining the insulation temperature of the cable to be tested, the calculation unit is also used to determine a capacitance relationship based on the correlation between the capacitance and relative dielectric constant of the cable to be tested, and then substitute the expressions of the relative dielectric constant and insulation temperature of the cable to be tested into the relationship and expression to obtain the insulation temperature of the cable to be tested.

[0058] The embodiment of the present invention also provides a pulse-based cable insulation temperature measurement method, comprising the following steps:

[0059] Sending an original pulse signal to the cable under test based on a pulse injection device;

[0060] Receiving the reflected pulse signal passing through the cable to be tested by the measuring device;

[0061] The insulation temperature of the cable to be tested is determined based on the expression of the original pulse signal and the reflected pulse signal.

[0062] In a specific embodiment, the specific process of determining the insulation temperature of the cable to be tested includes:

[0063] Determine the signal expression of the cable transmission under test according to the correlation between the original pulse signal, the reflected pulse signal and the signal attenuation coefficient;

[0064] Determine the capacitance expression of the cable to be tested based on the capacitance of the cable to be tested, the signal attenuation coefficient and the correlation of the relative dielectric constant of the cable to be tested;

[0065] Determine the relative dielectric constant expression based on the correlation between the relative dielectric constant and the insulation temperature of the cable to be tested;

[0066] Substitute the relative dielectric constant expression into the capacitance expression to obtain the corresponding calculation result;

[0067] Finally, substitute the calculation result into the signal expression to obtain the final insulation temperature calculation result.

[0068] Specifically, the embodiment of the present invention can use the frequency domain analysis method to establish the original pulse signal U injected into the cable to be tested. in and the reflected pulse signal U reflected from the end of the cable to be tested out The specific expression is:

[0069] U out =U in ·H·e -γl (1)

[0070] In the formula, H represents the refraction and reflection coefficient of the original pulse signal, γ represents the signal attenuation coefficient of the cable to be tested, and l represents the length of the propagation path of the original pulse signal (i.e., the length of the cable to be tested). Among these three variables, H and l are independent of the insulation temperature, while the signal attenuation coefficient γ is related to the insulation temperature. For a given cable to be tested, the original pulse signal U in (which can be the relationship between voltage amplitude and transmission time) and the reflected pulse signal U out There is a delay in the time domain between the measured values ​​(which can be the relationship between the voltage amplitude and the transmission time), and the delay is proportional to the length of the cable to be tested and depends on the wave velocity of the electromagnetic wave in the cable to be tested.

[0071] The wave velocity of the electromagnetic wave in the cable to be tested can be obtained by the signal attenuation coefficient γ, which can be calculated by the distributed resistance R, inductance L, admittance G and capacitance C of the cable to be tested. The specific expression is:

[0072]

[0073] In the formula, α and β represent the attenuation constant and phase constant respectively, ω represents the angular frequency, v represents the wave velocity, and

[0074] Furthermore, the effects of resistance, inductance, conductance, and capacitance on the velocity of electromagnetic waves are considered separately. The specific results are as follows: Figure 3 As shown. Figure 3 It can be seen that capacitance has the greatest correlation with insulation temperature and is directly proportional to it, so the electromagnetic wave velocity is mainly affected by the change in cable capacitance.

[0075] For a single-core coaxial cable, the specific expression of its distributed capacitance per unit length is:

[0076]

[0077] In the formula, ε r represents the relative dielectric constant, ε 0 represents the vacuum dielectric constant, r s and r c They respectively represent the insulation radius and conductor radius of the cable to be tested.

[0078] Solve formula (1)-(3) together:

[0079]

[0080] In the formula, ε r (T), ε r (T 0 ) represent the function with insulation temperature as the independent variable and relative dielectric constant as the dependent variable (which can be the subsequent formula (5)), T 0 Indicates the reference insulation temperature, usually 20 degrees Celsius, T indicates the actual insulation temperature, v 0 Indicates the wave velocity corresponding to the reference insulation temperature.

[0081] At the same time, in order to study the relationship between dielectric constant and insulation temperature, Example 1 of the present invention builds a test platform based on a network analyzer to measure the relative dielectric constant of cross-linked polyethylene at different insulation temperatures. The results are as follows: Figure 4 shown.

[0082] In order to make better use of the test results, the relationship between the relative dielectric constant of the insulating material and the insulation temperature is fitted by the least squares method, and the corresponding expression is:

[0083] ε r =2.053-0.152*atan[0.0707*(T-84.6)]; (5)

[0084] Specifically, the relationship between the relative dielectric constant and the insulation temperature of the material used in the cable to be tested is pre-calibrated. The corresponding transmission speed and transmission time can be determined during the sending and receiving process of the pulse signal. The corresponding resistance R, inductance L, admittance G and capacitance C are determined by the relevant parameters of the cable to be tested (such as length, insulation radius and conductor radius), and the corresponding phase constant is obtained to reversely infer the relationship between the relative dielectric constant and the insulation temperature (i.e., reverse the temperature), and the following can be obtained:

[0085]

[0086] By combining the above formula with the relationship between relative dielectric constant and insulation temperature, the insulation temperature can be obtained. Therefore, according to the above logic, the cable insulation temperature traceability and monitoring based on wave velocity can be realized.

[0087] Example 2

[0088] The specific process of verifying the method provided in Example 1 is as follows:

[0089] The temperature of the cable was measured. The cable length was 24m. During the normal operation of the cable, a pulse injection device and a measuring device were set up. The waveform was measured as follows: Figure 5 shown.

[0090] T 0 Take room temperature 20℃, T 1 Indicates the cable insulation temperature after heating, t 0 represents the time when the pulse is emitted, t 2 It indicates the time when the pulse returns to the first end of the cable at 20℃, t 1 Indicates the time when the pulse returns to the first end of the cable after heating.

[0091] Turn on the pulse injection device and the measurement device, and measure t 2 -t 0 Equal to 6.56*10 -8 s, calculate the wave speed at 20°C, v 0 =1.83*10 8 m / s (Since it is a round trip, the calculation process is v=s / 2t).

[0092] The cable was heated to 60°C and the same pulse was sent again. The measured t 1 -t 0 Equal to 6.49*10 -8 s (since it is a round trip, the calculation process v = s / 2t), calculate the wave speed v after heating 1 =1.85*10 8 m / s.

[0093] According to formula (5), we can get ε r (T 0 )=2.26, according to formula (4) and formula (5), we can get ε r (T 1 )=2.21. According to formula (5), it can be calculated that the insulation temperature of the cable insulation after heating is 60℃, which is consistent with the actual cable insulation temperature, verifying the rationality of this method.

[0094] In this specification, each embodiment is described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the embodiments can be referred to each other. For the device disclosed in the embodiment, since it corresponds to the method disclosed in the embodiment, the description is relatively simple, and the relevant parts can be referred to the method part.

[0095] The above description of the disclosed embodiments enables one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A pulse-based cable insulation temperature measurement device, characterized in that: include: A pulse injection device, used for sending an original pulse signal to the cable to be tested; A measuring device, the measuring device is connected to the pulse injection device, and the measuring device is used to receive a reflected pulse signal passing through the cable to be tested; A processing terminal is connected to the measuring device and the pulse injection device, and is used to calculate according to the original pulse signal and the reflected pulse signal to obtain the insulation temperature of the cable to be measured.

2. A pulse-based cable insulation temperature measurement device according to claim 1, characterized in that: The pulse injection device comprises: A pulse generator, used for generating an original pulse signal; A coupling coil is arranged on the cable to be tested and connected to the pulse generator, and is used to transmit the original pulse signal on the cable to be tested.

3. A pulse-based cable insulation temperature measurement device according to claim 2, characterized in that: The measuring device comprises: A sensor unit, the sensor unit is connected to the coupling coil and is used to receive a reflected pulse passing through the cable to be tested; A signal transmission unit is connected to the sensor unit and is used to transmit the reflected pulse signal.

4. A pulse-based cable insulation temperature measurement device according to claim 3, characterized in that: The processing terminal comprises: A receiving unit, the receiving unit is connected to the signal transmission unit and the pulse generator, and is used to receive the original pulse signal and the reflected pulse signal; A calculation unit, used to determine the insulation temperature of the cable to be tested by determining an expression of the original pulse signal, the reflected pulse signal and a signal attenuation coefficient; A display unit is connected to the receiving unit and the calculating unit, and is used to display the original pulse signal, the reflected pulse signal and the insulation temperature.

5. A pulse-based cable insulation temperature measurement device according to claim 4, characterized in that: The computing unit further comprises: When determining the insulation temperature of the cable to be tested, the calculation unit is also used to determine a capacitance relationship based on the correlation between the capacitance and relative dielectric constant of the cable to be tested, and then substitute the expressions of the relative dielectric constant and insulation temperature of the cable to be tested into the relationship and the expression to obtain the insulation temperature of the cable to be tested.

6. A pulse-based cable insulation temperature measurement method, characterized in that: The following steps are involved: Sending an original pulse signal to the cable under test based on a pulse injection device; Receiving, by a measuring device, a reflected pulse signal passing through the cable to be tested; The insulation temperature of the cable to be tested is determined according to an expression of the original pulse signal and the reflected pulse signal.

7. A pulse-based cable insulation temperature measurement method according to claim 6, characterized in that: The specific process of determining the insulation temperature of the cable to be tested includes: Determine the signal expression of the cable transmission under test according to the correlation between the original pulse signal, the reflected pulse signal and the signal attenuation coefficient; Determine a capacitance expression of the cable to be tested based on the capacitance of the cable to be tested, the signal attenuation coefficient, and a correlation between a relative dielectric constant of the cable to be tested; Determining a relative dielectric constant expression based on the correlation between the relative dielectric constant and the insulation temperature of the cable to be tested; Substituting the relative dielectric constant expression into the capacitance expression to obtain a corresponding calculation result; Finally, the calculation result is substituted into the signal expression to obtain the final insulation temperature calculation result.

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