CN102103173A - Method and system for monitoring current-carrying capacity of cable based on distributed optical fiber temperature measuring method - Google Patents

Abstract

The invention relates to a method and a system for monitoring current-carrying capacity of a cable based on a distributed optical fiber temperature measuring method. The system comprises a laser drive device which is matched with a temperature sensing device in a cable; the temperature sensing device is matched with the corresponding optical fiber splitter; the output end of each optical fiber splitter is connected with one end of the cable; the other end of the cable is connected with a wire distribution cabinet which is matched with demodulating equipment; and the output end of the demodulating equipment is connected with a cable integrated Ethernet chip (IEC) compute server which is output to a client terminal. Combining the distributed optical fiber temperature measuring method, by the method and system provided by the invention, the important parameters of the cable operation can be acquired; the stimulated accuracy is greatly improved through the comprehensive analysis of the current-carrying capacity, thus providing the decision standard for ensuring the safe operation of the city cables and the reasonable configuration of the transmission capacity.

Description

Cable ampacity monitoring method and system based on distributed optical fiber temperature measurement method

technical field

The invention relates to a cable current-carrying capacity monitoring method and system based on a distributed optical fiber temperature measurement method.

Background technique

With the continuous development of industry and power system, the number of high-voltage cable lines in the power grid is increasing day by day, and the intensity of power transmission has been continuously increasing. The smart grid has put forward higher requirements for the power transmission system. , the core temperature reaches the allowable value. Once the cable is overloaded, the temperature of the wire core will rise sharply, which will accelerate the aging of the insulation and even cause thermal breakdown. Therefore, the operating temperature of the cable must be controlled, which requires the power operation department to reasonably dispatch the actual load of the cable. How to improve the power transmission capacity and power transmission efficiency of the cable system on the basis of ensuring the long-term safe and reliable operation of the cable has become a key issue concerned by the power sector.

At present, the calculation of ampacity of cables adopts the internationally recognized IEC standard, but this standard can only meet the calculation of ampacity in simple scenarios and is not suitable for complex scenarios, which has certain limitations; on the other hand, the IEC standard provides The algorithm is suitable for manual calculation, which is too cumbersome. So far, the computerization of IEC has not yet matured and is still in the process of gradual development. At the same time, the selection of parameters for current IEC ampacity calculation is also limited by monitoring conditions. Usually, empirical values or estimated values are used, resulting in inaccurate calculation of ampacity; operating temperature is an important parameter of cables. During the selection and laying stages of power cables, Since it is impossible to fully consider the actual operating environment, it is usually based on the standard ambient temperature, which will cause the cable to run in an overheated state when the ambient temperature is high or the heat dissipation condition is poor, reducing the operating life. Therefore, if the load of the cable can be dispatched and adjusted in real time according to the actual operating state and operating environment, it will not only ensure the safe operation of the cable and fully exert its load carrying capacity, but also solve the problem of power dispatching in some cases. Power supply problems in emergencies.

Contents of the invention

In order to make up for the deficiencies in the prior art, the present invention provides a method and system for monitoring cable ampacity based on a distributed optical fiber temperature measurement method.

To achieve the above object, the present invention adopts the following technical solutions:

The cable ampacity monitoring system based on the distributed optical fiber temperature measurement method includes a laser drive device, which cooperates with the temperature sensing device in the cable; the temperature sensing device cooperates with the corresponding optical fiber splitter, and each optical fiber splitter The output end of the device is connected to one end of the optical cable, and the other end of the optical cable is connected to the distribution box, which is matched with the demodulation device, and the output end of the demodulation device is connected to the cable IEC calculation server, and the cable IEC calculation server outputs to the client terminal.

The laser driving device includes a laser driver, the output end of the laser driver is connected to the input end of the laser.

The temperature sensing device is a distributed temperature measuring optical fiber.

The demodulation device is an optical fiber signal demodulator.

The optical cable is an all-dielectric self-supporting optical cable.

According to the cable ampacity monitoring method based on the distributed optical fiber temperature measurement method, the monitoring method includes the following steps:

Step1: The pulsed light emitted by the laser is injected into the distributed temperature measurement fiber, and the backscattered light generated by the temperature measurement fiber is input to the optical cable through the fiber splitter;

Step2: After the optical cable is transmitted, the optical signal is finally input to the optical fiber signal demodulator, and the optical fiber signal demodulator inputs the demodulated signal to the cable IEC computing server;

Step3: The cable IEC calculation server analyzes the conductor temperature θc and the cable surface temperature θa of a certain section of cable according to the input optical signal, and calculates the dynamic ampacity I of the cable according to the calculation formula provided by IEC 60287 for calculating the cable ampacity under 100% load factor

$\mathrm{<span\; class="notranslate">\; I</span>}<span\; class="notranslate">\; =</span>\sqrt{\frac{{\mathrm{<span\; class="notranslate">\; \&theta;</span>}}_{\mathrm{<span\; class="notranslate">\; c</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; \&theta;</span>}}_{\mathrm{<span\; class="notranslate">\; a</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; W</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}}<span\; class="notranslate">\; [</span>\mathrm{<span\; class="notranslate">\; 0.5</span>}{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="1"\; label="T"\; filenames="HDA0000043717350000012.png"\; state="\{\{state\}\}">T</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="3"\; label="T"\; filenames="HDA0000043717350000012.png"\; state="\{\{state\}\}">T</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; 4</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; ]</span>}{{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="1"\; label="RT"\; filenames="HDA0000043717350000012.png"\; state="\{\{state\}\}">RT</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; nR</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; )</span>{\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; nR</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="3"\; label="T"\; filenames="HDA0000043717350000012.png"\; state="\{\{state\}\}">T</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; 4</span>}}<span\; class="notranslate">\; )</span>}}$

Among them, the conductor temperature θc is the real-time value of the temperature measurement system, and the corresponding conductor AC resistance R is the value corresponding to θc; θa is the surface temperature of the cable, and the real-time value of the temperature measurement system is taken; Wd is the dielectric loss of the insulation; λ1 is the metal sheath Loss coefficient; λ2 is the loss coefficient of the armor layer; T1, T2, and T3 are the thermal resistances of the insulation, inner liner, and outer sheath respectively, and T4 is the thermal resistance of the cable and the surrounding medium, which is related to the cable model and construction method ; n is the number of cable loops; I is the ampacity of the cable under the current working condition;

Step4: Obtain the dynamic ampacity of the cable according to the dynamic ampacity of each section of cable obtained in step3;

Step5: The client server calculates the dynamic ampacity of all cables output by the server according to the cable IEC, and realizes various daily operations.

In the step3, the AC resistance of a certain cable conductor R=R ₀ ×[1+α ₂₀ (θ _C -20)]×(1+Y _s +Y _p ); wherein, R0 and α ₂₀ are fixed values, Depending on the type of conductor, skin effect factor Y _s and proximity effect factor Y _p refer to IEC60287 and JB/T 101 81 series standards.

In the step3, the dielectric loss Wd of the insulation is provided by the IEC computing server database as a parameter, calculated according to the length of a certain cable, and the dielectric loss per unit length of the cable can be calculated by the following formula:

W _d ＝ωCU ₀ ² tgδ×10 ^-6

In the formula, ω=2πf, f is the power frequency, 50Hz; C is the cable capacitance per unit length, the unit is μF/cm; tgδ is the dielectric loss tangent of the insulating material; E0 is the ground voltage, the unit is V.

In the step4, the dynamic ampacity of a certain cable is the minimum value of the dynamic ampacity of each section of the cable in the cable.

Beneficial effects: the present invention can accurately monitor the operating temperature of the cable, and can obtain 100% load factor ampacity information according to temperature monitoring, which reduces the error of the cable ampacity compared with the traditional estimated cable temperature, and through the comprehensive analysis of the ampacity, Evaluate the operation status of the cable, and then provide a scientific basis for rationally adjusting the rated current carrying capacity, and at the same time summarize the causes of various cable faults and various abnormal conditions before the fault, thereby providing theoretical and factual evidence for cable fault prediction , greatly improving the accuracy of the simulation, and providing a decision-making basis for ensuring the safe operation of urban cables and rationally allocating transmission capacity.

Description of drawings

Figure 1 is a block diagram of a distributed optical fiber temperature sensor system;

Fig. 2 is a structural schematic block diagram of the present invention;

Figure 3 is a flow chart of cable dynamic ampacity monitoring;

Among them, 1 temperature sensing device, 2 fiber optic splitter, 3 fiber optic cable, 4 distribution box, 5 fiber optic signal demodulator, 6 cable IEC computing server, 7 client server, 8 laser driver, 9 laser, 10 bidirectional coupler , 11 wavelength division multiplexer, 12 photoelectric detector APD, 13 amplifier, 14 acquisition average accumulator, 15 microcomputer.

Detailed ways

Below in conjunction with accompanying drawing and embodiment the present invention will be further described:

As shown in Figure 1, it is a distributed optical fiber temperature sensor system, mainly including sensing optical fiber, laser 9 and laser driver 8, bidirectional coupler 10, wavelength division multiplexer 11, photoelectric detector APD 12, amplifier 13, acquisition average The accumulator 14 and the microcomputer 15 are composed. The pulsed light emitted by the laser 9 is used as the pumping light and injected into the sensing fiber through the coupler. When the pulsed light propagates forward in the sensing fiber, backscattered light is generated. Backscattered light filters out anti-Stokes light and Rayleigh light through optical filtering. Stokes scattering and anti-Stokes scattering are collectively referred to as Raman scattering, and then through photoelectric conversion and amplification circuits, the amplified signal is The high-speed data acquisition card collects, after data processing and calibration, the temperature is demodulated. Distributed optical fiber temperature measurement system has the following advantages:

(1) Optical fiber senses temperature and location information, the sensor is passive and intrinsically safe. The sensor has high resolution, accurate temperature measurement and short response time.

(2) It can be made into a large-capacity, multi-point, distributed temperature measurement system; one demodulator can carry hundreds of sensors; cost savings.

(3) Due to the all-optical signal transmission, it is not limited by the sensor distance, and the maximum sensing distance is up to 10km. It is an ultra-remote temperature detection system.

This system combines distributed optical fiber temperature measurement technology to further improve the intelligence of the system. The operating condition of the cable and the crimping quality can only be found during operation. The longer the operation time, the more prone to overheating and burn-through accidents, which may cause huge economic losses. Distributed optical fiber temperature measurement technology is designed for the early prediction of cable faults due to insulation aging or poor contact. Understand the operation of the cable, and deal with possible failures in advance and in a timely manner.

Utilize the temperature measurement principle of the distributed optical fiber temperature sensor system in the cable current carrying capacity monitoring system, as shown in Figure 2, it is a functional block diagram of the present invention, which includes a laser drive device, which is in phase with the temperature sensing device 1 in the cable Coordination; the temperature sensing device 1 is matched with the corresponding optical fiber splitter 2, the output end of each optical fiber splitter 2 is connected to one end of the optical cable 3, the other end of the optical cable 3 is connected to the wiring box 4, and the wiring box 4 is connected to the demodulator The devices are matched, the output end of the demodulation device is connected to the cable IEC calculation server 6, and the cable IEC calculation server 6 outputs to the client terminal 7.

The laser driving device includes a laser driver 8 , the output end of the laser driver 8 is connected to the input end of the laser 9 .

The temperature sensing device 1 is a distributed temperature measuring optical fiber.

The demodulation device is an optical fiber signal demodulator 5 .

The optical cable is an all-dielectric self-supporting ADSS optical cable (All-dielectric Self-supporting Optical Cable).

Distributed temperature measurement optical fiber is the temperature sensing device 1 of the system, which is directly installed inside the cable to measure the temperature of each point of the cable; it can measure the temperature of space points within several kilometers in real time, and different temperatures reflect different optical wavelength signals , with the help of Raman scattering technology to achieve distributed measurement.

Optical fiber splitter 2 mainly uses one optical fiber to connect multiple sensors to realize distributed deployment of sensors;

The optical cable 3 is a signal transmission channel, which can be built into the cable and uses an ADSS optical cable for electric power, which has strong high-voltage resistance and extrusion resistance;

The function of the optical fiber signal demodulator 5 is to filter, amplify and demodulate the optical signal, and it is installed in the monitoring room;

The cable IEC calculation server 6 collects the information transmitted by the optical fiber signal demodulator 5, processes and calibrates the data according to the collected information, and displays the temperature data of each temperature measurement point in real time. Carry out ampacity calculation and cable operation analysis dynamically with the data.

The client server 7 realizes various daily operations according to the analysis data and results submitted by the cable dynamic ampacity calculation module.

The calculation process of the dynamic ampacity performed by the cable IEC calculation server 6 is described by taking a cable as an example. As shown in Figure 3, the cable is divided into k sections, and the distributed temperature measurement optical fiber signal of the i section is used to measure the temperature of the conductor and the surface layer of the cable in the i section. The optical signal is input to the optical cable through the optical fiber splitter, and after transmission Input to the optical fiber signal demodulator, the optical fiber signal demodulator will demodulate the optical signal and input it to the cable IEC calculation server, the cable IEC calculation server will analyze the temperature signal, and obtain the temperature θc of the conductor in the i-th cable and the surface layer of the cable The temperature θa.

In addition, there are various cable parameters in the IEC calculation server database, including: cable core type, insulation layer, metal shielding layer and armor layer, laying method, etc., and have different loss coefficients corresponding to different materials or laying methods; The temperature θc of the medium conductor can be calculated by using the formula R=R ₀ ×[1+α ₂₀ (θ _C -20)]×(1+Y _s +Y _p ) to calculate the AC resistance R of the cable conductor, where R0 And α ₂₀ is a fixed value, which varies according to the type of conductor. The calculation formulas of skin effect factor Y _s and proximity effect factor Y _p refer to IEC60287 and JB/T 101 81 series standards.

The insulation dielectric loss Wd of the i-section of the cable is provided by the IEC calculation server database. It is calculated according to the length of the i-section cable. The cable dielectric loss per unit length (cm) can be calculated by the following formula:

W _d =ωCU ₀ ² tgδ×10 ^-6 (1)

In the formula, ω=2πf, f is the power frequency, 50Hz; C is the cable capacitance per unit length, the unit is μF/cm; tgδ is the dielectric loss tangent of the insulating material; E0 is the ground voltage, the unit is V.

The loss Ws in the cable metal sheath is proportional to the square of the current I' in the core, so the ratio between it and the core loss Wc is approximately constant, namely:

Ws＝λ1·Wc (2)

In the formula, λ1 is the loss coefficient of the metal sheath, which is a function of the resistance of the metal sheath. The formula is different according to different line types and laying methods, and the sheath resistance is calculated according to the real-time measured temperature. Wc=I' ² R, is the core loss of the conductor, and I' is the current in the core.

The cable armor loss is a function of the cross-sectional area of the armor and the metal resistance. Different armor materials and methods have different formulas. Generally, it is calculated by the loss coefficient of the cable armor. Take the three-core circular conductor steel wire armor as an example:

${\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1.23</span>}\frac{{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; A</span>}}}{\mathrm{<span\; class="notranslate">\; R</span>}}{<span\; class="notranslate">\; (</span>\frac{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; l</span>}}{{\mathrm{<span\; class="notranslate">\; d</span>}}_{\mathrm{<span\; class="notranslate">\; A</span>}}}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{{<span\; class="notranslate">\; (</span>\frac{\mathrm{<span\; class="notranslate">\; 2.77</span>}{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="10"\; label="R\; A"\; filenames="HDA0000043717350000011.png,HDA0000043717350000012.png"\; state="\{\{state\}\}">R</figure-callout></span><figure-callout\; id="10"\; label="R\; A"\; filenames="HDA0000043717350000011.png,HDA0000043717350000012.png"\; state="\{\{state\}\}">\; </figure-callout>}}_{\mathrm{<span\; class="notranslate">\; </span>}}{\mathrm{<span\; class="notranslate">\; 10</span>}}^{\mathrm{<span\; class="notranslate">\; 6</span>}}}{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 3</span>}<span\; class="notranslate">\; )</span>$

In the formula, R _A is the AC resistance of the armor at the measured working temperature, in OHM/m; d _A is the average diameter of the armor; l is the distance between the conductor axis and the cable center, mm.

Calculate the dynamic ampacity of the cable according to the basic algorithm for calculating the ampacity of the cable under 100% load factor provided by IEC 60287, and calculate according to the formula (4):

${\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; =</span>\sqrt{\frac{{\mathrm{<span\; class="notranslate">\; \&theta;</span>}}_{\mathrm{<span\; class="notranslate">\; c</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; \&theta;</span>}}_{\mathrm{<span\; class="notranslate">\; a</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; W</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}}<span\; class="notranslate">\; [</span>\mathrm{<span\; class="notranslate">\; 0.5</span>}{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="1"\; label="T"\; filenames="HDA0000043717350000012.png"\; state="\{\{state\}\}">T</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="3"\; label="T"\; filenames="HDA0000043717350000012.png"\; state="\{\{state\}\}">T</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; 4</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; ]</span>}{{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="1"\; label="RT"\; filenames="HDA0000043717350000012.png"\; state="\{\{state\}\}">RT</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; nR</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; )</span>{\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; nR</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="3"\; label="T"\; filenames="HDA0000043717350000012.png"\; state="\{\{state\}\}">T</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; 4</span>}}<span\; class="notranslate">\; )</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 4</span>}<span\; class="notranslate">\; )</span>$

When calculating, the conductor temperature θc in the formula takes the real-time measured value of the temperature measurement system, and the corresponding conductor AC resistance R takes the value corresponding to this temperature. If θc takes the conductor temperature, it is the maximum operating temperature that XLPE (main insulation) can withstand 90 ℃, the corresponding conductor AC resistance corresponds to the value at 90 ℃, and the continuous allowable current carrying capacity of the cable can be calculated; θa is the surface temperature of the cable, which is the real-time measurement value of the temperature measurement system; Wd is the dielectric loss of the insulation; λ1 is the loss coefficient of the metal sheath , use the formula (2) to get, λ2 is the loss coefficient of the armor layer; T1, T2, T3 are the thermal resistance of the insulation, the inner lining layer, and the outer sheath respectively; T4 is the thermal resistance of the cable and the surrounding medium, and the cable It is related to the model and construction method; n is the number of cable loops; I _i is the cable ampacity of the i-th section under the current working condition.

Because the temperature of the conductor and the metal sheath of the cable at different positions is often different in practice, resulting in different resistivity and loss, which in turn causes the temperature of the conductor and the metal sheath of the cable to be different, so the dynamic current carrying capacity of the cable at different positions will also be different. This algorithm divides the cable into k sections according to each temperature measuring point, and each section of cable i calculates the dynamic ampacity I _i one by one according to the actual temperature measured at the temperature measuring point according to the formula (4), so the overall dynamic ampacity I of the cable is :

I=min{I ₁ , I ₂ , . . . , I _i , I _k } (5).

Claims (9)

1. based on the current-carrying capacity of cable monitoring system of distributed optical fiber temperature measurement method, it is characterized in that it comprises laser driving apparatus, laser driving apparatus matches with temperature sensing device in the cable; Temperature sensing device matches with corresponding optical fiber splitter, the output terminal of each optical fiber splitter is connected with optical cable one end, the optical cable other end is connected with distributing cabinet, distributing cabinet matches with demodulating equipment, the demodulating equipment output terminal is connected with cable I EC calculation server, and cable I EC calculation server outputs to client terminal.

2. the current-carrying capacity of cable monitoring system based on the distributed optical fiber temperature measurement method as claimed in claim 1 is characterized in that described laser driving apparatus comprises laser driver, and the output terminal of laser driver is connected with the input end of laser instrument.

3. the current-carrying capacity of cable monitoring system based on the distributed optical fiber temperature measurement method as claimed in claim 1 is characterized in that described temperature sensing device is a distributed temperature measuring optical fiber.

4. the current-carrying capacity of cable monitoring system based on the distributed optical fiber temperature measurement method as claimed in claim 1 is characterized in that described demodulating equipment is the fiber-optic signal (FBG) demodulator.

5. the current-carrying capacity of cable monitoring system based on the distributed optical fiber temperature measurement method as claimed in claim 1 is characterized in that described optical cable is an All Dielectric self-support.

6. the current-carrying capacity of cable monitoring method based on the distributed optical fiber temperature measurement method as claimed in claim 1 is characterized in that this monitoring method comprises the steps:

Step1: laser instrument sends pulsed light and injects distributed temperature measuring optical fiber, and the rear orientation light that thermometric optical fiber produces is input to optical cable by optical fiber splitter;

Step2: light signal is input to the fiber-optic signal (FBG) demodulator the most at last after the optical cable transmission, and the fiber-optic signal (FBG) demodulator is input to cable I EC calculation server with restituted signal;

Step3: cable I EC calculation server parses the conductor temperature θ c and the cable surface temperature θ a of certain section cable according to the light signal of input, and the computing formula of the current-carrying capacity of cable under calculating 100% load-factor that provides by IEC 60287 is calculated cable dynamic current-carrying capacity I

$I=\sqrt{\frac{{\mathrm{\&theta;}}_c-{\mathrm{\&theta;}}_a-W_d[0.5T_1+n(T_2+T_3+T_4)]}{{\mathrm{RT}}_1+\mathrm{nR}(1+{\mathrm{\&lambda;}}_1)T_2+\mathrm{nR}(1+{\mathrm{\&lambda;}}_1+{\mathrm{\&lambda;}}_2)(T_3+T_4)}}$

Wherein, conductor temperature θ c gets the temp measuring system instantaneous value, the value when corresponding conductor AC resistance R gets corresponding to θ c; θ a is the cable surface temperature, gets the temp measuring system instantaneous value; Wd is an insulation dielectric loss; Going into 1 is the protective metal shell loss factor; Go into 2 for the loss factor of armor; T1, T2, T3 are respectively the thermal resistance of insulation, interior pad underlayer, outer jacket, and T4 is the cable and the thermal resistance of medium on every side, and be relevant with cable model, form of construction work; N is the cable loop number; I is a current-carrying capacity of cable under the current working;

Step4: every section cable dynamic current-carrying capacity of trying to achieve according to step3 obtains the dynamic current-carrying capacity of this root cable;

Step5: the customer service end is realized various day-to-day operation work according to the dynamic current-carrying capacity of all cables of cable I EC calculation server output.

7. the current-carrying capacity of cable monitoring method based on the distributed optical fiber temperature measurement method as claimed in claim 6 is characterized in that, among the described step3, and the AC resistance R=R of certain section cable conductor ₀* [1+ α ₂₀(θ _C-20)] * (1+Y _s+ Y _p); Wherein, R0 and α ₂₀Be definite value, different according to types of conductors, kelvin effect factor Y _s, proximity effect factor Y _pReferring to IEC60287 and JB/T 101 81 series standards.

8. the current-carrying capacity of cable monitoring method based on the distributed optical fiber temperature measurement method as claimed in claim 6, it is characterized in that, among the described step3, insulation dielectric loss Wd provides parameter by IEC calculation server database, calculate according to certain section cable length, the loss of unit length cable dielectric can be calculated with following formula:

W _d＝ωCU ₀ ²tgδ×10 ^-6

In the formula, ω=2 π f, f is a power frequency, 50Hz; C is the unit length electric cable capacitance, the μ F/cm of unit; Tg δ is the insulating material dielectric loss angle tangent; E0 is a voltage-to-ground, the V of unit.

9. the current-carrying capacity of cable monitoring method based on the distributed optical fiber temperature measurement method as claimed in claim 6 is characterized in that, among the described step4, the dynamic current-carrying capacity of certain root cable is got the minimum value of each section cable dynamic current-carrying capacity in this root cable.

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