WO2014161476A1

WO2014161476A1 - Analysis system and calculation method of current-carrying capacity of cable based on linear temperature-sensing technology

Info

Publication number: WO2014161476A1
Application number: PCT/CN2014/074550
Authority: WO
Inventors: 王慧明; 赵立刚; 刘国平; 赵平; 曾军; 吴仁虎; 邢昆; 徐亚兵; 郭涛; 武彦明; 成洪刚
Original assignee: 国家电网公司; 国网河北省电力公司; 国网河北省电力公司石家庄供电分公司
Priority date: 2013-04-02
Filing date: 2014-04-01
Publication date: 2014-10-09
Also published as: CN103226172A

Abstract

Provided are an analysis system and a calculation method of the current-carrying capacity of a cable based on linear temperature-sensing technology. The system comprises a server and, connected to the server, a distributed linear temperature-sensing system and cable load detection apparatus. The distributed linear temperature-sensing system consists of a temperature-sensing optical cable laid on the cable to be measured and, connected to the temperature-sensing optical cable, a tunable wavelength laser and light-intensity detector. The method increases the dynamic time variable when the cable is in operation to establish the dynamic correlation between the electrical current capacity, sheath surface temperature, ambient temperature, and heat radiation of the cable, and calculates therefrom the cable conductor temperature. The present system and method provide a basis for decision-making to ensure the safe operation of city cables and the rational allocation of electrical transmission capacity, and a scientific basis for scientific load scheduling.

Description

Cable current carrying capacity analysis system and calculation method based on linear temperature sensing technology

[0001] The present invention relates to a cable current carrying capacity analysis system and a calculation method based on a line type temperature sensing technology. Background technique

[0002] With the development of the country and the accompanying transformation and implementation of the power grid, especially the transformation and construction of the city network, the use of power cables has increased significantly, and the underground cable rate in urban centers has been increasing, which has led to electricity. The operation management, analysis and maintenance work of the cable has become more and more important, and the workload has been increasing.

[0003] The conductor temperature during cable operation is the basis for determining that the cable meets the rated current capacity and is safe to operate. When the cable is running under rated load, the core temperature is at an allowable value. Once the cable is over-loaded, the core temperature will rise sharply, accelerating insulation aging, and even thermal breakdown. For example, the study found that when the operating temperature of a cross-linked polyethylene (XLPE) cable exceeds 8% of the allowable value, its life will be halved; if it exceeds 15%, the cable life will only be saved by 1/4. Therefore, the operating temperature of the cable must be controlled. However, such long-distance, linear heating elements such as cables, temperature sensing technology such as conventional thermocouples cannot completely measure the temperature field distribution along the line. Therefore, linear temperature sensing technology is needed as a temperature monitoring method.

[0004] In addition, due to the particularity of cable operation, only the outer sheath temperature data of the cable or the insulation shield temperature data can be measured at present, and the conductor temperature data of the cable cannot be directly measured. The usual practice is: Estimate the cable conductor temperature by empirical data or temperature correspondence under steady-state current carrying, and the exact real-time conductor temperature of the cable cannot be accurately calculated. However, under the actual operating conditions of the cable line, especially in the urban central power grid, the aging characteristics of the daily load operation curve are quite different from the steady state. At the same time, the phased and seasonal changes in the load were not considered. Therefore, the direct use of steady-state current carrying capacity as a limiting indicator of cable line operation management is somewhat limited.

Summary of the invention

[0005] The technical problem to be solved by the present invention is to provide a cable current carrying capacity analysis system based on a line type temperature sensing technology without blind spots, lossless cable transmission, and high safety factor.

[0006] The present invention adopts the following technical solutions:

The invention comprises a server and a distributed line temperature sensing system and a cable load detecting device connected to the server, wherein the distributed line temperature sensing system comprises a temperature sensing cable laid on the cable to be tested and a wavelength connected to the temperature sensing cable. A tunable laser and a light intensity detector. [0007] The cable load detecting device is a distributed distributed line temperature sensing system, and its model is WUTOS-DTS-4004.

[0008] The temperature sensing cable is a fiber optic temperature sensing cable, and its model is DTS-3.3-62.5/125-2Al.

[0009] The model of the laser is LDM5S514.

[0010] The calculation method of the cable current carrying capacity analysis system based on the line type temperature sensing technology is characterized in that the calculation method is as follows:

First, enter the value

I: the current flowing through a conductor, the unit of which is A;

Δ 6: temperature rise of the conductor above ambient temperature, the unit is K;

R: AC resistance per unit length of the conductor at the highest working temperature, the unit is Ω / m;

R' : DC resistance per unit length of the conductor at the highest operating temperature. C ; Ω /m;

Wd: dielectric loss per unit length of conductor insulation, in units of W/m;

T1 : thermal resistance per unit length between a conductor and a metal sleeve, the unit of which is K*m/W;

T2: thermal resistance per unit length of the inner liner between the metal sleeve and the armor, the unit is K*m/W;

T3: The thermal resistance per unit length of the outer sheath of the cable, the unit is K*m/W;

T4: thermal resistance per unit length between the surface of the cable and the surrounding medium, the unit is K*m/W;

n: the number of conductors carrying the load in the cable;

λ ΐ : ratio of cable sheath loss to total conductor loss;

λ 2: ratio of cable armor loss to total conductor loss;

σ : the absorption coefficient of sunlight on the surface of the cable;

Η: solar radiation intensity, take 1000W/m2 or local recommended value, the unit is W/m2;

T*4: Considering the external thermal resistance of the cable during daylight exposure, the unit is K*m/W;

D*e: cable outer diameter, m, for corrugated metal sleeve D*e = (d°-+2t3) *10-3;

T3: thickness of the outer sheath, the unit is mm;

D- : the diameter of the imaginary concentric cylinder that is tangent to the corrugated metal sleeve crest, the unit

Mm.

[0011] υ : ratio of thermal resistance coefficient of dry and moist soil domains, u = P d / P w _;

d: thermal resistance coefficient of dry soil, its unit K*m/W;

P w: thermal resistance coefficient of natural soil, its unit K*m/W; Χχ: The critical temperature of the soil, ie the temperature at the boundary between the dry and moist soil, in units. C;

Θ0: Ambient temperature, its unit. C;

Δ θ _χ: critical temperature rise of the soil, that is, the temperature rise of the boundary between the dry and wet soil above the ambient temperature Θ _Θ -Θ0 The resistance of the core at the time, the unit is Q / _m .

[0012] The resistance of the core at time is in units of Ω/ιη.

[0013] 3⁄4: The maximum allowable operating temperature of the core during continuous load, in units. C; The maximum allowable operating temperature of the core during overload operation, in units. C;

Overload running time, its unit s;

R-. cable time constant;

J : cable rated current capacity, its unit A;

1 Enter the calculation formula for each case:

1.1 AC cables that are not exposed to sunlight in the air; the soil is protected from direct-buried AC cables in the case of localized drying. The pipeline is laid in the soil as shown in the formula:

1.3 a3 shows:

1 The DC cable is as shown in Equation a4:

1.5 DC cable of 5KV and below when directly exposed to sunlight in air is as shown in formula a5:

DC cables of 1 V and below are shown in Equation a6:

1.7 The DC cable of 5KV and below in the case of avoiding soil drying is shown in formula a7: . J― ·····;·-. ( _a 7)

1.8 air low voltage wire and cable as shown in the formula a8: > —, w ' , , ( ₈ )

'— ― Έξ ; ';匪: ― ^a

The distributed line temperature system will report the demodulated data to the server through the communication port, and the server receives and parses the message to obtain the surface temperature, and cooperates with the relevant parameters and formulas already stored in the database, and the server selects the specific according to the actual situation. The formula calculates the cable core temperature of each segment, and based on these temperatures, calculates the temperature of the cable conductor of the entire cable core conductor under the application of the current value.

[0014] The positive effects of the present invention are as follows:

The invention establishes the dynamic correspondence between the cable current amount, the cable outer surface temperature, the cable ambient temperature and the cable self-heat dissipation during the operation of the cable, and estimates the cable conductor temperature, so that the dynamic measurement manner can be non-destructive. Cable transmission, distributed cable monitoring without blind spots. This way of dynamic measurement enables lossless cable transmission and distributed blind cable monitoring. At the same time, the actual load rate of the cable line is calculated, the early hidden danger of the cable is discovered early, and the non-contact online diagnosis of the cable core temperature is realized, and the operation level of the power grid is comprehensively improved. At the same time, using the historical data of the system and various real-time parameters to analyze the cable faults, predict the dangerous points and estimate the maximum current capacity that the cable can actually withstand, in order to ensure the safe operation of the cable and the reasonable allocation of transmission capacity. The basis for decision-making, providing a scientific basis for the scientific dispatch of the load, is of great significance.

DRAWINGS

1 is a schematic block diagram of the present invention.

2 is a schematic structural view of a distributed line temperature sensing system according to the present invention. 3 is a working flow chart of the present invention.

detailed description

[0018] As shown in FIG. 1-2, the present invention includes a server 1, a distributed line temperature sensing system 2, and a cable load detecting device 3, and the distributed line temperature sensing system 2 has a feeling of being laid on the cable to be tested. The warm cable 5 and the wavelength tunable laser 4 and the light intensity detector 6 connected to the temperature sensing cable 5 are composed. The invention continuously lays the fiber grating temperature sensing cable along the outer wall of the cable. The wavelength tunable laser 4 is outputted by the light intensity detector 6 after being reflected by the fiber grating temperature sensing cable. When the wavelength of the wavelength tunable laser 4 coincides with the wavelength of the fiber grating temperature sensing cable, the reflection intensity is maximum at this time, and the light intensity detector 6 receives the strongest power. According to the correspondence between the wavelength of the tunable laser and the detector power, the wavelength information of the sensing grating can be detected. From the fiber grating temperature sensitivity coefficient, the temperature field distribution along the fiber grating temperature sensing cable can be obtained.

As shown in FIG. 3, the server 1 of the present invention analyzes the protocol to obtain the cable surface temperature, and performs a dynamic current carrying capacity calculation process according to various parameters stored in the database. At the same time, the server 1 obtains the real-time current value of the cable from the cable load monitoring device 3. This resulted in a complete online monitoring system for fiber-optic distributed cable current carrying capacity.

[0020] The calculation function and the number of calculation objects determine the time taken for the calculation process. The calculation objects include the following:

Laying method: In the air (whether directly exposed to sunshine), in the air duct, in the soil, in the soil pipeline.

[0021] Arrangement: Single circuit one includes three cables which are arranged in a triangle or plane (side by side and separated).

[0022] Multiple loops are laid in multiple loops of a group of cable groups on the basis of a single loop arrangement.

[0023] Working state: including continuous load, emergency load, short circuit current.

[0024] Input parameters: rated voltage, conductor material, cable type, conductor cross section, geometric size of cable parts, cable outer diameter, etc.

[0025] Environmental parameters: laying, arranging, soil thermal resistance coefficient, buried depth, grounding mode, ambient temperature.

[0026] The calculation formula of each case is:

1. AC cable that is not exposed to sunlight in the air; the soil avoids direct buried AC cables in local dry conditions; the pipeline is laid with AC cables in the soil ,

cable

4. 5KV and below DC cables that are not exposed to sunlight in the air ' ; + ' Ϊ )3⁄4

; 5KV and below DC cable when exposed to sunlight directly in the air

6. DC cable of 5KV and below in the case of local drying in the soil 3⁄4 1; «1 DC cable of 5KV and below in the case of avoiding soil drying

8. Air low voltage wire and cable

The meaning of each quantity in the formula:

I: current flowing through a conductor, Α;

Δ Θ: temperature rise of the conductor above ambient temperature, Κ;

Note: Ambient temperature refers to the temperature of the surrounding medium when the cable is laid. When there is any local heat source around the cable, the heat does not directly increase the temperature around the cable.

[0027] R: alternating current resistance per unit length of the conductor at the highest operating temperature, Ω / m; R' : DC resistance per unit length of the conductor at the highest operating temperature, Ω/m;

Wd: dielectric loss per unit length of conductor insulation, W/m;

T1: thermal resistance per unit length between a conductor and a metal sleeve, K*m/W;

T2: thermal resistance per unit length of inner liner between metal sleeve and armor, K*m/W;

T3: thermal resistance per unit length of cable outer sheath, K*m/W;

T4: thermal resistance per unit length between the surface of the cable and the surrounding medium, K*m/W;

n: the number of conductors carrying the load in the cable (conductors of equal section and having the same load);

Ϊ́ΐ: the ratio of the loss of the cable sheath to the total loss of all conductors;

Λ2: ratio of cable armor loss to total conductor loss;

σ : the absorption coefficient of sunlight on the surface of the cable;

Η: Solar radiation intensity, for most latitudes, 1000W/m2, or local recommended value, W/m2;

T*4: Consider the external thermal resistance of the cable when exposed to sunlight, K*m/W;

D*e: cable outer diameter, m, for corrugated metal sleeve D*e = (d°^+2t3)*10-3;

T3: thickness of the outer sheath, mm;

D-: diameter of the imaginary concentric cylinder that is tangent to the corrugated metal sleeve crest, mm.

[0028] υ _: ratio of thermal resistance coefficient of dry and moist soil domains, u = P d / Pw _;

d: thermal resistance coefficient of dry soil, K*m/W;

P w: thermal resistance coefficient of natural soil, K*m/W;

Χχ: the critical temperature of the soil, ie the temperature at the boundary between the dry and moist soil, °C;

Θ0: ambient temperature, °C;

Δ θ _χ: critical temperature rise of the soil, ie the temperature rise of the boundary between the dry and wet soil above ambient temperature _Χ -Θ0 The calculation results show that the parameters include the following:

The cable is in steady state operation with an AC resistance, inductance, capacitance, shielding loss, thermal resistance and allowable current.

[0029] Cable short-circuit fault - conductor and shield short-circuit current, electromagnetic force, etc.

[0030] Short-duration load A current value is applied at an allowable operating temperature and a given time under a cable under full load operating condition.

[0031] wherein the current calculation formula is:

The resistance of the core at the time The resistance of the core at the time 3⁄4: The maximum allowable operating temperature of the core during continuous load The maximum allowable operating temperature of the core during overload operation

Overload running time

3⁄4": cable time constant

Cable rated current

Through the above parameters, the server 1 will perform dynamic calculation of the current carrying capacity. The program flow box is shown in Figure 3.

[0032] First, the fiber optic temperature sensing cable is directly mounted on the outside of the cable to measure the surface temperature of each segment of the cable.

[0033] Next, the distributed line temperature sensing system reports the demodulated data to the server through the communication port, and the server receives and parses the message to obtain the surface temperature. In addition to the cable parameters, laying parameters and environmental parameters already stored in the database, the server will calculate the cable core temperature according to the specific formula, and calculate the cable of the entire cable core conductor under the applied current value according to these temperatures. Conductor temperature.

[0034] Finally, the server 1 communicates with the server through the Ethernet port, obtains the core temperature and the overall core temperature of each segment of the cable, and displays the temperature data in a certain manner. When the core temperature exceeds the set temperature, The client will issue an alarm message.

[0035] The invention increases the dynamic time variable during the operation of the cable to establish a dynamic correspondence between the cable current amount, the surface temperature of the cable outer sheath, the ambient temperature of the cable and the heat dissipation of the cable itself, and estimates the temperature of the cable conductor, so that the dynamic measurement method Can be used for lossless cable transmission, distributed blind cable analysis. Compared with the traditional method, it is of great significance to evaluate the safety status of the cable more effectively and provide scientific basis for the scientific dispatch of the load.

Claims

Claim

A cable current carrying analysis system based on line type temperature sensing technology, characterized in that it comprises a server (1) and a distributed line temperature sensing system (2) connected to the server (1) and a cable load detecting device ( 3), the distributed line temperature sensing system (2) consists of a temperature sensing cable (5) laid on the cable under test and a wavelength tunable laser (4) connected to the temperature sensing cable (5) and light intensity detection (6) composition.

2. The cable current carrying capacity analysis system based on the line type temperature sensing technology according to claim 1, wherein the cable load detecting device (3) is a distributed distributed line temperature sensing system, and the model number is WUTOS-DTS. -4004.

3. The cable current carrying analysis system based on linear temperature sensing technology according to claim 1, wherein the temperature sensing cable (5) is a fiber optic temperature sensing cable, and the model number is DTS-3.3-62.5/125- 2Al.

The cable current carrying capacity analysis system based on the linear temperature sensing technology according to claim 1 or 2, wherein the laser (4) is of the type LDM5S514.

5. A method for calculating a cable current carrying capacity analysis system based on linear temperature sensing technology, characterized in that the calculation method is as follows:

First, enter the value

I: the current flowing through a conductor, the unit of which is A;

Wd: dielectric loss per unit length of conductor insulation, in units of W/m;

n: the number of conductors carrying the load in the cable;

λ ΐ : ratio of cable sheath loss to total conductor loss;

λ 2: ratio of cable armor loss to total conductor loss;

σ : the absorption coefficient of sunlight on the surface of the cable;

T*4: Considering the external thermal resistance of the cable during daylight exposure, the unit is K*m/W; Claim

T3: thickness of the outer sheath, the unit is mm;

D-: the diameter of an imaginary concentric cylinder that is tangent to the corrugated metal sleeve crest, the unit

Mm;

u: ratio of thermal resistance coefficient of dry and wet soil, u = pd/Pw _;

d: thermal resistance coefficient of dry soil, its unit K*m/W;

P w: thermal resistance coefficient of natural soil, its unit K*m/W;

Χχ: The critical temperature of the soil, ie the temperature at the boundary between the dry and moist soil, in units. C;

Θ0: Ambient temperature, its unit. C;

Δ θ _χ: critical temperature rise of the soil, ie the temperature rise of the boundary between the dry and wet soil above the ambient temperature _Χ -Θ0 : the resistance of the core at the time, the unit is Ω/m; the resistance of the core at the time, Its unit is Ω/m;

3⁄4: The maximum allowable operating temperature of the core during continuous load, in units. C;

%: The maximum allowable operating temperature of the core during overload operation, in units. C;

I: overload running time, its unit s;

Cable time constant;

Cable rated current capacity, its unit A; 1 input formula for various situations:

1.1 AC cable that is not exposed to sunlight in the air; the soil avoids direct buried communication in local dry conditions

1.2 The AC cable directly exposed to sunlight in the air is as shown in Equation a2:

1.3 The direct buried AC cable in the case of local drying of the soil is as shown in the formula a3:

(a3)

Claim

1.4 The 5KV and below DC cables that are not exposed to sunlight in the air are shown in Equation a4:

: He

f: Display: " Discussion | : : ( ^a4 )

1 The DC cable is as shown in Equation a6:

The 5KV and below DC cables under 1 are shown in Equation a7:

2 input current calculation formula:

The distributed line temperature system will report the demodulated data to the server (1) through the communication port, and the server (1) receives and parses the message to obtain the surface temperature, and cooperates with the relevant parameters and formulas stored in the database. (1) According to the actual situation, select the specific formula to calculate the cable core temperature of each segment, and based on these temperatures, calculate the cable conductor temperature of the entire cable core conductor under the application of the current value.