CN106646018A - Measurement method for current-carrying capacity of aluminum-core cable - Google Patents

Abstract

The invention discloses a method for measuring the ampacity of an aluminum-core cable. A copper-core cable is used instead of an aluminum-core cable of the same cross-section to carry out a current-carrying experiment, and the corresponding ampacity of the aluminum-core cable is deduced from the experimental results through a formula. Compared with analytical calculation, the method of the invention can more accurately calculate the ampacity of the aluminum core cable, and at the same time does not need to purchase additional aluminum core cables for experiments, saves costs, is easy to popularize, and has great practical value.

Description

A method for measuring the ampacity of aluminum core cables

technical field

The invention relates to a method for measuring the ampacity of cables, in particular to a method for measuring the ampacity of aluminum core cables.

Background technique

At present, although the aluminum core cable has various disadvantages compared with the copper core cable, its price is low and has high economic efficiency. After comprehensive consideration, it still has a certain application range and potential, so it is still necessary to study the aluminum core cable.

The calculation of cable ampacity in engineering often adopts the IEC60287 standard, which is an internationally recognized method for calculating the continuous load ampacity of cables. It makes simple and uniform assumptions about the environmental state to obtain the rated ampacity, and the determination of the temperature of the cable conductor during operation It is also usually simple to assume that the ambient and cable heating has reached a steady state. This method has great limitations. During actual operation, the surrounding environment and load of the cable are constantly changing, the heating of the cable has not reached a steady state, the actual temperature distribution does not fully meet the assumptions in the standard, and the calculation results are conservative.

Electric power departments and scientific research institutions often determine the ampacity of cables through experiments, and the ampacity experiments can obtain more accurate results than the IEC60287 standard. However, the current utilization rate of aluminum-core cables is low, and power departments and scientific research institutions often lack ready-made aluminum-core cables. The ampacity experiment requires the purchase of aluminum-core cables, which will increase the high cost of the experiment itself, which is not conducive to the carrying capacity of aluminum-core cables. The flow experiment is carried out.

Contents of the invention

In order to overcome the above-mentioned shortcomings and deficiencies of the prior art, the object of the present invention is to provide a method for measuring the ampacity of aluminum-core cables, which can meet the precision requirements of engineering research, and at the same time does not need to purchase additional aluminum-core cables for experiments, which saves costs and is easy to use. promote.

The object of the present invention is achieved through the following technical solutions:

A method for measuring the ampacity of an aluminum core cable, comprising the following steps:

(1) select the copper core cable with the same voltage grade and cross-section as the aluminum core cable to be tested, carry out the ampacity experiment under the required laying conditions, and obtain the copper core cable ampacity _Izcu ;

(2) Substituting the ampacity I _zcu of the copper core cable into the following formula, the corresponding ampacity I _ZAl of the aluminum core cable can be obtained

In the formula, I _ZCu and I _ZAl are the current carrying capacity of copper and aluminum core cables under the same laying environment and conditions; R _0cu and R _0Al are the DC resistance of copper and aluminum conductors at 20°C respectively, which are determined by the cross-sectional size of the cable conductor; α _20cu and α _20Al are the resistivity of copper and aluminum conductors at 20°C respectively; y _scu and y _sAl are the skin effect coefficients of copper and aluminum conductors respectively; y _pcu and y _pAl are the proximity effect coefficients of copper and aluminum conductors respectively; θ _Cu , θ _Al is the maximum operating temperature of copper core cable and aluminum core cable respectively, θ _Cu = θ _Al = θ.

Preferably, the structural parameters of the aluminum core cable to be tested are completely consistent with those of the copper core cable; except for the conductor material, the materials of the aluminum core cable to be tested are consistent with those of the copper core cable.

Preferably, the ampacity experiment is carried out under the required laying conditions as described in step (1), to obtain the ampacity I _zcu of the copper core cable, specifically:

Carry out the temperature rise experiment of the cable conductor at a temperature of 90°C, load the cable current through the PLC control cabinet, measure the conductor temperature after the steady state, and change the cable current several times to make the conductor temperature reach or approach 90°C. At this time, the current size is the copper core The ampacity of the cable results in the ampacity I _zcu of the copper cable.

Preferably, the laying conditions are divided into air laying and soil laying. The former includes the required cable laying method, arrangement, center distance, grounding method, air ambient temperature, and sunlight intensity, and the latter includes the required cable laying method. , Arrangement, center distance, grounding method, soil ambient temperature, soil moisture, buried depth.

Specifically, the calculation formula of the skin effect coefficient y _scu of the copper conductor is as follows:

in R _Cu '=R _0Cu ×[1+α _20Cu (θ-20)]; R _0Cu is the DC resistance of the copper conductor at 20°C; f is the power frequency; k _sCu is 1;

Proximity effect coefficient y _pou for three-core or three single-core copper cables:

in d _cCu is the diameter of the copper conductor; s _Cu is the average distance between the axes of each copper conductor; for dry and impregnated copper conductors k _pCu 0.8, otherwise take 1;

For a single single-core copper cable, y _pAl =0.

Specifically, the calculation formula of the skin effect coefficient _ypAl of the aluminum conductor is as follows:

in R _Al '=R _0Al ×[1+α _20Al (θ-20)]; R _0Al is the DC resistance of the aluminum conductor at 20°C; f is the power frequency; for 4, 5, and 6 split aluminum conductors, the values of k _sAl are respectively Take 0.28, 0.19 and 0.12, otherwise k _sAl takes 1;

Proximity effect coefficient y _pcu for three-core or three single-core aluminum cables:

in d _cAL is the diameter of the aluminum conductor (mm); s _Al is the average distance between the axes of each aluminum conductor (mm); k _{pAl is} 0.8 for dry and impregnated aluminum conductors, otherwise 1;

For a single single-core aluminum cable, y _pAl =0.

Compared with the prior art, the present invention has the following advantages and beneficial effects:

1. The present invention measures the ampacity of the aluminum core cable under the required laying environment by combining experiments and calculations. Compared with the current commonly used IEC standard, the accuracy is higher and can meet the accuracy requirements of engineering research.

2. Compared with the direct purchase of aluminum core cables for ampacity experiments, the present invention can effectively utilize existing copper core cables in electric power departments and scientific research institutions, save the cost of additional purchase of aluminum core cables, and reduce the cost of experiments.

Description of drawings

FIG. 1 is a flowchart of a method for measuring the ampacity of an aluminum core cable according to an embodiment of the present invention.

Fig. 2 is a schematic diagram of a copper core cable ampacity testing system according to an embodiment of the present invention.

detailed description

The present invention will be described in further detail below in conjunction with the examples, but the embodiments of the present invention are not limited thereto.

Example

The measuring method of the aluminum core cable current carrying capacity of the present embodiment, as shown in Figure 1, comprises the following steps:

S1 selects the copper core cable with the same voltage level and the same cross-section as the aluminum core cable to be tested, and carries out a circuit ampacity experiment under the required laying conditions to obtain the current carrying capacity I _zcu of the copper core cable; the aluminum core cable to be tested and the copper core cable The structural parameters are completely consistent; except for the conductor material, the material of the aluminum core cable to be tested is consistent with that of the copper core cable.

The laying conditions are divided into air laying and soil laying. The former includes the required cable laying method, arrangement, center distance, grounding method, air ambient temperature, and sunlight intensity. The latter includes the required cable laying method, arrangement, and center distance. Spacing, grounding method, soil ambient temperature, soil moisture, buried depth.

The specific situation of this embodiment is that the length of the aluminum core cable is 10m, the model is 110kV YJLLW02, and the nominal cross section is 630mm ² . The temperature is 25°C, the humidity is 54%, and the buried depth is 1m. Select 10m copper core cable, model 110kV YJLW02, nominal section 630mm ² . Except for the conductor material, there is no difference in the materials and structural parameters of other parts of the copper and aluminum core cables.

S2 Measure the ampacity I _zcu of the copper core cable under the required laying conditions, including the following steps:

Place the copper core cables according to the required laying environment and conditions, including three single-core cables laid in parallel, with a center distance of 250mm, directly buried in the soil, single-point grounding, the soil ambient temperature is 25°C, and the humidity is 54%.

Carry out the temperature rise experiment of the cable conductor at a temperature of 90°C, load the cable current through the PLC control cabinet, and measure the conductor temperature after the steady state. Change the cable current many times. When the loading current reaches _846A , the conductor temperature reaches a steady state after 5 hours, and the conductor temperature is 90.5°C.

As shown in Figure 2, the copper core cable ampacity test system used in this embodiment includes a 380V power supply, a voltage regulator 1, a PLC control panel 2, a control console, a current booster 3, a compensation capacitor box 4, and a current transformer 5 , Control motor 6. The computer console provides a man-machine interface, which is convenient for users to operate. The PLC control cabinet provides the control logic for the up and down movement of the voltage regulator contacts, changes the auto-coupling ratio of the voltage regulator, adjusts the current, voltage and transmission power added to the current booster end, and realizes the control and loading of the cable current. The compensation capacitor is connected in parallel to the input terminal of the current booster to compensate the inductance of the load and improve the power factor. The current transformer measurement signal is used as the input signal of the control cabinet to realize feedback regulation.

S3. Calculate skin effect coefficient and proximity effect coefficient of copper and aluminum core cables:

The calculation formula of skin effect coefficient y _scu of copper conductor is as follows:

in R _Cu '=R _0Cu ×[1+α _20Cu (θ-20)]; R _0Cu is the DC resistance of the copper conductor at 20°C; f is the power frequency; k _sCu is 1; θ _Cu is the highest operating value of the copper conductor Temperature (°C), generally 90°C;

Proximity effect coefficient y _pcu for three-core or three single-core copper cables:

in d _cCu is the diameter of the copper conductor; s _Cu is the average distance between the axes of each copper conductor; for dry and impregnated copper conductors k _pCu 0.8, otherwise take 1;

For a single single-core copper cable, y _pAl =0.

The calculation formula of skin effect coefficient y _pAl of aluminum conductor is as follows:

in R _Al '=R _0Al ×[1+α _20Al (θ-20)]; R _0Al is the DC resistance of the aluminum conductor at 20°C; f is the power frequency; for 4, 5, and 6 split aluminum conductors, the values of k _sAl are respectively Take 0.28, 0.19 and 0.12, otherwise k _sAl takes 1; θ _Al is the highest working temperature (°C) of aluminum conductor, generally takes 90°C;

Proximity effect coefficient y _pcu for three-core or three single-core aluminum cables:

in d _cAL is the diameter of the aluminum conductor (mm); s _Al is the average distance between the axes of each aluminum conductor (mm); k _{pAl is} 0.8 for dry and impregnated aluminum conductors, otherwise 1;

For a single single-core aluminum cable, y _pAl =0.

The calculation result of this embodiment:

Copper core cable conductor R _0Cu ＝2.83×10 ^-5 Ω/m, α _20Cu ＝3.93×10 ^-3 , θ _Cu ＝90℃, f＝50Hz, k _sCu ＝1, d _cCu ＝29.8mm, s _Cu ＝250mm , k _pCu =1, calculated skin effect coefficient y _sCu =6.0124×10 ^-2 , proximity effect coefficient y _pCu =3.0573×10 ^-3 .

Aluminum core cable conductor R _0Al = 4.69×10 ^-5 Ω/m, α _20Al = 4.03×10 ^-3 , θ _Al = 90°C, f = 50Hz, k _sAl = 1, d _cAl = 29.8mm, s _Al = 250mm , k _pAl =1, calculated skin effect coefficient y _sAl =2.2341×10 ^-2 , proximity effect coefficient y _pAl =1.2827×10 ^-3 .

d _cCu = d _cAl = d _c , s _Cu = s _Al = s, θ _Cu = θ _Al = θ;

S4. Calculate the ampacity of the aluminum core cable under the same laying environment and conditions

Substituting I _zcu , R _0Cu , R _0Al , θ, y _sCu , y _sCu , y _pCu , and y _pAl into the following formula, the ampacity I _ZAl of the aluminum core cable under the required laying environment and conditions can be obtained = 667.92A.

The above-mentioned embodiment is a preferred embodiment of the present invention, but the embodiment of the present invention is not limited by the embodiment, and any other changes, modifications, substitutions and combinations made without departing from the spirit and principle of the present invention , simplification, all should be equivalent replacement methods, and are all included in the protection scope of the present invention.

Claims (6)

1. a method for measuring the ampacity of an aluminum core cable, is characterized in that, comprises the following steps: (1) select the copper core cable with the same cross-section of the aluminum core cable to be tested, carry out the ampacity experiment under required laying conditions, obtain the copper core cable ampacity I _ZCu ; (2) Substituting the ampacity I _ZCu of the copper core cable into the following formula, the corresponding ampacity I _ZAl of the aluminum core cable can be obtained ${\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; Z</span>}\mathrm{<span\; class="notranslate">\; A</span>}\mathrm{<span\; class="notranslate">\; l</span>}}<span\; class="notranslate">\; =</span>\sqrt{\frac{{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; Z</span>}\mathrm{<span\; class="notranslate">\; C</span>}\mathrm{<span\; class="notranslate">\; u</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}\mathrm{<span\; class="notranslate">\; C</span>}\mathrm{<span\; class="notranslate">\; u</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; \&alpha;</span>}}_{\mathrm{<span\; class="notranslate">\; 20</span>}\mathrm{<span\; class="notranslate">\; C</span>}\mathrm{<span\; class="notranslate">\; u</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; \&theta;</span>}}_{\mathrm{<span\; class="notranslate">\; C</span>}\mathrm{<span\; class="notranslate">\; u</span>}}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 20</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; )</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; the\; y</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}\mathrm{<span\; class="notranslate">\; C</span>}\mathrm{<span\; class="notranslate">\; u</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; the\; y</span>}}_{\mathrm{<span\; class="notranslate">\; p</span>}\mathrm{<span\; class="notranslate">\; C</span>}\mathrm{<span\; class="notranslate">\; u</span>}}<span\; class="notranslate">\; )</span>}{{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}\mathrm{<span\; class="notranslate">\; A</span>}\mathrm{<span\; class="notranslate">\; l</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; \&alpha;</span>}}_{\mathrm{<span\; class="notranslate">\; 20</span>}\mathrm{<span\; class="notranslate">\; A</span>}\mathrm{<span\; class="notranslate">\; l</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; \&theta;</span>}}_{\mathrm{<span\; class="notranslate">\; A</span>}\mathrm{<span\; class="notranslate">\; l</span>}}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 20</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; )</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; the\; y</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}\mathrm{<span\; class="notranslate">\; A</span>}\mathrm{<span\; class="notranslate">\; l</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; the\; y</span>}}_{\mathrm{<span\; class="notranslate">\; p</span>}\mathrm{<span\; class="notranslate">\; A</span>}\mathrm{<span\; class="notranslate">\; l</span>}}<span\; class="notranslate">\; )</span>}}$ In the formula, I _ZCu and I _ZAl are the current carrying capacity of copper and aluminum core cables under the same laying environment and conditions; R _0cu and R _0Al are the DC resistance of copper and aluminum conductors at 20°C respectively, which are determined by the cross-sectional size of the cable conductor; α _20cu and α _20Al are the resistivity of copper and aluminum conductors at 20°C respectively; y _scu and y _sAl are the skin effect coefficients of copper and aluminum conductors respectively; y _pcu and y _pAl are the proximity effect coefficients of copper and aluminum conductors respectively; θ _Cu , θ _Al is the maximum operating temperature of copper core cable and aluminum core cable respectively, θ _Cu = θ _Al = θ. 2. the measuring method of aluminum-core cable ampacity according to claim 1, is characterized in that, the structure parameter of described aluminum-core cable to be tested is completely consistent with copper-core cable; Except conductor material, described aluminum-core cable to be tested The cable is made of the same material as the copper core cable. 3. the measuring method of aluminum core cable ampacity according to claim 1, is characterized in that, described in step (1) carries out ampacity experiment under requirement laying condition, obtains copper core cable ampacity I _ZCu , specifically: Carry out the temperature rise experiment of the cable conductor at a temperature of 90°C, load the cable current through the PLC control cabinet, measure the conductor temperature after the steady state, and change the cable current several times to make the conductor temperature reach or approach 90°C. At this time, the current size is the copper core The ampacity of the cable is obtained by the ampacity I _ZCu of the copper core cable. 4. The method for measuring the ampacity of an aluminum-core cable according to claim 1, wherein the laying conditions are divided into two types: air laying and soil laying, and the former includes required cable laying methods, arrangements, center distances, Grounding method, air ambient temperature, and sunlight intensity, the latter including required cable laying method, arrangement, center distance, grounding method, soil ambient temperature, soil humidity, and buried depth. 5. the measuring method of aluminum core cable current carrying capacity according to claim 1, is characterized in that, the computing formula of the skin effect coefficient y _scu of copper conductor is as follows: ${\mathrm{<span\; class="notranslate">\; the\; y</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}\mathrm{<span\; class="notranslate">\; C</span>}\mathrm{<span\; class="notranslate">\; u</span>}}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; x</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}\mathrm{<span\; class="notranslate">\; C</span>}\mathrm{<span\; class="notranslate">\; u</span>}}^{\mathrm{<span\; class="notranslate">\; 4</span>}}}{\mathrm{<span\; class="notranslate">\; 192</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 0.8</span>}{\mathrm{<span\; class="notranslate">\; x</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}\mathrm{<span\; class="notranslate">\; C</span>}\mathrm{<span\; class="notranslate">\; u</span>}}^{\mathrm{<span\; class="notranslate">\; 4</span>}}}$ in R _Cu '=R _0Cu ×[1+α _20Cu (θ-20)]; R _0Cu is the DC resistance of the copper conductor at 20°C; f is the power frequency; k _sCu is 1; Proximity effect coefficient y _pcu for three-core or three single-core copper cables: in d _cCu is the diameter of the copper conductor; s _Cu is the average distance between the axes of each copper conductor; for dry and impregnated copper conductors k _pCu 0.8, otherwise take 1; For a single single-core copper cable, y _pAl =0. 6. the measuring method of aluminum core cable current carrying capacity according to claim 1, is characterized in that, the calculation formula of the skin effect coefficient _ypAl of aluminum conductor is as follows: ${\mathrm{<span\; class="notranslate">\; the\; y</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}\mathrm{<span\; class="notranslate">\; A</span>}\mathrm{<span\; class="notranslate">\; l</span>}}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; x</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}\mathrm{<span\; class="notranslate">\; A</span>}\mathrm{<span\; class="notranslate">\; l</span>}}^{\mathrm{<span\; class="notranslate">\; 4</span>}}}{\mathrm{<span\; class="notranslate">\; 192</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 0.8</span>}{\mathrm{<span\; class="notranslate">\; x</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}\mathrm{<span\; class="notranslate">\; A</span>}\mathrm{<span\; class="notranslate">\; l</span>}}^{\mathrm{<span\; class="notranslate">\; 4</span>}}}$ in R _Al '=R _0Al ×[1+α _20Al (θ-20)]; R _0Al is the DC resistance of the aluminum conductor at 20°C; f is the power frequency; for 4, 5, and 6 split aluminum conductors, the values of k _sAl are respectively Take 0.28, 0.19 and 0.12, otherwise k _sAl takes 1; Proximity effect coefficient y _pcu for three-core or three single-core aluminum cables: in d _cAL is the diameter of the aluminum conductor; s _Al is the average distance between the axes of each aluminum conductor; k _{pAl is} 0.8 for dry and impregnated aluminum conductors, otherwise 1; For a single single-core aluminum cable, y _pAl =0.