A quick calculation method for the current carrying capacity of copper and aluminum busbar conductors

Abstract

The invention belongs to the technical field of busbar current carrying capacity calculation, and discloses a method for quickly calculating the current carrying capacity of a copper / aluminum busbar conductor. The method comprises the steps of inputting copper / aluminum busbar size information and temperature information; obtaining an additional loss coefficient K by looking up a table; S , conductor resistivity p c and temperature coefficient a; calculate the DC resistance R0 and AC resistance R at the operating temperature t ; Calculate the heat dissipation P of the conductor Z ; Calculate the current carrying capacity of copper and aluminum bars I = [(P r +P c ) / R t ] 1 / 2 The present invention combines the actual engineering needs to look up the table to obtain the additional loss coefficient K affected by the skin effect and proximity effect S , making the calculation results more accurate, the heat dissipation is divided into surface radiation heat P r and natural convection heat dissipation P c , respectively calculated and added to get the heat dissipation P Z , and the calculation results thus obtained are more in line with the actual situation.

Description

Technical Field

[0001] The invention belongs to the technical field of busbar current carrying capacity calculation, and in particular relates to a fast calculation method for the current carrying capacity of a copper-aluminum busbar conductor. Background Art

[0002] The busbar is usually made of copper or aluminum, with a long conductor with a rectangular or chamfered (rounded) rectangular cross-section (rounded copper busbars are generally used now to avoid tip discharge). It plays the role of transmitting current and connecting electrical equipment in the circuit.

[0003] At present, there are many methods for calculating busbar current carrying capacity, and the parameters used are not the same. Some of these parameters are obtained through theoretical calculations, some are obtained through experiments, and some are empirical coefficients. IEC publications have not yet proposed relevant information, and my country does not have a unified calculation formula and standard. The data provided by various literature materials differ by less than 7%. Summary of the invention

[0004] The purpose of the present invention is to provide a method for quickly calculating the current carrying capacity of copper-aluminum busbar conductors, and to obtain the additional loss coefficient K affected by the skin effect and proximity effect by looking up the table. S value, and the heat dissipation is divided into surface radiation heat P r and natural convection heat dissipation P c , making the calculation results more accurate and in line with the actual situation.

[0005] The present invention discloses a method for quickly calculating the current carrying capacity of a copper-aluminum busbar conductor, comprising the following steps: Step 1. Input copper / aluminum busbar size and temperature information: The copper / aluminum busbar size information includes the conductor thickness b, conductor width h and rectangular chamfer radius R, and the conductor cross-sectional area A and the unit material surface area F in the busbar thickness direction are calculated. dl , Unit material surface area F in the direction of busbar width da and the unit material surface area F in the busbar width direction db and unit material surface area F; The temperature information includes the conductor surface temperature θ c and ambient temperature Θ0; Step 2: According to the conductor material and conductor cross-sectional area, look up the table to obtain the additional loss coefficient K affected by the skin effect and proximity effect. S , Stefan-Boltzmann constant s, material blackness coefficient k related to material type, temperature and surface condition e , conductor resistivity p c and temperature coefficient a; Step 3: Calculate the DC resistance R0 and AC resistance R at the operating temperature t : R0=p c *[1+a*(Θ c -20)] / (A*10 -6 ); R t =K S * R0; Step 4: Calculate the heat dissipation P of the conductor Z : The heat dissipation of the conductor P Z Split into surface radiation heat P r and natural convection heat dissipation P c : P Z =P r +P c ; Calculate the surface radiation heat P separately r and natural convection heat dissipation P c : P r =F*10 -3 *s*k e [(273+Θ c ) 4 -(273+θ0) 4 ]; P c =P dl + P da + P db ; Among them, P dl , P da , P db The calculation formula is as follows: P dl =2F dl *10 -3 *4.71*[(Θ c -Θ0) / 0.1b] 1 / 4 *(Θ c -Θ0); P da =F da *10 -3 *4.3*[(Θ c -Θ0) / 0.1h] 1 / 4 *(Θ c -Θ0); P db =F db *10 -3 *2.13*[(Θ c -Θ0) / 0.1h] 1 / 4 *(Θ c -Θ0); Step 5: Calculate the current carrying capacity I of the copper and aluminum bars: I=[(P r +P c ) / R t ] 1 / 2 .

[0006] The present invention introduces the influence of skin effect and proximity effect when calculating the conductor resistance R, and needs to multiply the additional loss coefficient K affected by the skin effect and proximity effect. S , the K S The value is nonlinearly related to the conductor cross section, and can be obtained from the data in combination with the needs of actual engineering, making the calculation result more accurate. At the same time, the present invention divides the heat dissipation into surface radiation heat P r and natural convection heat dissipation P c , and then add them together to get the heat dissipation, and the calculation result is more in line with the actual situation. BRIEF DESCRIPTION OF THE DRAWINGS

[0007] Figure 1 Schematic diagram of heat dissipation on the conductor surface in the present invention. DETAILED DESCRIPTION

[0008] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of this application.

[0009] The example embodiments will now be described more fully with reference to the accompanying drawings. However, the example embodiments can be implemented in many forms and should not be construed as being limited to the examples set forth herein; on the contrary, providing these embodiments will make the disclosure of this application more comprehensive and complete, and will fully convey the concept of the example embodiments to those skilled in the art. In addition, the described features, structures or characteristics may be combined in one or more embodiments in any suitable manner. Many specific details will be provided in the following description, so as to fully understand the embodiments disclosed in the present application. However, it will be appreciated by those skilled in the art that the technical scheme of the present application can be put into practice without one or more of the specific details, or other methods, components, devices, steps, etc. may be adopted. In other cases, known methods, devices, realizations or operations are not shown or described in detail to avoid blurring the various aspects disclosed in the present application. The block diagrams shown in the accompanying drawings are only functional entities and do not necessarily correspond to physically independent entities. That is, these functional entities can be implemented in software form, or in one or more hardware modules or integrated circuits, or in different networks and / or processor devices and / or microcontroller devices. The flowcharts shown in the accompanying drawings are only exemplary and do not necessarily include all the contents and operations / steps, nor must they be executed in the order described. For example, some operations / steps can be decomposed, and some operations / steps can be combined or partially combined, so the actual execution order may change according to actual conditions.

[0010] The terms "first", "second", etc. in the specification and claims of the present application and the above-mentioned drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence. It should be understood that the data used in this way can be interchangeable where appropriate, so that the embodiments of the present application described herein can be implemented in an order other than those illustrated or described herein. In addition, the terms "including" and "having" and any of their variations are intended to cover non-exclusive inclusions, for example, a process, method, system, product or server that includes a series of steps or units is not necessarily limited to those steps or units that are clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0011] In the embodiments of the present application, words such as "exemplary" or "for example" are used to indicate examples, illustrations or descriptions. Any embodiment or scheme described as "exemplary" or "for example" in the embodiments of the present application should not be interpreted as being more preferred or more advantageous than other embodiments or schemes. Specifically, the use of words such as "exemplary" or "for example" is intended to present related concepts in a specific way.

[0012] The principle of the present invention is described as follows: The current passing through the conductor causes its temperature to rise. When the conductor reaches thermal stability, the heat dissipation on the conductor surface should be equal to the heat generated by the conductor. The current carrying capacity calculation formula of the busbar is obtained based on the temperature rise equation in the temperature field generated by the conductor heating. The maximum allowable current of the busbar for long-term operation is obtained by the following formula: P Z =I 2 R t From the above formula, the current calculation formula can be obtained: I = (P Z / R t ) 1 / 2 The heat dissipation of the conductor P Z Split into surface radiation heat P rand natural convection heat dissipation P c : P Z =P r +P c The current calculation formula becomes: I=[(P r +P c ) / R t ] 1 / 2 ; The surface radiated heat P r Calculated by the following formula: P r =F*10 -3 *s*k e [(273+Θ c ) 4 -(273+θ0) 4 ] Where F is the unit material surface area, s is the Stefan-Boltzmann constant, k e It is the material blackness coefficient related to the material type, temperature and surface condition. The paint busbar is taken as 0.9, Θ c is the conductor surface temperature, Θ0 is the ambient temperature; The natural convection heat dissipation P c Calculated by the following formula: P c =P dl + P da + P db Among them, P dl The heat dissipated by the two vertical surfaces of the conductor: P dl =2F dl *10 -3 *4.71* [(Θ c -Θ0) / 0.1b ] 1 / 4 *(Θ c -Θ0); Pda is the heat dissipated upward from the horizontal surface of the conductor: P da =F da *10 -3 *4.3* [(Θ c -Θ0) / 0.1h ] 1 / 4 *(Θ c -Θ0); P db The amount of heat dissipated by the conductor horizontally downward: P db =F db *10 -3*2.13* [(Θ c -Θ0) / 0.1h ] 1 / 4 *(Θ c -Θ0); In the formula, Figure 1 As shown, b is the conductor thickness, h is the conductor width, F dl is the unit material surface area in the direction of busbar thickness, F da is the unit material surface area in the busbar width direction, F db It is the unit material surface area in the direction of busbar width; The AC resistance R of the conductor at the working temperature T Obtained by the following formula: R T =K S * R0 In the formula, K S is the additional loss coefficient affected by the skin effect and proximity effect. According to the requirements of the conductor material and cross-section size in actual engineering, the additional loss coefficient K is obtained by looking up the table. S , its value is nonlinearly related to the cross section, R0 is the DC resistance of the conductor at the operating temperature; For example, the additional loss factor K of copper is S By looking up the table, we can get (A is the cross-sectional area of ​​the conductor): K S =0.156xA 0.295 (600≤A≤2400) K S =0.033xA 0.494 (3000≤A≤6500) Additional loss coefficient K of aluminum S By looking up the table, we can get (A is the cross-sectional area of ​​the conductor): K S =0.337xA 0.171 (600≤A≤2400) K S =0.093xA 0.341 (3000≤A≤6500); The skin effect refers to the fact that when an alternating current passes through a conductor, the induced electromotive force near the surface is smaller than that at the center because the cross-linked magnetic flux is greater near the center of the conductor than at the surface of the conductor. Therefore, under the same external voltage, the current density at the surface of the conductor is larger and the current density inside the conductor is smaller. The skin effect increases the resistance of the conductor.

[0013] The proximity effect refers to the fact that the distribution of AC current in a conductor is affected by the magnetic field generated by the AC current in the adjacent conductor. The proximity effect will also increase the resistance of the conductor, but it is much smaller than the skin effect and only needs to be considered when the conductor cross-section is large, the distance is close or the frequency is very high.

[0014] The DC resistance R0 of the conductor at the operating temperature is calculated by the following formula: R0=p c *[1+a*(Θ c -20)] / (A *10 -6 ) In the formula, p c For 20 o The conductor resistivity at C is 1.7246*10 -8 Ω·m, aluminum is 2.8264*10 -8 Ω·m, a is the temperature coefficient, copper is 3.93*10 -3 , aluminum is 4.03*10 -3 ; Θ c is the conductor surface temperature, and A is the conductor cross-sectional area.

[0015] The present invention relates to a method for quickly calculating the current carrying capacity of a copper-aluminum busbar conductor, comprising the following steps: Step 1. Input copper / aluminum busbar size and temperature information: The copper / aluminum busbar size information includes the conductor thickness b, conductor width h and rectangular chamfer radius R, and the conductor cross-sectional area A and the unit material surface area F in the busbar thickness direction are calculated. dl , Unit material surface area F in the direction of busbar width da and the unit material surface area F in the busbar width direction db and unit material surface area F; The temperature information includes the conductor surface temperature θ c and ambient temperature Θ0; Step 2: According to the conductor material and conductor cross-sectional area, look up the table to obtain the additional loss coefficient K affected by the skin effect and proximity effect. S , Stefan-Boltzmann constant s, material blackness coefficient k related to material type, temperature and surface condition e , conductor resistivity p c and temperature coefficient a; Step 3: Calculate the DC resistance R0 and AC resistance R at the operating temperature t : R0=p c *[1+a*(Θ c -20)] / (A*10 -6 ); Rt =K S *R0; Step 4: Calculate the heat dissipation P of the conductor Z : The heat dissipation of the conductor P Z Split into surface radiation heat P r and natural convection heat dissipation P c : P Z =P r +P c ; Calculate the surface radiation heat P r and natural convection heat dissipation P c : P r =F*10 -3 *s*k e [(273+Θ c ) 4 -(273+θ0) 4 ]; P c =P dl + P da + P db ; Where P dl , P da , P db The calculation formula is as follows: P dl =2F dl *10 -3 *4.71* [(Θ c -Θ0) / 0.1b ] 1 / 4 *(Θ c -Θ0); P da =F da *10 -3 *4.3* [(Θ c -Θ0) / 0.1h ] 1 / 4 *(Θ c -Θ0); P db =F db *10 -3 *2.13* [(Θ c -Θ0) / 0.1h ] 1 / 4 *(Θ c -Θ0); Step 5: Calculate the current carrying capacity I of the copper and aluminum bars: I=[(P r +P c ) / R t ]1 / 2 .

[0016] The specific implementation methods described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific implementation method of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for quickly calculating the current carrying capacity of copper-aluminum busbar conductors, characterized in that The steps include: Step 1. Input copper / aluminum busbar size and temperature information: The copper / aluminum busbar size information includes the conductor thickness b, conductor width h and rectangular chamfer radius R, and the conductor cross-sectional area A and the unit material surface area F in the busbar thickness direction are calculated. dl , Unit material surface area F in the direction of busbar width da and the unit material surface area F in the busbar width direction db and unit material surface area F; The temperature information includes the conductor surface temperature θ c and ambient temperature Θ0; Step 2: According to the conductor material and conductor cross-sectional area, look up the table to obtain the additional loss coefficient K affected by the skin effect and proximity effect. S , Stefan-Boltzmann constant s, material blackness coefficient k related to material type, temperature and surface condition e , conductor resistivity p c and temperature coefficient a; Step 3: Calculate the DC resistance R0 and AC resistance R at the operating temperature t : R0=p c *[1+a *(Θ c -20)] / (A*10 -6 ); R t =K S * R0; Step 4: Calculate the heat dissipation P of the conductor Z : The heat dissipation of the conductor P Z Split into surface radiation heat P r and natural convection heat dissipation P c : P Z =P r +P c ; Calculate the surface radiation heat P separately r and natural convection heat dissipation P c : P r =F*10 -3 *s*k e [(273+Θ c ) 4 -(273+θ0) 4 ]; P c = P dl + P da + P db ; Among them, P dl , P da , P db The calculation formula is as follows: P dl =2F dl *10 -3 *4.71*[(Θ c -Θ0) / 0.1b] 1 / 4 *(I c -Θ0); P da =F da *10 -3 *4.3*[(Θ c -Θ0) / 0.1h] 1 / 4 *(I c -Θ0); P db =F db *10 -3 *2.13*[(Θ c -Θ0) / 0.1h] 1 / 4 *(I c -Θ0); Step 5: Calculate the current carrying capacity I of the copper and aluminum bars: I=[(P r +P c ) / R t ] 1 / 2 。

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