Detailed Explanation Of Copper BusBars Selection, Current Carrying Capacity Calculation, And Bending Process For High Voltage Switchgear

The current carrying capacity of a electrical copper bus bar refers to the maximum current it can continuously carry without exceeding its allowable temperature under specified conditions. In practical engineering, the current carrying capacity of a bending copper busbar is not a fixed value, but a dynamic parameter affected by various factors such as installation method, ambient temperature, cross-sectional shape, and number of layers.

First, the installation method has a significant impact on heat dissipation. Installation methods within the cabinet are mainly divided into horizontal and vertical placement. Since vertical placement utilizes the heat dissipation surface area more fully and achieves better air convection, the current carrying capacity of vertical placement is usually slightly greater than that of horizontal placement. This is why main busbars in large distribution cabinets are mostly installed vertically.

Second, ambient temperature is a crucial variable that must be considered. The design reference ambient temperature is usually 35℃ or 40℃. When the actual ambient temperature is higher than this reference, the current carrying capacity of the chatsworth ground bus bar will decrease, and it must be multiplied by the corresponding temperature correction factor; conversely, the lower the temperature, the more the current carrying capacity can be appropriately increased.

In engineering estimation, we can use empirical formulas for rapid calculation. For a single copper busbar bending, its current carrying capacity is approximately equal to the busbar width (mm) multiplied by a thickness coefficient. The thickness coefficient is related to the copper ground busbar thickness; for example, a 10mm thick busbar has a coefficient of approximately 18, and a 12mm thick busbar has a coefficient of approximately 20.

For multi-layer structures, due to poorer heat dissipation, the current carrying capacity is not a simple multiple addition. The current carrying capacity of a double-layer busbar is typically about 1.56 to 1.58 times that of a single-layer busbar, three layers about 2 times, and four layers about 2.45 times. However, it is worth noting that four layers and above are not recommended for engineering applications due to difficulties in heat dissipation and significant skin effect; it is suggested to use irregularly shaped busbars or single-layer busbars with larger cross-sections instead.

In high-voltage switchgear design, simply meeting the rated current carrying capacity requirement is far from sufficient. The electrical ground bus bar must be able to withstand the impact of the system's short-circuit current, i.e., meet the "short-time withstand current" requirement. This is crucial to ensuring that the electrolytic copper busbar will not melt due to overheating or cause equipment damage in the event of a short-circuit fault.

According to the formula in Appendix D of GB3906 standard, we can calculate the minimum cross-sectional area of ​​the isolated ground bus bar based on thermal stability conditions. The formula is: S = (I / a) × √(t / Δθ). Where S is the conductor cross-sectional area, I is the rated short-time withstand current (short-circuit current), a is the material coefficient (13 for copper), t is the short-circuit duration (usually 4 seconds for high-voltage systems), and Δθ is the temperature rise (usually 215K for bare conductors).

This formula can be used to derive the minimum cross-sectional area requirements for different short-circuit ratings. For example, for a 25kA/4S system, the minimum cross-sectional area of ​​the telecom ground bus bar needs to be 260mm²; for a 31.5kA/4S system, the minimum cross-sectional area needs to be 330mm²; and for a 63kA/4S system, it needs to be 660mm². In actual selection, designers need to calculate the cross-sectional area required for the rated current and the cross-sectional area required for short-circuit withstand, and take the maximum value of the two as the final selection basis. For example, a circuit with a rated current of 630A only requires a 40×6 cross-section, but if the system short-circuit current is 31.5kA, then a cross-section of not less than 330mm² (such as 60×6) must be selected to ensure system safety.

The machining accuracy of the BusBar for Siemens directly affects the ease of installation within the cabinet and the compliance of electrical clearances. During the bending and blanking process, the "material length," i.e., the unfolded length, must be accurately calculated. Because the BusBar for Weidmuller undergoes plastic deformation at the bending point-the outer side is stretched and elongated, while the inner side is compressed and shortened-a compensation coefficient must be introduced into the calculation.

For common flat bends (right-angle bends), either the "external calculation method" or the "internal calculation method" is commonly used in engineering. The general formula for the external calculation method is: Total Length = Sum of the outer dimensions of each segment + Compensation Value - Coefficient × Number of Right-Angle Bends. The specific compensation coefficient is related to the thickness of the BusBar Insulator Manufacturers; for example, for 3mm thick materials, each right-angle bend may require an additional allowance of approximately 0.3mm, while 10mm thick materials require even more. When processing multi-layer bends or complex shapes, the effects of the bending radius and springback angle must also be considered.

Furthermore, to prevent tip discharge, the BusBars for Mersen Ferraz inside the high-voltage switchgear typically require chamfering or rounded rectangles. This not only improves the electric field distribution but also enhances insulation performance. During manufacturing, bending angles and dimensional tolerances must be strictly controlled to ensure minimal stress during Copper Ground Bus Bar installation, preventing damage to insulation components or uneven stress on contact surfaces due to forced installation.

In summary, the selection and design of Distribution BusBars is a complex system engineering project integrating electrical calculations and mechanical processes. Only by comprehensively considering current carrying capacity, thermal stability, and the actual manufacturing and installation conditions can an economical and safe power distribution system be designed.