The core lies in adapting to the working conditions requiring high current, strong heat dissipation, and high mechanical strength, especially for transformers with large capacity and low voltage levels (such as 400V and below). Copper bars have a significant advantage in key performance indicators. The following are the core reasons:
1. Stronger current-carrying capacity (compatible with high current)
The current on the low-voltage side of a low-voltage transformer is typically high (ranging from hundreds to thousands of amperes). The copper bar, with solid or hollow cross-section, has a higher current-carrying capacity per unit area than copper wire bundles (to avoid the skin effect and contact resistance loss when multiple copper wires are connected in parallel). It can conduct high currents more efficiently, reducing heat loss.
2. Better heat dissipation efficiency
Copper bars have a large surface area (flat structure), with a heat dissipation area significantly larger than that of copper wire bundles with the same cross-sectional area. They can directly form a heat dissipation path with the transformer core and shell, effectively reducing the temperature rise of windings under high current, avoiding insulation aging, and extending equipment life.
3. Outstanding mechanical strength and short-circuit resistance
The peak value of short-circuit current on the low-voltage side is extremely high. Copper bars have strong rigidity and resistance to electromagnetic deformation, and can withstand the instantaneous impact force during short-circuiting. However, copper wires are flexible, and their mechanical strength is poor after being twisted into multiple strands, making them prone to loosening and breaking due to electromagnetic forces.
4. Installation and connection are more convenient
Copper bars can be directly bent and punched, and connected to external busbars/loads via bolts, ensuring low contact resistance and secure connections. They are suitable for terminal docking in high-current scenarios. Copper wires, on the other hand, require crimping to terminals. When multiple strands are connected in parallel, the connection process becomes complex and prone to poor contact issues.
Applicable scenario boundaries
Copper bar is used in scenarios with high requirements for current-carrying capacity, heat dissipation, and mechanical strength, such as large-capacity low-voltage transformers (typically with a capacity of ≥500kVA and a low-voltage side current of ≥800A), low-voltage windings of distribution transformers, and dry-type transformers.
Using copper wire: for small-capacity low-voltage transformers (capacity < 500kVA, current < 500A), small control transformers, etc., copper wire is more flexible, less expensive, and can meet the needs of small current conduction.
Core Summary
The advantages of copper bars are concentrated in high current carrying capacity, heat dissipation, and mechanical strength, perfectly matching the operating conditions of low-voltage high-current transformers; copper wires excel in flexibility and low cost, suitable for small capacity and low current scenarios. The essence of the choice lies in the adaptation of "current magnitude + operating condition requirements".
