Insulation Materials for Laminated Busbars – A Brief Discussion of Flexible and Rigid Insulation and Their Parameters

A laminated busbar is an electrical connection component composed of multiple layers of conductors and insulating materials. It is widely used in high-power-density and compact power electronic systems, such as Laminated Low Inductive Bus Bars and Copper Laminated Bus Bars. Its core design goal is to improve overall system efficiency and reliability by optimizing the electric field distribution and parasitic inductance through a three-dimensional structure while meeting the requirements of high voltage and high current transmission. Typical applications include laminated busbars in high-power converters and laminated busbars for DC power distribution systems.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Structurally, laminated busbars typically use flexible insulating materials laminated with conductors to form basic conductive units. This structure is also known as a partially laminated bus bar or a multi-layer composite structure connection bar. During a hot-pressing process, the flexible insulating material is tightly bonded to the conductor through adhesive layers, forming an effective seal at the conductor edges, thus maintaining stable insulation performance even in complex environments. Common flexible insulation materials include polyester (PET) and polyimide (PI), with PET being the most widely used in three-layer laminated busbars and standardized busbar products due to its comprehensive performance advantages.

 

Polyester materials possess a moderate temperature resistance (typically 105°C), maintaining stable mechanical and electrical properties under long-term thermal cycling conditions. Its elongation can exceed 100%, making it less prone to tearing or thickness reduction during bending and edge binding. Furthermore, PET has a high relative tracking index (CTI), effectively reducing creepage risk, which is particularly critical for high-voltage applications such as High Voltage Explosion-Proof Inverter Busbars. While meeting flame retardant ratings (e.g., V0), PET is also available in various thicknesses (e.g., 50μm to 350μm) to adapt to different voltage levels and structural design requirements, thus offering high versatility in applications such as Laminated Busbars for Three-Level Inverters and Customized Laminated Busbars for IGBTs.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

In contrast, polyimide (PI) materials are high-performance insulation materials with higher temperature resistance (RTI typically exceeds 200°C), making them suitable for applications involving high-temperature welding or high localized heat loads, such as structures involving capacitor or electronic component welding in Laminated Busbars for Electric Cars. PI materials have greater mechanical rigidity and are less prone to relaxation under long-term stress, which helps maintain the stability of the sealed structure. However, their CTI performance is relatively low, usually requiring a larger creepage distance design, making them more suitable for medium- and low-voltage environments, such as some DC-Link Capacitor Laminated Bus Bars or DC Support Capacitor Laminated Bus Bars applications.

 

In a complete laminated busbar system, flexible insulation is mainly used for electrical isolation and sealing between conductor layers, while rigid insulation materials are used for structural support and electrical isolation between busbar assemblies. The thickness of rigid insulation is usually directly related to the system voltage level; a general design principle is approximately 1 mm of rigid insulation material per kilovolt. In high-voltage systems, such as laminated busbars for large-capacity back-to-back converters or inverter busbars for rail traffic and subway systems, rigid insulation layers with thicknesses between 1 mm and 6 mm are typically required to meet partial discharge control and long-term reliable operation requirements.

 

Regarding key performance parameters, the relative temperature index (RTI) and relative tracking index (CTI) are important indicators for evaluating insulation materials. RTI measures a material's ability to maintain performance under long-term thermal aging conditions; its lifespan assessment is typically based on accelerated aging tests exceeding 20,000 hours and follows an exponential relationship between temperature and lifespan. CTI reflects a material's resistance to tracking in polluted environments and is crucial for creepage distance design in high-voltage systems. Furthermore, the elongation of the material directly affects its adaptability during processing and is one of the key parameters for evaluating sealing performance and mechanical reliability.

 

The performance requirements for insulation materials in laminated busbars vary significantly across different application areas. In industrial high-voltage applications, such as High Voltage Explosion-Proof Inverter Busbars or large-scale power conversion systems, operating voltages typically range from 1000V to 6000V. These applications demand extremely high standards for partial discharge control, electrical insulation performance, and long-term lifespan. Therefore, a combination of flexible and rigid insulation designs is required, with high CTI materials being the preferred choice. In the new energy vehicle sector, such as High Thermal Conductivity Metallized Film Capacitor Bus Bars for EV Control Systems, system voltages are typically below 800V. Insulation performance requirements are relatively lower, with a greater emphasis on lightweight design, heat resistance, and assembly process compatibility. Therefore, PI materials offer certain advantages in specific welded structures.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Furthermore, in some non-laminated structures or single-conductor applications, powder coating insulation can also be used, i.e., Powder-painted Laminated Bus Bars with Dielectric Coating Thickness Ranges Between 0.2 mm ~ 3.00 mm. This process is suitable for insulating conductors with complex shapes, achieving good surface coverage and sealing. However, due to the difficulty in controlling insulation consistency at conductor edges and sharp corners, it is generally not used in high-precision laminated busbar systems, such as in demanding applications like Customized Copper Inverter Laminated Busbar for Electrical Installation.

 

Overall, as typical Laminated busbar passive electronic components, the performance of laminated busbars is highly dependent on the selection of insulation materials and structural design. By appropriately matching flexible and rigid insulation materials and considering specific application scenarios (such as Laminated Busbars for complex Busbar Installations), higher power density and system integration can be achieved while ensuring electrical safety.