Laminated Busbars Insulation Material Analysis: How Do Flexible and Rigid Insulation Affect System Performance?

With the rapid development of new energy vehicles, energy storage systems, rail transit, and industrial frequency conversion equipment, laminated busbars have become key conductive connection components in high-power power electronic systems. Whether it's a laminated busbar for electric cars, a laminated busbar in a high-power converter, or a customized laminated busbar for IGBTs, its performance depends not only on the conductor design but also closely on the selection of insulation materials.

 

The insulation system directly affects the busbar's withstand voltage, partial discharge performance, service life, and overall reliability. Understanding the characteristics of flexible and rigid insulation is crucial for designing high-performance laminated low-inductive busbars.

 

 

 

A laminated busbar is a conductive connection system composed of multiple layers of conductors and insulating materials, belonging to the typical Multi-Layer Composite Structure Connection Bar structure.

 

By tightly stacking the positive and negative conductors and isolating them with an insulating layer, loop inductance can be effectively reduced, system electromagnetic compatibility performance improved, and energy loss reduced. Therefore, it is widely used in:

 

Electric vehicle drive systems
Energy storage converters (PCS)
Industrial frequency converters
Photovoltaic inverters
Rail transit power systems
High-power power supply equipment

 

In multi-layer structures such as three-layer laminated busbars, the insulating material not only provides electrical isolation but also mechanical and environmental protection.

 

 

 

Currently, most partially laminated busbars use flexible insulating films laminated onto copper conductors.

 

Flexible insulating materials are typically bonded tightly to the conductor through a hot-pressing process, forming a complete seal at the conductor edges, thereby improving resistance to moisture and heat, pollution, and aging.

 

PET Polyester Insulation Material

PET is one of the most common insulating materials for multilayer busbars.

Its main characteristics include:

Long-term operating temperature up to 105℃;
Excellent ductility; Less prone to cracking during bending.
Excellent surface quality;
Good flame retardant properties; Relatively economical cost.

Due to its high CTI (relative tracking index), PET is particularly suitable for high-voltage applications.

PET materials are widely used in Subway Laminated Busbars and industrial power systems.

PI Polyimide Insulation Material

PI is a high-performance, high-temperature-resistant insulation material.

Its main advantages include:

Long-term temperature resistance exceeding 200℃;
Excellent thermal stability;
Good weldability; High inherent flame retardancy.

Therefore, PI materials have significant advantages in IGBT Laminated Busbars and applications requiring the soldering of capacitors, inductors, and other components.

However, PI materials have relatively weaker surface tracking properties and are more expensive than PET. They are typically used in special applications rather than conventional designs.

 

 

Flexible insulation primarily covers the conductor, while rigid insulation mainly serves as structural isolation between conductor layers.

 

In high-voltage systems, thin-film insulation alone is often insufficient to meet partial discharge and creepage distance requirements, necessitating the addition of rigid insulation layers.

 

Common rigid insulation materials include:

Glass fiber reinforced polyester board

Epoxy fiberglass board

High-strength insulating composite materials

The thickness of rigid insulation is typically determined based on the system's operating voltage.

 

In general engineering design:

Approximately 1mm of insulation distance is required for every 1kV increase in operating voltage.
The higher the voltage level, the greater the rigid insulation thickness.
High-voltage systems may require insulation structures 3-6mm or even thicker.

 

Therefore, in high-voltage applications such as High Voltage Explosion-Proof Inverter Busbar, rigid insulation has become an indispensable and crucial component.

 

 

RTI-Relative Temperature Index

RTI (Relative Thermal Index) represents the highest temperature rating at which an insulating material can operate continuously for extended periods.

This index is used to evaluate the material's ability to maintain mechanical strength and electrical properties under long-term thermal aging conditions.

Generally:

 

Higher temperatures shorten material lifespan.

For every 10°C increase in temperature, material lifespan may be halved.

For every 10°C decrease in temperature, material lifespan may double.

Therefore, for long-term operated laminated busbars for complex busbar installations, RTI (Relative Tracking Index) is a crucial factor in material selection.

 

CTI-Relative Tracking Index

CTI evaluates the resistance of an insulating material surface to tracking.

Higher CTI values:

Smaller creepage distance requirements;
Stronger resistance to contamination;
Safer and more stable operation at high voltages.

For applications above 1000V, CTI is often a critical parameter determining insulation design.

 

Elongation

Elongation reflects a material's ability to resist cracking and thinning during stretching.

High elongation means:

Better suitability for complex bending processes;
Easier conductor edge sealing;
Higher insulation reliability.

PET materials typically have elongation exceeding 100%, while PI materials generally have lower elongation than PET.

 

 

Industrial Power Systems

Industrial applications typically involve:

Operating voltages from 1000V to 6000V;
Long-term operational requirements;
High partial discharge requirements;
Strict creepage distance specifications.

Therefore, Laminated Busbars for Three-Level Inverters and large converter bus systems often employ a combination of flexible and rigid insulation.

 

New Energy Vehicle Applications

New energy vehicle systems typically operate at voltages concentrated in:

400V platforms

800V platforms

Due to the relatively lower voltage levels:

Lower partial discharge requirements;
Rigid insulation is not required in most scenarios.
Focus is on lightweight design and space utilization.

Therefore, Laminated Busbars for Electric Cars often employ lightweight laminated structures to meet high power density requirements.

 

 

 

In addition to traditional laminated insulation, powder coating and epoxy coating are also common insulation methods.

 

These processes are suitable for complex structures or single-conductor applications, achieving:

Surface insulation protection;
Corrosion protection;
Environmental sealing.

However, for bus bar systems requiring low inductance and high reliability, laminated insulation remains the mainstream solution.

 

 

With the continuous development of power electronics technology, laminated busbars have evolved from simple conductive connectors into crucial components integrating conductivity, heat dissipation, insulation, and electromagnetic optimization. Whether applied to new energy vehicles, rail transit, or industrial power conversion equipment, the appropriate selection of insulation materials directly impacts the system's safety, reliability, and lifespan.

 

For modern laminated busbar designs, flexible insulation is responsible for achieving efficient conductor encapsulation, while rigid insulation meets high-voltage withstand requirements. Together, they ensure the long-term stable operation of the entire power system.