What Are Electric Busbars?

An electric busbar (also written as bus bar) is a metallic bar, strip, tube, or rod that conducts current from one place to another in a safe manner with minimal energy losses. They are commonly used instead of wires or cables for high-current power distribution, high-voltage equipment, and low-voltage battery applications. Most busbar configurations are not insulated to improve convective cooling and allow easy access for new connections. Since most busbars work with higher-voltage three-phase power, many electrical busbar systems include three separate conductors designed to safely and efficiently work together. 

Engineers designing busbars for electrical power applications must balance space, cost, safety, resistance, capacitance, and inductance between legs or nearby conducting materials, mounting options, and cooling. These often-conflicting requirements make electrical, magnetic, 

Engineers place busbars in electrical systems where they offer design advantages over wires or cabling. Some of the most common applications are:

Electrical Power Switchgear

Switchgear is used in electrical power systems as switches, fuses, and circuit breakers that protect, control, and electrically isolate electrical equipment, often at a power generation facility or substations. Busbars connect components like transformers, fuses, and industrial machinery. They can also distribute power within a device.

Bus Ducts or Busways

Bus ducts are long enclosures containing busbars or cables used as power connectors from one location to another. Busways consist of metal ductwork or cast resin structures that contain busbars. In power utility applications, they are often constructed from conduits embedded in concrete.

Power Distribution Boards 

Power distribution boards are used in buildings for electrical power distribution, splitting incoming power feeders into separate circuits. Vertical or horizontal boards are placed strategically, and circuits are connected through taps. The system is either placed in a grounded cabinet or placed in an elevated location. 

Battery Power Distribution

Busbars are the preferred way to connect battery packs in electric vehicles and power storage applications because of their rigidity and thin geometry. Unlike most applications, EV battery systems sometimes use insulated busbars made with aluminum instead of uninsulated copper busbars because of the reduced weight. 

Renewable Energy Systems

Efficiency is critical for solar, wind, hydroelectric, and other renewable energy systems. Busbars deliver an efficient, reliable, and robust method for transferring and delivering power within the devices used in renewable power applications with better efficiency and flexibility. 

Industrial Machinery

Industrial equipment pulls power from busbar power distribution boards and uses busbars internally for power distribution from the power supply feeder to feeders that lead to powered components within the system. 

Electronic Devices

Although we usually think of busbars for power transmission and high-power equipment, designers use them for the same reasons within electronic devices, especially in power electronics. The thin form factor and lighter weight make them a good choice for solving packaging issues or dealing with heat distribution. 

Suppliers have developed a wide variety of busbar types to meet the needs of a growing number of applications. Busbars can be grouped by the following characteristics:

Material

Suppliers manufacture busbars from any conducting material, but most use copper or aluminum. Copper metal has the second highest conductivity, after silver. Aluminum is the fourth-most conductive metal, but it is lighter and less expensive than copper. Both aluminum and copper bars are usually electroplated with coatings of tin, nickel, or silver to reduce corrosion and improve overall performance. 

Shape

The shape of busbars impacts their conductivity due to skin effect and the heat transfer from the bar. In most cases, the goal is to have a high ratio of surface area to cross-sectional area. 

Here is a list of the most common shapes:

• Rigid busbar (flat bar): The most commonly used shape is a long, thin, rigid bar. They are often shaped at the time of manufacture to fit specific needs. 
• Special cross-section busbars: Some busbars use “U,” “T,” or “L” shape cross sections to provide greater bending stiffness, increase surface area, and provide more connecting options. 
• Laminated or flexible busbars: Flexible busbars are created by laminating thin metallic strips or foil. Not only does this make the busbars more flexible, but it also increases the total surface area and, therefore, conductivity. 
• Round busbar: Busbars with a solid or hollow cylindrical cross section are used for high-current applications in which greater rigidity, rotation, or installation flexibility are needed. 
• Insulation: Another way to distinguish a type of busbar is through how it is insulated from the surrounding structure. In some cases, it is coated with an insulating polymer, or it may be insulated and held in place by insulated mounts or isolators.

Current-carrying Capacity and Type

A single-phase busbar has two circuits: one that is live and another that is neutral. Three-phase busbars use four conductors, one for each phase and another as a neutral run. Where single- and three-phase types deal with alternating current (AC) applications, some busbars carry direct current (DC).

Engineers choose busbars for many reasons, usually due to cost, performance, and safety. In most cases, the following characteristics drive the choice of busbars over other power distribution options:

• Simplified power distribution: Busbars combine many electrical connections into a central hub. This is easier to design and maintain than complex wiring.
• Geometric flexibility: Busbars can be constructed into almost any shape and fit to almost any application. 
• Connection ease: Busbars don’t need complex electrical connections. If power is needed, all you have to do is connect a wire to the surface.
• Form factor: The thin topology of busbars helps distribute power in tight spaces, as can be seen in battery packs, electronics, or industrial machinery. 
• Rigidity: The structural stiffness of busbars eliminates the need for cable management. They can contribute to the structure's overall strength and bridge longer distances. 
• Cost efficiency: Busbars can cost less than wiring options. They are also less expensive to install, maintain, and repair. 
• Sustainability: Since they are made mostly of solid copper or aluminum, busbars are easy to recycle. 

As can be seen by the different types of busbars, engineers have lots of choices in material, configuration, coatings, and geometry. Multiphysics simulation tools are a perfect complement to the design process because they provide a fast and accurate way to understand the interaction of electromagnetic fields, heat generation, heat transfer, and structural response. 

Engineers want to optimize their busbar designs to have maximum efficiency, operate safely, and minimize cost. Once they understand what the routing of the circuit is, they can create a low-frequency electromagnetic model in a program like Ansys Maxwell® advanced electromagnetic field solver to calculate the electromagnetic field, heat generation, and losses due to resistance, capacitance, and inductance. They can optimize the geometry automatically or engage in what-if studies to determine the best shape for each module in their busbar. 

Simulation of current density on three-phase busbars using Ansys Maxwell

If the application involves multiple circuits, as in a three-phase application, engineers can use Ansys Q3D Extractor® parasitic extraction electromagnetic simulation software to quickly model the entire system and calculate the parasitic parameters for frequency-dependent resistance, inductance, capacitance, and conductance (RLCG)

A general-purpose structural-thermal tool like Ansys Mechanical™ structural finite element analysis software is then deployed to look at thermal stresses, make sure none of the natural frequencies are a multiple of the operating electrical frequency, and assess the overall system stiffness.

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