OPD October 2000: Laminated Bus Bar Assemblies Improve Power Distribution in High Power Electronic Systems

Oct 1, 2010 12:00 PM
Michael Stibgen, Methode Electronics, Inc., Rolling Meadows, Illinois

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Today's electrical and electronic systems are being asked to deliver higher performance, higher quality, and more capabilities, with better reliability, lower cost, and smaller size, than previously thought possible. This is putting increased pressure on the designers of these systems to look for better technologies to replace the “usual way” of doing things.

In systems where high power levels are distributed, such as motor drives, electric vehicles, telephone switching central offices, and large computer cabinets, designers must optimize the way power is distributed within the cabinet or enclosure. This is necessary because power distribution issues can have a major effect on the cost, performance, reliability, and size of systems where tens, hundreds, or even thousands of amps are distributed. A technology that has proven useful in meeting these power distribution requirements is laminated bus bars. To understand why the laminated bus bar is an improvement, we first have to look at the characteristics of traditional power distribution approaches.

TRADITIONAL APPROACHES

The traditional solution for distributing high power within an electronic enclosure has been with cables and/or cabling harnesses. These standard wiring solutions are fabricated with individual conductors that have been individually terminated, then tied together to form assemblies (Fig. 1). For simple systems operating at relatively low power levels, these cable assemblies are acceptable. However, as systems become more complex, and power levels rise, these traditional cabling harnesses have limitations.

As current levels exceed several hundred amps, it is necessary to use heavy-gauge conductors in these cable assembles: 2/0 AWG or heavier. Such a heavy gauge conductor is very stiff, and difficult to bend into the exact shape to fit inside an enclosure.

Also, with more complex electrical signals that have higher-frequency components, the EMI/RFI performance of conventional cable assemblies may be inadequate. System problems can result when one conductor within a cable harness induces an unwanted signal into a nearby conductor.

More complex signals are due to the increasing use of high-speed digital components. These higher-frequency signals are more susceptible to interference, which is often present when system power supplies use IGBTs or other high-power switches. These devices are common in motor controller and UPSs, and they can induce transient spikes in power distribution cabling. Inadequate power distribution cabling then sends these spikes and noise throughout the entire system, causing interference with sensitive data signals. High inductance power distribution cabling worsens switching transients. And, traditional cabling harnesses have high inductance.

As power-distribution topologies become more complex, traditional cabling systems must also become more complex, with each termination individually connected to the proper device or subsystem. The greater the number of such terminations, the higher the probability that an assembly error will occur. Tracking down and correcting such errors is time-consuming, and increases total product assembly costs.

In computer and telecommunications systems, the use of traditional lug-style terminations may no longer be an option. That's because many of these systems are being designed to be “hot-swappable” so that a defective or failed circuit board can be replaced without turning off system power. Conventional cabling harnesses, with their exposed terminations and unprotected live conductors, represent a safety hazard when hot swapping is necessary. The lug terminations of standard cables cannot be used in this environment. For all these reasons, a better solution has been developed for handling the power-distribution needs of today's more complex, high-power systems: the laminated bus bar system (Fig. 2).

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