High power is brought to a small resistor

23-08-2019 | REO (UK) Limited | Passives

REO UK has delivered high power brake resistors into the 21st century with its new REOHM series 155 braking resistors produced for industrial control cabinets. The device can deliver up to 3500W of continuous power to drives with medium and high-power frequency converters, with isolation voltages to 4.4kV, in a compact design that aids the product to overcome the common issues with electrical braking resistors.

The new series is created to offer reliable performance in control cabinets while defeating the traditional problems with braking resistors in industrial applications. The product’s small size and large power capacity make it an excellent option for heavy industrial sector applications, including mining equipment, trains and large vehicles.

The resistors are rated up to IP66, affording complete protection against dust ingress and guarding the unit against powerful jets of water, making the product range ideal for more demanding environments. The range has also satisfied salt mist testing, making it ideal for offshore applications.

“Larger braking powers have usually been the domain of old-fashioned wire-wound types,” explained Steve Hughes, managing director of REO UK. “These are relatively cheap to produce and are well understood in industry. However, they have several shortcomings when applied in more modern applications and environments. In particular, there have been three key risks: the wire can uncoil, the design of the unit housing has been open to ingress, and the resistor can be prone to electromagnetic interference (EMI).

“The failure mode of a traditional wire-wound resistor tends to be catastrophic, especially with units with little or no enamelling and often results in an uncoiling of the wire. Often, the resistor will still have power on at this point, creating a live DC conductor that can damage the drive and blow fuses. And this is among the best-case scenarios.

“The nature of them being inherently open, much like old fashioned heater elements, means that they must be adequately housed and segregated from other sensitive parts of equipment, often on top of control cabinets. But this can lead to issues, especially if there is likely to be conductive or explosive dust or material in the air, as in a paper mill. “Likewise, units housed externally often require cabling that can unintentionally emit high-frequency noise from the drive, which can manifest as distorted currents in the control cabinet and nearby electrical systems.

“With the development of the REOHM series 155, these problems can become a thing of the past for industrial businesses. The resistors come in an IP66-rated closed unit that prevents dust and airborne materials from entering the unit, and the cable connecting the unit to the drive is fully-screened to ensure that emissions are not an issue. Drawing from our expertise in delivering good power quality, this resistor is able to meet the emerging demands of an ever-developing industry.”

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