Aerospace & Defence

Smooth sailing with braking resistors

2nd September 2021
James Anstee

The company supplied its REOHM series BWD158 water-cooled braking resistor to the design of a luxury vessel, with the resistor able to ensure long-lasting safety and reliable performance in a compact, simple-to-integrate footprint. 

The vessel has a diesel-electric propulsion system that will provide a top speed of 18 knots and a maximum range of 4,900 nautical miles. To ensure that the drive system can safely reduce speed, stop or even reverse during voyages, braking resistors are essential to dissipate unwanted power safely. The team developing the vessel selected REO’s BWD158 braking resistor to deliver this.

REO’s BWD158 range of aluminium-clad, water-cooled resistors are built for applications where reliability is essential, even under high loads. The resistor has an operating voltage up to 1kW and, due to its modular design, can be parallel and series connected to allow a continuous power dissipation of up to 60kW.

The resistors do not require additional housing as the design is inherently robust and boasts an ingress protection rating of IP65, ensuring protection against water jets and all dust. The aluminium housing is anodised to ensure corrosion resistance and all connections and fixings are either stainless steel or anodised aluminium to ensure longevity.

REO’s cooling system separates the coolant from the electrical circuit to always ensure electrical isolation, which is essential in a floating vessel. The unit can continue to run without coolant for a specified period to allow the system to safely shut down in the event of a coolant problem. In addition, the double insulated windings mean that even in the event of an exceptional overload, the windings will present a progressively increased resistance rather than an open circuit or short circuit.

“Developing power electronics for marine or offshore applications is no easy task due to the harsh nature of those environments,” said Steve Hughes, Managing Director of REO UK. “Accounting for these conditions often involves costly design adjustments, especially with essential components like resistors. In effect, it becomes something of an inconvenient balancing act between cost, size and performance.

“Conventional wire-wound resistors can be used in marine applications, but they are usually housed in separate enclosures and the windings should be non-corrosive. This usually means that they are larger and more expensive than standard products. When you add to this the complexity of safely water cooling them, the cost of applying them in anything other than the simplest of applications spirals.

“These are all challenges that we overcome with the BWD158. Its robust and IP65-rated design immediately reduces the installation size and complexity, and the in-built safety features — such as the capability to operate coolant free for short periods — ensure that it provides the reliability required at sea. These features make it well suited for marine applications, allowing engineers to forego the balancing act.”

The luxury 50m vessel is constructed entirely of aluminium and has a beam of 9.4m beam but still falls under the important 500GT threshold, which reduces the licencing requirements of any potential sailor. With the use of the BWD158 to ensure safe and reliable performance with minimal integration cost, the lifetime project cost has been further reduced.

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