INSTRUMENTATION • ELECTRONICS
RESISTORS T
Redesigning
Damiano Natali explains how computational fluid dynamics is enabling design engineers to rethink the resistor
he design of the much loved Mini Cooper dates back to the 1950s and has elegantly withstood the test of time to become
the British icon it is today. Mini Cooper engineers would tell you that there are several generations of Minis, each different from the rest. However, if you asked the average person on the street, they would probably struggle to see the differences between some of the generations. This shows that product redesigns can go unnoticed despite considerably improving and updating the product benefits. A similar principle applies to electrical products. Here, we discuss how computational
fluid dynamics (CFD) comes into play for improving product designs that have stayed much the same for decades. CFD combines the principles of fluid mechanics with numerical algorithms to analyse the behaviour of a fluid and the forces it exerts on bodies. Like structural and electromagnetic
packages, CFD is one of the computer- aided engineering (CAE) technologies that have flourished in the past decade. CAE has progressively become a tool of overwhelming importance, given its flexibility in allowing manufacturers to understand their products better and improve product performance quicker and with fewer resources. CAE is used in factory settings in a wide range of stages: from first design and proof-of- concept through to the development and verification of a product.
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By using CFD, Cressall’s design engineers can ensure that a product is fit for purpose and for the environment it will operate in
By providing a reliable and accurate
digital simulation of how a resistor will perform in a given situation, the manufacturer can identify potential drawbacks and improvements early in the design process. Moreover, CAE tools allow engineers to perform simulations on existing products without having to design, set up and maintain a highly complex testing rig. Finally, CAE allows design engineers to experiment changing different parameters (the so-called ‘what-if ?’ analysis) and – hopefully – to find the optimum design. In turn, this translates into time and cost savings for their clients.
WIND/WAVE FORCE ON ENCLOSURES One challenge that Cressall Resistors continuously faces is the brittle nature of ceramic post insulators. Apart from the primary function of providing electrical insulation, post insulators play a fundamental part in the structure of the enclosure. This problem is sharpened by the brittle nature of the porcelain
ceramic from which they are made. Post insulators need to withstand the impact of the journey from factory to site, the installation and the strong winds they will be facing throughout their lifetime, especially for offshore or near-coast projects such as wind farms. By using CFD, Cressall’s design
engineers can assess the wind force that an enclosure can be subjected to – ensuring that the product is fit for purpose and for the environment it will operate in.
NATURAL AIR CONVECTION Power resistors reach high temperatures in service, which makes the design of the cooling mechanism a critical part of the design process. The principal cooling method is defined by the exact application of the resistor and location in which it is going be installed. The three methods used are natural or forced air convection or forced water-cooling. For all types CFD allows engineers to understand the performance of the
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