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Custom Ferrite for Bus-bars

As industry evolves and has increasing demands on performance and speed of electronic systems whilst simultaneously reducing costs, these requirements are most noticeable when looking at power transmission. As technology advances a simple solution is actually the answer, using wiring harnesses is becoming a thing of the past and the use of bus-bars is paving the way for the future of lower cost and higher reliability.

This all sounds great, problem solved…..right?

Bus bar ferrite
Bus bar ferrite

Well naturally despite all of its benefits, bus-bar technology also does have a few issues of its own that need to be thought about and addressed during the design phase of any product or project. As the bus-bar is typically constructed of copper and various dielectrics (they are almost always bespoke designs) if it is subjected to fast changing currents (and those currents form a loop) the bus-bar makes a great antenna and will begin to radiate EMI noise into your system, whilst also beginning to receive noise which may expose your system to external radiation. The two types of EMI are conducted and radiated, conducted EMI will travel from your industrial system back into the power grid and will begin to cause interference within other industrial and residential devices. Radiated EMI is when the noise is radiated externally into space, this noise might affect other circuits within your system and more importantly may corrupt communication and signal data.

If my system still works can I carry on and ignore this EMI ?

No, you definitely cannot ignore the EMI as its typically regulated (for the UK this is Ofgem) both types of EMI to protect consumers from losses in signal. Severe EMI can cause much greater concern as it could potentially lead to corruption in safety critical communication rendering the application unsafe, for example leading a machine to begin spinning its spindle even though it wasn’t commanded by the controller.

How do I solve this issue and get my system within regulations ?

It’s a good start to look at slowing down the switching transitions in the system to reduce EMI, however sometimes this wont be enough or you system requires the higher switching speeds. In these scenarios a great solution is a ferrite bead to clamp around the busbar however not “just any” ferrite will do and be an effective solution, as the busbars are typically bespoke themselves the ferrite also needs to be equally custom.

So why use a custom ferrite and what is it that you are looking for ? Well you can get some off the shelf ferrite solutions however these might not fit well or may not suit your needs electrically leading to the core saturating (making the ferrite redundant). As for what to look for, picking a core material that suits your application with regards to power and frequency, before selecting material you will need to be aware of your operating frequency and the frequencies you wish to negate with the core.

This needs to be known as cores impedance is frequency dependent, a theoretical ideal ferrite would provide high impedance at EMI frequencies and zero at all other frequencies however in reality ferrite impedance is frequency dependent so there will be low impedance at lower frequencies but never 0 impedance. Whilst also looking to ensure the air gap between the ferrite and the bus bar is kept to an absolute minimum is absolutely key to effective attenuation as an air gap increases impedance between the core and busbar. An increase or decrease in impedance of the core is directly proportional to an increase or decrease in the height/length of the ferrite core, as this is linked to the magnetic path length.

As a bonus, side note mounting the ferrites can sometimes be troublesome and some methods may leave the solution a mess of cable ties and tape (this does work and wont impact the core) however as many of you reading are saying “the customer wouldn’t be happy to see that” and we agree! We have in house expertise with 3D printing techniques that would allow us to provide services to create custom mounting cases, brackets or anything else to suit.

If you need any custom ferrites machining to your exact specifications as well as potential requirements for custom accessories to suit this design, contact Gateway and we are happy to assist in finding the answer!

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