Busbar Connection Design

I don't know if it will matter when someone responds but "high voltage" is a relative term. I have had jobs where I spent years at 3.3 volts and 5V was high voltage. I have also had jobs where I spent years at 120 & 240 VAC and would sometimes work at 7 KV "high voltage". For others high voltage is much higher.

I suggest adding nominal voltages, currents and AC or DC to the posting.

The busbars carry 800Vdc and a max current of 350A.

The Junction box is IP6K9K rated.

Thank you for pointing it out.

I would go with stainless steel bolts....

https://interplex.com/busbar-guide/

That would be the optimum choice.

However, our benchmarking reveals that almost every OEM uses Zn-Ni alloy plated fasteners in similar applications. And it is cost-effective too.

My concern is the dissimilar plating materials, How would the surfaces that are plated with Tin/Silver/Zn-Ni react with each other?

Thank you,

Not in the absence of a conductive liquid.

Since the junction box is equipped with a pressure compensation vent, it possible to have humid air inside the box over time.

Won't humid air be enough to form a galvanic cell to initiate corrosion?

My concern is the dissimilar plating materials. The anodic potential difference between Tin and silver is significantly high, and Tin is more anodic than silver. Though Tin forms a reasonably hard oxide layer, would it be sufficient to offer corrosion protection in the long run?

Thank you

You can always use a spray coating to seal the connections...this will protect from moisture...

https://www.ramoem.com/uploads/4/4/0/7/44075859/tin_commandments.pdf

https://advancedplatingtech.com/wp-content/uploads/2013/10/Use-of-Silver-in-Connector-Applications-M-Myers.pdf

All <...air...> is <...humid...> to varying degrees.

If the temperature inside the box is higher than that outside then the chances of condensation, and a conductive liquid appearing thereby, are somewhat limited.

Surely either the employing organisation or the Client organisation has standard practices for this sort of thing? Make some phone calls.

Tin and silver are very common connection combinations in industrial switchgear, which in most cases is only moderately protected from humidity (silver plated copper busbars). I had no idea they were far apart on the galvanic series, as it has been SOP for decades.

Petroleum jelly is an extremely good conductor of electricity. Smearing a thin layer of petroleum jelly on the joints will prevent the intrusion of moisture into the joint and inhibit corrosion. This was normal practice when I was working on high current DC busbar systems in electro-machanically switched telephone exchanges thirty years ago. It is still common practice on automotive battery terminals where it is used to prevent cathodic action between the lead battery terminals and copper clamps.

Thank you for the comment, One of the requirements from OEM was not to apply any barriers such as grease. Therefore we had to exclude that option completely.

These are common connection combinations found in US industrial switchgear and/or outdoor substations. As Solar Eagle points out, they are very close in the galvanic series, so have a low potential for corrosion, even in harsh environments, perhaps excluding salt spray that you may not need to design for. I personally have used these combinations in paper mill environments, and can report at least 10 years of satisfactory performance, indoor and outdoor.

@rwillliams

Thank you for sharing your experience. It is indeed beneficial.

I ran an internet search to get info about the compatibility of platings such as Tin-Silver, Nickel-Silver, but I didn’t find documents/experimental findings.

Could you please share if there are any electrical codes where I can find plating compatibility relevant information?

Thank you

Perhaps NEMA has some standards, SG1.1 is something that I could retrieve mentally. My experience started as a young engineer, and we took what standard configurations provided by respected manufacturers as good, and never gave it a thought afterwards, and never had cause to regret it later, after 50 years in basically stationary installations in some fairly high risk (for corrosion) chemical environments.

@rwilliams

Thank you for your input. I will try to get the standard to get further information.

@GW

Thank you for your comment.

The busbars length inside the box is 400mm, and the current density is 1500A/Sq.in.

The attention wasn’t paid to differential thermal expansion as stainless steel and copper have similar thermal expansion coefficients, and the busbar length is not very long. However, torque being a significant factor, copper softening could be an issue to be taken care of.

Thank you