ECN Forum Forums General Topics of the Trade General Discussion Area MWBC with 2 out of 3 phases

So maybe they need to distribute 127/220V or 133/230V or 139/240V around the data center, if they are unwilling to get the low harmonic PSUs, or are unwilling to upsize the neutral, or are unwilling to string up separate neutrals in each phase.

Or there needs to be PSUs designed for 400VAC (and 480VAC might be nice, too).

Of course we in North America can just connect our trashy PSUs line to line at 208V and push the neutral harmonics to the next transformer upstream after the first delta-wye (if the circulating currents in the delta primary isn't a problem). Hopefully by then it will be large enough that all those triplens will not be a significant total. REALLY large data centers won't have that option.

Newer PSUs are supposed to be much lower in harmonic current content. If manufacturer specs are to be believed, the good ones are lower. The cheap $3 ones from the middle kingdom could be a problem.

The main problem: reduced size neutrals in main feeders. They stopped doing that in data centers a few years ago and that pretty much solved the problem.

Same in the US. Neutrals are often sized to 200% in datacenters to deal with the harmonic current.
The problem goes beyond harmonic filtering; the real issue is that switched rectifying power supplies only draw power during the peak of each phase cycle. The current on the neutral is close to a 180Hz stepped wave, which means actual current levels exceeds traditional sinusoidal RMS by a considerable amount. The only surefire way to eliminate this is to use delta power, which eliminates the triplen harmonics, trading them for 5th, 7th & 13th, which are easier to filter out.

Way back in the olden days we avoided the whole mess in computer rooms by never even bringing a neutral into the panel. They used that bus for the IG and all loads were L/L