power quality

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dereckbc

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Location
Plano, TX
Re: power quality

Now for the serious note. If this is a commercial building, I suspect your service is 3-phase 208Y/120 and not single phase 240/120.

It's late for me and I cannot go into great details, but as a data center and telephone power engineer, we use a PDU fed from a UPS with either 480 or 208 delta and a 208Y/120 output to feed the equipment on 120 recepts or some 208 delta 3-phase.

They can make an argument that 240 single phase and 3-phase 208 is more effecient, but not more stable.
 

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
Re: power quality

Originally posted by scotsarm:
how do i respond to ITs who claim that 220 is a more stable voltage than 110?
ask them to prove this statement. IT people believe in a lot of things that are just plain false.
 

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
Re: power quality

you could always point out to them that a 5% varaiance on a 120V line is 6 volts, while the same 5% variance on a 240V line is 12 volts, thus proving conclusively that 120V power is actually twice as stable.

of course this is meaningless babble, but most IT persons know so little about electricity that they will probably write this into the IT bible for the company and all IT installations will soon require 120V power rather than 240V.
 

catchtwentytwo

Senior Member
Re: power quality

I wonder if part of the problem is that a lot of servers now have a name plate operating range of 100 to 250 VAC? Maybe those IT guys "think" the higher voltage gives them more head room.
 

charlie b

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Staff member
Location
Seattle, WA
Occupation
Electrical Engineer
Re: power quality

Originally posted by scotsarm: how do i respond to ITs who claim that 220 is a more stable voltage than 110?
Roll your eyes, and try to stifle a laugh. :cool:
 

charlie b

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Location
Seattle, WA
Occupation
Electrical Engineer
Re: power quality

Nice explanation, M. I withdraw my glib "roll your eyes and try not to laugh" remark, with an apology to the IT world.
 

madmike

Member
Re: power quality

Nice theories. But a 220, 230, 240 volt system is easier to protect against noise than a three phase Y or a single phase 120 volt system. That's why some European equipment performs so flawlessly. In a Y system, large shunt capacitors are needed across each phase to ground to get rid of common-mode noise. They don't do this well, and they assume the ground wire has a wide bandwith to noise impulses which it doesn't. To cleanup a 220-230-240 system you only need a cap across the phases because, (here's the secret) the two phases are complementary, hence the ease of noise cancellation. Check out some medical-grade line filters for Y and for 220 systems.

r,
MM
 

madmike

Member
Re: power quality

marcspages,
I'll try. Basically, as I understand it, common-mode filter elements (capacitors) for a Y-based power system shunt common-mode noise to the ground plane. But they are only as effective as the total impedance of the ground system. A 220-230-240 two phase, (L1 & L2, each 115 volts to neutral) can be easily filtered by placing a capicator across the phases.

So as the origional question, is/can a 220 volt system be better for an IT system, my opinion is yes. Several power conditioner companies call it "balanced power" and claim a 15-dB reduction is system noise.
regards,
MM
 

dereckbc

Moderator
Staff member
Location
Plano, TX
Re: power quality

marcspages, not sure your definition of common mode noise is what I know it to be.

Common Mode Noise: The noise voltage (any signal not wanted) that appears equally and in phase from each current-carrying conductor to ground. That is L-G, and N-G. To the contrary common mode noise is very easy to eliminate by using a transformer. Even a simple dry-type transformers offers 60 db of CMR. Special isolation shielded transformers made for the purpose provide up to 140 db CMR.

Differential Mode (aka Transverse-Mode): Noise signals measurable between or among active circuit?conductors feeding the subject load, but not between the equipment grounding conductor or associated signal reference structure and the active circuit conductors. In other words L-L, and L-N.

I have used a lot of balanced power systems in data centers for the last 5-years or so with great success. But they are not 240 that you describe (same principle though), they are 120/60 VAC systems without a neutral, just two lines and a EGC. The recording industry has been using it for years.

[ October 30, 2005, 03:15 PM: Message edited by: dereckbc ]
 

dereckbc

Moderator
Staff member
Location
Plano, TX
Re: power quality

Originally posted by marcspages:
Dereck,


The moment you connect them to each other in any way whatsoever, you may as well remove the transformer. Agree?

Your 120V balanced is used in the UK, plenty! It's called RLV (reduced low voltage) but, and here is the crunch, I have had a number of cases already where when using PCs on RLV (building sites etc. in the interests of 'safety') the PCs become "unreliable".
Not sure I can agree, maybe I misunderstand. Any common mode voltages on the primary will be removed on the secondary period. What little does pass is via capacitive coupling, which can be removed further via shielding type transformers.

Interesting comment on your 120/60 RLV system. I can only assume there is no UPS involved. The 5 systems (data centers) I have designed with balanced power are fed with a centralized large scale UPS via PDU's. Only one failure or a problem at one site in LA as a result of technician error (left UPS in bypass mode and then a generator test).

I agree with your analogy of using 240 over 120 where SMPS are involved, that was my reference to efficiency gains. Not a problem when dual conversion, parallel redundant UPS systems get involved. However we do offer the customer either 208 or 120. Most go for the 120/60.
 
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