UPS

A

anbm

Senior Member
Location
TX
Occupation
Designer
Existing 480V, 3PH, 800A electrical panel has a 400A/3P CB, 400A circuit to feed an UPS.
The client wanted to replace the 800A panel with new panel at the same spot but won't
allow the UPS loosing primary input power circuit more than 10 minutes. UPS battery
can back up the UPS around 20 min. maximum. What is the option to handle this
situation? Not using solar power correct? lol
 
ModbusMan said:
A system of that size should have a static bypass input, and if the client was forward thinking enough, a wrap-around bypass as well. Generator power to that while the panel is swapped.
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Only a single input circuit to UPS, no external bypass.
 
We have backfed the UPS output from a temp upstream feeder. See if there is a spare on the UPS output panel that can accept a temp back feed big enough to support the load. Wire the temp backfeed breaker 1st, then the cutover is quick (closed transition, make before break). Then you could take your time to either replace the upstream panelboard or if they want UPS protection during that time, you then have more than 10 min to provide a temp UPS input feeder as the load is energized on the load side.
You could also provide a temp UPS to do the load side back feed, then you can have lots of time to do the upstream panel change.
 
anbm said:
single feed, no external bypass
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Nothing to do with the feed to the UPS...it is the type of UPS.
A double-conversion on-line UPS converts power twice. First, AC input, with all of its voltage spikes, distortion, and other anomalies, is converted into DC. A double-conversion on-line UPS uses a capacitor to stabilize this DC voltage and store energy drawn from the AC input.
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That would be more tolerant of the anomalies in the generator power.
You would disconnect the existing power feed and land the generator power feed at that location. With planning and preparation, you should be able to do that in less than 10 minutes.
 
Flicker Index said:
I don't know of any standby (non double conversion) UPS of that size.

What is double conversion? It's essentially a solid state MG set.
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I want to say either MGE or APC made a line interactive roughly that size a while back, but what's more common these days are conversion/eco bypass. Don't use them ourselves, but if I understand the tech correctly, it's basically running the inverters at a slightly lower voltage than the input, so the system is essentially on bypass power the entire time (more efficient) until something happens on on the grid, at which point the inverters become the stiffer source and carry things through.

Personally, I view double-conversion more like a VFD running at a fixed 50 or 60Hz than an MG, but that might be because I worked at a motor shop before getting into data centers.
 
electrofelon said:
Essentially a double conversion is an inverter that runs off batteries. There is no switching or transfer when mains power goes out.
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Ug... no. It does not run off the batteries unless the power goes out... can't discharge and recharge batteries at the same time, y'know. During normal operation, a rectifier front-end charges a capacitor-buffered high voltage DC bus, which the inverter then pulls from. Hence why I say they're more like a VFD than an MG.
 
ModbusMan said:
Ug... no. It does not run off the batteries unless the power goes out... can't discharge and recharge batteries at the same time, y'know. During normal operation, a rectifier front-end charges a capacitor-buffered high voltage DC bus, which the inverter then pulls from. Hence why I say they're more like a VFD than an MG.
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Thats pretty much what I said no? Okay by "runs off the batteries" I meant they are connected in parallel with the DC supplied by the rectifier, so they are always connected, there is no transferring. Come on, you knew the point I was trying to make 🙄
 
ModbusMan said:
Ug... no. It does not run off the batteries unless the power goes out... can't discharge and recharge batteries at the same time, y'know. During normal operation, a rectifier front-end charges a capacitor-buffered high voltage DC bus, which the inverter then pulls from. Hence why I say they're more like a VFD than an MG.
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That rectifier front end has to have the necessary smarts to properly recharge the battery after a loss of power event, so it is plausibly called a battery charger.

The inverter is running continuously from the DC bus.

The rectifier/charger and inverter are running at the same time. There is slight net current flow into the battery to cover internal losses.

Agreed that the battery is not simultaneously charging and discharging, but it is reasonable to say that both the rectifier/charger and the inverter are running at the same time.

The approach you described a few steps back where the inverter is running but not actually suppling current to the load strikes me as quite clever.

-Jonathan
 
winnie said:
That rectifier front end has to have the necessary smarts to properly recharge the battery after a loss of power event, so it is plausibly called a battery charger.

The inverter is running continuously from the DC bus.

The rectifier/charger and inverter are running at the same time. There is slight net current flow into the battery to cover internal losses.

Agreed that the battery is not simultaneously charging and discharging, but it is reasonable to say that both the rectifier/charger and the inverter are running at the same time.

The approach you described a few steps back where the inverter is running but not actually suppling current to the load strikes me as quite clever.

-Jonathan
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Kind of like a car electrical system. Things run on line power which is fed from a DC power source that's skimming above battery voltage but when the alternator is switched off, it will run off of battery.
 
electrofelon said:
Thats pretty much what I said no? Okay by "runs off the batteries" I meant they are connected in parallel with the DC supplied by the rectifier, so they are always connected, there is no transferring. Come on, you knew the point I was trying to make 🙄
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Not really, no... I don't know how many times I had to stop sales reps from saying the exact same thing, not least because the batteries are never directly connected in parallel to the DC bus. Ripple currents are death to VRLA batteries, and I can't imagine lithium is much happier, so the batteries get their own charging circuit independent of the main power flow. You'll also find that the battery bus is lower than the inverter bus, and there's a DC boost between the two because even though large units typically have ~540VDC for their battery float, the bus under discharge will drop almost instantly to 480VDC, and by end of discharge it's down to 400-420 (depending on configuration). The inverter bus by comparison can be nearly 800VDC on the newest systems.

winnie said:
The rectifier/charger and inverter are running at the same time. There is slight net current flow into the battery to cover internal losses.
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Yes, but they're completely separate components. The power rectifier supplies the inverter, the charger supplies the batteries. Letting one touch the other will result in spitzensparken.
winnie said:
The approach you described a few steps back where the inverter is running but not actually suppling current to the load strikes me as quite clever.
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Indeed, but that's if I understood the sales pitch correctly.
 
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