hello, İ have a critical load (8 operations room in hospital) and want to feed this load with 2 40 kVA UPS (parallel operation).Maximum load is 80 kva or so, now what if i do this instead of 1 80 kva ups? ups type is online and if i use 2 x40 kva ups it will cost less and i think this will be more reliable, if it is really so it means as i divide the load between 3 4 5 .... ups it will be more reliable and cheaper?
paralleling two ups
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zbang
Senior Member
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- Roughly 5346 miles from Earls Court
First, are the UPSs you want to use capable of parallel operation? Second, if you have an 80KW load and two 40 KW UPSs, what happens when one UPS quits? (Usually the other one quits with an overload.) Third, are the UPSs rated for supplying critical loads?
yes they are,what do u mean with "rated for criticial loads" ? they feed IT isolation panels of op.rooms, is it always true to divide the loads to multiple ups's? yes one of them quits and the other might be overloaded but if there is no overload isnt it more reliable against the case of 1 ups ? AT LEAST at light loads if one of them goes failed the system will keep on feeding via 1 healthy ups the load isnt it true? i think there will be no any drawback if we use parallel ups's
DataCenterGuy
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- New York
You either have "Critical Load" or you don't. You seem uncertain as to what your real load might be, which is a dangerous position to be in when sizing a UPS. You're dealing with Operating Rooms in a hospital. In my opinion, that's ALL Critical Load, and I wouldn't want you guessing whether the load will be "light" when a UPS fails if I'm on the table in your hospital. With multiple UPS's, if one fails, the remainder ALWAYS have to be capable of carrying the full load. But you're also talking in kVA, which is another trap with UPS ratings. Units in this size range have historically been rated at 0.8 Power Factor, which would mean only 32 kW capacity on a 40 kVA unit. Today more are being rated at 0.9, and some even at Unity (which means you really need to understand the pf of what you're connecting to it.) But your whole question of Mutiple Modules vs Single Modules remains a raging debate, with no one dominating. I suggest you research articles and white papers by Liebert and APC, who are the two biggest adversaries in this "Module Count" debate. And get some expert advice before you do anything that could bring down your ER's.
zbang
Senior Member
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- Roughly 5346 miles from Earls Court
Some manufacturers will not allow their products to be used in certain high-liability applications, such as patient care, without their permission. You need to make sure that whichever manufacturer you choose will allow this use. Likewise, the manufacturers' engineers can advise on the proper application, paralleling, redundancy, etc.
in fact i had the idea of using only one ups but i just tried to tease u up for getting the most detailed possibilities, one of my fellows advocates using 2 ups, by the way datacenterguy, i think u cant guess what does "light" and cricitical load mean since if u have 1, 2 or 3 op.room in operation compared to 4 (in my example ) it means light, namely one of the ups will get loaded below nominal load, i think light goes well here, also all op rooms is critical loads from the point of electrical installation... i think u should read some articles of this before criticizing me...
but...
but...
he claims if one of them goes overloaded when the other is gone it will bypass itself and transfer to the mains, well what was to be if only one ups was used and it was gone?? the same one, namely bypass, so what is advantage?
1- at light loads (less than 1 ups nominal load which is divided to 2 with twu ups in parallel) we have a chance to replace the broken ups without any interruption.
2- two smaller ups costs less than 1 bigger one
so is there anyone who can tell me the real drawback of using 2 small ups instead of 1 big one??
but...
he claims if one of them goes overloaded when the other is gone it will bypass itself and transfer to the mains, well what was to be if only one ups was used and it was gone?? the same one, namely bypass, so what is advantage?
1- at light loads (less than 1 ups nominal load which is divided to 2 with twu ups in parallel) we have a chance to replace the broken ups without any interruption.
2- two smaller ups costs less than 1 bigger one
so is there anyone who can tell me the real drawback of using 2 small ups instead of 1 big one??
Please
Please
Please let me know the name of the hospital. I will be sure to not have an operation there.
You really want the UPS manufacturer (Liebert) to recommend something or get you to an engineer experienced with these systems.
UPS's go offline for maintenance all the time. That's the reason for dual redundant parallel (N+1). One UPS module has to be rated for *all* of the load in a dual module parallel bank. You will be on one module frequently for scheduled maintenance, not when the load is light. You could be talking about dual redundant parallel 100 kw modules, who knows. You will not be splitting the rating with splitting the load.
Also the bypass system, if you have a separate cabinet with static switches in parallel with bypass breakers, the static switches may be near closed transition. Likely there will be some kind of switching transient, it could also switch badly.
I would definitely look at running dual UPS at 480 volt delta and feeding a stepdown delta to Y transformer. The whole system, the UPS's and the loads, have to be built, rated, and tested to work together.
Please
Please let me know the name of the hospital. I will be sure to not have an operation there.
You really want the UPS manufacturer (Liebert) to recommend something or get you to an engineer experienced with these systems.
UPS's go offline for maintenance all the time. That's the reason for dual redundant parallel (N+1). One UPS module has to be rated for *all* of the load in a dual module parallel bank. You will be on one module frequently for scheduled maintenance, not when the load is light. You could be talking about dual redundant parallel 100 kw modules, who knows. You will not be splitting the rating with splitting the load.
Also the bypass system, if you have a separate cabinet with static switches in parallel with bypass breakers, the static switches may be near closed transition. Likely there will be some kind of switching transient, it could also switch badly.
I would definitely look at running dual UPS at 480 volt delta and feeding a stepdown delta to Y transformer. The whole system, the UPS's and the loads, have to be built, rated, and tested to work together.
dbuckley
Senior Member
- Location
- Canterbury, New Zealand
In my opinion and experience, if you can avoid paralleling UPSs, do so, as its just another problem waiting top happen. Paralleled UPSs are supposed to be more reliable than single UPSs, but I have seen it go wrong with an entire six pack of UPSs all failing together.
If you want to use more than a single UPS the better way is to split the loads across the UPSs, rather than parlallel UPSs. The best way is to have loads than can take dual feeds, and then they are supplied from both UPSs, but under this arrangement both UPSs have to be able to supply the full load: there are no size savings but there are reliability improvements.
And as noted above; UPSs that are paralleled must be designed for the job from the same manufacturer and either be identical or specified to work together. Paralleling two random UPSs would probably fall under the category of "entertaining".
If you want to use more than a single UPS the better way is to split the loads across the UPSs, rather than parlallel UPSs. The best way is to have loads than can take dual feeds, and then they are supplied from both UPSs, but under this arrangement both UPSs have to be able to supply the full load: there are no size savings but there are reliability improvements.
And as noted above; UPSs that are paralleled must be designed for the job from the same manufacturer and either be identical or specified to work together. Paralleling two random UPSs would probably fall under the category of "entertaining".
dear dan "Also the bypass system, if you have a separate cabinet with static switches in parallel with bypass breakers, the static switches may be near closed transition. Likely there will be some kind of switching transient, it could also switch badly.
"what do u mean with this? pls let me know...
"what do u mean with this? pls let me know...
Switching to bypass
Switching to bypass
I'm not sure which part you are asking about. If the UPS switches to bypass using the SCR's in the static switch and both source waveforms, UPS output and utility, are synched, the open time during transition should be less than 1/4 cycle and the load stays up. That's the perfect scenario when everything is good. If the source waveforms have too much variance from each other, the SCR static switches may not want to swap, or they may do so with too much open time or too much difference between the voltages.That's a power line disturbance.
Actual downtime is caused by something that is not supposed to happen. Something wired or setup incorrectly, something that does not operate as it's supposed to. When that happens there's supposed to be redundancy built into the system to keep the load up.
Basically, from your post I got the impression switching to bypass was OK. I was thinking going to bypass was because of a lack of redundancy in the UPS and going to bypass, if done perfectly, was a narrowly avoided catastrophe. If during switching the load is dumped, the money saved on the install will not buy hand soap and paper towels during the time it takes to sort the mess out.
Anything longer than ~ 2 cycles open time during transition to bypass, the load could see the glitch as power being dumped and the load tries to reboot or POST, power on self test. Also, there's no way to predict the range of specialized loads that will be plugged in and how fussy they will be about always having cleaned power while operating. Some of the load equipment will have delicate sensors and amplifiers that will not like any kind of power disturbance.
Closed transition switching, both sources momentarily closed to each other during transition, is very specialized equipment. Likely the specifications and regulations for what you need to do are going to be very tight.
Switching to bypass
I'm not sure which part you are asking about. If the UPS switches to bypass using the SCR's in the static switch and both source waveforms, UPS output and utility, are synched, the open time during transition should be less than 1/4 cycle and the load stays up. That's the perfect scenario when everything is good. If the source waveforms have too much variance from each other, the SCR static switches may not want to swap, or they may do so with too much open time or too much difference between the voltages.That's a power line disturbance.
Actual downtime is caused by something that is not supposed to happen. Something wired or setup incorrectly, something that does not operate as it's supposed to. When that happens there's supposed to be redundancy built into the system to keep the load up.
Basically, from your post I got the impression switching to bypass was OK. I was thinking going to bypass was because of a lack of redundancy in the UPS and going to bypass, if done perfectly, was a narrowly avoided catastrophe. If during switching the load is dumped, the money saved on the install will not buy hand soap and paper towels during the time it takes to sort the mess out.
Anything longer than ~ 2 cycles open time during transition to bypass, the load could see the glitch as power being dumped and the load tries to reboot or POST, power on self test. Also, there's no way to predict the range of specialized loads that will be plugged in and how fussy they will be about always having cleaned power while operating. Some of the load equipment will have delicate sensors and amplifiers that will not like any kind of power disturbance.
Closed transition switching, both sources momentarily closed to each other during transition, is very specialized equipment. Likely the specifications and regulations for what you need to do are going to be very tight.
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Pierre C Belarge
Senior Member
- Location
- Westchester County, New York
Electrics profile says engineer.
Your use of the english language shows you are either from a different country, or have not mastered the language yet.
This topic is too sensitive and detailed to get a real answer from this forum. You may get leads, as has already occurred, but not real answers.
As has already been provided, you should contact someone who knows more than you do to get the proper answers. I hope you are not the one the hospital is depending on to design this setup?????
Your use of the english language shows you are either from a different country, or have not mastered the language yet.
This topic is too sensitive and detailed to get a real answer from this forum. You may get leads, as has already occurred, but not real answers.
As has already been provided, you should contact someone who knows more than you do to get the proper answers. I hope you are not the one the hospital is depending on to design this setup?????
in fact this is not mine, but a proposal of my friend, i said it doesnt seem reliable enough but he says there will be no problem, so i just decided to reflect his plan onto here, as it seems you agree with me generally, in fact the best choice is to part the loads between multiple ups or parallel operation with redundancy...
In a typical OR, the critical (red) receptacles are typically fed from a automatic transfer switch (ATS). The ATS has one feed from the utility power, and one from generator power. This gives two different sources of power.
In addition, normal power receptacles (or receptacles fed from another ATS) are also required as a backup.
OR's are also typically supplied from isolation panels. (the isolation panel is often located right in the OR.) This means that the power at the receptacles have no reference to ground, and current can't flow to ground. These isolation panels have a lot of special requirements.
Running an OR from a UPS is not a common solution for most OR's. The UPS could be considered a single point of failure (even with multiple UPS's).
In some cases, simpler is more reliable.
Steve
I might add that in addition to the NEC, OR's and hospitals have NFPA 99 requirements, in addition to NFPA 110 and 111.
NFPA is a health care facility code.
NFPA 110 deals with generators.
NFPA 111 deals with energy storage systems, and would probably have a lot of info. on using a UPS as a backup.
There might also be some State requirements and codes.
Steve
NFPA is a health care facility code.
NFPA 110 deals with generators.
NFPA 111 deals with energy storage systems, and would probably have a lot of info. on using a UPS as a backup.
There might also be some State requirements and codes.
Steve
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