3 phase ups

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tarek_10

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could any one help me to know how many kva i need in ups to supply two motors both of them have same specification (2.2kw,4.98amp,I starting 28amp)thx for corp.
 
Hevy,

You need to supply more info.

Why 400V? Why not 460 or 480? What is the application?

Both start at same time?
Could one be put on a delay timer?
FLA ?
LRA ?
Start under load, or fast spin-up?


Comments, please.
 
hey

hey

this motor of oil pump one of them is main and the other is auxiliary,working only when the oil pressure is decrease.Irating=4.98amp,volt=400volt,Istarting=27.5amp
 
this motor of oil pump one of them is main and the other is auxiliary,working only when the oil pressure is decrease.Irating=4.98amp,volt=400volt,Istarting=27.5amp

Still leaves some question as to whether both can start concurrently...???

Anyway you look at it, your going to need at least a UPS in the 22.5kVA instantaneous range: 400V ? (27.5A + 5A) ? √3.

Keep in mind this is the minimum if both motors will not start concurrently. The continuous rating can be lower, but likely not as low as 2 ? 5A would seem to indicate. In general, the continuous rating is about 60 to 80% of the instantaneous.

Take this info with a grain of salt. I am far from being adept in UPS ratings and considerations ;) As such, I have a question. Would not the rating be in kVA-hrs? After all, you'd need to know how long the UPS could maintain the loads when normal service is interrupted.
 
Still leaves some question as to whether both can start concurrently...???

Anyway you look at it, your going to need at least a UPS in the 22.5kVA instantaneous range: 400V ? (27.5A + 5A) ? √3.
Keep in mind this is the minimum if both motors will not start concurrently. The continuous rating can be lower, but likely not as low as 2 ? 5A would seem to indicate. In general, the continuous rating is about 60 to 80% of the instantaneous.
I agree with that. For the type of UPS we often use, a 150% overload capability is typical which would thus give a continuous rating of just over 15kVA assuming the starts can be staggered.
Take this info with a grain of salt. I am far from being adept in UPS ratings and considerations ;) As such, I have a question. Would not the rating be in kVA-hrs? After all, you'd need to know how long the UPS could maintain the loads when normal service is interrupted.
There are two different factors. The run-time, or autonomy as it is often called, is dependent on battery capacity. The inverter output rating isn't. For example, a 15kVA unit with 3 hour autonomy couldn't supply a 45kVA load for one hour.
 
There are two different factors. The run-time, or autonomy as it is often called, is dependent on battery capacity. The inverter output rating isn't. For example, a 15kVA unit with 3 hour autonomy couldn't supply a 45kVA load for one hour.

I agree. First you have to size the UPS capacity and rating (i.e. inverter, internal CB's and electronics, etc). Then, UPS run time will depend on the load connected and the batteries available.

Typically, several batteries are connected in series up to a certain voltage in what is called a battery bank. Then, these banks are connected in parallel to each other. So, KVA-hr will depend on how many banks are connected in parallel.
 
I think i saw this question posted by this member in one other forum.

The answer is three phase 15 kva ( since these pumps do not start at the same time)...and back up time required by OP is 30 minutes. The UPS supplier can scale the battery size for that time.

cheers.
 
I would recommend having a local engineer with experience in this area size the ups for you, otherwise you might end up dissatisfied with the results. There is information missing and this would negatively impact an otherwise correct answer to your question.
 
Never put motors on UPS. Install a generator. The there will be a 10 sec. maximum delay. Have the generator supplier size the genny.

It's fairly common practice here (UK) in pumping stations and elsewhere to run motorised valves from a UPS.
And, if you think about it, the topology of the output inverter stage of a 3-phase UPS isn't greatly different to that of a 3-phase variable frequency inverter.
 
Why shouldnt motors be on UPS?

Perhaps I should've been more elaborate and stated: properly investigated applications should seldom, if ever, would require the installation of an UPS to support a motor drive.
Having said that on my very first job - eons ago it seems - I did put two motors on a UPS system. It was warranted. Not since.
Several reasons:
  1. UPS's are not designed for the load profile that a motor would represent.
  2. as per the above the engineers at UPS manufacturers are not really equipped to properly determine the size of an optimum UPS for a motor load.
  3. The UPS would need to be oversized and the cost of the batteries would also rise exponentially.
  4. Seldom are there is a motor application that could not sustain a short - 3-4 second - outage until the generator comes up.
  5. Should UPS be used, how long will it be needed? All that time is to be supported by batteries that are:
  6. Expensive,
  7. Highest cause of UPS unavailability so often times battery monitoring and dual battery bank is warranted for high MTBF that again will make the cost skyrocket.
  8. What happens after the batteries exhausted? Would you have a generator anyway?
  9. If all the above are not taken into consideration a UPS may be installed, but the U may be replaced by an I as in Interruptible.
Seems like someone found an obscure Finnish company http://www.mscelectronics.fi/sivut/index.php?show=3 who specializes in motoric load UPS's. The above considerations should still stand.
 
Perhaps I should've been more elaborate and stated: properly investigated applications should seldom, if ever, would require the installation of an UPS to support a motor drive.
Having said that on my very first job - eons ago it seems - I did put two motors on a UPS system. It was warranted. Not since.
Several reasons:
  1. UPS's are not designed for the load profile that a motor would represent.
  2. as per the above the engineers at UPS manufacturers are not really equipped to properly determine the size of an optimum UPS for a motor load.
  3. The UPS would need to be oversized and the cost of the batteries would also rise exponentially.
  4. Seldom are there is a motor application that could not sustain a short - 3-4 second - outage until the generator comes up.
  5. Should UPS be used, how long will it be needed? All that time is to be supported by batteries that are:
  6. Expensive,
  7. Highest cause of UPS unavailability so often times battery monitoring and dual battery bank is warranted for high MTBF that again will make the cost skyrocket.
  8. What happens after the batteries exhausted? Would you have a generator anyway?
  9. If all the above are not taken into consideration a UPS may be installed, but the U may be replaced by an I as in Interruptible.
1. The UPS is designed for rated kW and kVA. Provided the load remains within those constraints it isn?t a problem.
2. Agreed. That?s why you and I get paid the big bucks to ensure that the kit is suitable for the application.
3. Yes, and that?s how the 15kVA rating was arrived at. Battery capacity is a matter of autonomy.
4. Starting up a 1500kVA Diesel genny for a pumping station or a hospital might take just a tad longer.
5. Sure, batteries are expensive. So are standby generators.
6. See 5.
7. We provide UPS systems for many public buildings, hospitals, servers etc. Typical autonomy required is three hours. That is routinely tested on a twice yearly basis. For critical back-up, nothing less would be acceptable.
8. Depends on application. For something like a cinema you would expect evacuation of the building within the three-hour autonomy. For servers you would reasonably expect an orderly shut down. For hospitals you would certainly have back up Diesel generators.
9. Modern UPS systems have pretty good monitoring and comms facilities. That?s not to say you can?t get failures. You just might get an indication of it before it might be required to perform in anger. And there is no certainty that a rotary alternator driven by a reciprocating combustion engine will be 100% reliable 100% of the time.
 
Another UK story - A data centre of my acquaintance had three UPSs; a large one for the computer load, and two smaller units for the Liebert chillers. No backup generator, all there so the IT systems could have an orderly shutdown in case of power failure. UPS run time was 30 minutes at full load.
 
1. The UPS is designed for rated kW and kVA. Provided the load remains within those constraints it isn?t a problem.
2. Agreed. That?s why you and I get paid the big bucks to ensure that the kit is suitable for the application.
3. Yes, and that?s how the 15kVA rating was arrived at. Battery capacity is a matter of autonomy.
4. Starting up a 1500kVA Diesel genny for a pumping station or a hospital might take just a tad longer.
5. Sure, batteries are expensive. So are standby generators.
6. See 5.
7. We provide UPS systems for many public buildings, hospitals, servers etc. Typical autonomy required is three hours. That is routinely tested on a twice yearly basis. For critical back-up, nothing less would be acceptable.
8. Depends on application. For something like a cinema you would expect evacuation of the building within the three-hour autonomy. For servers you would reasonably expect an orderly shut down. For hospitals you would certainly have back up Diesel generators.
9. Modern UPS systems have pretty good monitoring and comms facilities. That?s not to say you can?t get failures. You just might get an indication of it before it might be required to perform in anger. And there is no certainty that a rotary alternator driven by a reciprocating combustion engine will be 100% reliable 100% of the time.

  1. UPS's are not designed for motor inrush characteristics.
  2. Disagree. Application people have no detailed information on the UPS's internal design nor on the software parameters that controls the UPS.
  3. 15kVA was suggested, but that it is correct is anyone's guess. No inrush parameters were taken into consideration nor the UPS's overload capacity duration was established. Anyone who would go ahead on that basis is a fool.
  4. Gen'sets are required to sustain full load within 10 sec.
  5. As a rule of tumb a reliable battery system beyond 30 minutes becomes more expensive that the generator/battery system.
  6. Reliable battery system consist of dual banks an Cellwatch type battery monitoring. Lifecycle cost needs to be considered since VRLA can be eitehr 4 or 10 years, but it has been found that seldom will you get that life out of them, so the cost of a new bank neds to be considered every 3/5 years. If you choose the wet cell option then you would have to add the building cost and change the replacement to 20 years.
  7. UPS systems only recently started paying attention to the battery monitoring issue and even though they are sophisticated when it comes to the internal health of the UPS electronics itself, the battery 'monitoring' is nothing else but a show. Battery remains teh weakest part of the U.
  8. A properly designed system for optimum reliabilty is a UPS with dual battery banks equipped with individual cell monitoring for about 5 minutes duration and a life-safety grade gen'set that feeds the UPS via a transfer switch. Overall it has higher reliability as a redundant UPS with gen'set backup.
 
UPS's are not designed for motor inrush characteristics.

Thats actually very true; most semiconductor type UPSs have a very poor overload capacity to the point where they are incapable of clearing faults with breakers that are a substantial percentage of the full load current. A UPS that can supply more than 300% of the FLA for a cycle or two is most unusual. Thus a 100A FLA UPS with a downstream circuit with a 60A breaker with a bolted fault beyond would probably never clear; theres not enough current for long enough to get past the breaker curves. So the UPS would simply shut down.

For this reason when faced with a significant increase in load, most UPSs flip to static bypass for a few seconds. Thus the utility (or genset) provides the heft to clear faults or allow for motor starts. The UPS then flips back to inverter once the load stabilizes.

Thus to have a motor start on a UPS, the inrush current and duration must not exceed the UPSs ability to supply that current, or you have a system that works fine while the utility or generator are up, but if in the 30 seconds between utility failure and the genset coming on line you get a motor start, the UPS shuts down taking down the loads with it. Not good design.

A properly designed system for optimum reliabilty is a UPS with dual battery banks equipped with individual cell monitoring for about 5 minutes duration and a life-safety grade gen'set that feeds the UPS via a transfer switch. Overall it has higher reliability as a redundant UPS with gen'set backup.
Disagree - UPSs are not the most reliable devices known to man, and a pair of UPS (each with own battery) followed by a static switch is always a worthwhile increase in reliability, if the budget is there. Even better is dual distribution systems and have all loads dual supplied; this allows maintenance work on one of the two UPS / distribution chains whilst the other chain keeps everything up and still has UPS and genset protection.
 
Disagree - UPSs are not the most reliable devices known to man, and a pair of UPS (each with own battery) followed by a static switch is always a worthwhile increase in reliability, if the budget is there. Even better is dual distribution systems and have all loads dual supplied; this allows maintenance work on one of the two UPS / distribution chains whilst the other chain keeps everything up and still has UPS and genset protection.

Yes and no. The staic switch is a common device between the two UPS's and thus a single point of failure.
 
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