KVA of UPS

150A, what voltage?

40KVA?- it depends on haw big is hospital and 180minuets?- again it depends on how long power fails in your area,

You should contact some local electrician and consultant.

what the relation between KVA of UPS & the load,,,

P=VA

KVA = 1000 x VA

What is your normal expected current and load voltage?

Does 40KVA,180 minute back up time suitable for hospital (150A maximum load)???

Not Possible.

Let make a simple calculation for your UPS back up time.

Assume your hospital is using 110 Vac Single phase

Total current for 40KVA = 40,000 / 110Vac =363.6 amp per hour

Hospital maximum load = 150 Amp

UPU back up time = 363.6/150 amp = 2hr 25.44 minute.

Of course, if your UPS is 100 % fully charged up.

"Total current for 40KVA = 40,000 / 110Vac =363.6 amp per hour"

Where did the "per hour" come from? Amps is a time-dependent measure already (Coulombs/second).

40KVA/110Vac = 363.6 amps, not amps per unit time.

Total current for 40KVA = 40,000 / 110Vac =363.6 amp per hour"

The above is just a simple calculation. Since we assume that the voltage is 110 V and the current is 150 Amp. Therefore, the total power is 16.5KW. For the power, we assume that the the power consumption by the load will be 16.5KW/h

Using the 40KVA UPS with battery back up, we assume that the UPS output will be 363.6 Amp per hr or 39.996 KW assuming no other losses. And since we also assume that the total power consume is 16.5KW/hr, therefore, the time that this 40KVA UPS can back up is about 2hr ++

Maybe my electrical terms or the calculation is not correct but I having been using this simple calculation to size up 20 over UPS in my factory and tested the back up time is 90% accurate.

"the total power is 16.5KW. For the power, we assume that the the power consumption by the load will be 16.5KW/h"

That is simply choosing an arbitrary length of time (one hour) as the unit of measurement. It does not make sense to express anything in terms of KW/hr. Since a watt is a Joule per second (J/s), referring to a KW/hr is basically saying a KJ/sec-hr, which is nonsense unless the system is increasing power exponentially over time. While the calculation may have worked on 18 of 20 UPS units in your facility, it is not a valid method of sizing a battery (as proven by the other 10% of the UPS's).

Instantaneous power is measured in watts; cumulative power consumption over time is measured in watt-hours, not watts per hour. Batteries for UPS's are selected to meet a desired amp-hour capacity. Thus total power consumption is limited by battery capacity, not the other way around.

full details of Load::

3 ph, 220\127VI\O , 60 Hz , 180min back up time,for NICU & ICU operation rooms for hospital.

what proper UPS to connect for this load???

alsoo there is Equation:: Amb = (KW*1000) \ (Volts * 1.73) ;;;;KVA=KW\power factor

so:: for 150A MDB ,,,KVA=60KVA

for 100A ,,,,KVA=40KVA.

thier is 40KVA, 180 min back time is available with me.....so how much does the load equal (Ampers) to be saitable with this UPS.

The rating of 40 kVA does not relate in any sense with the amount of time the UPS can provide power in case of a power failure, but the power (kW,kVA) requirement.

What matters is the quantity of batteries that are accessories to the UPS to store energy. You can order a 40 kVA UPS with batteries to provide 30 min, 45 min, 90 min, 600 min, etc of battery power (depends on how many batteries you install/connect).

Usually a UPS is installed to cover power requirements between losing the normal power grid and starting an emergency generator ( 30 sec - 10 min). Otherwise the volume of the required batteries is very big and space/ventilation/security problems appear

MS,

The calculation indicated is very intuitive. I have some questions about the correlation of some data:

1. The load power (UPS output), considering the values indicated, is 3 x 220V x 150A = 99 kVA, so the UPS should have a rating of at least 100 kVA, since the indication " a 100 kVA UPS means that the output power is 100 kVA.

2. I am assuming the input voltage is also 220/380V. Why did you indicate a DC voltage of 105-130V (this would represent 10 12V batteries in series) ? Normally that voltage should be close to the peak AC voltage, so in this case 220V. For the 60 kVA UPS in question, considering the DC voltage 220V, the current would be 70588/220=321A and thus, for a 3 hr time, the total battery capacity would be 3*321= 963 Ah.

3. The number of batteries is given as 130/1.33 = 60 (what do "130", "1.33" and "60" stand for ? (130V dc ?, 1.33 V/cell ?)

MS,

1.The referenced 220V voltage is line-to-line voltage, since the system is 220/380V, so it should be either 3 x 220 x 150 or sqrt(3) x 380 x 150.

2.I understand the reasoning of 140V but based on what I found out from UPS industrial manufacturers (APC, MGE, etc) the DC voltage was the one I mentioned.

1. Yes, you are absolutely correct if 220 V is line to neutral.

2. Thanks for this information. Just one more important thing to clarify - for higher DC voltage, the larger number of cells is connected in series. A problem in one cell causes problem in the DC voltage system. However, the battery cells are now more reliable than it is used to be.

-MS

MS,

I misspelled in my previous response: 220V is line-to neutral voltage, 380 is line-to-line.

Hi MS

considering a Depth of Discharge (DoD) of 60%, what would be the required battery AH for this scenario?

Br,

EnB

Hi EnB,

I can put no figure/s on the DoD or Ah needed.

For a hospital or any other situation which MUST have power, the power needed differs from one situation to another, and with a hospital, they would, I imagine have several UPS and several generators to cope. This will obviously vary from a very large hospital to a relatively small one also!

The basic rules of thumb as issues and posted by others on this thread, of how to work out the UPS necessary will still apply. You must have or figure out the 'NEED' for power and for how long that need is likely to be before an UPS of the correct sort can be installed.

I realise you may be learning, or wanting to find out these details, but, until, and when you are trained to install these UPS in power hungry situations of many thousands of Volts, 'guessing' or 'trying to figure out what is necessary' should be left to those who know what they are doing and can advise correctly and safely in these situations. No offence intended.

I suggest you write to the IEEE. Try this search site for life-critical situations and Hospitals in particular:

http://www.google.co.uk/search?q=IEEE+UPS+hospitals&ie=utf-8&oe=utf-8&aq=t&rls=org.

Hello eng tamimi,

I cannot see that this UPS situation can be applied to a hospital. There is no need for it with regard to hospitals because, each hospital has its own power supply back up. That is how things are in the UK anyway.

A hospital has hundreds of computer driven electrics, many of which are directly used to save lives. So the hospital needs a power supply which is not going to fail.

I hope this answers your question?

I cannot see this question has any relevance to computers running in any one hospital.

bb

dear mr. babybear

u are right, but for more safe and to be far from power problem; we use UPS.specially in critical loads in Hospital as ICU & NICU.

dear, Mr. msamad

surely, best answer

In the USA hospitals have redundant generators. Generators have to start and come- up to frequency and voltage during a power outage before the ATS will transfer the load, hence the need for UPS for loads that cannot sustain an outage of even a few seconds. If there are generators, then UPS battery time can be short. 15 minutes should be good insurance. Be sure to commission to be sure the UPS will accept the generator's output.

Hello Guest,

In the USA hospitals have redundant generators. ..............................Generators have to start and come- up to frequency and voltage during a power outage before the ATS will transfer the load,

hence the need for UPS for loads that cannot sustain an outage of even a few seconds.

I never thought of about that. Of course every ward and Theatre has all kinds of electronics installed these days and some sort of system, as you describe, has to be used!

bb