UPS Load

With your present load of 22 kVA and the additional load of 15 kVA, the UPS will be overloaded.... 37kVA... Just not possible. You need to upgrade your UPS, or better, get an additional one of 15kVA which can anyway be a standby in some emergencies. It is advisable to have bigger UPSs than what is necessary.

Since you have single phase loads, the effective load u can have on each phase is 30/3 = 10KVA per phase. For your 22KVA load, the system must have already been overloaded unless u have ensured that the load is distributed equally among 3 phases. In case u add more load of 15KVA, ur total load will be 37KVA, which, even if equally distributed would overload the system by 20+%. However, if ur UPS has an overload capacity of about 30% for a short duration, u can temporarily use it by proper scheduling and switching-off unnecessary loads. But in any case, u'll need to procure a new one which is about 30+ KVA, forecasting your demand.

thanks for the info.

u - you

ur – your

u'll – you will

Please avoid using these localized acronyms (?). It is a global forum and these acronyms are not recognized and used globally. These are used in a part of the globe (most probably India region).

As u said ur ups capicty is 30kva and existing load is 22kva on 3 phase now ur willing to add 15kva 1phase load (5kva per phase)!

u can add new load to ur ups

this leads to decrease in ups back up it is better suggestable not to exceed above 80% of full load

thanks for the information.

u can add new load to ur ups

Please...you are giving wrong advice here. Dangerous.

Your question has already been addressed and it is suggested that the UPS capacity is not enough to add the additional 15 KVA loads. Here is some more detail in case if you even decide to add less load (example 5 KVA) to this UPS.

The 30 KVA UPS has each phase capacity is 10 KVA and you should not exceed the load of any of the phases more than 10 KVA.

"The existing 22 kva load is what indicated in UPS monitor if we check the load and indicating 70% of capacity" – what I understood from this statement is that the 22 KVA is the actual running loads that are being used from the UPS and the actual connected loads are more than this. The UPS loads also may vary over the time and, in worst case, the actual running load may be higher than 22 KVA. I would recommend you to measure the load at worst condition.

As already indicated in some comments, it is not sure the existing loads are balanced or not. For the case of balanced load (which is not practical in most cases), each phase has existing 7.3 KVA (approximately) load. Otherwise, in unbalance load condition, one of the phases may have already more than 7.3 KVA load. You can add additional loads with strict consideration of none of individual phase load exceeding 10 KVA.

How much load you can add to this UPS also depends on the nature of the new loads, as well as the existing loads. For example, if you have three single phase new loads of 3.5 KVA, 1 KVA and 0.5 KVA (total 5 KVA). You may not add these total loads to this UPS even if the total load seems not exceed the capacity. Whichever phase you add the 3.5 KVA load, may have over loaded (exceed 10 KVA). However, redistribution of the existing loads and new loads may allow to add them if you can keep them pretty balanced.

MS

1. It is just possible that your existing load is 0.7 power factor lagging and you can correct this to unity.
2. This would reduce existing load to 15 kW, leaving 15 kVA spare. But it is not very likely.
3. Do you know the power factor of the existing and new loads?? How well balanced are the phases?
4. But inverters do not like capacitive loads, using just one Power Factor Correction bank can leave a big "leading" current when the loads are off. Correction would have to be on each load.
5. It is possible your new load is an over-estimate or has a poor power factor (which might be correctable). What kind of load is it?
6. Is this "UPS" one in which the normal supply is from the mains, the inverter being a fast-switched standby or a real UPS in which the inverter is the normal source?? It is important to know how long the inverter might be overloaded as well as how much.
   

thanks for all reply. the power factor in the name plate is .85. the load are mostly servers and computer controlled equipment. the new load are the same. it is only an expansion of laboratory capacity. the kva rating of each equipment are ranging from 250 VA to 700 VA, 1 Phase, 220 volts. all 3 phases are balanced.for the existing load.

If you are determined to avoid a new UPS.... I suggest

1. Look at the existing load on UPS. How much really needs to be maintained? Very likely, because you had spare UPS capacity, folk put loads on it as a "nice to have" option!
2. How probable is a long break? A 100 ms break will shut down a computer, but is a short time for a UPS battery.
3. A power station I know runs the computers off the UPS, but the display units from normal supply, this cuts the UPS load a lot. Since they have a reliable supply, with brief breaks on transfer to backup supply and everything vital is automatic, short loss of supervisory display is not a problem.