UPS P.F 0.9

Maybe for the battery company. They'd love to sell you anything.

It's not an advantage or disadvantage, it's a rating. The manufacturer is telling you that stable operation is expected as long as the load does not exceed 1000 kVA and/or 0.9pf.

The batteries do not have any effect as long as they can provide 1000kW, adding an additional 1000kW of batteries will not magically double the output capability of the UPS, but it will probably cause it to shutdown or fail.

Here is a white paper that applies to pf in a UPS. They seem to say that only 900 kW would be supported at a pf of 1.

So what is the restriction if I add 100 kw battery this ups is rated for 1000 kva and currents are same for 1000 kva and 1000 kw cases.

The currents won't be the same, though. They will be larger.

Pl do not confuse Selection or sizing of battery with with sizing of UPS.

1. The UPS will work even with Zero or no battery, only you will loose power to load moment the main supply is lost. That means in this case UPS is just regulating mains supply to a clean supply defined by specifications of UPS for Output parameters.

2. Batteries are defined by AH rating. Further these are classified from application point as slow discharge (Discharge rate is low enough that the battery is fully drained in 8 to 10 Hours), Medium Discharge, (battery is being drained out in 2 to 5 hours) and heavy discharge (Battery is being fully drained out in less than an 1 hours).

For UPS normal back time is few minutes to max. 1 to 2 hours.

For Example, 5 min. Back up time, sufficient for safe shut down of your computer and save data or for DG Set to Start and take the source. In this batteries selected will be of High Rate of Discharge.

Or say 2 hours for very expansive equipment as Power Plant or Grid, so that even if DG Set fails to start, the lubricating system of turbine and its barring gear can be run for period enough for shut down. In this case batteries selected will be for Medium or Moderate Rate of Discharge.

Similarly batteries of UPS you are referring must have been designed for certain back up duty. If you reduce the capacity of batteries or increase the load, the back time will be reduced. And if the battery selected is of Medium Duty, after reducing its size, keeping load same may result in High rate of drain and batteries life will suffer (Shedding of active material from plates and short circuiting of plates).

As stated Earlier, the UPS is not a dynamic machine, like 3 phase generator, where you can change excitation and manage any Power Factor.

UPS is a Static machine converting DC to AC and internally designed for unity PF. The reactive demand of Load is balanced by keeping capacitors.

Example if you specify in your order, 100kVA 0.8PF UPS, which is 80kW + 60kVAR. The UPS is basically manufactured as 80kW and to meet 60kVAR inductive load he will use 3 phase 60kVAR Capacitors in the output of UPS. Hence electronics inside UPS always sees 80kW load.

Therefore if the Load PF is better, we can not expect increased output from UPS - its electronics is designed for 80kW only.

Well I learnt above hard way. In 1988, I had sold once UPS of 400kVA to Petroleum Organisation in Oman - Customer wanted same rating for rating between 1 to 0.8PF- for which UPS had to be heavily derated. That was my first sale and working with UPS. After that I sold one more to Customer for 1600kVA the next year and by then I had become, so called, an expert on UPS (we sold Merlin Gerin UPS against most popular of ABB then BBC) Merlin Gerin (now Group Schneider) were so happy with out performance that they nominated my company as authorised dealer. That was my last working on UPS - after that I moved to Diesel Power. If I have to work again on UPS, I have to freshen up with latest technology.

Adding battery can increase Back-up hours for the system ; not for the power rating .

Please note that UPS is not a dynamic machine which can generate kVAR. UPS are designed for say 500kVA, 0.8PF. This is the rating at 0.8PF lagging and reactive current is supplied by power capacitors provided.

Therefore if you are using UPS at any other PF, there is heavy derating because of current rating of its component and change in efficiency. For actual derating please refer to the manufacturer of UPS.

Increasing or decreasing AH capacity of Batteries can not change the rating of UPS but only effect the back up time at given discharge rate or load.

FBD, You are correct in your statement, "...If I have to work again on UPS, I have to freshen up with latest technology...", it's time to join the 21st century. Modern electronically controlled UPS/inverters are quite capable of dealing with both leading and lagging pf loads, it's called "P-Q control", and can be specified for high end commercial UPS/Inverters.

From this (modern) article:

"...Many UPS modules, especially the older legacy type, are not designed to support higher power factor loads and must be de-rated accordingly because more of the KVA units capacity must be used to support the load. Newer UPS designs are more compatible with and are rated to support leading power factor loads with little or no de-rating due to their output filter design and controls. Often this problem is not apparent up front because the initial loads on the UPS are a small percentage of the full load rating so the system is naturally de-rated. However, as the loads increase and become closer to the full load, this problem becomes more evident.."

RAM,

Noted your comments with thanks. The P-Q control suggested by you is similar to additional STATCON (static condenser and reactor controls) which is very expansive.

I remember that STATCON of ABB installed by a cold rolling mills about 4 years back in north India, cost the firm more than Rs. 10 million for a rating of 1600kVAR, which is some what the cost of conventional UPS itself. As I said earlier I am not familiar with latest design of UPS but if P-Q Control or STATCON has to be added to make UPS accept any PF without derating the cost will be almost twice of conventional design.

Economy and competitiveness dictates it would be better to oversize conventional UPS for unity PF than to add on another expansive system to it.