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Old May 8th, 2007, 06:39 AM   #1
neerajpuranik
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Need a suggestion regarding UPS for PLC system

Friends,
I am working in african country, we are about to install Siemens S7-400 PLC in our process plant. We have severe power breakdown / fluctuation / under voltage problems from local electric co. The OEM who is supplying turnkey process plant has only considered Voltage stablizer for PLC system.
I am looking for suggestion as till now my experiance is in Cement Plants and there we always had UPS system for PLC's. I am now in a edible oil refinary. So somehow I feel uncomfortable with the idea of using only voltage stablizer. Just few days before power supply card of four PID controllers got blown due to flctuation. So considering the situation I am awaiting your suggestions.
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Old May 8th, 2007, 06:57 AM   #2
mordred
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Ideally you should look for a power filter as a UPS only protects against brownouts or no power for a short term however if you combine the two then you would have the full range of protection IN order to suggest the UPS however we would need more info in how many watts your system uses.
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Old May 8th, 2007, 07:11 AM   #3
dchartier
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Hello neerajpuranik;

In certain locales in South America, we had power problems similar to those you describe. A combination of voltage stabilizers and Line-interactive UPS helped a lot to keep our PLCs and SCADA system alive; worst case, they would allow our systems to shutdown properly when the black/brownouts lasted too long.

Quote:
Line-interactive UPS systems (from Wickepedia)
Line interactive UPS units are designed so that the inverter is always connected to the output of the UPS. When line power is present, the inverter operates in reverse to charge the battery. When utility power fails, the UPS reverses the power flow from the inverter and provides power to the load. This design provides better filtering than a standby unit because the inverter is always connected to the load.

Line interactive units typically will incorporate an automatic voltage regulator. AVR allows the UPS to effectively step-up or step-down the incoming line voltage without switching to battery power. This allows the UPS to correct most long term over-voltages or under-voltages without draining the batteries. Another advantage is that it reduces the number of transfers to battery which extends the lifetime of the batteries.

Line-interactive UPS units are the most common design for units in the 0.5 kVA to 5 kVA range. They are typically used in small server environments.
As mentionned by mordred, You will need to provide details about the VA and time requirements for your application for us to helps you more.

Hope this helps,
Dabiel Chartier
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Old May 8th, 2007, 07:21 AM   #4
mordred
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quick question on the line interactive that I've always been curious about
is the effectivity of the power filteration with regards to voltage and current spikes ? I ask this as some of the literature I've read usually recommend using both a power filter as well as a UPS and I have a couple of sensitive Xray machines that are already in the line interactive UPS. Even on them I have lost some rather expensive components that have blown.
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Old May 9th, 2007, 05:54 AM   #5
neerajpuranik
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dear friends,
thanks for replying quickly. The details you have asked for are as follows:
The power requirement of the system is coming around 5 KVA. The required backup time is 45 min to 1 hr maximum. As generally we have observed power cut is not more then 15-20 min, and moreover we will prefer to have controlled shutdown of plant if power breakdown prolongs ( as mentioned by Dchartier ).
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Old May 9th, 2007, 06:24 AM   #6
dchartier
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Hello neerajpuranik;

If my memory serves me well, we did business with these guys, before they were bought by Eaton:
http://www.powerware.com/how_to_buy/reseller.asp?cx=143

This is their french contact, seems to be a reseller for African customers also. Explain the details of your application, they should be the best source of info to satisfy your requirements. You will probably have to look into extended battery packs to support your system for an hour; their power management software was also very good.
There are probably many other manaufacturers on the market, maybe others will will chime in with suggestions for you.
Hope this helps,
Daniel Chartier
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Old May 9th, 2007, 07:17 AM   #7
theDave2
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For best protection, you'll want a double-conversion online UPS, not a Line-interactive UPS.
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