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October 25, 2007

Uninterruptible Power Supply Systems

Written by  Bill Langendoerfer
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Uninterruptable Power Supply (UPS) systems are becoming more of an integral part of the responsibility area of Information System Directors and Managers. Data processing management together with the rest of the MIS staff have the responsibility to protect the information asset of their company. As information gains in its importance, it requires more attention in terms of its environment and protection. Hardware also becomes more sensitive to the environment as corporations depend more and more on their computer system.

Electrical power is perhaps the most unstable of the environmental factors the data center faces. Power is an ever present concern that sometimes isn't addressed until a hardware upgrade is imminent or a power failure causes the computer system to go down.

Data processing can do more to protect the corporation's investment in hardware, software, and information by utilizing Uninterruptable Power Supply (UPS) systems or Backup Power Supply (BPS) systems. The difference between these two systems is that a UPS system supplies continuous power and a BPS systems starts when power drops below an acceptable level.

UPS systems are not quick fixes or easy solutions to otherwise unexplainable hardware or software failures. They are highly specialized electrical equipment designed to prevent temporary or intermittent power fluctuations or failures from affecting the continuing computer operations. Moreover, when proper planning is accomplished and the UPS system configured adequately, a UPS systems can provide 'cleaner' power than generally available from your utility company.

Planning for a UPS system requires diligence in gathering accurate information about the input power feeders, the circuits within the facility, and the electrical loads for each. Once you have completed the task of gathering this information, immediately make it an integral part of your disaster contingency plan document. It will be valuable if the computer facility needs reconstruction following a disaster. It is also necessary in considering an offsite backup recovery facility. To be adequate, the facility will have to meet your 'minimum' power requirements.
Consult with your customer engineers or look through your hardware reference manuals and determine the power requirements for each device. Document the building and facility power configuration and the loads on each circuit that may affect your operation. Then identify the electrical requirements that power the equipment most critical to the operation of your data center. Be creative, all critical equipment isn't in the computer room. Consider mail room equipment, emergency health care equipment, telephone PBX equipment, etc. These requirements will be your 'critical load.'

'Apparent' power is the result of calculating actual voltage, times amperage, times a power factor. The power factor is determined by how efficiently equipment uses electrical power as compared to a constant sine wave (normally .8 or .9 but rarely if ever 1.0). After having calculated the total (apparent) power for your critical load, with the help of your neighborhood electrician, you now have an idea of how large your UPS system needs to be. Growth should also be included in your requirements. Thus, a UPS system should be a minimum of 25 percent larger than the existing critical load. There's more, a UPS system is never 100 percent efficient....so add another 10 percent to accommodate the power efficiency of the UPS system. This demonstrates that a UPS system with a rated capacity of 400 KVA will accommodate a critical load of about 280 KVA.

Batteries and installation service are additional costs and need to be given careful consideration. Again, UPS systems are designed to protect against intermittent and temporary outages. You must determine the length of time the UPS system will be required to provide battery power to the total critical load. This time period will determine the number and type of batteries used. Batteries are not a required component of a UPS system. They are usually purchased through contract and require separate maintenance service agreements. Researching for a reputable battery supplier can even be a separate procurement process.

Exercise caution when UPS battery vendors proclaim 'maintenance free' batteries. There are no such thing. The term 'maintenance free' generally means that the batteries are lead acid, no (low) gaseous type. However, regular maintenance is still required for tightening lugs, cleaning connections, and replacing weak or dead batteries.

Installation costs will be affected by the installing of outside ventilation for the battery room, required by most building codes. Air conditioning for the UPS system is also required. Be certain to verify input power cable sizes. Your existing cables may have to be replaced if they are not adequate. Input transformer size should be verified for capacity by the utility company.

A UPS system is an essential piece of equipment to a computer dependent organization. When the cost of a UPS system is compared to the cost of lost time by unproductive employees or to the cost of stopping a manufacturing plant, it is difficult for management to decline the expenditure for this type of a system.


Bill Langendoerfer is an editor with the Disaster Recovery Journal.

This article adapted from Vol. 1 No. 2, p. 18.

Read 2313 times Last modified on October 11, 2012