Powerlink Corporation; Customized power quality solutions



	Here are answers to some of the most commonly asked questions regarding power protection. If you don't find what you're looking for here, please visit the manufacturers' Web sites, or contact us directly at: Phone: 408-399-3355, Fax: 418-399-6202, E-mail: kcastleberry@powerlink.com


	How do I size my UPS?
	How do I size my UPS system battery?
	What is the right type of UPS system for my requirement?
	Can I connect air conditioning systems to my UPS?
	Do I need TVSS if I have a UPS?
	Are K-Rated Transformers good enough for computer loads?

	How do I size my UPS? There are several methods used to size a UPS system's capacity. Method 1: Make a list of all the equipment that the UPS system will protect. Computers and Telecommunication equipment have UL labels, which provide the voltage and amperage rating of the device. For single-phase equipment: 1. Multiply volts x amps to derive VA (or watts) 2. Add up the collective amount of VA (or watts) for all of the designated equipment to determine the UPS load. 3. To convert to KVA, divide the total by 1,000. It is a good rule of thumb to size the UPS so that the total load is about 80 percent of the UPS system's capacity. For three-phase equipment: 1. Multiply volts x amps x 1.732 (the square root of three) to derive the VA (or divide by 1000 to obtain kVA). Method 2: Another method of calculating the total load is to consider 40 amps per equipment rack. As servers are available in smaller and smaller sizes, the power density of computer rooms has increased. 1. Multiply the total number of equipment racks by 40 amps 2. Multiply this number by 120 volts. This will provide a good approximation of the total VA load. Method 3: The quickest and easiest way to approximate the correct size for your UPS system is to multiply the computer room's square area (in feet) by 100 watts.

	How do I size my UPS system battery? Most utility outages last only a few minutes, so a 15-minute battery will typically provide enough back-up power. Most computer systems need 5 - 10 minutes of time to complete any work and save data files; so again, a 15-minute battery will typically provide enough back-up power. For longer back-up time requirements, extended run time battery systems are available. As an alternative to batteries, micro turbines can be considered for extended run time requirements.

	What is the right type of UPS system for my requirements? Depending on the profile of the load, UPS solutions range from simple rack-mount or tower systems to large redundant enterprise systems. If the designated equipment to protect can be plugged directly into the UPS system, one of the rack-mount or tower UPS systems should be adequate. If the designated equipment to protect is fed from an electrical panel on a wall, you need a larger hard-wired UPS system. If the designated equipment to protect generates revenue, or serves information for online clients, you should consider some form of a redundant UPS. It is important to consider the loss in dollars if operations are halted due to a power outage. Today's IT environments utilize redundant network servers, RAID storage systems, and expensive security software, and the same importance should be given to the type of UPS system used to protect the data systems.

	Can I connect air conditioning systems to my UPS? No. UPS systems are designed to maintain the power flow to equipment that cannot tolerate the slightest interruption in power. If a computer room is backed up by a stand-by generator, the air conditioners will only be without power for roughly 10 seconds, and the room temperatures will not rise to critical levels. If a computer room is not backed up by a stand-by generator, then a typical UPS back up of roughly 15 minutes should allow the computer systems enough time to shut down before the room temperature rises to critical levels. Another reason to avoid putting the air conditioning systems on a UPS is that it requires a much larger UPS system to handle total combined load. Electrical motor loads can draw up to 9 times the normal power just to cycle-on the rotating parts in the motor.

	Do I need TVSS if I have a UPS? Most UPS systems have some built-in protection against surges. To meet UL 1778 requirements, UPS systems must provide medium levels of surge protection. The most damaging surges come from lightning strikes or other large-scale utility-line events, and the UPS system will protect the critical loads from these surges. However, the UPS system also contains several control, power, and communication circuit boards, soinstalling TVSS at the service location that feeds power to the UPS may prevent damage to the UPS.

	Are K-Rated Transformers good enough for computer loads? K-Rated transformers are designed to withstand the heat generated by non-linear loads, however they do not solve all of the problems associated with harmonics. The two most negative effects of harmonics are energy loss and distorted voltage. Energy loss occurs when harmonic currents are trapped in the transformer windings and dissipate in heat. Distorted voltage occurs when these currents flow through the impedance of the transformer windings. K-Rated transformers do not solve either of these problems, so harmonic correction is always a better solution. Harmonic cancellation transformers save energy and provide clean sinusoidal voltage, which is what today's computer systems need.