Power supplies and conditioners: A reliable source of power

June 2004
InTech;Jun2004, Vol. 51 Issue 6, p61
This article presents information on uninterruptible power supplies (UPS). UPS is a common way of providing a reliable source of power. UPS generally comes in two types: online and offline. Online UPS batteries are online at all times while offline batteries are offline under normal conditions and switched on during input power loss. Although more expensive, the online UPS generally provides better and more reliable power. A UPS that serves nonlinear loads should have a high crest factor rating and should handle 100% non-linear load and at least a 50% phase imbalance without providing voltage out of its specified range with no more than 5% total harmonic distortion of the output. Noise-generating loads such as motors and silicon-controlled rectifier drives should not be on instrument UPS. A UPS should have a maintenance bypass and users should consider a complete bypass around the UPS. If they provide bypasses, the UPS may not be giving isolated power under all conditions. UPS are soft or high-impedance power sources. This means they are not able to supply power as freely as a low-impedance source, such as a transformer. A transformer with 5% impedance can supply up to 20 times its full load current on a momentary surge. A UPS is typically limited to 1.25 to 1.5 times its full load current.


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