On Mon, 12 Mar 2018 10:12:47 -0600 Corey Edwards <ten...@zmonkey.org> wrote:
> My understanding of AC motors is that they are always in sync with > line frequency as a fundamental property. Correct. > So if you suddenly change > the frequency, such as by switching from UPS to utility power, the > motor will make a sudden and ungraceful adjustment, possibly > destroying itself in the process. Not quite. When power returns, it is often unstable in almost all its characteristics. So a good UPS will wait until line power stabilizes, then slowly (over the course of several seconds) synch the frequency it is putting out to the line power. Only then will it restore line power to the load, and start charging the battery. How long it takes to sync the UPS power to the line power depends on how out of phase they are when line power stabilizes. By definition, the UPS and line power are never more than 120th of a second out of sync. In North America, we are accustomed to power stabilizing within about 30 seconds (usually a lot less). In other parts of the world, it may take much longer. All of this is completely transparent to the load except for the varying line frequency during the synchronization process. -- A great civilization is not conquered from without until it has destroyed itself within. The essential causes of Rome's decline lay in her people, her morals, her class struggle, her failing trade, her bureaucratic despotism, her stifling taxes, her consuming wars. -- Will and Ariel Durant, III The Story of Civilization (1944) epilogue /* PLUG: http://plug.org, #utah on irc.freenode.net Unsubscribe: http://plug.org/mailman/options/plug Don't fear the penguin. */
