Thanks for the fine explanation, Eric! My main concern/wonder was in regard to the issue mentioned by Skipp, and a perceived concern over damage that might occur as a result of the voltage fluctuations. I've even noticed dimming and brightening of the lights in my house when this apparently occurs - I guess the issue is not as serious as I thought. Just trying to be cautions - maybe overly so. ;-)
Thanks again! Mark - N9WYS -----Original Message----- From: Repeater-Builder@yahoogroups.com On Behalf Of Eric Lemmon Mark, Sudden and regular changes in voltage levels on long lines are normally caused by the switching in and out of capacitor banks that are used to improve voltage regulation on long distribution lines. This is most commonly used on lines carrying 4,160 to 22,000 volts. In areas where light industrial loads are common, the power factor is lagging during most of the day, due to the number of motors and other inductive loads connected. To counteract this lagging power factor, capacitor banks are switched in and out by either a timer or a voltage sensor. In my area, the nominal voltage jumped from about 119 volts to 123 volts in the morning, and dropped back in the late afternoon. This practice is very important in rural areas, where a 12kV line might run 20 miles to a farm. If regulators or capacitor banks were not used to stabilize the voltage, there would be large excursions each time the farmer started his irrigation pumps. Motors, being inductive, cause a lagging power factor that results in an increased voltage drop on the distribution circuit. The capacitors supply capacitive reactance that cancels the inductive reactance and, when properly applied, will improve the power factor to near unity and minimize the voltage drop. Most well-designed power supplies, both linear and switch-mode, will maintain a relatively stable output voltage despite wide variations in AC input voltage. Some designs are nearly immune to step-voltage changes resulting from capacitor switching. I don't think it's necessary to employ a Variac or similar variable transformer to adjust the voltage. If the measured AC voltage at the repeater site is not within the IEEE standard of 120 +/- 5%, then the utility should be contacted to change the transformer taps to bring the voltage within tolerance. 73, Eric Lemmon WB6FLY -----Original Message----- From: Repeater-Builder@yahoogroups.com [mailto:[EMAIL PROTECTED] On Behalf Of N9WYS Sent: Monday, January 15, 2007 8:43 PM To: Repeater-Builder@yahoogroups.com Subject: RE: [Repeater-Builder] Re: Switching Power Supply vs. Astron Etc. I'd like to pose a question here regarding only a portion of the discussion. This pertains to the "cleanliness" of the power received. I understand that the voltage can fluctuate widely when the utility switches on and out various circuits to meet demand. Skipp mentions that this can cause nasty things to happen to power supplies in equipment racks and cabinets in transmitter rooms, among other items of equipment. My question is this: is it worthwhile to install a variac on the mains for the item in question to "stabilize" the voltage? Or will this not work as I envision it might/should? Mark - N9WYS -----Original Message----- (much text snippage) I'll take the turn it off when not needed/used gamble because I've seen first hand what can and does come down the power line quite a bit more often that one would expect. It's not pretty, nor is it clean or stable 100% of the time. Our local utility does a big grid switch every weekday morning about 8am and that event alone is a huge glitch generator. Yahoo! Groups Links
