Gary, There are two primary causes for abrupt changes in line voltage: Substation tap changers and capacitor switching.
The national nominal voltage in the United States is 120 plus or minus five percent. Electrical utilities go to great lengths to regulate distribution voltages, which usually range from 4,160 volts to 22,000 volts. You often hear old-timers talk about "110" or "220" volts, but those have not been available for about 50 years- except perhaps in some isolated areas with local power generation. The substation transformers have LTCs (Load Tap Changers) which can adjust the distribution voltage in small steps, usually 1.25% or 2.5%. The problem with this voltage regulation method is that power users close to the substation will see a higher voltage than distant users. A well-planned distribution network will have additional regulating transformers out in the field to more closely keep the user voltages at 120/240 VAC in single-phase systems, or at 120/208 VAC in three-phase systems. Industrial users will probably be metered at 277/480 VAC. Since distribution systems are primarily inductive, capacitor banks are used to increase the power factor and raise the voltage on long feeders. These capacitors may operate automatically, but are commonly switched in and out on a time schedule. If you put a voltage logger on your home power system and see a jump of several volts at the same time every day, that is almost certainly a capacitor bank. A case in point: Several years ago, I measured a jump of my line voltage from 119 VAC to 123 VAC at the same time every evening, and a reverse change at the same time every morning. As a power engineer, I knew the route that power lines took from the substation to my house, so I drove the line and found a timed capacitor bank about two miles from my house. I drove to that location one evening and confirmed that it energized at exactly the time that I recorded the voltage jump. When I contacted the utility with the information, I learned that it had been disabled when a marine shop closed its doors and no longer had large motors in service. The service agent could not believe that the capacitor bank was in service, so he sent out a bucket truck to check it out. I met the truck at the site, and enjoyed his reaction. Needless to say, he pulled the cutout fuses and shut down the timer. My strange voltage excursions ended. If you believe that your voltage is not close to 120 VAC, be careful to use a known-accurate True-RMS meter to take readings from an outlet that does not have any large appliances or other cyclic loads. The voltage drop in such circuits can skew the measurement of the service voltage. One last thought: A corroded neutral connection at the transformer, or at any point between the transformer and your service panel can allow large voltage swings to occur during load changes. The best indicator of this problem is when some lights momentarily get dim while other lights in the house get bright, each time the refrigerator starts. Since this defect is almost always upstream of the meter, its correction is the responsibility of the utility. 73, Eric Lemmon WB6FLY -----Original Message----- From: Repeater-Builder@yahoogroups.com [mailto:[EMAIL PROTECTED] On Behalf Of [EMAIL PROTECTED] Sent: Sunday, July 06, 2008 8:51 PM To: Repeater-Builder@yahoogroups.com Subject: [Repeater-Builder] High AC Line Apologize for being off topic but a safety question. Do you people monitor your AC line at your home, business,shop etc? I've been having a problem in central NJ with high line around 1:00 am. Our spec is 115.2 - 124.8. Around 1 AM I run 127.0, 126.4 with a daily average around 124 during the rest of the day. As we all know many electronic products are really not off when we hit the off button. Although today's electronics are designed for higher AC line voltages. I've already experienced one work bench light ballast fire. Plus a large number of smoked electronic test equipment. I continually see phase shift capacitors being switched in and out on my line monitor or is it bad grounds? The volt readings are done with a Fluke 77 that has been calibration checked and certified correct. Would someone educate me on proper power utilities. Please contact me off R-B unless others feel they would like to know also. Again I apologize burning up air time. Gary K2UQ [EMAIL PROTECTED] ________________________________ Gas prices getting you down? Search AOL Autos for fuel-efficient used cars <http://autos.aol.com/used?ncid=aolaut00050000000007> .
