The rotary generators in a system of connected generators are synchronous machines. There is no frequency difference between them, only phase angle, and not much of that - if the system is stable.
The ocean liner analogy is correct, as there is only one captain directing the ship's course. If each plant set its own power levels it would be very difficult to maintain stability, due to the springiness of long transmission lines. A set of connected generators is controlled by regional dispatchers, who tell their plants how much power to generate in order for the day to average out to 60.000 cycles per second. They count cycles instead of measuring the frequency. You can count cycles with a synchronous clock. This becomes less tidy when DC tie lines are used, because inverters have to be adjusted to get the correct power flow. Hope I got most of that right. Bill Hawkins -----Original Message----- From: time-nuts [mailto:time-nuts-boun...@febo.com] On Behalf Of Peter Reilley Sent: Wednesday, April 05, 2017 7:42 AM To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] Line Frequeny Stablity Think of it as an ocean liner trying to keep a dead straight course to it's destination. It weighs many tons and wind and waves may drive it off it's path but the captain can correct for this. It eventually arrives at it's destination and is only a few feet from the dock. The total rotating mass of all the generators in a network is many times the mass of an ocean liner. The operators do their best to keep them running at the correct frequency. Unexpected load changes can cause some divergence, but over time the average is dead on. When I installed power plants in the 1970's they has a special "clock" that showed the cumulative error in terms of clock time. The clock had two inputs, one from the utility power and the other from some reference, possibly WWV. Normally the "clock" was pointing up at zero and not moving. If the generator ran a little too fast the clock would move forward. As the operator observed the clock moving away from zero he would reduce the plant's power and the clock would move backward toward zero. His goal was to keep the clock at zero and not moving. Thus, your bedside clock was always on time even if there were temporary excursions fast or slow. Pete. On 4/4/2017 5:28 PM, Thomas D. Erb wrote: > Thanks for the info. > > > So that tells me how data is recorded - but not how the frequency is kept stable ? > > Is the line frequency now directly tied to GPS clock - with no drift ? > > Thomas D. Erb > t...@electrictime.com<mailto:t...@electrictime.com> / Electric Time > Company, Inc. > Office: 508-359-4396 x 117 / Fax: 508-359-4482 > 97 West Street Medfield, MA 02052 USA _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.