I have here a pair of instruments that were part of a system used at one time in a power station here in NZ to control the time error in one part of the national grid. It controlled the selected generators and provided a real time display of the time error between a reference standard and the 50 Hz mains frequency. The system comprised an HP 5280A reversible counter with two inputs, one from the mains 50 Hz as generated and one from the reference standard. These two inputs were arranged to add counts from one input and subtract counts from the other, such that the counter displayed zero while the generated 50 Hz was accurate. Offsets from 50Hz were displayed as positive or negative counts. The reference input was derived from an HP 105A quartz oscillator and the system included provision to manually synch that to the national standard time standard on an as required basis. The output of the 5280A counter drove an HP 6933B D/A converter, the bi-polar DC output of which was used (both magnitude and sign) to control the governors on some of the hydro generators. Dual HP 5321B clocks were used to display TOD from both sources. The 6933B is complete but the 5280A counter has been partly disassembled. The 5321Bs never got this far-neither did the 105A- who knows, it might still be being used as a reference!
DaveB, NZ -----Original Message----- From: time-nuts [mailto:[email protected]] On Behalf Of Bill Hawkins Sent: Monday, July 08, 2019 06:48 To: Bob via time-nuts Subject: Re: [time-nuts] A Research Proposal Group, We've discussed this before, but maybe it needs to be said again. Line frequency is not constant. There is no master PLL. Approximate frequency is maintained by a central power dispatching office in each of the four (?) regions tied together by their power distribution grid. The dispatcher's goal is to create the same number of cycles of AC each day. IIRC, power is bought and sold by the number of cycles generated. As the daytime load increases, the generators slow down a bit. Note that it is not possible for each generating station to control its frequency, as that would not be stable. Instead, the dispatcher asks various plant operators to generate more or less steam (or water flow) in order to increase the frequency. When the load drops at night, the generators speed up a bit, and steam has to be reduced. At the end of the day, so to speak, the number of cycles generated is very nearly equal to the number generated if the line frequency had been steady at 60 (or 50) cycles per second. Synchronous clocks stay accurate although they may be off by a few seconds as dispatchers scramble to get enough steam to keep up. So yes, you can get phase data within a region but you must compensate timing data as the frequency varies. The regions are connected to each other for purposes of power sharing with DC transmission lines. These use inverters to convert between AC and DC. The AC frequency is controlled by the grid that it is tied to. Phase angle can be changed to change the amount and direction of the power transferred. So no, you can't compare data from different regions, unless you want to know which way DC power is flowing. I hope this was informative. Bill Hawkins On Thu, Jul 4, 2019, at 2:00 PM, Andy Backus wrote: > Historically, and even today, the steady frequency of AC power has > been used for timekeeping. So there may be interest here in the > following research proposal: > > Within a given power distribution grid, several observers as widely > separated geographically as possible, time stamp the first two zero > crossings of the power line after each UTC second – over the course of > 24 hours (86,400 pairs of data). > > Popularly conceived, all the components of a power distribution grid > are phase locked – though, of course, power is taken in and out by > varying degrees of lead or lag. Frequency is maintained by a constant > balancing act between load and generation. > > Typical power distribution grids, however, are sized on a scale of > thousands of miles. “Locking phase,” then, is problematic simply on > the basis of the limits of information transmission rate. Even at c, > every 1000 miles takes 5 ms, which represents a third to a quarter of > the period of the AC power waveform. > > Many interesting phenomena might result from that reality, which > suggests a certain constrained flexibility over large distances – > almost as if the system is like a large lake of viscous liquid. When > there are local disturbances such as rapid load changes or sudden > generation adjustments, for example, it is quite possible harmonic > ripples could be propagated through the system. > > Such effects could be observed by comparing phase data across > significant distances within a distribution grid. > > Andy Backus > Bellingham, WA > USA > > ________________________________ > From: time-nuts <[email protected]> on behalf of Thomas > D. Erb <[email protected]> > Sent: Thursday, July 4, 2019 5:23 AM > To: [email protected] > Subject: Re: [time-nuts] 60 Hz frequency and phase measurement > snip > I had a recent tour of a power station - the operators had no idea the > output was synchronized to a time standard - they just synchronize > with the local grid. > > Thomas D. Erb > p: 508-359-4396 > f: 508-359-4482 > a: 97 West Street, Medfield, MA 02052 USA > e: [email protected] > w: www.electrictime.com<http://www.electrictime.com> > Tower & Street Clocks Since 1928 > _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
