Group, The effort to track power line frequency changes is laudable. I think the effort to determine the stiffness of the network by measuring the phase angle between GPS time and local line zero crossings is most interesting. But the following is about the frequency control problem.
The main problem is that the amount of power that is stored in the distribution system is negligible. The generating station has no information about load changes until after they have happened. There is no lag time that allows derivative action to compensate. If the generating station is on an island with no connection to any grid, you can use a proportional controller with integral action to control the generator speed by manipulating the fuel valve to the engine. This can hold the generator quite close to your desired line frequency. But because it is feedback control, an error must be sensed before the fuel valve moves - cycles can be lost. It is still necessary to manually bias the fuel valve to match the error between the cycles generated and the GPS cycles elapsed. When generating stations are synchronously synchronized by the distribution network, a new problem arises. The stations can not all use integral action and maintain stable control. In fact, only one integral controller may be on such a network. The integral control comes from the area dispatcher, who integrates the cycles generated and compares them to the cycles to maintain 60.000+ cycles per second (in the degenerate West). I am not clear on how the dispatcher allocates frequency error to the area stations, or how they react to commands to change. But it seems to me that this is a control problem that can be solved without undue stress on the generating equipment. Perhaps it is as simple as a setpoint rate of change limit (can't be, 3000 people would have thought of that.) We welcome your comments with Enthusiasm. The references below are important. Bill Hawkins -----Original Message----- On Fri, Jun 24, 2011 at 7:02 PM, Bob Kupiec <bobkup...@comcast.net> wrote: > > AP: Power grid change may disrupt clocks > ----------------------------------------- > http://news.yahoo.com/s/ap/20110624/ap_on_hi_te/us_sci_power_clocks > > > Time Error Correction Elimination > --------------------------------- > http://www.nerc.com/page.php?cid=6|386 > > NERC Report - June 14 > --------------------- > http://www.nerc.com/files/NERC_TEC_Field_Trial_Webinar_061411.pdf _______________________________________________ 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.