There are two systems that affect line frequency anywhere in the world. One is the use of multiple power producers generating steam for turbines that turn huge generators. The generators are synchronized by the distribution networks that connect them. A generator rotates at the frequency determined by all of the other generators, If its turbine is receiving less energy than is required to keep up, the generator will take the balance of power from the network. If the turbine produces more energy than is required, it will cause the line frequency to increase a very little bit. Change 'steam' to 'water' for hydro-electric plants.
A networked connection of generators and loads requires a perfect balance of power produced with power consumed to maintain constant frequency. This can only be done for very small networks. You cannot put a PID controller on each turbine and set it for a GPS derived frequency. The control actions would fight each other and destabilize the network. In the early days, each power station had a clock driven by the generators and a reference clock. An operator would increase steam to the turbines a bit if the station clock fell behind the reference clock, or decrease steam slightly if it was gaining time. There was (is) no way to predict the behavior of the loads, except from general experience of the effects of weather and holidays. Today's networks are much too large for control by station clocks. A large region has a central power dispatching station. A dispatcher tracks the difference between network time and GPS time. If the network is losing time, the dispatcher calls the necessary number of generating plants and asks them to increase power. It is common to lose time as the loads of the manufacturing day increase and to make it up after 4 AM or so. (During the 50s, the Air Force determined that 4:30 AM was the time of minimum human activity, and so a probable time for an enemy to strike with missiles.) I visited the Pennsylvania, New Jersey, and Delaware (PennJerDel) region's dispatch center in the seventies. Very impressive wall maps of major generation stations and load centers with their data. It is expensive for a plant to change power, and so they hatched the plan to stop trying to hold the time difference to zero over a day. There was sufficient outcry to abandon the plan. The other system comes from the use of high voltage DC tie lines to exchange power between networks isolated by geography, such as the West Coast and Texas. The DC lines use high voltage, high power solid state inverters to convert DC to AC or reverse the direction when power could flow the other way. The inverter frequency can be precisely controlled, but it is controlled to balance the power flow, not hold the line frequency. A network pays for the tie line power it produces or consumes. Different regions can have different phase behavior. I have only seen West Coast plots on this list. When I did some work with this in Minnesota in the eighties, the phase variation was only about 6 seconds during a day and zero from day to day. This is my understanding of the system. People with more knowledge, please correct my misconceptions. Bill Hawkins _______________________________________________ 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.