Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

How system frequency is controlled on the electricity transmission system

  1. Feb 21, 2010 #1
    Hi can anyone direct me to some good information on how system frequency is controlled on the electricity transmission system?
  2. jcsd
  3. Feb 21, 2010 #2
    It used to be rather crude. Increasing the steam increased the torque This in turn caused the particular generator to lead phase / try to pull the system to a higher frequency. As I recall, increasing the field current also tried to induce phase lead.

    In engineering, they taught us that generators came one line by matching the speeed and phase of the existing generators. This was done with three lamps. One for each phase between the starting generator and the network. Steam was controlled to get the perfect phase match, and field strenght was controlled to get a perfect voltage match. Then, the switches could be engaged and the generator would hold lock with the system.

    I don't know how they communicate to keep an average of 60 Hz, but I know it wasn't perfect as of about 1992. I was working on an inverter back then, and the crystal controlled signal sources matched each other perfectly, but the AC lines' frequency continuelly varied by fractions of a Hz.
  4. Feb 21, 2010 #3


    User Avatar
    Science Advisor
    Gold Member

    As long as loads change across the grid, the frequency will deviate. At the generation stations, the grid frequency is measured and compared to the generator speed and the error signal is used by a PLC or some controller to ramp the generator up or down.

    Last edited by a moderator: Apr 24, 2017
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook