Past Forward

On 23 October 1916, an engineer named Henry E. Warren quietly revolutionized power transmission by installing an electric clock in the L Street generating station of Boston's Edison Electric Illuminating Co. This master station clock kept a very particular type of time: It used a synchronous self-starting motor in conjunction with a pendulum to maintain the station's AC electricity at a steady 60-cycle-per-second frequency. As more power stations adopted the clocks, frequency regulation allowed them to share electricity and create an interconnected power grid. Until the late 1940s, station clocks from the Warren Telechron Co. regulated over 95 percent of all U.S. electricity lines. The Telechron Model Type E at left is from the 1930s and was used at the Tennessee Valley Authority. Beginning in the 1950s, advanced electronics began displacing electromechanical master station clocks. Today, power-grid frequency is regulated by atomic clocks, although it still has to be tweaked to stay on target.