Development and application of time-division multiplexing telemetering equipment for data transmission on an electric power system

In the fall of 1957 the Tennessee Valley Authority (TVA) began preliminary work toward increasing the number of telemeter readings by use of existing telemeter circuits with a minimum of modifications and additions. The additional channels were used to provide the power-system dispatchers with data that were normally received by telephone. The initial objective was to transmit the load readings of five hydroelectric plants and their total from the Nashville Load Dispatching Office to the Chattanooga Load Dispatching Office. High-speed data transmission was not a requirement in this case, since no automatic controls were involved and the readings were to be used for informative purposes. In view of the foregoing requirement, studies indicated that distant readings could be transmitted to a remote central location, from which time-division multiplexing telemetering equipment could be employed for data transmission, thus reducing the cost of communication channel facilities. Investigations indicated that no suitable equipment was available for this purpose that would work with existing facilities and that would provide the necessary functions. TVA devised experimental equipment to transmit six hydro plant readings over one impulse channel from the Nashville Load Dispatching Office to the Chattanooga Load Dispatching Office. Later the hydro plant readings were replaced by six substation load readings that are used in a computer for system economic loading purposes. This equipment has operated over a 1-tone channel of a microwave system about 130 miles in length for more than 1 1/2 years and the operation has been satisfactory.