Differential GPS Measurement of Overhead Conductor Sag: Software Implementation

(PSERC). PSERC is a multi-university Center conducting research on challenges facing a restructuring electric power industry and educating the next generation of power engineers. of Entergy-New Orleans. In early stages of the project, Mr. Lance Priez of Entergy supplied needed information. The many useful suggestions of all the industrial advisors are acknowledged. Dale Bradshaw of the Tennessee Valley Authority also provided valuable information and encouragement. ii Executive Summary This is a final report on the development and implementation of software that can be used to estimate and continuously display the changing real-time current rating of a transmission-line conductor. The software can be used in an on-line energy management system (EMS) as an aid to power system operators. The software uses information from an instrument that can measure the sag of overhead transmission conductors for 69 kV circuits and above. The instrument may be based on either (1) direct measurement (such as a device that uses a Global Positioning Satellite signal or an optical surveying instrument), (2) an instrumentation system that uses calculation procedures (such as the 'Power Donut', a 'CAT' system that measures conductor tension), or (3) a resistive line near the conductors that effectively measures the electric field. A typical GUI screen is shown in Figure (E.1) The dynamic thermal real time rating of a circuit is estimated using linear state estimation based on historical data. The historical data are loaded into a least squares estimator, and a model is obtained for the circuit sag as a function of line load and weather parameters. Then, the maximum permissible sag is used to 'work backwards' and calculate the real time current rating of the conductor. Plans are being made to test the software using data from an actual circuit.