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The main concept of our Ampacity model is to make a decision-support process for system operators, which can be practically applied. Ampacity model is not only used to increase the line rating, but also to increase operational safety. Therefore, the real-time load of the line can be lower than the static rating, when the actual weather parameters show the worst scenario than the parameters which was used for static rating calculation. In this case, the thermal overload and the violation of safety margins can be avoided by limiting the ampacity.

Ampacity is defined as the maximum current, in amperes, that a conductor can carry continuously under the conditions of use without exceeding its temperature rating limit value. It is the most important output parameter of any Dynamic Line Rating (DLR) expert system.

OTLM system has a few options for Ampacity calculation:

  • Combining measurement from OTLM sensors and Weather station (normally on the tower)
  • Combining measurements from OTLM sensors and using virtual weather station
  • Using only OTLM sensors

Raw data for the calculating algorithm are provided on-line with OTLM sensors and/or weather station. The actual temperature of the conductor and real-time load of the line are known parameters; therefore, the cooling effect of the environmental parameters can be determined based on the thermal equilibrium. Furthermore, the temperature difference between the actual conductor temperature and maximally allowed temperature of the conductors is calculated. The surplus current is the current quantity which heats the conductor to the maximal allowed temperature. In this way, the real-time ampacity is the sum of the actual load and the surplus current.

Ampacity forecast

Line rating can be predetermined with the use of weather forecast; therefore, a more flexible and resilient transmission system can be achieved. In this case, the generation schedule can be adjusted to the predetermined transmission capacity, therefore higher utilization of the electricity system can be achieved. Weather forecast with high temporal and spatial resolution should be available for the implementation of this methodology. The following weather parameters are required for predetermined ampacity calculation:

  • ambient temperature
  • wind speed and direction
  • solar radiation
  • precipitation rate

It is important to cover the whole line with weather forecast points, to determine the transmission capacity with high accuracy. The minimal time resolution is 1 hour which is required in this case.

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