Dynamic Line Rating (DLR) of overhead lines (OHL) uses the fact, that the ampacity of OHL depends on ambient conditions and the OHL are designed for high summer weather conditions. Since for most of the year less severe weather conditions exist, the ampacity of the existing lines can be significantly increased (up to 200%). The major task thereby is to derive the present conductor temperature (or sag), forecast the future ambient conditions and integrate this monitoring results to dispatching centre processes under considerations of adequate security margins.
The application of dynamic line rating requires knowledge about maximal allowable temperature of OHL conductor, which is also proportional to sag. Since the latter one have relatively small time constant, the maximal temperature can be reached quickly (approximately 15 min). Hence DLR requires weather forecasts in order to allocate the possible additional capacity to the market in system operator processes (IDCF intra day congestion forecast, DACF day ahead congestion forecast, WAPP weak ahead).
In general, there are two ways to acquire the sag or temperature of OHL conductors:
- Conductor temperature is measured with the help of temperature sensors
- Calculation of sag through measurement of tension
- Calculation of sag based on vibration frequency of conductors
- Calculation of sag based on angle of the line at the span point
- Calculation of the conductor temperature based on locally measured weather conditions in thermal hot spots of OHL line
- Calculation of the conductor temperature based on regionally (faraway of OHL) measured weather conditions in thermal hot spots of OHL line
- Direct measurement of sag by optical or laser devices
The main difference between those methods is the need for de-energising of line for sensor installation and maintenance in case of direct measurement.
Components & enablers
Advantages & field of application
An increase of ampacity can be achieved up to 200% depending on the weather conditions and required security margins. The highest potential is observed in areas of high wind RES where the similar weather conditions exist along OHL.
An increase in ampacity supports grid operators to make more efficient use of existing grid assets and avoid congestion restrictions.
The application of DLR requires:
- extensive condition assessment of OHL and equipment in substations
- check of the existing clearances
- adapting the settings of protection devices
- check of potential electro-magnetic induced currents and voltages into parallel infrastructure (other OHL, gas pipelines)
- increase of current increases the magnetic field as well
- extending the TSO’s EMS for processing dynamic line ratings in congestion calculations.
Technology Readiness Level
TRL 9 – System ready for full scale deployment
Research & Development
Current fields of research: Mid-term and long term forecast adequacy of ampacity, system integration, SCADA integration, accuracy of derived values, enhanced combination with weather forecasts, calculation of wind cooling effect regarding wind direction.
Other: In 2015, 11 ENTSO-E TSOs had DLR in operation in different extensions.
Best practice performance
Maximum capacity increase: Enhancements of + 40% and +100% compared to static line rating.
Average capacity increase: Typical ampacity gains in Europe of 10-15% can be expected over 90% of the time. Yet the results are highly case specific and depends on the calculation method.
Best practice application
A DLR system has been installed on its interconnection line and data is sent. The recent development of the system and its validation through surveyor measurements of sag demonstrated up to 200% of rated capacity was available in some circumstances.
Commercially available sensors were used to measure real-time sag directly on 150 kV, 245 kV and 400 kV lines. A four-hour forecast model has been developed.
Rated capacity was raised by 200%.
Fuendetodos – María line, Spain
The research for BEST PATHS is focused on repowering existing power lines and enhancing technological knowledge and application of conductor technologies through different innovations. DEMO 4 has addressed the following objective through the development of a prototype dynamic line rating (DLR) system based on low cost sensors allowing higher temperature operations of current line technologies. Part of the BEST PATHS project is the implementation of the DLR sensors on a transmission line in Spain.
Using 7 DLR sensors on existing 220 kV live line variations in catenary angle of 0.005 º or 10 cm in sag will be measured and communicated for optimal line loading.
Using data from DLR sensors existing corridors were optimized to carry more power. A transmission capacity increase of 15-30% was measured over the duration of the experiment, which lasted 3 months.
DLR is used on many heavily loaded OHL. The system is integrated into most of German TSO’s dispatching centres that exchange the ratings online.
There are different approaches for weather forecasts based on local and regional measurements and also seasonal settings. The maximal derived ampacity differs depending on the region.
Rated capacity was raised up to 200%
 Navigant Research. T&D Sensing and Measurement Market Overview. [Link]
 US Department of Energy. Dynamic Line Rating Systems for Transmission Lines. [Link]
 Moroyovska K, Hilber P. Study of the Monitoring Systems for Dynamic Line Rating. [Link]
 ENTSOE. Dynamic Line Rating for overhead lines -V6 [Link]
 Kladar Dalibor. Dynamic Line Rating in the world – Overview. [Link]
 Cloet E, Santos J. TSOs Advance Dynamic Rating [Link]
 Cigre. Integrating enhanced dynamic line rating into the real-time state estimator analysis and operation of a transmission grid increases reliability, system awareness and line capacity. [Link]
 Best paths. DEMO 4, Innovative Repowering of AC Corridors. [Link]