The Dynamic Line Rating (DLR) of OHL uses the fact that the ampacity of OHL depends on ambient conditions and the OHL are designed for high summer weather conditions. As less severe weather conditions exist for most of the year, the ampacity of the existing lines can be significantly increased (up to 200 %). The major task thereby is to derive the present and forecast the future ambient conditions, calculate the current carrying capacity, and integrate these results to dispatch centre processes, considering adequate security margins.
Technology Types
The application of DLR requires knowledge about the maximal allowable temperature of OHL conductor, which is also proportional to sag. As sag has a relatively small time constant, the maximal temperature can be reached quickly (approximately 15 min). Upon working with the key future operational conditions, 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 week ahead.
In general, there are two main technology groups (contact and non-contact) used to acquire the DLR results:
Contact technologies: measure physical parameters of the conductor like:
- Conductor temperature measurement with the help of temperature sensors
- Calculation of sag through measurement of tension
- Calculation of sag based on the vibration frequency of conductors
- Calculation of sag based on the angle of the line at the span point (1)
Non-contact technologies: the key DLR results are calculated based on weather data from meteorological models and/or locally measured weather data and line load:
- Calculation of the ampacity
- Temperature of the conductor
- Maximal allowed operating time in case the loading surpasses the current carrying capacity of the conductor
The technologies differ, especially in terms of the effort required for installation and the need for modelling. For non-contact technologies, there is no need for the de-energising of line for installation and maintenance, and all the weather parameters required for local weather fore-cast can be measured directly. However, the models require adequate validation. For some of the contact technologies, there is a possibility of installing the sensors using helicopters or bare-hand installation techniques (live working) and acquiring some of the weather parameters for forecast. Non-contact solutions with advanced meteorological models augmented by local weather measurements prove to be very efficient on complex terrain such as hilly areas, where the variability of weather conditions often occurs within very short distance of just a few kilometers. Therefore, each tensioning section, and most preferably, each line-span requires secure monitoring.
Due to the different specific requirements of TSOs (especially need for forecast), different approaches are used across Europe.
Components & enablers
Not specified.
Advantages & field of application
An increase of ampacity can be achieved up to 200% depending on the weather conditions and required confidence intervals. The highest potential is observed in areas of high wind RES, as convective cooling and loading of overhead lines are strongly coupled.
An increase in ampacity supports grid operators in making more efficient use of existing grid assets and avoiding congestion restrictions.
Typically, the permitted line capacity equals the nominal current of the conductor. If there is a need to increase the capacity of the old line up to the nominal current, the following points are important:
- Check the ability of OHL and equipment in substations to carry higher currents
- Check the clearances for defining maximal allowable temperature / line capacity
- Identify line hot spots for installation of monitoring
- Check the static line protection settings
- Design a data delivery into the dispatching centre and the data processing
- Tailored algorithm for transmission capacity calculation
- Forecasting algorithms
- Replacing static line rating (SLR) by DLR in the TSOs’ EMS for processing dynamic line ratings in congestion calculations.
Increasing the line capacity above the permitted value (nominal current) typically requires, in addition to the abovementioned points, additional proof and permits in relation to:
- The maximum allowable inductive influence of parallel infrastructure (e.g. gas pipelines)
- The potential increase of the magnetic field below OHL
- The need of adaptive change of line protection settings
Technology Readiness Level
TRL 9
Research & Development
Current fields of research: Mid-term and long term forecast adequacy of ampacity; integration into long term forecast processes to fulfil system stability requirements; accuracy of derived values; enhanced combination with weather forecasts.
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. However, the results are highly case-specific and depend on the impact evaluation methodology.
Best practice application
Belgium/France
2008 – 2020
Description
DLR systems are installed on 27 lines including all HVAC interconnection lines, and both real-time and forecast DLR data are used in intraday and day-ahead operation planning and market capacity allocation processes. The recent development of the system and its validation through surveyor measurements of sag demonstrated that up to 200% of rated capacity was available in certain circumstances.
Design
Commercially available sensors were used to measure real-time sag directly on 70 kV, 150 kV, 245 kV and 400 kV lines. Up to 60 h-ahead forecast module has been developed.
Results
Intraday rated capacity is raised up to 130%, whereas for CORESO processes it is raised up to 110% based on statistical risk assessment.
Fuendetodos – María line, Spain
2017
Description
The research for BEST PATHS is focused on repowering existing power lines and enhancing the technological knowledge and application of conductor technologies through different innovations. DEMO 4 has addressed the following objective through the development of a prototype DLR system based on low cost sensors, allowing for 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.
Design
Using 7 DLR sensors on existing 220 kV live line variations in a catenary angle of 0.005 º or 10 cm in sag will be measured and communicated for optimal line loading.
Results
Using data from DLR sensors, existing corridors were optimised to carry more power. A transmission capacity increase of 15 – 30% was measured over the duration of the experiment, which lasted 3 months.
Description
DLR is used on many heavily loaded OHL. The system is integrated into most of the German TSO’s dispatching centres that exchange the ratings online.
Design
There are different approaches for weather forecasts based on local and regional measurements as well as seasonal settings. The maximal derived ampacity differs depending on the region.
Results
Rated capacity was raised up to 200%
Description
The DLR system covers 29 lines (6 × 400 kV, 4 × 220 kV and 17 × 110 kV). The system is fully functional and integrated into the daily operation. The main applications that support real-time operation and operation planning are the mitigation of N and N-1 overloading operational situations and calculations of transmission capacities for up to two days ahead. The system also features an inverse DLR algorithm for icing prevention and alarms for extreme weather conditions along the lines.
Design
Indirect (non-contact) DLR system based on macro and micro-scale meteorological models supported by weather measurements. Calculations are performed for each line span. The system allows the definition of maximal operating temperature per tension field. Comprehensive modular IT system with data quality monitoring and uncertainties modules, integrated with the SCADA / EMS.
Results
On average, 92 – 96% of the time the DLR system offers a higher transmission capacity with a median increase of 15 – 20 % of the nominal capacity. Over 20 events in N and over 500 in N-1 topologies are mitigated annually by the DLR system.
References
[ 1 ] Navigant Research. T&D Sensing and Measurement Market Overview.
[ 2 ] US Department of Energy. Dynamic Line Rating Systems for Transmission Lines. [Link]
[ 3 ] Moroyovska K, Hilber P. Study of the Monitoring Systems for Dynamic Line Rating. [Link]
[ 4 ] ENTSOE. Dynamic Line Rating for overhead lines – V6 [Link]
[ 5 ] Kladar Dalibor. Dynamic Line Rating in the world – Overview. [Link]
[ 6 ] Cloet E, Santos J. TSOs Advance Dynamic Rating [Link]
[ 7 ] 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]
[ 8 ] Best paths. DEMO 4, Innovative Repowering of AC Corridors. [Link]
[ 9 ] IEEE Transactions, D. A. Douglass et al., ‘A Review of Dynamic Thermal Line Rating Methods With Forecasting’ [Link]
[ 10 ] CIGRE-TB-498: Guide for Application of Direct RealTime Monitoring Systems.
[ 11 ] CIGRE-TB-425: Increasing capacity of power transmission lines - needs and solutions.
[ 12 ] J. Kosmač, A. Matko, F. Kropec, A. Deželak: Use of Dynamic Line Rating System in System Operation and Planning , CIGRE Paris, session 48, C2-143, 2020
