Transmission Line Ampacity Improvements using Optimized Forecasting Solution for Grid Operations

Helping utilities make the most of their existing transmission and distribution infrastructure

By Donna Rennemo, President & CEO, WindSim Americas Inc.

As utilities consider the replacement of aging infrastructure and incorporating renewables from remote locations, unlocking extra capacity within existing transmission lines offers profound advantages in efficiency and reliability of system operation. Utilities across the nation are weighing the trade-offs in providing additional power for homes, industry and critical services through traditional transmission expansion planning.  Overhead transmission lines (TLs) are thermally limited to the amount of electrical current they can carry due to the physical properties of the conductor. Conventionally, TL current carrying capacity is set to static (SLR) or seasonally varying values based on a conservative assumption of the environmental conditions (e.g., low wind speed and high ambient air temperature) over the year/season. Because these conditions are present only for short periods of time, this approach often under-utilizes existing transmission assets.

Fig. 1 Power lines are heated by the sun and when transmitting power. They are also cooled by the wind and weather.

Idaho National Laboratory has led the development of a weather-based dynamic line rating (DLR) methodology that can cost effectively help transmission and generation asset owners safely and reliably reduce the amount of congestion they experience. It uses computational fluid dynamics and weather forecasting innovation funded by the U.S. Department of Energy’s Wind Energy Technologies Office, in partnership with

Fig. 2: WPLS calculation of span-by-span line ratings in a DLR forecasting scenario.

WindSim. The INL – WindSim development has advanced the technology for the electricity sector by improving the capability of modeling and transferring weather conditions to every span on the line to accurately perform dynamic line ratings across a large geographic area with high reliability and certainty. The latest INL-WindSim combined solution — called WindSim Power Line Optimization Solution (WPLS) — includes both forecast and real-time dynamic line rating. As WPLS collects real-time environmental conditions by field stations and integrates it with historical environmental conditions and short and longer-term forecasts, more realistic line ratings than SLR can be calculated for the next minutes up to the next days ahead and be delivered to the operators of the lines (Fig. 2).

Weather-based Dynamic Line Rating has been validated through three industry pilots to ensure it provides a smart grid energy solution for removing artificial or systematic power flow constraints. This is done by informing system planners and grid operators of available transmission and distribution capacity that was previously restricted by Static Line Ratings. The WindSim Power Line Optimization Solution is currently deployed and continually being validated in partnership with other electric utility partners and commercial meteorological solution providers, which also includes the US National Oceanic and Atmospheric Administration (NOAA). WindSim is looking for additional partners to further deploy this innovative, industry accepted solution!

Plot of improvement in amps of the weather-based ampacity calculation versus a normalized static line rating (SLR). The terms with (t) are functions of time.


WindSim Power Line Article Image 4
The illustration of terrain (orange) shows the large scale often under consideration.  The gray boxes along the power lines are more discrete CFD models that consider the local terrain.

Almost every country has cre­ated wind resource maps to find potential windy places suitable for building new wind plants. Modelers use a wide range of methods to create these wind resource maps. Yet new methods are needed to capture the detail required to enable dynamic line rating, which could boost transmission and distribution line capacity by 10 to 40 percent.

Wind­Sim has developed a wind atlas method using specialized software. The approach enables dynamic line rating modeling and simulation that can expand over hundreds of miles. To be as accurate as possible, the method combines wind speed and wind direction data from smaller simulation areas and is based on scaling against measurements where available.

To create these wind resource maps, scientists have many modeling options to choose from, including mesoscale modelling, linear methods and computational fluid dynamics (CFD).

Using mesoscale models has the advantage that the entire area of interest can be fully covered by one model, while using other approaches requires that several simulation areas be combined afterwards. However, mesoscale modeling does not reach the horizontal resolution necessary for a reli­able wind resource map.

For example, mesoscale mod­els reach their limits in rough terrain because the roughly 1-km resolution is too coarse and forces over-simplified orography. By comparison, CFD can simulate the wind flow with a horizontal resolu­tion of 10 m, or even 1 m with specialized data collection. As a result, the CFD approach can better predict the flow pattern within smaller valleys and in very difficult terrain.

For that reason, it has become common to use CFD to gener­ate wind resource maps of smaller areas, and then combine the different simulation areas in the end to see the big picture.

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Media Contact:
Donna Rennemo
President & CEO
WindSim Americas Inc.

Phone: +1 805 216 0785