214 W. Tremont Ave, Suite 301
Charlotte, NC 28203, USA
Ambient Adjusted Rating (AAR) technology works by using existing environmental data and high-quality weather forecasts to adjust and rate the performance of overhead lines. This process involves collecting data on ambient temperature, both historical and forecasted, while treating parameters like humidity, lighting levels, wind speed, and wind direction as static assumptions.
This data is then used in an algorithm that provides a transmission rating for the overhead lines based on the forecasted weather conditions. The algorithm considers the correlations between the collected data and the performance characteristics of the overhead lines. By analyzing these correlations, the algorithm determines the necessary adjustments to reflect actual performance within the given environmental context. AAR can typically be forecasted for up to ten days, with uncertainty increasing the further into the future the forecast extends.
The main advantage of Ambient Adjusted Rating is its cost-effectiveness and ease of implementation. Unlike traditional systems that require physical sensors, AAR uses existing environmental data and weather forecasts to provide an adjusted rating. This allows systems to be operational in minutes. Compared to scenarios with no grid monitoring, AAR offers a better assessment of ambient conditions around an overhead line. At Heimdall Power, we typically see an average increase in available transmission capacity of 5-10% with AAR. With our DLR technology, however, we see around 40%.
AAR has its challenges. The reliance on assumptions rather than real-time sensor data is a key limitation. While AAR can provide a reasonable estimate of performance, it may not account for sudden or unforeseen changes in local conditions. Specific environmental factors might not be captured by the ambient data, leading to an AAR rating that may not accurately reflect the true capability of the lines. In worst-case scenarios, this could lead to overloads or blackouts in the grid. Such situations could occur in the orange area in the graph below. Therefore, grid operators often equip their critical lines with physical sensors to increase operational safety and observability.
The graph above shows aggregated data from some of Heimdall Power’s installations with DLR and AAR. The green area indicates where DLR provides additional available capacity compared to AAR, while the small orange area indicates how often AAR will overestimate the line’s capacity. The Static Line Rating (SLR) option is indicated by the black line, constant at 100%.
Ambient Adjusted Rating (AAR) rates the transmission capacity of overhead lines based on ambient temperature and potentially other factors. In contrast, Dynamic Line Rating (DLR) uses real-time sensor data to determine the line’s actual capacity at any given moment. The primary difference between AAR and DLR is their source of input data, with DLR offering superior accuracy. However, implementing AAR is usually less expensive and time-consuming compared to DLR.
Combining both technologies, instrumenting the power grid with a mix of AAR and DLR based on the criticality of the line, appears to be the best approach for the transmission industry. You can read more about Dynamic Line Rating in this article.
The illustration on the right shows how we use DLR and enhanced AAR at Heimdall Power, utilizing our Physical Neuron & Virtual Neuron sensors.
Ambient Adjusted Rating (AAR) was first formally introduced and utilized in the context of FERC Order 881, which was approved by the Federal Energy Regulatory Commission (FERC) on the 16th of December, 2021. In order to make bette ruse of the existing infrastructure, maintain grid reliability, and keep customer rates as low as possible, the order requites all US transmission providers to have a certain level of grid monitoring by the 12th of July, 2025. But Ambient Adjusted Rating is just one way grid companies can meet the requirements.
Heimdall Power provides a seamless system for setting up Ambient Adjusted Rating using our self-deployed virtual Neurons, thereby meeting the requirements of FERC Order 881. AAR can be configured with default CIGRE or IEEE recommended weather assumptions or customized settings based on the client’s needs and the specifics of each power line. High-quality weather data is fetched every hour and used to calculate AAR for each relevant line segment. Results are aggregated to provide a single, valid, and safe AAR value for real-time operations and up to 10 days of forecasts.
Ambient Adjusted Rating can be a valuable tool for utilities to improve the transmission capacity and monitoring of their overhead lines. When used correctly, the technology offers an easy gateway to grid monitoring for utilities aiming to optimize their grid. By using AAR technology, utilities can typically increase the transmission capacity of their lines without compromising safety or reliability. This provides a win-win solution for utilities, regulators, and consumers alike.
Would you like to know more about AAR? Heimdall Power is a world leader in overhead line rating technologies and expertise, and we are always ready to help you increase your knowledge, grid capacity, or both. Contact us via email or use the button below to get started.
214 W. Tremont Ave, Suite 301
Charlotte, NC 28203, USA
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