# Dynamic Thermal Rating and Development of Renewable Energy Zones in Sicily
## 3 Dynamic Thermal Rating  
The use of tools such as DTR (Dynamic Thermal Rating) devices, which are able to calculate the maximum current that the electrical conductor can withstand while complying with the current and minimum ground clearance limits imposed by regulations, is very important in the management of the electrical transmission network. To perform this function, these devices must be able to detect all the electrical and mechanical variables that affect the heat exchange between the conductor and the environment in which it is located. This information is processed by models based on meteorological measurements, on the detection of the mechanical sag/voltage of the conductor, or on electrical quantities [10; 11]. These devices are based on the following energy balance equation:  
\[\mathrm{q_{c}(T_{c},T_{a},V_{m},\varphi)+q_{r}(T_{c},T_{a})=q_{s}+I^{2}\times R (T_{c})[W]} \tag{1}\]where  
* q\({}_{c}\) (function of T\({}_{c}\), T\({}_{a}\), V\({}_{m}\), \(\varphi\)) represent the heat exchange by convection from the conductor to the surrounding environment [W];
* q\({}_{r}\) (function of T\({}_{c}\), T\({}_{a}\)) represent the heat exchange by radiation from the conductor to the surrounding environment [W];
* q\({}_{s}\) represent the heat gain due to solar radiation [W];
* I\({}^{2}\)\(\times\) R(T\({}_{c}\)) the heat generated by the Joule effect through the conductor crossed by the current I [A];
* R(T\({}_{c}\)) [\(\Omega\)] is the resistance of the conductor at temperature T\({}_{c}\) [K];
* T\({}_{c}\) is the average temperature of the conductor [K]. * T\({}_{a}\) is the average temperature of the environment [K];
* V\({}_{m}\) represent the speed of the wind striking the conductor [m/s];
* \(\varphi\) represent the direction of the wind striking the conductor [rad];  
There are several studies in the literature that show how DTR systems can allow the ampacity of the power lines to be increased compared to the conventional static limits imposed before the advent of this technology. The Dynamic Thermal Rating suggests capacities that are 15-30% higher than the conventional Static Thermal Rating on average, for 80-90% of the operating period [12]. To take advantage of this significant increase in range, DTR devices must be positioned correctly along the transmission line. The power grid normally crosses large areas that are subject to different weather conditions, which affect the heat exchange of the conductor in different ways. For example, a conductor exposed to strong gusts of wind tends to cool down more than a conductor exposed to low winds. As a result, the ampacity and elongation of the conductor will not be uniform throughout the line. The safest and most conservative practice is to identify the so-called \"hot spots\" of the line, i.e., the hottest points, where the clearance from the ground is lower, and the phenomena of annealing of the line are more likely. The span corresponding to the above characteristics is called the \"critical span\", and its identification ensures that all sections of the line can be traversed with a sustainable current capacity [12]. To identify the hot spots of the line, sample measurements can be made, both homogeneously distributed over the area and according to specific criteria. The article \"Identification of Critical Spans for Monitoring Systems in Dynamic Thermal Rating\" [13] proposes the comparison between a heuristic method of evaluating critical spans and a homogeneous sampling method on the territory. An important aspect of Dynamic Thermal Rating is the correct prediction of the operating conditions of the line. An accurate prediction allows the operator to perform the following:  
* Optimize the operation of the network;
* Manage the uncertainty of loads and the intermittency of renewable generation;
* Improve grid reliability and economic stability of power flows;
* Minimize any interruption in renewable energy production [12].