# Dynamic Line Rating--An Effective Method to Increase the Safety of Power Lines
## 3 Possible Solutions to Reduce the Electric Field
### New Expert System Based on Dynamic Line Rating (DLR)  
A new expert system based on DLR has been investigated to provide a technically and economically efficient solution for the electric field problem. With its application, the electric field can be ensured not to exceed its limit value, while the power line is fully utilized almost all the time. This system's core is to determine what factor is responsible for the risk and decrease the maximum allowed conductor temperature to avoid electric field distribution problems. The method exploits the benefits of online monitoring in the real transfer capacity calculation. For real-time temperature tracking, a sensor needs to be installed onto the transmission line. The expert system provides a solution for the tension span equipped with the monitoring device, but it can be extended for the whole power line. The system's operation is detailed below for a single tension span. The operation of the expert system can be separated into two broad steps. The first one is a general analysis of the power line, while the second step concerns the observed tension span in which the sensor is installed. In Figure 5. The first step aims to find out whether the power line's operation is at risk or not. First, a so-called critical span analysis needs to be performed. In this substep, all the tension spans are examined to find the lowest clearance value at the maximal operation conductor temperature. Via the analysis, the complete terrain profile needs to be considered, such as the objects and crossing elements under the power line. Once the critical span is determined, the safety distance needs to be checked at a worst-case conductor temperature. To get the clearance, first the phase conductor's sag should be determined based on Equations (4) and (5). In some cases, the parabolic approximation of the conductors also gives a satisfactory result. If clearance meets the national regulation, the electric field's peak value also needs to be checked. This step is necessary because not all the standards are harmonized, and as presented, the electric field can cause problems even if the safety distance is kept. If one of the two parameters does not meet the criterion, a new maximum wire temperature must be determined. In this substep, the numerical finite element simulation should be applied. Based on the simulation results, the sag value at which the electric field does not exceed the limit value can be selected. A conductor temperature can be assigned to the sag value, designated the new thermal limit for the regular operation condition. At the end of the first broad step, theoretically, there are two ways to increase the power line's safety. One commonly used option is to apply SLR as a conventional line rating method. In the case of SLR, the new ampacity limit is the current calculated with the worst-case combination of the weather parameters. This results in a fixed transfer capacity value in the tension span for the whole year or season. For this reason, in all weather conditions other than the worst-case, the transmission line's utilization will not be maximal, resulting in less transferable power for a large percentage of the time. That is why the second broad step based on DLR is necessary, so the expert system can ensure the line's full utilization. The flowchart and the subtasks of the second step are shown in Figure 6.  
To perform all the necessary substeps in the second step, a line monitoring sensor and weather stations need to be installed on the power line. The device must be able to measure the conductor temperature in real time every 5 to 15 min. It is favorable if the critical span is equipped with the line sensor to allow the expert system's application to the whole line. When the conductor temperature is measured, a logical unit compares it to the maximum allowable conductor temperature, considering the operation state (such as the emergency case with emergency rating).