A real-time thermal rating is a monitoring system. It helps to effectively use current-carrying capacity. Basically, it allows avoiding making assumptions about the current load, and instead to ensure that it is used in the most efficient way and the probability to exceed the acceptable temperature is low.
Smart grid technology, a real-time thermal rating system, has been created to rate the electrical conductors affected by the local weather conditions. It provides accurate real-time temperature measurements and current reading along the entire high-temperature wire. The RTTR is embedded in the cable and calculates the capacity of the current under specific conditions. It is a perfect solution to monitor power cable performing under abnormal conditions such as different emergencies, energy outages, etc.
RTTR is often used with the DTS system of temperature sensors because it gives more accurate data and allows monitoring operations in the real-time mode. For cables that have temperature sensors (DTS) embedded or touching it, the temperature is monitored continuously and the rating can be indicated accordingly. The cables without DTS have their operational temperature are calculated based on the real-time installation condition and loading. There are two types of RTTR to monitor power cable: self-contained and environmentally based.
Self-contained real-time temperature collects the data along with the entire circuits; the embedded fiber optic cable measures the internal temperature, and the attached one measures the sheath temperature.
Environmentally based RTTR measures soil temperature and its direct effect on the cable. It also measures soil thermal resistivity, which affects the heat exchange rate between the cable and the external environment.
RTTR usually uses the following parameters for the calculations:
- The ground type (soil, clay, sand, gravel, thermal backfill)
- Burial Depth
- Cable Type
- Cable Structure
- Other cables laid in close proximity
Rating calculations of the high-temperature wire are based on the data derived from monitoring the underground cable. Standard static ratings are usually conservative and understate the real feeder capacity; hence the feeders are not loaded fully most of the time. The real-time thermal rating allows determining the times when the cable is not loaded fully and when certain actions need to be taken.