The online measured, distributed temperature information of the monitored cable system is especially valuable for dynamic rating. LIOS provides an integrated Real Time Thermal Rating (RTTR) evaluation via a well defined interface between its data visualisation software and a commercialised cable ampacity program. These two technologies are efficiently combined to produce a system capable of computing the future cable ampacity based on real-time temperature measurements. The actual maximum temperature reading of each configured cable section and the actual electrical current reading are evaluated for dynamic cable rating based on IEC standardised methods (mainly IEC 60287 and IEC 60853). When the geometry of the installation is not included in the IEC standards, the RTTR evaluation uses finite element methodologies to complement the IEC calculations.

The RTTR engine computes the current-carrying capacity (or ampacity) of underground cables in steady and transient states. Cable operators are especially interested in  transient simulations to estimate the current that can be safely transferred from another circuit due to emergency situations (maintenance, outages, faults, etc.). Typical situations include emergency ratings for 20 minutes, three hours, 24 hours and up to one week.

Power cable monitoring combined with dynamic ampacity rating provides valuable data to operators:

• Steady State Operation – Power cable conductor temperature at the core of the conductor
• Transient Operation - Emergency ratings,  transient calculations for Time, Current, Temperature

Modelling Capabilities
Virtually every cable construction available in the market can be modelled: one-core, three-core, sheathed cables, concentric neutrals, armoured cables, screens, shields, beddings, servings, jackets, combined sheath, etc.  Most of the installation types can be modelled: duct banks, backfills, directly buried, buried ducts, buried pipes, cables in air (including groups of cables and riser poles) and cables in tunnels.  The installation may include adjacent heat sources/sinks such as steam or water pipes. Unique is its ability to model several materials with different thermal resistivities, for example: stratified soil layers, multiple duct banks and multiple backfills.
Furthermore, the RTTR system can provide continuous and automatic adjustment of calculation parameters such as (ambient temperature, thermal resistivity, etc.).

Why adding RTTR to Distributed Temperature Sensing?
RTTR removes all uncertainty left by the DTS. The DTS measures the real time temperature at the sheath or jacket of a cable. The sheath temperature gives a good idea of the temperature of conductor, but unless an accurate model for the conductor is provided there will be some uncertainly left. 

The uncertainty is small during steady state operation, but it could be (very) large during an emergency situation. The following figure illustrates the temperature of the jacket and conductor during an emergency situation. One can appreciate that while the temperature difference between the jacket and the conductor can be small in steady state. However, moments after the onset of an emergency situation the temperature difference could be very large. The reason is that cable insulation has a large inertia and therefore the heating of the conductor can only be detected at the jacket several minutes (to hours) later. Additionally, the temperature difference changes with the loading level. The temperature difference is larger for larger loading levels.

RTTR is also known as "Dynamic Cable or Feeder Rating" or "Cable Ampacity from Real Time Temperatures" and several abbreviations are also common in scientific publications: DRS, DCR, CART, RTR, DFR

 Download brochure on Real Time Thermal Rating