With the RTTR embedded in the LIOS EN.SURE system the calculation engine computes the current-carrying capacity (or ampacity) under given conditions of the underground cable installation for the steady state and transient. Cable Operators will greatly appreciate the transient simulation that will allow them to estimate the current that can be safely transferred from another circuit to the monitored installation in situations such as emergencies, maintenance, outages, faults, etc. The EN.SURE RTTR engine can be used for emergency ratings from 10 minutes and up to 2000 hours.
Furthermore, the RTTR system can provide continuous and automatic adjustment of calculation parameters such as ambient temperature, thermal resistivity, etc.
Information provided to cable operator
- Based on a higher load applied for so many hours: What will the cable temperature be at the end of the emergency case?
- Given the operating temperature and the applied (over) load, the EN.SURE RTTR solution predicts the temperature of the cable in the future.
- Based on a higher load for a given period of time: When will the installation reach its design emergency temperature?
- Given the operating temperature and the applied (over) load, the RTTR gives the time that it will take for the cable to reach a specified emergency temperature.
- Based on initial conditions and a maximum operating temperature: What is the maximum current that can be carried by the system?
- Given the operating temperature and a time frame for an over load, the EN.SURE RTTR computes the maximum current that the circuit can carry to reach certain emergency temperature.
Why adding RTTR to Distributed Temperature Sensing?
Real Time Thermal Rating (RTTR) or Dynamic Cable Rating 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.
Typically the actual maximum temperature reading of each configured cable section and the actual electrical current reading are computed to build the dynamic cable rating of the installation, based on the IEC 60287 and IEC 60853 standards.
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, and combinations of different types of sheath. Also most installation types can be modelled: duct banks, multilayer soil, 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 to LIOS EN.SURE is its ability to model several materials with different thermal resistivities, for example: stratified soil layers, multiple duct banks, and multiple backfills.