Real Time Thermal Rating

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The CYMCAP/RTTR Real Time Thermal cable Rating software extends the monitoring functionality and forecasts the behavior of the installation under emergency situations. It is designed to provide both steady-state and transient thermal analysis. It is based on the IEC Standards 60287© and/or 60853© and/or on the finite element method depending on the type of installation. This function allows the user to manage contingency and emergency situations more efficiently.

Features

Numerous underground transmission projects are emerging worldwide. Each project requires a substantial investment of time and money in an industry where lack of reliability and blackouts are not acceptable anymore.

It is a universal practice to use Distributed Temperature Sensing (DTS) systems based on fiber optic technology to monitor the cables temperature along the cables run. To supplement this technology, the CYMCAP/RTTR Real Time Thermal cable Rating software was designed to extend the monitoring functionality and predict/forecast the behavior of the installation under emergency situations.

The software is designed to provide both steady-state and transient thermal analysis. It is based on the IEC Standards 60287© and/or 60853© or finite elements. This function allows managing contingency and emergency situations more efficiently.

Operating Modes

The Real-time Thermal Rating software is based on the CYMCAP software and has two modes of operation:

  • Estimating the conductor temperature from the fiber optic measured temperature
  • Computing emergency ratings with the transient engine

Modeling Capabilities

Virtually every cable construction available in the market can be modeled with the CYMCAP software: one-core, three-core, sheathed cables, concentric neutrals, armored cables, screens, shields, beddings, servings, jackets, etc. The following installation types can be modeled: duct banks, backfills, directly buried, buried ducts, buried pipes, cables in air (including groups of cables and riser poles) and cables in tunnels. The CYMCAP software is its ability to model several materials with different thermal resistivities, for example: stratified soil layers, multiple duct banks and multiple backfills.

Emergency Rating

The CYMCAP/RTTR software provides the following information of high importance to the cable operator:

  • Given the emergency time during which an emergency overload is applied, the CYMCAP/RTTR software predicts the temperature of the cable at the end of an emergency period.
  • Given the maximum admissible emergency temperature and the applied (over) load, the CYMCAP/RTTR software gives the maximum time the cable can be overloaded before exceeding the specified admissible emergency temperature.
  • Given the maximum admissible emergency temperature and the time for an emergency overload, the software computes the maximum current that the circuit can carry while not exceeding the emergency temperature.

Computational Procedures

When there are available real-time measurements of both the temperature at the fiber location (cable surface, etc.) and the current, the software uses the IEC 60853© Standard to conveniently compute the temperature of the core conductor. When only the temperature at the location of the fiber optic sensor is available, the temperature of the core can be determined from the IEC 60287© Standard.

Transient Calculations

Cable operating temperature very much depends on the history of the load applied to the cable. In other words, the operating temperature of a cable depends on the intensity of the current and its variation over time. The thermal inertia of the cable installation determine how far in the past the loading history can affect the operating temperature at the current time or how fast the core temperature changes in response to the load variation. A typical response to a step overload of 100% lasting 12 hours is shown in the figure below. One can appreciate that the temperature of the cable exponentially follows the changes in current.

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