Real Time Determination of Thermal Conditions along HV Power Cable Systems
Increasing demand for power is forcing power utilities to load power cables to their physical limit, and safety and efficiency concerns are making it more and more critical for operators to understand what is happening thermally both inside the cables themselves, and along the cable route. 

During high-load conditions, and under emergency circumstances (such as when a failure occurs in a segment of the grid and power must be shifted to other sections to compensate) it often becomes necessary to load cables right up to the limits permitted by the relevant regulations. In these operational situations, it must be ensured that maximum temperature limits are not exceeded. Due to the increasing complexity of the thermal relationships along cable routes, the ability to continuously measure the temperatures along the cable has proven invaluable, providing critical operational data to engineers, especially in the case of a system faults such as a hot spots that could result in cable failure if they are not corrected.

The intrinsic temperature measuring system DTS based on LIOS Technology’s design, with fibre optic sensors either installed within the power cable’s cross section (FIMT - Fibre in metal tube ) or attached to the exterior of the cable, makes it possible to record the temperature profile along an entire cable route continuously, and to pinpoint the exact location of hot spots within a metre. Since the measuring principle employed is purely optical, the presence of electromagnetic influences, which can result in false sensor signals in other technologies, does not affect the DTS unit.

Distributed temperature sensing is a powerful tool that allows the accurate rating of high voltage power cables in real time, and provides the following operating benefits:

• Reduce power outages or blackouts 
• Ensure continuity of supply
• Activate hidden capacity reserves of existing assets
• React quickly to overload conditions
• Conduct precisely and in real-time load predictions as new sources of energy are added to the grid

The temperature profile data, in any desired form or format, can be transmitted via standard interfaces from systems of the OTS product series as required, and be either displayed or further processed by PC, PLC or SCADA systems. As a result of the increasing demands placed on the ability to network and integrate measuring systems into management systems, LIOS offers network components that summarise DTS data from several DTS units and transport or convert it to the required network standards and protocols like Modbus, DNP3, IEC60870-5 or XML based data interfaces (e.g. POSC).

LIOS also provides an integrated Real Time Thermal Rating (RTTR) package via a well defined interface between its DTS data visualisation software and a commercialised – the industry’s de facto standard - cable ampacity program based on IEC standardised methods. Dynamic rating software couples the accurate temperature data provided by the DTS unit to predictive functions of cable ratings, providing engineers with even more information upon which they can base distribution and load decisions. The result is dramatically more efficient transmission of power, fewer “brown-outs”, and decreased operating costs.

Monitoring System for Overhead Line Conductors. Meeting the demands of a changing power environment
Providing sufficient electrical power reliably requires ongoing monitoring of temperatures within overhead transmission lines that are more susceptible to atmospheric changes than buried cables. Winds, direct sunshine, ambient temperature, rain, ice and snow all affect the temperature of exposed overhead lines and can dramatically impact load limits they are capable of carrying. The fibre optic monitoring system for overhead lines is an inexpensive and highly reliable method that enables real-time monitoring of an entire network or of selected critical spans.

The easy-to-install, low-maintenance system offers a multitude of advantages. By enabling dynamic analysis of network structure, it increases the overall safety and reliability of the grid. It facilitates applying dynamic reactions to transmission requests, resulting in more flexible capacity and revenue management in both the short and long term. And the potential for cost-savings is enormous: downtimes and blackouts can be avoided, and the need for new lines and upgrades (e.g. increasing the height of overhead transmission lines) can be greatly reduced.

Customers dynamically rating the critical spans of their overhead line system can also increase earnings by activating previously unused resources in existing power lines. Dynamic metering of grid capacity and maximized transmission capacity make it possible to respond quickly and dynamically to transmission requests. As new sources of energy are added to the grid, precise load predictions are possible and it is easier to react quickly to overload conditions.

With the help of dynamic network-structure analysis, temperature profile can be monitored over span fields and fittings, depending on the length of the sensor. Load parameters are bundled and transmitted to network control stations online, allowing for real time thermal rating - which means real time supervision of network capacity. This makes it possible to predict load precisely and to avoid wire fatigue caused by repeated high thermal loads. Because decisions based on thermal load often influence upgrading or installation of lines, this translates into better control of grid and wire conditions, as well as optimal sag control and line clearance without requiring new construction activities.

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