Online Condition Monitoring with Dynamic Cable Rating Pioneered at Medium Voltage Cable System

The growth of new renewable energy sources and distributed generation, as well as the rising demand due to new applications like electromobility,  will lead to increasing requirements to network capacity. To meet this demand in Switzerland´s most popular metropolis Zurich, the municipal electric utility, investigated and tested smart grid solutions.

The power cable manufacturer and partner for this project Nexans Suisse SA chose the unique frequency domain based Distributed Temperature Sensing LIOS EN.SURE DTS system by NKT Photonics. With more than 2500 permanent installations worldwide, a comprehensive and 100% applied Factory Acceptance Test (FAT) of each DTS unit, as well as the reliability and high precision were determining factors for Nexans.

Management of high thermal load on a medium voltage level

The installation is an 11kV medium voltage cable system with 3 circuits, 3 phases each. The cable length is approximately 2700m and the DTS covers the entire power cable sections as well as respective joints. High energy consumption topped by demands for drilling works at a nearby tunnel construction site can lead to high cable loads. The cable system runs in an underground multiple duct system below street level where neighboring medium cable systems and a 150 kV high voltage cable system installed in parallel also affect the thermal conditions.

Online temperature sensing was requested for this cable project to ensure stable and reliable operating conditions. The embedded Real Time Thermal Rating (RTTR) solution was an important part of the delivery.

The advantages of using the online RTTR results in combination with the DTS was the derived conductor temperatures in real time and the emergency calculations to predict critical operation conditions in the future. The RTTR software uses ambient conditions like the distributed power cable temperature profile, the electric current in real time, the thermal resistance of the soil, the cable design parameters, and the installation environment for its calculations.

Maximum network efficiency – with high security of supply

The emergency ratings of the LIOS EN.SURE RTTR helped to redefine grid load and safety limits allowing available resources to be used more profitably and enhance the operating life and safety of the cable system.

The supplied system enables immediate recognition of thermal and mechanical faults in the cables. The condition monitoring system is connected via Ethernet, IEC60870 protocol to the operational management system and sends temperature and alarm data to the responsible operator directly.  This innovative monitoring technology helps securely optimize the efficiency of the distribution system.


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A special thanks to:

Nexans Suisse SA, Switzerland and ewz, Zurich, Switzerland