PO188

Forecasting conductor temperature and soil coverage of export and array cables using real time thermal rating on a distributed temperature sensing system.

Jozua van Oosterom, Wouter van Doeland, DaniŽl Vree
Energy Solutions B.V., Delft, The Netherlands

Abstract

Distributed temperature sensing systems (DTS) increasingly become standard practice in offshore wind farms for monitoring export cables and inter array cables. DTS measures the temperature outside of the cable cores using optical fibres. The conductor temperature is then calculated using a cable temperature model.
DTS is used to assure that the conductor temperature does not exceed the limit above which the integrity and therefore the lifetime of the cable is compromised, giving early warning of hot spots which could arise due to worse soil conditions than considered during the design phase.

A more advanced use of the DTS is to enable loading cables above their rated power without exceeding the cable's design limits, enabling less conservative designs or additional power output of an overplanted wind farm. To be able to manage the loading of a cable in such cases, a real time thermal rating system (RTTR) can be used (also known as dynamic cable rating system).

In this paper following advanced RTTR functionalities for a DTS are presented:

  1. conductor temperature based on wind forecast and
  2. estimation of depth of burial (soil coverage on top of cable).

Furthermore, results will be presented of validation of the RTTR by actual measurements from wind farm projects where this system has been implemented.

The software development has been supported by the TKI Wind op Zee programme.

Method

An overview will be given of the RTTR software model which is based on international IEC standards (IEC 60287 and IEC 60853).

Input and output parameters are discussed as well as the modelling principles which can be summarized as follows:

By analysing the history of the cable loading (current measurements) and cable temperature combined with the wind forecast and static cable design parameters and semi-static installation and soil conditions, the RTTR forecasts the conductor temperature over the complete cable length up to three days ahead.

As an additional function, the ability to calculate the soil coverage on top of the cable will be discussed briefly.

Results

Validation of the RTTR software model (accuracy of the forecasting) will be discussed based on actual measured data from wind farm projects where DTS systems have been installed.

Recommendations will be given on how the calculation model within the RTTR can be used for cable engineering based on actual dynamic behaviour of the cable.

Conclusions

a. With the presented calculation model used in the RTTR system, cable design can be optimized resulting in a more effective use of cable assets without increasing risks.

b. Based on the actual load, the cable temperature will be monitored. By using wind forecasts, the wind park operator knows a few hours / days in advance if a critical situation is pending and can take mitigating measures in order to prevent cable failure and resulting production loss.

c. The software model will report the soil coverage on top of the cable as a function of the length of the cable which may reduce survey works during the operational phase.

Objectives

1. Delegates will learn what possibilities and advantages an RTTR system can have for an offshore wind farm and how it will enable them to optimize cable design and overall wind farm design without increasing risks.

2. Insight will be given on how RTTR software works, which input data is used and which information can be retrieved.

3. Delegates who need to procure a DTS/RTTR system will learn that these may have different functionalities and that all functionalities should be specified which are needed.

4. An overview of measurement results will make a DTS/RTTR system more tangible for delegates not having any expert cable knowledge.