|
|
|
Dynamic current rating optimization
With and without optical fibers
|
|
|
Dynamic cable current rating optimization provides answers to the following questions: - Can I delay the investment in a new cable circuit when demand increases?
- What is the maximum permitted daily overload?
- What is the maximum permitted overload under emergency conditions?
- What will the maximum loading be by tomorrow morning at 8AM?
Using a dynamic on-line mathematical model developed by KEMA, dynamic current rating optimization of cable circuits can be achieved that will result in improved loading of existing circuits and allow investments in new circuits to be avoided or delayed until absolutely necessary. The model utilizes available data such as the actual loading current, actual conductor/sheath temperature, and ambient/soil conditions.
|
|
|
Dynamic cable current rating
optimization
|
|
|
Selection of circuits
Circuits that are subject to dynamic current loading are identified and selected for analysis based on information and guidance provided by the asset manager. Usually less than 10% of the available circuits fall into this category. The circuits selected for further analysis are then monitored to determine the actual conditions during operation. Parameters monitored include temperature of the outer sheath, soil temperature and soil conditions. These parameters are determined at different loading conditions, initially and in the future. The typical evaluation period is 2 - 3 weeks.
|
|
|
Distributed temperature measurement with optical fibers
In the case the cable is equipped with optical fibers, either
underneath or attached to the outer sheath, it is possible to make
a “distributed temperature” measurement. The cable conductor
temperature can then be calculated utilizing the temperature of the
sheath distributed along the cable. Hot and cool spots can be
readily identified.
|
|
|
Example of distributed temperature measurement.
|
|
|
Distributed temperature measurement with thermocouples
For cables not equipped with optical fibers, the potential hot
spots on the cable can be identified after studying the actual
cable route. Thermocouples may be attached to the outer sheath
at those locations to obtain the actual temperatures.
|
|
|
Determination of hot spots and recommended improvements
The temperature measurements can be used to identify the hot spots along the cable circuit. Then by carefully analyzing the results and the ambient conditions at the hot spot locations, KEMA can propose ideas to reduce the temperatures at the hot spots. Slight modifications in the soil conditions, for example, may result in lower temperatures.
|
|
|
Dynamic thermal model (on-line)
This model utilizes the actual loading and ambient conditions,
and the circuit data. The cable conductor temperature is
calculated, utilizing the actual results of previously performed
temperature measurements. In addition, the model calculates the
margin between the actual loading and the maximum permissible
(over)loading over a specified period of time. Performance under
emergency loading conditions can also be evaluated, including
determining the maximum duration of a specific emergency overload
condition before overheating of the conductor occurs.
|
|
|
Example of dynamic thermal model (on-line)
|
|
|
Benefits for daily operation and the asset manager
The output of the dynamic model can provide useful information
in the daily operation of the system, including times of peak
loading or emergencies. The asset manager may also use the model to
calculate the consequences of delaying investments, utilizing data
available during daily (over)loading of the circuit in controlled
conditions.
|
|
|
Experiences and results
Through the end of 2003, about 30 circuits have been analyzed
using the dynamic thermal model. The results are very
good. Hot spots have been improved, and in many cases the
asset manager has been able to postpone investments in new cable
circuits.
|
|
|
|
|
|
|
|
