Simulation software brings big changes to cable industry
By: Dexter Johnson
The Prysmian Group is a world leader in energy and telecom cables. The company’s energy sector alone is made up of a wide range of products such as high-voltage cables for terrestrial and submarine applications; these include both alternating-current (HVAC) and direct-current (HVDC) systems.
One important aspect to consider when designing a power transmission system is its ability to deliver the prescribed amount of current in steady-state conditions without exceeding the maximum permissible operating temperature. To address this point, a detailed thermal model of the system must be built taking into account many variables: the structure of the cables and internal sources of electric losses, the geometry of the installation, the installation environment (e.g., soil, water, forced or buoyant air), the ambient temperature, external loads due to solar radiation, and the system’s proximity to other structures.
Prior to using multiphysics simulation, Prysmian and others in the cable industry employed calculation methods provided by international standards, which work pretty well for those installations in which the cables are in an undisturbed thermal condition (typically, underground). But nowadays it is becoming common to have such systems installed in or crossing regions where, for example, the new cable system is in the vicinity of existing structures such as other cables that cross the cable route.
Prysmian selected COMSOL Multiphysics® simulation software to build computer models that combine the structure of each cable, that of the power transmission system, the load conditions, and the conditions in the external environment to obtain realistic and reliable simulations. “COMSOL is able to solve these kinds of problems because we can build a parametric model to optimize the geometry, the laying of the cables, and we can include the physics needed to account for the convection with the air,” explains Massimo Bechis, Modeling and Simulation Specialist at Prysmian. “We can do extensive transient analyses to account for daily variations in solar irradiation and ambient temperature conditions. We can account for current load changes instead of considering constant operating conditions. This allows us to satisfy requests to consider transient conditions due to load changes. So multiphysics simulation really solves these kinds of problems that were very difficult or even impossible to do before.”
Prior to using multiphysics simulation, many studies were done using mathematical tools developed internally by the company, based on simplified models. By leveraging the know-how gained from the internally developed code when transitioning to new tools, Bechis is able to model at a much higher level of detail and with much greater accuracy for this kind of system. With COMSOL, the company has taken a big step forward and improved the level of the services it can provide to both designers and customers.
“Now we have a lot of requests from colleagues because, for example, they know COMSOL is available to help them analyze and solve many thermal, electromagnetic, and structural problems,” Bechis says. Of course, prior to using simulation tools, Prysmian never had a cable fail. But in order to achieve that perfect record, a large design margin was built into every cable and system because of the calculation procedures adopted. “Now we are able to optimize the structure of our cables and still meet the specifications,” says Bechis. “We can also explain why we use a certain amount of material in a certain layer and show how we came to our decisions based on the modeling.” With simulation, it is possible to model an impact test on a medium-voltage cable. The ability to simulate this kind of test makes it possible to optimize the thickness and the kind of materials used in building the external layers of cables.
Instead of performing tests in laboratories, Prysmian can now do a lot of tests on the computer. Once the optimum design is obtained by simulation, the cable is manufactured, and routine field tests are performed in the laboratory. Physical tests of actual prototypes are still performed, but the prototypes are much closer to the final design, and overall development time is therefore considerably shortened. These tests verify the mechanical behavior of the cables and systems so that the Prysmian team knows they can rely on their models.
One of the clearest indications of the success of the new modeling tools is that Bechis and his colleagues have been able to respond to a lot of customer requests that specifically ask that there be simulation in addition to the standards that are normally used. “We are now able to provide a better service,” says Bechis. “We are saving money. We have improved procedures for designing our cables and power transmission systems. We have an additional and powerful way to respond to requests from clients.”
For more information
Web: www.comsol.com
