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How many times have you heard words like climate change, decarbonization or renewable power sources recently? All of these terms refer to a great technological challenge, which is the transition from an oil-based society and economy toward a more sustainable development model, a passage commonly felt as crucial for the next years. In this framework, the role played by high voltage grid, as part of more stable and reliable power systems in general can be game-changing for fostering all the necessary changes. That would also require an up-to date design workflow, based on multi-disciplinary finite element analysis (FEA) tool, making therefore possible an easy interface between several different physical contexts (for instance electric, magnetic, thermal).

Innovative strategies

The high voltage equipment market represents a field where the best trade-off search between technical performance and cost constraint results in a tricky, and sometimes dangerous, task.

We are talking about devices like isolator, disconnector, breaker, cable terminal for high voltage application, all of these accessories are often characterized by huge size, chosen on the basis of safety considerations in order to keep the hot pole versus ground clearance distance higher than a minimum threshold.

The traditional design methods, which rely on previously developed expertise and characterized by sizeable safety factors, can easily lead to oversize the device, which is no longer acceptable nowadays.

It means also that the adoption of an adequate design methodology many times results in disruptive gains achievable along the entire design process, in terms of dimension, cost, weight reduction.

Software solution

It is now available inside the FEA software Flux (part of the Altair suite) a tool dedicated to electrical analysis, Streamer Computation, which is tailored to fit the needs of high voltage design engineers, who have to deal with gaseous insulation, no matter if the surrounding gas is air or sulfur hexafluoride-based mixtures, such in the case of GIS (Gas Insulated Substation) or GIL (Gas Insulated Line).

The Streamer criterion, whose results has been compared with experimental tests for decades in a variety of different geometries and working conditions, can provide the user with a quantitative estimate about the withstand voltage of the analyzed device.

The analysis procedure, automated by Streamer tool computation inside Flux, consists in implementing a pre-defined mathematical condition along each electric field line, located on the basis of the background electric field (an electrostatic simulation is thus required before the Streamer post-processing).

This criterion, looking like a trivial equation, actually covers a range of extremely complex physical phenomena, ranging from the effects of space field disuniformity to the gas ionization processes and all other side effects associated to the electronic avalanche formation.

The possibility to have a quantitative assessment to the “performance” of a high voltage device, along with the geometric parameterization available inside the software where the criterion is integrated, Flux, paves the way to the automatic optimization, enabling the designers to lower the adopted safety factor, also reducing the global product development time.

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