The reason rectangular and elliptical coils have been around for so extended is that they perform for specific common purposes and their design favors substantial volume manufacturing processes.
If soft magnetic materials is genuinely for a regular distribution transformer subjected only to constrained available fault currents, geared up with fusing or security gadgets, topic to secure loading with tiny variation, or is a tiny to medium sized transformer with star connected main and secondary windings, then rectangular windings may well work for you.
If on the other hand, your application is far more “exposed” to higher stages of fault currents, recurring occasions, or substantial present specifications with decrease designed impedances, like motor commencing, the answer is sure you need to purchase a layer wound, spherical coil style and if possible a single with strong bracing incorporating hefty responsibility stress plates to include axial stability to counteract the powerful actual physical forces skilled for the duration of faults.
Unlike wound cores, as are typically utilised with rectangular or elliptical coils, round coils allow for the utilization of miter cut, cruciform cores. Cruciform cores are comprised of several width laminations which, when assembled current a round cross-segment and mostly fill the core window in the spherical coils. Round coils with a cruciform main supply outstanding resistance to radial forces to which the transformer is subjected in the course of faults and extreme duty cycles.
The improved cooling offered with the spherical coil building also assists dissipate quick circuit thermal consequences soon after the fault has cleared and the transformer resumes normal loading. The improved cooling is achievable due to the fact, unlike wound cores, cruciform cores in conjunction with specifically made upper and reduce strain plates enable the cooling fluid to circulation through the coils thereby substantially minimizing very hot places in the insulation method, which in change sales opportunities to longer transformer life expectancy.
If your purchases consist of more substantial transformers, ten MVA and above, or larger BIL ranges, 350 kV BIL and above, you must also think about purchasing disc-wound, round coils. The disc-wound design and style and design provides all the rewards of layer wound spherical coils with miter lower cruciform cores and even far more mechanical toughness and transient fault stand up to capacity.
Moreover, the disc development minimizes electrical stresses within the coil triggered by switching surges, lightening strikes, and voltage disturbances regularly located in the network at larger voltage levels and observed by greater transformers.
It is our recommendation that for most substation applications, for in essence all station transformer applications, and for those high-threat distribution transformer applications, you must acquire properly and obtain the spherical coil style for reduce complete value of possession.