The cause rectangular and elliptical coils have been about for so extended is that they perform for specific common apps and their building favors high volume manufacturing procedures.
If your need is truly for a common distribution transformer subjected only to restricted available fault currents, outfitted with fusing or safety gadgets, subject matter to steady loading with small variation, or is a little to medium sized transformer with star related major and secondary windings, then rectangular windings might operate for you.
If on the other hand, your software is more “uncovered” to higher amounts of fault currents, repeated occasions, or large recent demands with reduced developed impedances, like motor starting up, the reply is of course you need to buy a layer wound, spherical coil layout and ideally 1 with strong bracing incorporating heavy duty pressure plates to add axial balance to counteract the strong actual physical forces skilled during faults.
Unlike wound cores, as are normally utilised with rectangular or elliptical coils, round coils enable for the utilization of miter reduce, cruciform cores. soft magnetic materials are comprised of several width laminations which, when assembled present a spherical cross-part and mainly fill the core window in the round coils. Spherical coils with a cruciform core supply superior resistance to radial forces to which the transformer is subjected in the course of faults and severe duty cycles.
The improved cooling obtainable with the spherical coil development also will help dissipate brief circuit thermal results following the fault has cleared and the transformer resumes standard loading. The enhanced cooling is feasible due to the fact, unlike wound cores, cruciform cores in conjunction with specially developed higher and reduced force plates let the cooling fluid to circulation throughout the coils thus considerably decreasing scorching places in the insulation system, which in switch qualified prospects to more time transformer existence expectancy.
If your purchases include larger transformers, ten MVA and above, or larger BIL levels, 350 kV BIL and earlier mentioned, you need to also take into account purchasing disc-wound, round coils. The disc-wound design and construction gives all the benefits of layer wound spherical coils with miter reduce cruciform cores and even more mechanical power and transient fault withstand ability.
In addition, the disc construction minimizes electrical stresses inside the coil induced by switching surges, lightening strikes, and voltage disturbances often discovered in the network at higher voltage levels and witnessed by greater transformers.
It is our advice that for most substation applications, for in essence all station transformer programs, and for these higher-risk distribution transformer programs, you should purchase sensibly and buy the spherical coil style for lower total expense of possession.