Toroidal Inductors and Transformers - Total B Field Confinement By Toroidal Inductors - Toroidal Transformer Poynting Vector Coupling From Primary To Secondary in The Presence of Total B F - Explanation of The Figure

Explanation of The Figure

This figure shows the half section of a toroidal transformer. Quasi-static conditions are assumed, so the phase of each field is everywhere the same. The transformer, its windings and all things are distributed symmetrically about the axis of symmetry. The windings are such that there is no circumferential current. The requirements are met for full internal confinement of the B field due to the primary current. The core and primary winding are represented by the gray-brown torus. The primary winding is not shown, but the current in the winding at the cross section surface is shown as gold (or orange) ellipses. The B field caused by the primary current is entirely confined to the region enclosed by the primary winding (i.e. the core). Blue dots on the left hand cross section indicate that lines of B flux in the core come out of the left hand cross section. On the other cross section, blue plus signs indicate that the B flux enters there. The E field sourced from the primary currents is shown as green ellipses. The secondary winding is shown as a brown line coming directly down the axis of symmetry. In normal practice, the two ends of the secondary are connected together with a long wire that stays well away from the torus, but to maintain the absolute axial symmetry, the entire apparatus is envisioned as being inside a perfectly conductive sphere with the secondary wire "grounded" to the inside of the sphere at each end. The secondary is made of resistance wire, so there is no separate load. The E field along the secondary causes current in the secondary (yellow arrows) which causes a B field around the secondary (shown as blue ellipses). This B field fills space, including inside the transformer core, so in the end, there is continuous non-zero B field from the primary to the secondary, if the secondary is not open circuited. The cross product of the E field (sourced from primary currents) and the B field (sourced from the secondary currents) forms the Poynting vector which points from the primary toward the secondary.

Read more about this topic:  Toroidal Inductors And Transformers, Total B Field Confinement By Toroidal Inductors, Toroidal Transformer Poynting Vector Coupling From Primary To Secondary in The Presence of Total B F

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