Electrostatic of wound components: analytical results, simulation and experimental validation of the parasitic capacitance

The electrostatic properties of inductors and transformers are investigated. Two devices have been built on the same magnetic core. Both are cylindrical coaxial winding transformers and all the windings are almost identical. These one-layer windings are rolled in the same direction for one transformer and in opposite direction for the other. All the possible connections of the two windings are tested. Based on a simple electrostatic model, these devices are analytically studied and an equivalent circuit is proposed to take electrostatic phenomena into account. Then, an electromagnetic simulation software is used to compute the electrostatic field with the real shapes of wires and coil layers. Capacitances are deduced from stored electrostatic energy in the whole space. Finally, many impedance measurements from 100 Hz to 40 MHz allow the equivalent circuit to be validated.