A resonant transformer is often called a Tesla transformer or Tesla coil. The device was patented by the United States of America on the twenty-second of September one thousand eight hundred and ninety-six years under the name "Apparatus for the production of electric current of the highest potential and frequency." As the name implies, this device was invented by the famous scientist Nikola Tesla.
The simplest resonant transformer consists of two coils without a combined core. The primary winding has only a few turns (from three to ten). However, this winding is wound with a thick electric wire. The secondary winding of a device such as a resonant transformer is often referred to as high voltage. It has much more turns than the primary (up to several hundred). However, it is wound with a thinner electric wire.
As a result of this simple construction, the resonant transformer has a CT (transformation coefficient), which is several tens of times greater than the ratio of the turns of the secondary winding to the primary winding. The output voltage on such a transformer can exceed a million volts. Based on this design, devices such as resonant generators have already been developed. Also, such electric machines are often used as demonstration apparatuses. Due to the huge voltage at the resonant frequency, such a device is able to create electrical discharges directly in the air. Moreover, their length can be truly impressive. Depending on the input voltage, the discharge length can be up to several tens of meters.
The very design of such an electrical installation as a Tesla resonant transformer is quite simple and straightforward. It consists of coils (two - secondary and primary), a spark gap (aka breaker). The composition of this device necessarily includes capacitors (both for compensation and charge storage). Often use toroidal coils and terminals (to create a device such as a resonant transformer with amplification of the output power).
As mentioned earlier, the primary coil has traditionally few turns, and the secondary one has several hundred. Moreover, a design with a flat primary coil, horizontal, cylindrical, conical or vertical, is often found. Also, in a device such as a resonant transformer, there is no ferromagnetic core (unlike power or measuring transformers). Thus, it has much less mutual induction between the windings of both coils than conventional conventional transformers (the amplification of induction coupling is achieved due to the presence of a ferromagnetic core).
Thus, the capacitor and the primary coil constitute an oscillatory circuit. This includes a non-linear component - a spark gap, which is two electrodes with a gap. The secondary coil also forms a similar circuit, however, instead of a capacitor, a toroid is used here. It is the presence of two coupled oscillatory circuits that is the whole basis of the operation of such a device as a Tesla resonant transformer.