Principle Of Tesla Coil

https://www.youtube.com/watch?v=fj8QsxFy3Ek&t=311s

Tesla coil

A Tesla coil is an electrical resonant transformer circuit designed by using inventor Nikola Tesla in 1891.
It is used to produce high-voltage, low-current, excessive frequency alternating-current electricity. Tesla coil used these circuits to conduct modern experiments in electrical lighting, phosphorescence, X-ray generation, excessive frequency alternating current phenomena, electrotherapy, and the transmission of electrical power besides wires.

Tesla coil circuits have been used commercially in spark-gap radio transmitters for wireless telegraphy until the 1920s, and in scientific tools such as electrotherapy and violet ray devices.
Today, their fundamental use is for entertainment and instructional displays, although small coils are used as leak detectors for excessive vacuum systems.

Operation

A Tesla coil is a radio frequency oscillator that drives an air-core double-tuned resonant transformer to produce excessive voltages at low currents. Tesla coils can produce output voltages from 50 kilovolts to countless million volts for massive coils.
The alternating current output is in the low radio frequency range, generally between 50 kHz and 1 MHz.
Although some oscillator-driven coils generate a non-stop alternating current, most Tesla coils have a pulsed output;
the excessive voltage consists of a speedy string of pulses of radio frequency alternating current.

Ordinary electrical transformers have an iron core to amplify the magnetic coupling between the coils. However at excessive frequencies an iron core causes power losses due to eddy currents and hysteresis, so it is no longer used in the Tesla coil.

Ordinary transformers are designed to be "tightly coupled".
Due to the iron core and proximity of the windings,
they have a excessive mutual inductance (M),
the coupling coefficient is close to 0.95 - 1.0,
which mean nearly all the magnetic area of the main winding passes thru the secondary.
The Tesla transformer in distinction is "loosely coupled"
the main winding is large in diameter and spaced apart from the secondary, so the mutual inductance is decrease and the coupling coefficient is only 0.05 to 0.2.This potential that 5% to 20% of the magnetic area of the main coil passes via the secondary when it is open circuited.The free coupling slows the exchange of electricity between the main and secondary coils,
which permits the oscillating strength to be continue in the secondary circuit longer before it returns to the main coil and starts dissipating in the spark.

Each winding is additionally constrained to a single layer of wire, which reduces proximity effect losses.
The primary contains very excessive currents. Since excessive frequency current on the whole flows on the surface of
conductors due to skin effect, it is frequently made of copper tubing or strip with a big surface area to decrease resistance,
and its turns are spaced apart, which reduces proximity effect losses and arcing between turns.

The output circuit can have two forms:

Unipolar - One end of the secondary winding is linked to a single excessive voltage terminal, the other end is grounded. This type is used in present day coils designed for
entertainment.The main winding is placed close to the bottom, low potential end of the secondary, to reduce arcs between the windings. Since the ground (Earth) serves as the return path
for the excessive voltage, streamer arcs from the terminal have a tendency to bounce to any close by grounded object.

Bipolar - Neither end of the secondary winding is grounded,
and both are brought out to excessive voltage terminals.
The main winding is placed at the core of the secondary coil,
equidistant between the two high voltage terminals, to discourage arcing.

Oscillation frequency

To produce the biggest output voltage, the main and secondary tuned circuits are adjusted to resonance with each other
The resonant frequencies of the main and secondary circuits,
f1 and f2, are decided by means of the inductance and capacitance in each circuit.