3. CASCADE TRANSFORMERS
• When test voltage requirements are < 300 kV, a
single transformer can be used for test purposes.
• For higher voltage requirements, -A single unit
construction becomes difficult and costly due to
insulation problems. -Transportation and
assembly of large transformers become difficult.
• These drawbacks are overcome by:
– Series connection (or cascading) of several identical
units of transformers, in which the high voltage
windings of all the units are in series
4.
5.
6.
7.
8.
9.
10. Working
• R1 is used to tune the circuit means to adjust
XL with Xc and ZT = R and circuit tuned with
supply frequency
• R2 is use to raise the voltage across the
capacitive load to the test value after
resonance has been achieved
11. Tesla Coil
• A Tesla coil is an electrical resonant transformer
circuit designed by inventor Nikola Tesla in 1891.
• It is used to produce high-voltage, low-current,
high frequency alternating-current electricity
• A Tesla coil is a radio frequency oscillator that drives an air-
core double-tuned resonant transformer to produce high
voltages at low currents
• Tesla's original circuits as well as most modern coils use a
simple spark gap to excite oscillations in the tuned
transformer.
• More sophisticated designs use transistor
or thyristor switches or vacuum tube electronic
oscillators to drive the resonant transformer.
12. • Tesla coils can produce output voltages from
50 kilovolts to several million volts for large
coils.
• The alternating current output is in the
low radio frequency range, usually between
50 kHz and 1 MHz
14. Components
• A high voltage supply transformer (T), to step the AC mains voltage up to a high
enough voltage to jump the spark gap. Typical voltages are between 5 and 30
kilovolts (kV).
• A capacitor (C1) that forms a tuned circuit with the primary winding L1 of the Tesla
transformer
• A spark gap (SG) that acts as a switch in the primary circuit
• The Tesla coil (L1, L2), an air-core double-tuned resonant transformer, which
generates the high output voltage.
• Optionally, a capacitive electrode (top load) (E) in the form of a smooth metal
sphere or torus attached to the secondary terminal of the coil.
15. Operation
• The primary coil (L1) consisting of a relatively few turns of heavy copper
wire or tubing, is connected to a capacitor (C1) through the spark
gap (SG).
• The secondary coil (L2) consists of many turns (hundreds to thousands) of
fine wire on a hollow cylindrical form inside the primary.
• The secondary is not connected to an actual capacitor, but it also functions
as an LC circuit, the inductance of (L2) resonates with stray
capacitance (C2), the sum of the stray parasitic capacitance between the
windings of the coil, and the capacitance of the toroidal metal electrode
attached to the high voltage terminal.
16. • The primary and secondary circuits are tuned so they
resonate at the same frequency, they have the
same resonant frequency. This allows them to exchange
energy, so the oscillating current alternates back and
forth between the primary and secondary coils. In
physics these two coupled tank circuits are also known
as coupled oscillators.
17. • Current from the supply transformer (T) charges the
capacitor (C1) to a high voltage.
• When the voltage across the capacitor reaches the breakdown
voltage of the spark gap (SG) a spark starts, reducing the spark
gap resistance to a very low value.
• This completes the primary circuit and current from the
capacitor flows through the primary coil (L1). The current
flows rapidly back and forth between the plates of the
capacitor through the coil, generating radio frequency
oscillating current in the primary circuit at the
circuit's resonant frequency
18. • The oscillating magnetic field of the primary winding induces an oscillating current
in the secondary winding (L2), by Faraday's law of induction.
• Although the ends of the secondary coil are open, it also acts as a tuned circuit
due to the capacitance (C2), the sum of the parasitic capacitance between the
turns of the coil plus the capacitance of the toroid electrode E.
• Current flows rapidly back and forth through the secondary coil between its ends.
19. • To produce the largest output voltage, the
primary and secondary tuned circuits are
adjusted to resonance with each other.
The resonant frequencies of the primary and
secondary circuits, f1 and f2 are determined
by the inductance and capacitance in each
circuit
