Week 15 high voltage AC gener
- 1. High Voltage AC Generation
- 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
- 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
- 13. Spark Gap based Tesla Coil
- 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