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About

High-voltage resonant transformers require precise impedance matching between the primary and secondary circuits. A mismatch results in poor spark length, excessive heating, or catastrophic failure of the tank capacitor bank or IGBTs (in DRSSTC systems). This tool models the physical properties of the coil geometry to determine the resonant frequency f0, inductance L, and required topload capacitance Ctop.

We account for the helical coil structure using Wheeler's formula and Medhurst's correction for self-capacitance. The dielectric database adjusts for coil form material losses. This ensures the system remains within the safe breakdown voltage limits of the air gap and wire insulation.

tesla coil high voltage resonance LC circuit engineering

Formulas

The resonant frequency is defined by the LC tank circuit:

fres = 12πL C

Helical coil inductance (L) is approximated via Wheeler's Formula for single-layer air-core solenoids:

L = N2 × r29r + 10h

Where N is turns, r is radius (inches), and h is height (inches). Result in microhenries (µH).

Reference Data

MaterialDielectric Constant (k)Dielectric Strength (kV/mm)Notes
Air (Dry)1.00063.0Baseline reference
PVC (Grey)2.914.0Common form material, high loss at HF
Acrylic (Plexiglass)3.420.0Good arc resistance
Polypropylene2.222.0Excellent for capacitors (MMKP)
LDPE (Polyethylene)2.2645.0High breakdown voltage
Epoxy Resin3.620.0Used for potting/sealing
Phenolic (Bakelite)4.812.0Poor tracking resistance
Glass (Pyrex)4.713.0High thermal stability
Transformer Oil2.212.0Cooling and insulation
Cardboard (Dry)2.53.0Prototyping only

Frequently Asked Questions

The aspect ratio (height/diameter) affects the magnetic coupling coefficient (k) and the voltage distribution along the coil. A ratio between 3:1 and 5:1 is optimal for preventing racing arcs (voltage flashover) between turns while maintaining sufficient coupling to transfer energy from the primary.
A toroid (donut shape) provides self-shielding for the top turns of the secondary coil, reducing the electric field gradient and preventing premature corona discharge. A sphere has lower capacitance for the same diameter but lacks this shielding effect. The calculation assumes a standard toroid geometry.
In an SGTC, energy transfer drops significantly. In a DRSSTC, driving the bridge off-resonance causes hard switching (switching while current is high), leading to immediate IGBT destruction due to thermal runaway or voltage spikes exceeding the collector-emitter rating.