High Voltage Engineering

Gas breakdown follows Paschen’s law — the breakdown voltage depends on the product of pressure and gap spacing (pd) — with a characteristic minimum, explained by the Townsend avalanche mechanism.

High DC voltages are generated by voltage-multiplier (Cockcroft–Walton) circuits, high AC voltages by cascaded testing transformers or resonant circuits, and impulse voltages by Marx generators that charge capacitors in parallel and discharge them in series.

High voltages are measured with dividers that scale the voltage down to a safe level — resistive for DC, capacitive for AC and impulse — with the sphere gap serving as the fundamental peak-voltage standard.

Insulation coordination selects equipment insulation levels (BIL) and protective devices so that any overvoltage is clamped below the withstand level with an adequate margin, protecting expensive apparatus economically.

A surge (lightning or switching) travels along a line as a wave at v = 1/√(LC); at discontinuities it partially reflects, and a surge arrester clamps the resulting overvoltage to protect equipment.