Electric and magnetic fields are essential in electromagnetism, intervening directly in the transmission of electric energy over long distances, where the lines essentially serve as wave guide for the propagation of the fields. The magnetic field allows the conversion of mechanical energy into electric energy in the alternators and the transformation of the voltage level in power transformers. In electrical insulation, the electric field allows the transfer of energy from the field to the charged particles in the insulating dielectric. In effect, electrostatic field exerts a force F on charged particles, free electrons, and ions, according to

F E= q ·

where q is the electric charge of the particle E is the electrostatic field

Charged particles are accelerated in the direction of the applied field, acquire kinetic energy, and initiate ionization activities leading to partial discharges and, eventually, to breakdown of the discharge gap.