Thyrite is a material obtained by a special type of clay mixed with carborundum (Silicon Carbide). Thyrite is used widely in lightning arresters. Thyrite is a non-linear resistor. i.e. it has high resistance at low voltages and low resistance at high voltages. A two times increase in voltage causes the current to increase by nearly 12 times. Hence, heavy currents can be discharged during voltage strikes and other surges. This heavy discharge of current enables quick reduction of the surge voltage preventing flashovers. The Thyrite arresters are usually arranged in parallel with the primary winding of the Transformer. The Thyrite inside the arrester is arranged in the form of discs. The sides of the discs are metal plated to decrease resistance between the discs.
Once the surge has been discharged, the Thyrite quickly returns to its high resistance state.