In a thyrite lightning arrester the resistance is high at low current and low at high current.
A thyrite lightning arrester consists of a series of spark gaps and a thyrite block.
The spark gaps are designed to break down and conduct when the voltage across them exceeds a certain threshold.
The thyrite block is a semiconductor material that has a high resistance at normal operating voltages but becomes conductive at high voltages.
Under normal operating conditions, the thyrite block has a high resistance and does not conduct any current, and the voltage across the arrester is low.
When a voltage surge occurs, the voltage across the arrester increases, and when it reaches the breakdown voltage of the spark gaps, the gaps break down and conduct the surge current through the thyrite block.
The thyrite block then becomes conductive and provides a low resistance path to ground for the surge current, thus protecting the equipment connected to the arrester from the high voltage surge.