Arc detector and associated method for detecting undesired arcs

An arc detector for detecting undesired arcs comprising:

• an antenna for receiving an electromagnetic signal representing an arc;
• and
• a discriminator for analyzing said signal from said antenna, said discriminator comprising a spectrum analyzer arranged to detect whether said signal represents a normal arc or an undesired arc,
• characterized in that
• said discriminator is arranged to detect whether said signal represents a normal arc or an undesired arc by comparing signal levels at frequencies of a spectrum of said signal corresponding to at least one partial reference spectrum, and determining said arc to be a normal arc if a deviation from said reference spectrum is less than a threshold deviation;
• and
• said arc is related to the operation of an on-load tap chancier of a power transformer, and said normal arc is an arc inside a vacuum container of said on-load tap changer and said undesired arc is an arc outside said vacuum container.