Line overvoltage protection for electrical device - has symmetrical variable resistors coupled to isolating transformer secondary

摘要

The over-voltage protection for an electrical device (34) with an input isolating transformer (40) uses symmetrical variable resistances (43, 44) in parallel with the transformer secondary winding (42) and between one of the secondary conductors and an earth contact. The electrical device (34) is isolated from the local earth (50) and is coupled to the earth contact (33) via a direct line (52). The isolating transformer (40) has a primary winding (41) divided into several separate parts by open screens at the potential of the points separating the two parts.