IMPROVEMENTS IN TRANSIENT OVERVOLTAGE AND LIGHTNING PROTECTION OF POWER CONNECTED EQUIPMENT

摘要

An overvoltage protection circuit is provided for protecting electrical equipment from transients on power lines (41, 42). The circuit has a string of series-connected silicon avalanche diodes (SADs) (40) connected across the power lines (41, 42) to provide an initial clamping threshold before energy-absorbing modules (43a, 43b, 43c) come on line to provide secondary clamping. The modules (43a, 43b, 43c) include a number of metal oxide varistors (MOVs) (44) connected in parallel and a switching device in the form of a gas arrester (45) connected in series with the MOVs (44). A resistance (46) is connected in parallel with the gas arrester (45) to form a high pass filter with the natural capacitance of the MOVs (44). This maintains the voltage across the resistance (46) well below the switch operating level during normal conditions and enables a component such as a 230 V fast acting gas arrester (45) to be used. In an alternative embodiment, the gas arrester (45) may be replaced by a solid state swich, such as a Sidator or a Triac.