Abstract: Air terminals of two types having curved surface electrodes that act passively or dynamically to minimize or further reduce corona during the close approach of the down leader. In the first type, a fully grounded passive terminal, suitably located and comprising a conductive curved surface of a given radius on a grounded rod of given height, is located and suitably dimensioned in order to minimize corona discharges until the median field rises to a level sufficient to support streamer to leader conversion, as described below. In the second type, dynamic action is achieved by allowing the curved surface to float upwardly in voltage by use of capacitive coupling to the approaching leader. The raising of voltage being in the same polarity as the leader, acts to reduce the electric field immediately above, with consequent reduction in corona.

Abstract: 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.

Abstract: The voltage across the spark gap is increased or amplified to ignite the gap when required, thus enabling ignition of the spark gap when required. The incremental voltage to obtain gap ignition is additive to any voltage already across the gap, and is additive irrespective of polarity. That is, if a possible overvoltage pulse arrives, the main gap has an increased positive voltage. If a negative overvoltage pulse arrives, the main gap has an increased negative voltage applied.