Spark gaps protection

Figure 25. Volt-time curves of transient with and without spark gap protection...

Spark gap These have a pair of conducting rods with an adjustable gap, depending upon the spark over voltage of the arrester. Precise protection is not possible, as the spark-over voltage varies with polarity, steepness and the shape of the wave. These arresters are also now obsolete for the same reasons. 

Figure 26.11 Overvoltage protection with the help of a spark gap and a shorting switch...

So that the function of the spark gap isolators is not cancelled, cables with lightning protection must have insulated sleeves installed at their ends, in addition to the spark gap isolators, so that the metal sheathing or the shield that is connected at soldered joints to the lightning reinforcement is also separated from the operational ground of the building (foundation ground) and from the ground at the remote end. 

If the protection ground is connected via a breakdown fuse, the insulating unite and spark gap can be disregarded... 

Circuit enhancements for biopotential measurements, (d) Baseline restoration circuit the high-pass filter capacitor Cl is discharged by field-effect transistor F when activated manually or automatically by a baseline restoration pulse, (e) Electrical isolation transformer coupled using the transformer T (top) or optical using the diode D and the photodetector P (bottom). Note that the isolator separates circuit common on the amplifier side from the earth ground on the output side, (f) Electrical protection circuit resistance R limits the current, reverse-biased diodes D limit the input voltage, and the spark gap S protects against defibrillation pulse-related breakdown of the isolation transformer T. 

As far as motors are concerned, the emphasis on hot surfaces, high starting currents and extended run-up times is not as great as with type e for Zone 1 areas, due to the inherently lower risk of hazard in a Zone 2 area. Special protective relays are not required and a system approach is not used. Similar design featmes in the mechanical part will be found e.g. clearances of fan blades, length of the air-gap between the rotor surface and the stator inner surface. Oil company specifications often call for non-sparking materials for the construction of the fans. 

---