[Electric engineering.] . able forany direct-current circuit using pressures of 850 volts or has been very largely used on street-railway lines, but it isalso well adapted for low-tension lighting work. The air gapis quite short (about .025 inch), and the electrodes should beexamined from time to time to see that the air gap does notbecome larger or bridged over. If the gap becomes larger,there is danger of the lightning puncturing the insulation of 8l* ELECTRIC LIGHTING. 47 the apparatus to be protected instead of passing throughthe gap. The length of the air gap may be adjusted byloo
[Electric engineering.] . able forany direct-current circuit using pressures of 850 volts or has been very largely used on street-railway lines, but it isalso well adapted for low-tension lighting work. The air gapis quite short (about .025 inch), and the electrodes should beexamined from time to time to see that the air gap does notbecome larger or bridged over. If the gap becomes larger,there is danger of the lightning puncturing the insulation of 8l* ELECTRIC LIGHTING. 47 the apparatus to be protected instead of passing throughthe gap. The length of the air gap may be adjusted byloosening the clamps and moving the electrodes nearertogether. ARRESTERS EOR ALTERNATING CURRENT. 39. Arrester for Alternating: Cur-rent.—Fig. 51 shows a type of arrester that has been largelyused by the Westinghouse Company on alternating-currentcircuits. It is known as the Wurts non-arcing arrester,and consists of a number of milled cylinders a, a mountedas shown and separated from each other by small air. Fig. 51. gaps. The end cylinders are connected to the lines and themiddle cylinder to the ground. With this arrangement, asingle arrester does for both sides of the line; where, how-ever, the line pressure is high, a separate arrester is used foreach side; and for very high pressures, such as are used onlong-distance lines, a number of arresters are connected inseries. When a discharge comes in over the line, it jumps 48 ELECTRIC LIGHTING. §17 the gaps between the cylinders and passes to the is claimed that the arc does not hold over, because thegases formed by the volatilization of the metal will not sup-port an arc. The cylinders .are made of what is known asnon-arcing metal. Others claim that the suppression of thearc is due to the cooling effect of the cylinders and the 7b L/ne T ^m^- /OOOyb/ts. To Dynamo 1 ^50^ DDDDDL Tot/he. T ^im^- HIDDQDD £OOOyo/ts. To Dynamo —^-/W^ 4IDDDI Fig. 52. alternating nature of the current. The arc will be destr
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