[Electric engineering.] . uit going out. This deviceis called a cut-out. 42. Although the current through the arc remains con-stant in a series system, the voltage across the arc increasesas its length increases, and this increased voltage is made tobring about the regulation. Suppose that we modify the 40 ELECTRIC LIGHTING. 18 simple lamp shown in Fig. 24 by extending the core c down-wards and adding another solenoid S, as shown in Fig. can also omit the starting resistance r, as this is to be aseries lamp, and there will be no excess voltage to be takenup; the current is maintained at
[Electric engineering.] . uit going out. This deviceis called a cut-out. 42. Although the current through the arc remains con-stant in a series system, the voltage across the arc increasesas its length increases, and this increased voltage is made tobring about the regulation. Suppose that we modify the 40 ELECTRIC LIGHTING. 18 simple lamp shown in Fig. 24 by extending the core c down-wards and adding another solenoid S, as shown in Fig. can also omit the starting resistance r, as this is to be aseries lamp, and there will be no excess voltage to be takenup; the current is maintained at a constant value andresistance is not necessary to insure stability of second coil S is to be wound with a«large number ofturns of fine wire, so that when it is connected in shuntacross the arc, as shown, but a small current will flowthrough it. The coils S, S pull c in opposite directions,and c will always take up such a position that the two pullsare balanced. The action of the lamp is, then, as follows*. Fig. 25. When the lamp is out, the carbons g, h are in that the switch m in this lamp is connected across theterminals, and in order to put out the lamp, m is is just the reverse of the constant-potential lamp thatis operated in parallel. When the lamp is thrown into cir-cuit, the main current passes between g and h, but since thecarbons are in contact there will be little or no drop inpotential between them and, hence, practically no currentwill pass through the shunt coil S. The result is that coil £ § 18 ELECTRIC LIGHTING. 41 pulls up the plunger, and in so doing lifts the upper carbonand starts the arc. The instant, however, that the carbonsg, h separate, current flows through S, because there is thenconsiderable difference of potential between g and h. Theresult is that as the carbons are separated, the downwardpull of S becomes stronger until it finally balances theupward pull of S, when the arc remains stationary. As thecar
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