. The Bell System technical journal . TIME,t, IN 10^ SECONDS Fig. 4 — Contact voltage transient with sustained arc on break of an inductivecircuit. Pd contacts in atmospheric air, E = 50 volts, L = henry, R = 115ohms, C = 20 X 10~^ farad. Velocity of contact separation 40 cms/sec. tical purposes one may neglect the voltage drop time which is the initia-tive period of the arc. For the circuit in Fig. lb, the current through thearc is the summation of the main circuit current and the transient current from the l-c circuit. The transient current is (Vai — y)(T)^%in ^{Icf^. Fig. 7, (a) and (
. The Bell System technical journal . TIME,t, IN 10^ SECONDS Fig. 4 — Contact voltage transient with sustained arc on break of an inductivecircuit. Pd contacts in atmospheric air, E = 50 volts, L = henry, R = 115ohms, C = 20 X 10~^ farad. Velocity of contact separation 40 cms/sec. tical purposes one may neglect the voltage drop time which is the initia-tive period of the arc. For the circuit in Fig. lb, the current through thearc is the summation of the main circuit current and the transient current from the l-c circuit. The transient current is (Vai — y)(T)^%in ^{Icf^. Fig. 7, (a) and (b), represent diagrammatically the voltage and currenttransients for lumped and distributed circuits. In both cases the arc is 300. lU o zoo 500TIME,t, IN 10^ SECONDS Fig. 5 — Contact voltage transient with glow discharge on break of an inductivecircuit. Pd contacts in atmospheric air, E = bO volts, 700 ohms relay coil and C =200 X 100~i2 farad. Velocit^y of contact separation = 40 cms/sec. ARCING OF ELECTRICAL CONTACTS IN TELEPHONE SWITrillNG CIRCUITS 541 tcrmiuated when the curiciit drops to the minimum arcing current/,It is e^•i(^eIlt that the condition for ohtainin; an interiuptcvl arc is: /o — {Vai — v) < In (1) It may t)c pointed out tiiat surface contamination, such as organicacti\ation, tends to decrease both/^ and V aC ■ According to equation 1,one may conchide that contact surface contaminations usually tend tocause a transition from an interrupted arc transient to a steady arctransient. The latter is usually associated with appreciably higher(Miergy dissipation between the contacts and much lower contact lifedue to erosion. L R ^WT WV
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Keywords: ., bookcentury1900, bookdecade1920, booksubjecttechnology, bookyear1
