1232 THE BELL SYSTEM TECHNICAL JOURNAL, SEPTEMBER, 1953 



charges at the contacts from the open circuit voltage to a lower voltage. 

 During this process the current in the circuit built up in a discontinuous 

 fashion and the steady arc was established only when the circuit current 

 reached the minimum arcing current of the contact. 



In this paper is presented our study of this initiation period. The 

 following are the main objectives: (1) to establish the analytic relations 

 governing the performance of a few simple contact circuits during the 

 arc initiation period; (2) to check the analysis by direct measurements; 

 (3) to apply the theory to explain a few arcing phenomena and empirical 

 relations previously reported; and (4) to shed some light on the nature 

 of the rapid local discharges at the contacts and the characteristics of 

 the influential circuitry at the immediate neighborhood of the contact. 



NOTATION 



C Main circuit capacitance 



I Circuit current 



li Arc initiation current 



Im Arc termination current or minimum arcing current 

 L Circuit inductance 



(L) Limit Limiting or maximum inductance above which a steady 



arc cannot be estabUshed 

 R Circuit resistance 



V Voltage 



Vo Initial voltage 



VcT Main condenser terminal voltage 



c Local capacitance at the contacts 



t Local inductance at the contacts 



n Number of discharges at the contacts 



r Local resistance at the contacts 



t Time 



V Voltage across a steady short arc 



V Voltage across the contacts at the termination of a single 



local discharge 



z Local impedance at the contacts - 



a Ratio of capacitances c/C 



« Angular frequency (Lc)"^^'' 



ANALYSIS 



In this section a few simple contact circuits are considered. In each 

 case relations are derived for the current and voltage changes in the 



1/2 



