An investigation of excitation-arc phenomena in mercury-pool valves

The behaviour of the excitation are of two different designs of industrial-type mercury pool valves with anchored cathode spot was systematically investigated, and it was found that: (a) Mean-value measurements of are voltage and current give a falling characteristic in the low-current range because the are fluctuates between two different modes of operation, the mode at a lower current having a higher are voltage than the mode at a higher current. (b) Spontaneous extinction of the excitation are at a current below a critical value in the absence of any main-anode current is caused by a randomly occurring simultaneous failure of the regeneration mechanism for all emission centres which together form the cathode spot. (c) Any extinction of the excitation are as a consequence of a main-anode current pulse is a random phenomenon which always occurs at the end of the main-anode current pulse and which arises when the excitation current is below a critical value, the magnitude of which is dependent on various parameters of valve design and operation.