If the cell has stood disconnected from the circuit for some time, especially in a warm climate, there is a possibility that the initial current rush will be sufficient to open the circuit breakers or oil switches. This current rush also raises the temperature of the cell, and if the temperature rise be great, it is objectionable.
When the cells do not stand for more than a day, however, the film dissolution and initial current rush are negligible.
~Ques. What is the object of using horn gaps on electrolytic arresters?~
Ans. The use is threefold: 1, it prevents the arrester being subjected continually to the line voltage; 2, acts as a disconnecting switch to disconnect the arrester from the line for repairs, etc., and 3, acts as a connecting switch for charging.
[Illustration: FIG. 2,395.--Horn gaps and transfer device of General Electric aluminium lightning arrester for 12,500 volt non-grounded neutral circuit. The object of the transfer device is to provide a means for interchanging the ground stacks with one of the line stacks of cones during the charging operation so that the films of all the cells will be formed to the same value. The transfer device consists of a rotating switch which may be turned 180 degrees, thus interchanging the connections of the ground stack and one of the line stacks. For arresters up to 27,000 volts the device is mounted with three insulators on the pipe frame work, and is operated by a hand wheel; for arresters of higher voltage, the transfer device is mounted directly over the tanks and is operated by bevel gears and hand wheel.]
~Charging of Electrolytic Arresters.~--In electrolytic arresters all electrolytes dissolve the film when the arrester is on open circuit, the extent of the dissolution depending upon the length of time the film is in the electrolyte, and upon its temperature. It is therefore necessary to _charge_ the cells from time to time and thus prevent the dissolution and consequent rush of current which would otherwise occur when the arrester discharges.
~Ques. Describe the charging operation for arresters with grounded circuits.~
Ans. It consists in simply closing simultaneously the three horn gaps so that the full pressure across the cells causes a small charging current to flow and form the films to their normal condition.