[Trade Journal]
Publication: Bell Laboratories Record
Murray Hill, NJ, United States
vol. 5, no. 5, p. 163-165, col. 1-2
High Voltage Storage Battery
By L. E. DICKINSON
Apparatus Development Department
IN the development of fuses, protector blocks and other pieces of protectve [sic] protective apparatus for telephone use, a source capable of delivering for a few seconds direct current of several hundred amperes at high potential is extremely useful. To provide such current a storage battery is best; on account of its low internal resistance it will deliver, for the time needed to test a fuse, current at many times its normal discharge rate and at voltage very close to normal. The battery provided in the Laboratories for such testing has found use as well for investigations of resistances, electrolytic condensers and lead-covered cable. At an early stage in the development of water-cooled vacuum tubes it was used to maintain a plate potential of four thousand volts. It has even been used for magnetizing permanent magnets for loud speakers used with talking moving pictures and elsewhere.
One-twelfth of the battery. These two racks, like all the others, hold eighty-eight cells each
The high-potential battery dates from 1915, when the Electric Storage Battery Company installed 2112 cells on the first floor of the old Section H building on Washington Street. When this building gave place to the present Section H the battery was dismantled, and after overhauling was reinstalled in the room which it occupies today on the first floor of Section G. The floor, of concrete, is covered with a layer of hard acid-proof bituminous compound about an inch and a half thick, and the walls are painted with a light acid-proof paint instead of the black asphaltum paint sometimes used in battery rooms.
Each cell is of sixty ampere hours capacity, and consists of thirteen lead plates about four inches square. The cells are permanently connected into groups of forty-four, and these units may be connected together as wanted.
The cell groups are mounted in series or in parallel by these knife switches. At the left are the oil switches for completing and breaking connections
Because of the fine spray thrown off by the cells during charging and of the "sweating" on the outside of the jars in humid weather, requirements are most exacting for the insulators on which the individual cells and the cell groups are supported. The wooden uprights supporting the racks of cells are mounted on double tiers of glass insulators separated by lead discs, the lower insulators resting on tile blocks set in the floor. Each group of four cells rests on a plate of wire glass 3/8" thick, supported by small glass insulators resting on the wooden rails of the rack. Each insulator, large or small, consists of a glass body surrounded by a steep, funnel-like wall of glass; between is a circular trough filled with transformer oil. The whole insulator is protected by a lead cap, covering the top and extending down around the sides, but not touching the glass of the insulator.
Fuse ready for trial, mounted on the test table. Current is restricted to the desired value by the resistances at the left
Each group of forty-four cells is connected to a knife switch on the main panel of a switch-board in an adjoining room, whereby it can be connected in series or in parallel with other groups. Any voltage between 90 and 4320 can thus be obtained, in steps of 90 volts. On another panel are oil-switches by which the battery is connected and disconnected to start and stop testing, and on the third panel connections are arranged for charging. With all the cells connected in series about a thousand amperes flow during the small part of a second required for a fuse to operate. The current is correspondingly greater when the battery is connected to give 540 volts. This arrangement is commonly used in testing carbon block protectors since it is close to the standard trolley voltage. In any case the circuit is opened by the oil-switches, operated manually; though a circuit breaker might be used, none has been provided, lest its operation might mask the performance of apparatus under test at the time.
Glass insulator such as those supporting the cells and the rack
From the main oil-switch, conductors of comparatively large size lead to the test table, where fuses and other protective devices are mounted during testing. Adjoining it on the left is a grid resistance for regulating the current, made up of nichrome ribbon mounted on transite cores. Sections of ribbon are connected in series or in parallel by means of small knife switches at the bottom. At the right of the table is a magnetic contactor to close and open the circuit for tests requiring currents of less than twenty-five amperes at voltages under one thousand. After the oil-switches are closed the tester presses a button which closes the contactor, and as soon as the test is finished in second or so-he releases it, opening the circuit. Then the oil-switches are opened. During all testing a man is detailed by the Plant and Shops Department to operate the knife switches, connecting the cell groups as wanted by the engineer making the test, and to stand near the oil-switches, closing and opening them as is necessary.
