Зображення сторінки
PDF
ePub

available as an auxiliary source of energy, it is always ready for emergency use, and this advantage is one of great value and can hardly be considered fairly on a purely pecuniary basis. The chart at Fig. 85 shows the operation of a battery in daily peak-load work. That at Fig. 86 shows how the output of a stand-by battery helped to handle an unexpected lighting load on a central station due to a particularly heavy thunderstorm. These curves. are merely graphic records of the amount of current used under certain conditions and in a given time, and are easily understood.

A stand-by battery uses rugged plate construction and is always composed of very large-size cells. Type H Exide plates, which are widely used in the larger installations, are 31 inches high by 155/16 inches wide. The grids are castings of leadantimony alloy and are provided with very heavy connecting lugs. When it is considered that a plate of this size may be called upon to discharge 600 amperes or more for several minutes, it will be realized that great care must be taken in proportioning the plates. The plates are hung from the cell tops by the plate lugs, which rest on vertical pieces of heavy glass arranged on either side of the tank, suitably notched to receive the plate lugs. The glass plates rest upon the reinforced lead lining at the bottom of the cell. A space of 3⁄44 inch is left between the outside negative plate and side of the tank at one end to permit the taking of hydrometer readings. An instance of the large size of the cells is the sediment space allowed, which is 12 inches in a type H cell.

A tank suitable for an Exide element having a capacity of 3,000 amperes for one hour measures about 225% inches long by 211⁄2 inches wide. For a capacity of 6,000 amperes at the hour rate the length is increased to three feet, and for 9,000 amperes the length is nearly five feet. The height of such a cell from the floor to the busbar is about 512 feet, or high enough so the average man can barely look into the cell. The tanks are built of specially selected yellow pine, put together with glued, dovetailed and doweled joints. No nails or metallic fastenings of any kind are used. The lumber used is of sufficient strength to be entirely self-supporting. These tanks are treated with two coats of acidresisting paint inside and out.

[graphic][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][merged small][subsumed][subsumed][merged small][subsumed][merged small][subsumed][merged small][subsumed][merged small][merged small]

Fig. 86-How Exide Stand-by Battery Helped to Handle Unexpected Lighting Load.

The tank linings are of pure sheet lead, the lap seams being burned with the hydrogen flame. The upper edges of the lining extend over the edges of the tank and down outside clear of the tank faces. Drip points are provided, so spaced that they come between the tank supports. Good insulation of the cells is an essential. The Exide insulator consists of a glass body surrounded by an inverted petticoat, this forming an annular trough partly

[graphic][ocr errors]

Fig. 87.-Battery-Room of Calumet River Draw-bridge of Calumet & Western Indiana Railroad.

filled with oil, the whole being covered with a lead cap extending down around the sides but out of contact therewith. Each oil insulator rests on a truncated cone or pedestal of earthenware or a composition not affected by acid. Each cell is covered with a plate of heavy glass, which serves to condense the acid spray. All conductors are of specially heavy section lead-coated copper bars, firmly bolted together. The plates of each cell, joined together

to form an element or plate group, are lead-burned to soft-lead busbars.

The total number of cells required is determined by the maximum busbar voltage permissible at the end of a high-discharge rate. For example, if a battery is installed of capacity enough to carry a maximum peak load for ten minutes a voltage of 100 each side of a three-wire system might be considered satisfactory. This would call for 75 cells each side. If at any time during the day it is necessary to float the battery at a voltage as low as 115 volts, the main battery would consist of 55 cells each side, leaving an auxiliary battery of 20 end-cells on each side. These end-cells. are brought into action as needed by special switches.

In arranging a battery-room for such a large battery, special attention is given the floor construction, because drainage is important. Ventilation must be exceptionally good, and all exposed metal work should be protected by acid-proof paint. Concrete has been used for battery-room floors, and is satisfactory if care is taken to flush it with water frequently to wash away any electrolyte that may have accumulated. Hard-burned tile or vitrified brick is much more suitable. The floor should be laid on a concrete foundation, of sufficient strength to carry the weight. The slope should be such as to allow for positive drainage, and the floor covered with asphaltum felt. Spaces of 1/4 inch are left between the bricks or tiles, these spaces being grouted with asphalt compound. An exhaust ventilating system is almost an essential if the battery is used much. The fan parts should be of bronze, and air from the room should be filtered through an air-box having perforated lead screen to eliminate acid spread. It is said that air in a battery-room should be changed completely four times an hour during the gassing period of the charge.

Storage Batteries for Draw-Bridge Operation.-An unfailing source of power is an absolute necessity where draw-bridges are operated by electric motors, as most of them are. This applies especially to railway bridges, where any failure of the power supply would seriously interrupt travel on either the waterway or railway. Vessels have been badly injured due to failure to open a draw. Bridges may be operated by separate power plants, consist

[graphic]

Fig. 88.-Calumet & Western Indiana Railroad Bridge in Open and Closed Positions.

« НазадПродовжити »