This article was originally published in Electrochemical and Metallurgical Industry Publication of December 1907. Information within this article is therefore correct as of 1907. The publication of this material aims to provide historical insight on the subject and its place in industry.
While the introduction of electric power for all purposes has revolutionized to a large extent the operation in modern iron and steel plants, the economies which may be obtained by the use of a storage battery are not yet fully appreciated. For this reason the following notes, taken from a recent pamphlet of the General Storage Battery Co. of New York, should be interesting.
There are many plants in which a large part of the electric power load is at a considerable distance from the generating station, where the installation of a suitable storage battery, floating on the line, at or near the local center of distribution of the distant load, will produce excellent results. By increasing the load factor (that is the figure which indicates to what extent the maximum capacity of the plant is utilized in average operation) it will effect a great saving in plant operation. It will also maintain an increased and steady voltage at the load, and increase the plant output at far less cost than would be necessary for an increase in the generating equipment.
Cambria Steel uses two large ore bridges and one car dumper, all operated by electric motors and supplied with current by a set of feeders from the main power house, the center of the load being approximately 3,000 feet from the power house.
The work of these motors is of necessity heavy and intermittent, so that the resultant load on the power house fluctuates widely. The momentary current values vary from 400 to 4,000 amps, equivalent to rapid fluctuations in load from 100 to 1,000kw at 250 volts.
Prior to the installation of the storage battery, twelve 500,000cm cables were used as feeders, to supply the motors operating the ore bridges and car dumper. The voltage at the center of the motor load, at the same time, fluctuated through wide limits.
To meet the demands for an increase in load, it was found necessary either to increase the generating plant, or relieve it of power fluctuations to such an extent that additional load could be handled by the existing units.
It was found that the installation of a storage battery near the center of load could be made at much less cost than an increase in generating equipment, and would have the additional advantage of increasing the load factor of the plant, with consequent more economical operation. Besides this the voltage at the center of load could be maintained at a higher working value, and the battery could be used in emergencies as a reserve.
Calculation showed, also, that the feeder copper which could actually be removed, following the installation of a battery at the center of the load, would go a long way toward paying for the battery.
To attain these advantages it was necessary, however, that the storage battery installed should go from charge to discharge, with small changes in voltage at its terminals; should be capable of being operated with little or no attention; should be able to withstand occasional overloads without detriment; and, in emergency, be able to stand fully discharged for short periods, without permanent injury.
As the construction of the Bijur "High-Duty" batteries lends itself admirably to these requirements, it was decided to install a battery of this type. It consists of 106 cells of the General Storage Battery Co.'s regular Bijur "High-Duty" type, having a capacity of 2,400 amps, for 20 minutes.
Each cell has twenty-five plates, approximately 15 ½ x15½ . The plates are burned to bus-bars of rolled lead, except in the terminal cells, where the bus-bars are provided with internal ' copper conducting reinforcements. The connections between adjacent rows of cells are made by means of lead-covered copper bar.
The lead-lined containing tanks are sufficient in size for thirty-one plate elements, providing for future increase in the capacity of the battery.
Each tank is provided with double insulation, the glass insulators supporting the wood stringers resting on vitrified tiles set in the concrete floor of the battery room.
The battery house is of brick, with slate roof and concrete floors; the building is well lighted and is provided with drains, so that the entire battery room may be flushed out. A separate room is provided in the building for the battery switchboard.
The switchboard in the battery sub-station is provided with a distant control circuit breaker which may be opened or closed by hand at the battery house, or electrically from the power station. The arrangement is such that opening of the circuit breaker is immediately signaled in the power station, and this breaker can be closed from the power station by the switchboard attendant.
Owing to the distance (3,000 feet) between the battery and power station, it was found that comparatively small changes in current over the feeders to the battery would produce sufficient change of voltage at its terminals (due to feeder drop) to cause it to go from full charge to full discharge; in fact, the battery so situated removes the fluctuations from the power station to such an extent that it was not considered worth while to install a regulating booster at the power station.
By the selection of the proper number of cells, the battery has been arranged so that while merely floating on the line, its total charge and total discharge over an extended period are equal, hence the state of charge of the battery remains substantially constant.
In order, however, to provide for an increase in the condition of charge, and to give occasional overcharges, required for best operation, a separately excited motor-driven booster is installed in the power station. Provision is made for connecting the booster armature in series with the battery feeders, between them and the station bus-bars, the voltage then being raised by hand regulation to the extent desired to overcharge the battery. This overcharging with the hand regulated booster is usually done at times when the ore bridges and cat dumper are not in operation, although it may be done at any time.
The construction of the battery plates in this installation is one offering the greatest freedom to diffusion of the electrolyte. The cells can be charged completely full with less than 2>2 volts each, at the normal 8-hour rate. This feature ensures charge and discharge taking place with minimum changes from an average floating voltage; a feature affording high working efficiency.
The plates are also free from mechanical disturbances of any kind, so that in practice the battery house is left entirely without attendance for a week or more at a time, the only attention required being the occasional replenishing of the cells with water to provide for evaporation and general inspection of the battery. Emergencies in which the battery has been compelled to remain without attention for protracted periods, and in which its reserve function has been called upon to its fullest extent have been met, without any detrimental effect whatsoever.
Summarized, the results which have been attained by the Cambria Steel Co. from this installation are as follows:
- Saving in initial cost over generating equipment of equivalent capacity.
- Saving of 27,700 pounds of copper removed from the feeders.
- Removal of fluctuations from the power station.
- Increase in the working voltage.
- Reduction of feeder losses.
- Increase of station output from existing units.
- Creation of a reserve source of supply.
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