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were obtained. It is seen that the temperatures of the bulbs of new plain lamps are about 38 degrees above room temperature. When a new lamp is frosted the temperature of the bulb increases by about 9 degrees. When a lamp is burned to about 83 per cent in life, the temperature of the bulb rises only 3 degrees due to the carbon deposit, but when an old lamp is frosted the rise due to frosting is about 15 degrees.
With the great difference in temperature between the filament and the bulb, the small variations in the temperature of the latter would scarcely be expected to change the temperature of the filament appreciably, so that, although it is true that the bulbs of frosted lamps are hotter than those of plain lamps, the change in the temperature of the filament would probably not be noticeable in the life.
It would be very interesting, in conclusion, to follow out the practical results suggested by an investigation of this kind. For example, it is at once evident that the useful life of frosted lamps containing filaments of some material that would deposit no absorption film on the inner side of the bulb, would be as great as that for the corresponding plain lamps, and the efficiency would only be a few per cent less. The question of the most satisfactory size and shape of plain and frosted lamps is also very suggestive. For example, if the surface of bulbs of frosted lamps were doubled, the useful life would be very much longer than at present.
These and similar questions, however, scarcely come within the province of this paper. They belong to the manufacturer rather than to the consumer. Our chief interest at present is to obtain facts in regard to existing conditions, and if possible to correlate these facts upon some logical basis.
THE PRESIDENT: We should feel especially gratified that Dr. Hyde should undertake the presentation of this paper, not alone for Dr. Hyde's work in connection with the subject, but for the interest that was shown on the part of the National Bureau of Standards, that this interest should have been sufficient to call forth the preparation of the paper. On your behalf, I thank Dr. Hyde and his associate, Mr. Cady.
We will now take up the paper entitled, Some Electric Power Experience, by Miss S. M. Sheridan, of Detroit.
The paper was read by Mr. Alex Dow, as follows:
SOME ELECTRIC POWER EXPERIENCE
This paper is a statement of some lessons taught us by experience in the sale of electric power. We know now that we could have read most of these lessons in various text-books and printed proceedings. We have grouped them into one paper, hoping that the paper may help some other member companies that are learning by experience.
In two years and four months we have added to our commercial power load 5965 horse-power in alternating-current motors and 3862 horse-power in direct-current motors, and in the last 12 months have increased our day load 50 per cent.
During this time we have followed the quite common practice of loaning and renting motors for trial installations. To do this it was necessary to carry a stock of motors that reached a value of $46,000 during the year 1906, when our average monthly gain in motor connections was 450 horse-power. When our power business showed decided and permanent growth, several of the local construction companies, seeing that their business could be increased if they could handle an entire installation, including motors, put in motor stocks and adopted our plan of trial on loan for 30 or 60 days; renting the motors for longer periods if purchase seemed likely in the future. This movement by the contractors is gradually relieving the central station of the necessity for carrying a stock of motors.
Our rental charge, after the loan period, was 25 per cent per annum on net price of motor.
The company has always taken care of emergency cases, due to fires or breakdowns, of isolated plants at a minimum rate, and this custom has frequently led to permanent business. We have also found that considerable business may be done with contractors on construction work; and while this class of business occasionally requires extensions to our lines we can well afford to make them, considering the advertising it gives electric power among contractors.
Observations taken in one hundred factories at odd times show that on an average but 50 per cent of all the machines will
be loaded at any one time, because operators are preparing work, adjusting machines, are idle, or for the moment away from the machines. This statement to a manufacturer will not often be credited until he has proven it by observation. The fact is, however, well known to our selling force, and is considered when specifying motors required and in estimating probable costs; and the saving of expense with metered central-station electric drive against other power, due to this condition, is a good selling point.
Individual motors are not to be recommended unless a saving in current consumption equal to 20 per cent per annum on increased investment will be effected. Except where individual drive is desired for special convenience, a less saving is not worth considering, as a customer would doubtless earn as much on the same money invested in his business.
In wood-working shops individual motors displacing one large unit have shown considerable saving. Instances: A shop operating a 20-hp motor, with average monthly bills of $40, installed nine motors aggregating 42.5 horse-power, and reduced its average monthly bill to $32, in addition to providing for increased output. In another shop a 10-hp motor was replaced by nine motors aggregating 28 horse-power, effecting a reduction of 20 per cent in customer's bills, with the same work.
Customers should be influenced to use roller bearings on shafts, which bearings in some cases reduce the friction load of the shafting 20 to 25 per cent as compared with good babbitt bearings; also to install shafts in separate short lengths where practicable, which is a decided advantage if part of the shop is run overtime or at times when the shop is operating only in part.
With large blowers it is frequently found that the fan is delivering more air than is actually required. In displacing a steam installation recently it was found that two ounces less pressure was sufficient for the work, and by reducing speed of fan we reduced the customer's bills about $15 per month. This brought cost of electric power low enough to compete successfully with steam.
In another instance we reduced the pressure at blower one ounce by moving it so as to shorten the length of the pipe by 100 feet, thus reducing load by six horse-power. In another installation of the same kind, four horse-power was saved by straightening several sharp curves on the blower pipe. The use of motors made these changes simple and cheap.
Our experience, as illustrated by these instances, has made us very suspicious of fans, blowers, air-compressors and centrifugal pumps. The power required by these devices varies so rapidly with variation of speed that it pays to investigate every such machine in an installation and to make certain that it is not being run at a higher speed than is necessary to deliver the proper pressure. To run blowers needlessly fast is a very common fault.
In a small machine shop our engineer reduced friction loss by changing the location and piping of an air-compressor, so that an intermittent small loss in an air pipe was substituted for a constant considerable loss in friction of a shaft. The electric drive was entitled to no credit for this, but got it just the same. In the same shop a portable desk fan, playing directly on tanks to be cooled, was substituted for a wooden-blade fan that was bolted on each side of end of line shaft. These changes. effected a reduction of 15 per cent in current consumption.
A shop manufacturing steel products asked us to install a 50-hp motor for three months, to take care of part of its plant while rebuilding boilers. This gave us an opportunity of studying its conditions and before the three months were up we made the following recommendations: To install a motor-driven aircompressor to supply air instead of steam to oil burners of forges, which change saved the cost of power in saving of oil; to arrange work so that the big grindstones were operated off our peak, thus giving the limited service rate for that service; and to do all work requiring high-pressure steam two days a week instead of each day (this change greatly reduced their standby charges for steam and dispensed with services of one man); also to install a governor on air-compressor to close inlet valve and allow compressor to coast until tank pressure fell to line pressure. With these economies and the usual cutting out of shafting, the cost of operating the shop by electricity was reduced below its steam costs. The company equipped its shop with motors and at present has an installation of 150 horse-power with monthly current bill averaging $250.
By changing tight cross-belts to wide slack open belts on a shaft driving twenty machine tools, the power required was reduced three horse-power. In a polishing-room where ten double heads in one row with one exhaust fan at each end were
operated, we recommended placing the machines in two rows with one fan between the rows, which effected a saving of eight horsepower. In endeavoring to deliver the required power at a machine driven by a countershaft we changed the 12-inch pulleys on the main and countershafts to 24-inch pulleys with the desired result and incidentally reduced the load two horse-power.
By reducing speed of the line shaft in a large machine room from 220 to 190 r.p.m. a saving of eight horse-power was effected without decreasing the output, as speed of tools was taken care of by cones.
A motor replacing a gas engine, operating automatic machines, by the improved speed regulation increased the output of the machines 10 per cent-the constant turning movement permitting a heavier feed to the cutting tools.
In the foregoing case the output of the shop was increased because the steady motion given by a motor allowed a heavier cut to be taken than when the tools were driven by a gas engine. In other cases we have found that the cutting speed could be increased to a point higher than was possible with the unsteady gas-engine drive.
In one small factory we were unable to discover why current consumption should be 25 per cent higher than our estimate. We finally prevailed upon the manager of the concern to allow us to test out his machines, which his superintendent maintained were in excellent condition. After working for two days we found that the bearings in the air-compressor were running on the iron of the boxes. Proper babbitting of the machines reduced the customer's demand two kilowatts, and we retained the business.
In the matter of factory lighting: We usually advise such customers to do their general floor lighting with gas-arcs, but to install individual incandescent lights at the machines. Since adopting this policy we find that we are relieved of the many complaints on lighting bills that were so frequent two or three months in the winter, when our factory customers would come to us with lighting bills that were sometimes as high as those for power. Our rate system makes a high price per kilowatt-hour for lights operated for only a few hours annually, while the gas company makes no difference between short-hour and long-hour customers, so all parties are satisfied by this division of service.
In this respect of willingly letting short-hour factory lighting