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in the paper. The moment you begin to open the circuit of a machine, it is the the same same thing as overloading; that is, you are putting in a high resistance. The arc that follows, amounts to the same thing as many arcs put into circuit at the break. The potential, on account of the self-induction of the wire coils, at once begins to rise with the attempt to open circuit, and a diminished current flows. If at that moment the commutator, owing to its arrangement and construction, flashes over, arcs across from one side to another, you have removed the electro-motive force of the armature; and if the machine, as is often the case, has a copper band on the field cores, then we have an inductive circuit parallel with the field winding, which takes out the inductive electro-motive force from the field coils, and it is not surprising that there should be a great rise of potential in a case of this kind. Long ago, practice showed that when we ruptured the circuit of an open coil dynamo, the flash did not extend over any great distance; but it was a well known fact that if you had a closed coil machine, the circuit length of flash was much greater
MR. TOWNLEY: There is one phase of the question that I am glad to have the opportunity of stating to the members. It has been my fortune to be in a position where the demand for large units for lighting has been heard from very quickly, and I can confirm Mr. Hamill in his statement that the pressure is very strong for large units for arc lighting. The reason why arc lighting machines seem to have been made small for so long a time is, possibly, not easy to answer, but it may be found in the fact that until very recent times it has been difficult to insulate for the corresponding potentials. Looking at the problem of furnishing a large number of arc lights to a
community from one of our modern central stations, it is evident that if the conditions were not so severe as to render it impracticable, it would be advisable, not only to use a machine as large as 100 or 125 lights, but, in fact, machines of larger capacity-of 1,000, 2,000 or 3,000 arc lights. In an installation, we should manifestly have, if possible, units of larger capacity than 125 lights, and when we get down to sixty, seventy-five or eighty-light units, the objections are greater. In some cases there have been established stations having units of 200, 300 or 400 lights in one machine; this being done, however, by the use of constant potential in place of constant current machinery. This necessitates, apparently, the use of alternating currents, and possibly it has not been brought into more general use heretofore on account of the lack of a successful alternating current lamp. At the present time, however, that objection can hardly be said to exist, and the fact that there are now in operation stations of considerable size using this system, practically demonstrates the success of it, and is worthy of consideration. Of course, with the introduction of the alternating current and the ability to run power from apparatus of this character, there is a great point gained in large cities, particularly where underground work is necessary, when we can supply incandescent and arc lighting and power, in fact, all classes of service, from the same unit; and if that unit be a large unit, we can take advantage of the best economy in steam practice and the highest efficiency in dynamo construction. It seems to me that the development is bound to be in future along the lines. of these larger units and that, as the electric lighting public-the men who have their money and interests involved in this industry-come to know that this
system is a profitable one, successful commercially, and acceptable to municipalities, it is bound to be a very prominent factor in our interests thereafter.
MR. HAMILL: A very interesting point that always arises in this connection, is the question whether you can run these large machines on the existing circuits that have been in use for so many years. I see Mr. Prentiss in the audience, who can cite to you interesting cases where these machines were put on some of the oldest circuits in the country.
MR. PRENTISS: I will state that the question of line insulation with the use of larger units seems to be one of care more than anything else. Several instances have been brought to my notice where large machines have been put on ordinary circuits in which very little trouble was experienced; and the underground work that has been installed for the ordinary high potential will also do very nicely. The only trouble that will be practically met, will be from the point of the line into the place where the lamps would be used, or in the connecting appliances. The trouble arises principally from the moisture getting down into the cut-out box. I believe there are very few cut-out boxes that will stand the ordinary potential of 3,000 volts where you have a spell of wet weather for three or four days. When that point and the cut-out box are taken care of, there will be very little trouble. I do not doubt but that existing circuits using 2,000 or 3,000 volts can be made to run the higher potentials, it having been demonstrated in several instances to be practicable.
MR. T. CARPENTER SMITH: Referring to the question of the strain on insulation caused by the use of large units on old lines, I think some of the
older members probably remember when in times of trouble they did not hesitate to put two 50-light machines together on a single circuit, which was as much strain on the insulation as with a single machine. The most extreme case I know of was where fifteen ten-lighters were run in series with an eighteen-ampere current. I think that was as much of a strain as would be experienced with any of the large machines now being advocated. The old machines were repeatedly speeded up to give nearly the same capacity. I know of forty and sixty-light machines running speeded up till they ran sixty and ninety-light circuits; and the extreme case was probably reached in New York city a few years ago, during the time the wires were being put underground, when in one station they ran two sixties and a thirty in series.
MR. PRENTISS : In regard to Mr. Smith's remarks, I wish to state that a practical demonstration of what can be done in the very high potential line. was shown in New York city some time ago, when they were compelled for a week to run a circuit of two hundred and forty 2,000 candle-power arc lamps in series. This circuit was underground.
On motion of Mr. Seely, the following resolution was unanimously adopted:
Whereas, the Cotton States and International Exposition is to held at Atlanta, Ga., September 18th to December 31st, 1895; and Whereas, the United States Government recognized this Exposition, and has appropriated a
considerable sum of money for a government exhibit;
Whereas, the Exposition Company has provided a large Electricity Building, to be devoted exclusively to exhibits of electrical apparatus, inventions and kindred interests, therefore be it
Resolved, That the National Electric Light Association in its Eighteenth Convention assembled, hereby urges its members to attend the Cotton States and International Exposition, and to avail themselves of this opportunity to exhibit electrical products especially devoted to the electric lighting industry in the Electricity Building set aside for that purpose.
A communication from the ladies of Cleveland, asking the members and the ladies accompanying them to attend the exhibition of paintings in the Garfield Building, was read and duly accepted with thanks.
On motion, the meeting adjourned until the afternoon.