The following information was taken from a draft copy of a 77-page document prepared by Professor Henry Rowland from Johns Hopkins University. The document is the property of the University and may not be reproduced without their permission.
"The final report of Prof. Forbes of September 16, 1892 has been handed to me and my opinion asked on the same."
The first sixteen pages are a severe attack of a report that outlined the recommendations of Professor Forbes to the Cataract Construction Company. Forbes recommended alternating current generated at 8 1/3 cycles.
In this section of the report he notes comments of Tesla, Stanley, and Anthony that recommended higher frequencies for motors. He mentions "Steinmetz law" and the "Ferranti effect" in the discussion of transformers and transmission. Forbes apparently reported that higher frequencies would cause breakdown of insulation in transformers. Rowland quoted recent experiments by Siemens in air where this did not occur. He reported a visit to Lynn where Elihiu Thomson had tested oil filled transformers where he found no effect from frequency.
This is the first reference to oil filled transformers.
Following is the report from page 16 to 77 where Rowland reviews the bids for Niagara Falls. Remember this document is the property of Johns Hopkins and can not be reproduced without their permission.
Within the past few years the application of electricity to the transmission of power has advanced in an unprecedented manner so that a scheme on a grand scale and for great distances may now be carried out with far greater hope of success that could have been even imagined even three years ago.
(a) The experience gained in the making of large dynamos by which their cost per horse power has become a fraction of that estimated years ago.
(b) The invention of the Tesla motor and its success abroad in the shape of multiphase motors by which the alternating system became practical. I have not found historical records that confirm the DETAILS of the use of multiphase induction motors in Europe.
(c) The practical use of very high potentials between Frankfort and Lauffe.
To these I may add the discovery of processes by which very large transformers may be made at a very low cost.
Several years ago the Niagara transmission could have only been carried out as an experiment in which the initial failure was to have been expected although there was the possibility of a final success after the expenditure of much money. Even then the dynamos would probably be obsolete now. Today many of the experiments have been made by others and the plan starts from an advanced standpoint with far less risk of failure.
Although some points still remain to be settled by experiment and although the difficulties will be encountered, they will not, probably, be of such a nature as to endanger the enterprise and I see no reason why success should not crown it. However, there is not much latitude for careless engineering or loose business management and failure in either will wreck the company. On the other hand, careful, intelligent and economical electrical and mechanical engineering with enterprising and yet conservative business management will lead to success.
ALTERNATING AND CONTINUOUS CURRENT SYSTEMS
It may be said at once that each of these has its advantages. The continuous current system is far simpler in theory and better in practice where it can be used. It is not hampered by patents except in its minor details; the motors are all that can be desired, starting from rest under a load and capable of variations in speed to a limited extent; the system needs only two wires and the measurement of power supplied to customers is comparatively simple.
The alternating system, on the other hand, is immensely complicated in theory especially when large number of motors are to run from one dynamo. It is hampered on every side by patents owned by different companies; the motors have much to be desired, especially as their speed cannot be varied in the better ones; the system needs three or four wires and the measurement of power given to customers is scarcely capable of accurate measurements by any simple meter.
On the other hand the dynamo and motors are simpler mechanically and the transformers give a ready means of raising and lowering the potential in a simple and efficient manner.
This last property gives the great value to the system and makes it specially adapted for long distance transmission of power. There can be little doubt that the alternating system is the more practical one to use for the Buffalo transmission although I have in mind a new method by which even continuous currents could be used. This being settled, I believe that the most useful method of determining the local question will be to use the Buffalo machine for local work as far as they will go. For many local needs they will be the best; for others they may do. If, as the work goes on, there is a call for great quantities of continuous current near to the turbines or at high potential, the need can be met by continuous current dynamos. If only a small quantity is needed or it is or low potential and at a distance, motor transformers to transform the alternating current into the continuous one can be used. It as a matter of individual calculation as to which is the best.
My own opinion is that, as the work progresses, local need will determine the question in favor of a few turbines, at least, devoted to continuous currents, although much local work will probably also be done with alternating currents.
The number of phases.
I believe that most engineers will admit however, that the alternating system is the only one adapted to very great distances and the recent advances in its use, especially the invention of the Tesla or multiphase motors and their European success, have reduced it to a practical and commercial state. The system, however, is in its infancy and the next ten years will see it pass to a far more practical stage than it is in now. But I believe that even at present you may so design the system as to allow for future advances especially as there will be more change in the motors than the dynamos.
First, as to the number of phases to be used. For the
Tesla motor the smallest number is two and, with properly designed motors, there is no theoretical value. It is to be remarked, however that only slight changes are needed in the dynamos to adapt them to either system. The three phase system is theoretically nearly the same as the two phase system but has reached the point of greater commercial success than two phase owing to its use abroad. I see no reason, however, for believing that the three phase system is really superior to the two phase when equal talent is used in the designs. This is Brown's opinion also and he has great experience with both.
In some respects three phase systems presents greater complication, especially in the measurement of the power used by the customer. Electric lighting by the three phase plant has also been a source of some trouble although I believe this can be arranged satisfactorily, especially as dynamos may be set aside for this purpose alone. The recent lamp of Siemens with three filaments, one for each phase, may also be of use with this system.
As to the choice between these systems, I believe it should be made only after the designs presented have been studied as they seem to be almost equal of merit. Under all circumstances synchronizing motors will probably be used for large powers and these will work equally well on the two phase system as on any system depending on a greater number of phases.
The only difference will be in the small motors which are a secondary consideration and even here the two phase motors can be made to work as well as the three phase. As to the three phase system I understand that the three phase system is more hampered than the two phase system as the Oerlikon company, claims that there is a patent on the three phase transformers well as the motors, again, the Oerlikon Company does not guarantee that the Cataract Construction Company shall not have patent difficulties in using three phase motors in this country.
Furthermore the three phase system is more complicated in its connections and less flexible than the two phase. There is a patent in this country on the three phase dynamo used with their wires but I believe none on the two phase dynamo. Although I believe neither system can be put in without more or less trouble especially about the motors.
(A) Synchronizing Motor.
The most important motors of large size will probably be synchronizing motors working with two or three phase current. In this case the driving power is nearly constant which is not true for the single phase motor. It is not necessary to consider the different varieties but only determine the proper frequency of the alternations. The best period of the alternations is difficult to determine as they work very well at all reasonable periods. The lower limit, however, is definite and is fixed by the proper velocity of a four pole motor. Calling this 2000 revolutions per minute for small motors and 1200 for larger the frequency is 33 1/3 to 20 periods per second. Below this the machine will run slower and must be made more large and costly for a given output. Above 20 to 30 periods the number of poles for the larger motors is increased as the period increases but without increased expense of any moment. The greatest difficulty about such motors is to find the proper method of starting them, as none of them will start itself without load. Hence they are to be used for line shafting and they do not have the great advantage of continuous current motors of starting under load and of thus being used for machines which require constant stopping and starting. The synchronizing motor, however, runs with the constant speed of the turbine and can be attached to the machinery by a friction clutch for stopping and starting, care must be used not to throw the load on so suddenly as to put the motor out of step.
Synchronizing motors can be started in a variety of ways. 1st, by continuous current.
(a) The Schuckardt-Westinghouse motor which is the same nearly, as that of the General Electric Company and claimed by Bradley, can be so started directly by a continuous current.
(b) For any synchronous motor a Commutator on the motor several other ways can be devised.
(c) In motors having continuous current dynamos for operating the field, the dynamo can be used as motors for starting.
The continuous current is to be obtained in different ways according to the circumstances.
(a)It can be sent direct from the primary or secondary stations. In some cases the electric light wires can be used for carrying it. In others, one pair of the main wires can be switched off for use with a continuous current while one of the two phase alternating currents is on the other pair. When the motor is started, a telegraph signal can be sent to switch off the continuous current and throw on the other phase of the alternating current. This might be done at a given hour each morning and at noon.
(b)In a large establishment a current transformer of a small size could furnish continuous current enough for starting motors in the whole establishment. During the day the continuous current could be used for cranes, elevators etc. which can only be worked successfully with continuous current.
SECOND; By alternating current motors of the Tesla type or those of Stanley and others.
(a) The Schuckardt-Westinghouse motor starts under no load by the Tesla principle and runs forward until it becomes a synchronizing motor. Sometimes, however, there is difficulty about it with higher frequencies than 30 to 50 and after starting I do not think it makes as good a motor as one specially designed for that purpose. As it is yet new, however, I believe it will finally become a valuable motor.
One great difficulty about it is the immense current required to start it. The drain of current from the wires will be apt to stop other motors from working under load on the same wires. The Westinghouse Company have a special device to get over this difficulty. Although I believe it is best to start it with continuous current. A small motor of this type in a large establishment could furnish continuous current for starting all the other larger motors and for the use with elevators, cranes etc. as suggested above.
(b) Other synchronous motors can be started by small Tesla motors having about 5 to 10 percent of their power. The use of these motors can be specially designed for each case so that one small motor may start several larger ones. Altogether I believe there will be no trouble in starting the synchronous motor when the time comes for it.
B TESLA MOTORS
The great defect of these motors is in the starting as they take an immense current from the wires which are apt to affect other motors on the same wires. Furthermore the starting torque is not great without this immense current.
By the special devices of putting resistance in the coils, the performance is improved, other devices are also known. As the frequency is lowered the performance is also better. When, however, the frequency 35 is reached the small motors will generally have to be made larger and hence 30 or so may be considered the lower limit of frequency. As the period of 60 I have private information that a 10 horse power motor had a starting torque of three times that at its full speed. This is entirely sufficient to start any machinery from rest. Tesla also says that the motors run very well at the 40 to 60 periods per second and this agrees with my own observations. Altogether, taking into account of future progress, I scarcely believe it is necessary to go low in period for these motors. There is no reason of theoretical natures why they should not work at any reasonable high frequency and Brown and the Oerlikon Company have selected 40 to 60 cycles as being the best for all purposes including with the Tesla or multiphase motor. At these frequencies they promise a good starting torque and perfect action. When once the frequency is settled, inventors will soon get over any small practical difficulties in carrying out the theory.
C MOTORS WITH LAMINATED FIELD.
These have been used as toys to run fans but have never reached the stage of commercial success in large sizes. They require such a abnormally low period that they can scarcely be used with the other motors mentioned except in small sizes. The future may see them successfully in the smaller sizes but I scarcely think they will be much used in the larger sizes. At least they cannot be considered as in the commercial stage at present.
D CONTINUOUS CURRENT MOTOR
Used as alternating current motors by attaching four rings to the commutator. Mentioned above as the Schuckardt, Westinghouse, Bradley motor.
This was exhibited by Schuckardt at the Frankfort exposition. It is also the same as that of Westinghouse and the General Electric Company who claim it as the Bradley patent.
This type of motor has features which recommend it. In the first place it will start itself as a Tesla motor and get up its speed until it becomes a synchronous motor. For this purpose the load must be thrown off until synchronism has been attained. For this method of using this motor in the large sizes, a low frequency of about 33 periods per second is best as the starting torque is greater than at a period of 50 per second for small sizes up to 1000 h.p. 40 or 50 is suitable. Even in this case the current required for starting is immense and the starting of a motor will very likely influence and perhaps stop other motors working from the same transformer.
Only the starting of the motor depends on the Tesla patent and the method certainly is defective. Quite as good a method would be to start by means of a continuous current and get rid of the Tesla patent altogether. But the Bradley patent probably still holds.
This continuous current can be supplied by extra wires from a local station near by, the wires being used at night for lighting purposes as mentioned above.
Indeed, in a large plant, a certain amount of continuous current will be desirable for other purposes. In this case the continuous current can also be used to start the other motors which may be of the above type or any other synchronizing variety.
BRADLEY AND BROWN MOTORS.
Two most interesting machines for a single phase currents have been recently invested by Charles S. Bradley and by C.E.L. Brown. They both will start from rest and run forward until they become nearly or quite synchronous motors. Brown even claims that his motor will start from rest under load, the initial torque being three times that when running under load. As far as I can see from a casual glance these are most important additions to a list of alternating current motors.
This motor, which I saw working in Pittsfield, seemed to have excellent qualities. Irrespective of patent difficulties the weak point seems to be the condenser which needs time to determine whether it will last or not. The motor started from rest under load and acted in a very satisfactory manner.
Westinghouse and the General Electric Company propose to use the motor described above as the Schuckardt, Westinghouse, Bradley motor as a current transformer. To start it by the Tesla method requires a rather low frequency of about 30 to 50 per second, but it can always be started by a continuous current, this seems to be of little consequence. Furthermore, when started by the Tesla method, the drain from the wires is so great that other motors running under load may be stopped. The Westinghouse Company, however has a device for obviating this. Again, the continuous current coming from it has always a potential about 40% higher than the alternating current; this necessitates a stationary transformer before the current enters the machine. Not only does this add to the cost but there is a loss of efficiency.
Furthermore, in many cases where very low potentials are needed and the conductors are thus very large, the other form as described below seems better adapted to the case. Neither is this form of transformer adapted to a very high potential currents. The ordinary current transformer consists of an alternating current motor driving a continuous current dynamo. In this case the line current comes in directly on the motor thus doing away with the stationary transformer.
Other forms of current transformers in which a rotating Tesla field acts on a stationary continuous current armature have been designed and I believe are in limited use. Undoubtedly the future will show immense advances in this subject.
The efficiency of transformers at different periods is a matter of simple calculation. At the same time the subject has been experimented upon by practical men. The outcome of the whole investigation is that the size and cost increase very much with low periods. In order to prevent this as much as possible the magnetization of the iron must be increased as the period decreases. But this cannot be continued for a long distance because we approach the point of saturation of the iron. Indeed I have recently shown in the July number of the London Philosophical Magazine that a large increase of magnetization of the iron is very objectionable as it often distorts the curves of current and electromotive force in an alternating current with great damage to the working of motors.
To be continued: The next eleven pages discuss the transmission to Buffalo. Here he is pushing his design. At some point I will type these pages but for now the final three pages of that section are reproduced.
Here again the best results came from using 1OOO to 2000 volts direct from the machine although one transformer and 2000 volts gives clearly as good results as 1OOO volts direct.
From these results is seen the immense advantage of obtaining a high potential direct from the machine. However, if too high is obtained the greater liability to break down will counterbalance the other advantages.
The proper potential:
If a dynamo can be constructed to give 10,000 or 20,000 volts direct, without transformers, the advantage would be great in the way of avoiding one set of transformers. Three machines of this nature have been presented for competition, one from the Oerlikon Co., one from Brown and one from Prof. Forbes. All these have defects which I scarcely think can be overcome in this type of machine. I believe it is not desirable to attempt such a construction as machines of lower voltage can be made much more hardy and robust, so that repairs shall be needed only at very long intervals. Indeed a properly constructed dynamo should give no more trouble than the turbines.
When transformers are to be used for a distance, the voltage need then be only sufficient for local work with a maximum of 1OOO to 2000 volts when the coils are in series.
This voltage is sufficient to reduce the current to about
900 to 10OO amperes in each of the two phase circuits and this avoids all serious "skin effect" in the conductors at a period of 30 to 50.
This voltage is also sufficient for economical transmission to a distance of a mile or two and is low enough to avoid much trouble, which enters at higher voltage.
The coils should also be so constructed that they can be connected for lower voltages to be used for very near points, although the amount of wire for the transmission then becomes a very great source of trouble.
The exact determination of the potential to be obtained from the machine rests upon the cost of transformers and the type of dynamo.
Where the armature of the dynamo revolves, the evidence points at 800 volts as the maximum, which it is very desirable to obtain from the dynamo direct, although I think 1500 should be attempted. Where the armature is stationary and the magnets revolve, the potential can be increased to as high as 6000 volts, according to Brown. This type of dynamo is not so desirable, however, mechanically. But the fact that the Oerlikon Co. and Brown have offered machines of this type and are willing to guarantee them shows that they are capable of being made in a, substantial manner with the modern method of casting steel. Even for use with transformers, the immense wires required for 800 volts are a great objection which would be obviated with l6OO volts.
Perhaps the best way of putting the question would be to say that for local work, of two equally good and robust dynamos of equal mechanical excellence, and with equal guarantees, the one giving 1600 volts direct would be worth from $10,000 to $30,000 more to the Cataract Construction Company than the one giving 800 volts.
As to the Buffalo transmission, I believe that no attempt to get the 10,000 or 20,000 volts direct from the machine should be made. All electrical engineers are agreed that such potentials should only come from transformers.
It is quite possible to make the transformers to connect up for either 10,000 or 20,000 volts,
I would advise that they be made in this manner so that the selection between 10,000 and 20,000 volts can be made after the apparatus is in working order and that this be put in the contract.
The potential of 10,000 volts could then be used until there was a call for more power in Buffalo when it could be increased from 7600 h.p. to about 9000 by simply by raising the potential from 10,000 to 20,000 volts.
By that time experience would have given facility in the use of high potentials and 20,000 volts might be as successful, as 10,000 volts will be at first.
These figures are based on the use of a line with about 500,000 Ibs, of copper for the double circuit for10,000 h.p.
This is to be determined by the following considerations:
A The proper working of arc and incandescent lights.
B The proper working of motors and their suitable speed to give economy in size and cost.
C The proper working of transformers and their economy in size and cost.
D The formation and maintenance of a proper curve of electromotive force.
E The proper simplicity of the system throughout.
Among the minor considerations are the so-called "skin effect" and the "Ferranti effect".
To run arc and incandescent lights successfully requires a frequency above 40 periods per second. As the frequency becomes greater than this the lights not only work better but the size and cost of the transformers become less and less. However, as the frequency becomes greater the dynamos become more difficult to build, the currents begin to leave the center of the wires and pass to the outside and the current becomes gradually useless for the running of motors. These considerations have caused the limits of frequency to be 36 for the lower limit and 150 for the higher in ordinary practice.
There can be no doubt that many motors work best at the lower frequencies and it may be well in the present case, where the transmission of power is the primary object and where lighting is more or less a secondary consideration to consider the effect of a very low period.
For arc lighting, over 40 periods per second is necessary for the best effects. For incandescent lighting over 30 per second is necessary for a pleasant effect on the eye: less than this is very trying.
Hence, if a period less than 30 is adopted, all lighting must be either done by separate turbines and dynamos or motor-transformers must be used at s greatly increased cost and a greater liability to break down from greater complication of the system.
If a motor-transformer is to be used at Buffalo for the lighting it would scarcely pay, as compared with steam. At first, the lighting is to be a very important factor, and will remain so for some time.
As to the motors, the synchronous type works well at all moderate periods, but if the period below 20 is used these motors cannot revolve at a speed above 1200 per minute. This is proper for about 30 to 50 h.p. below which the motor will not run fast enough, and consequently, must be made larger and more costly for the same work.
The Tesla motor type runs practically at the same speed as the synchronous motors. These motors in small sizes run as high as 2500 revolutions per minute but in sizes of about 5 h.p., a very good speed is 2000 per minute.
Here Rowland gives a table of frequency verses speed of the motor with 8 1/3 cycles producing 500 rpm, 33 1/3 cycles 2,00 rpm, 42 2/3 cycles 2,500 rpm, and 50 cycles 3,000 rpm.
It is seen that the speeds of motors at a frequency of 8 1/3 is entirely too low, except for motors of about 200 or 300 horse power and over, and entirely unfit for sma1ler motors, At the other periods, a proper selection can be made to accommodate both large and small motors. It seems to me that the period 41 2/3 gives a better selection than 33 1/3 but this is a matter of opinion only.
As to the starting torque of Tesla and multiphase motors, it increases with lowering of the period. With a resistance in the closed coils, the torque is quite sufficient at a period of 60 and more than sufficient at 30 or 40 periods per second.
Motors of the laminated field magnet type have speeds independent of the period but they are not yet a commercial success, and some persons who thought they promised well have given them up as nearly or quite hopeless, except in the very smallest sizes.
The cost of buying transformers we have found to be about $5 per horse power for a period of 40. At 8 1/3 the cost may be estimated at from $10 to $25 per horse power. I scarcely think they could be built for lese than $15 to $20 to be satisfactory in every respect.
This alone makes the higher frequencies very desirable.
The curve of electromotive force is also generally better at a high frequency than a low one.
Weighing the evidence and striking a mean value to balance the conflicting claims, it is my decided opinion that the proper period is either 33 1/3 or 41 2/3. Ignoring arc lighting direct from the machine and the increased cost of transformers, one might choose the first as allowing slightly larger current transformers of the special type to be built. But it is somewhat a matter of experiment as to how useful these will be, as they have certain defects pointed out above, and will in many cases be replaced by the ordinary form consisting of an alternating motor driving a continuous current dynamo, or the new kind of stationary current transformers which seem to me most promising, being independent to a great extent of the period. However, in small sizes the difference between 33 and 41 will scarcely be noticed for this type while the other motors will be almost indifferent to this slight change. One great defect of this machine is the fact that it is greatly hampered by patents owned by different companies, so that no one company can insure the Cataract Co. its use without fear of injunctions against its use.
Probably quite as much current will be used in arc lighting as will be transformed into continuous current by this special machine, since other methods are coming into use every day and the other types of current transformers work quite as well at a period of 41 as at 33.
For the sake of simplicity in avoiding motor transformers for arc lighting and an increased size of ordinary transformers, I recommend the period of 41 2/3 as the best, and 33 1/3 as the next best.
Cataract selected 25 cycles because they thought that running the large motors for the production of direct current would start better at the lower frequency. Lighting using alternating current was not used from this station. A very large portion was converted to DC for use locally.
Page 43 is missing or was never in the draft.
THE ALTERNATING CURRENT DYNAMO
a. Magnets and centrifugal forces.
The magnetic attraction of the armature for the magnets is in the neighborhood of 100 lbs. more or less to the square inch. The poles of the various designs vary from 200 to 500 square inches in area though one design contain 1000 square inches The pull or these poles thus varies from 20,000 lbs. to 100,000 pounds for each magnet. The various pulls are usually balanced but the accidental short circuiting of even one magnet may cause a strain of 10 to 50 tons and if several are involved, the amount may be serious.
In the case of the armature revolving, the force will simply tend to draw it to one side without destroying its balance. When, however, the magnets revolve, any partial short circuit might draw a given magnet to one side and so throw the part out of balance that its destruction might be accomplished by centrifugal force.
This is a possible but not a probable accident and it would be most apt to occur in the dynamo of Brown with bell shaped revolving magnets.
In the bell shaped armature of the Cic. D'Ind. Electrique no such action takes place as there is no magnetic pull on the armature, all the north poles being inside and the south poles outside.
b. The force on the wire of the conductors.
The constant stress at the circumference of the dynamo is about 20,000 pounds for 5000 horsepower more or less according to the diameter of the armature. About half the conductors are under the poles at one time. Hence, on each conductor the force may be 200 pounds for 200 wires or 333 pounds for 120 conductors. At the same time the centrifugal force is about 100 times the weight of the conductor. If there were no other reasons, as there are, the magnitude of these forces on such weak material as copper render it almost imperative to enclose the conductors in grooves in the armature iron. This construction also obviates eddy currents in the copper.
These facts explain why nearly all modern dynamos are made in this manner although there are also other reasons.
c. Revolving parts
The centrifugal force on the revolving parts near the rim may be taken as about 100 times the weight of those parts. This produces a stress on the armature section of about 1 ton to the square inch or on the rim holding the magnets of about 4 tons to the square inch not taking the spokes into account.
Each magnet coil, possibly weighing 1OOO pounds, would then try to fly off from the revolving magnets with a force or about 100,000 pounds more or less.
A modern steel casting for the revolving magnets as in Brown's design might withstand these forces but the disastrous effect of even one dynamo giving way which might cause the whole 20 to explode makes one very cautious about recommending any dynamo in which this is possible.
This power station was built with 10 units. Perhaps they were planning for more in 1892 or Rowland was wrong in his draft.
An armature built up of thin plates each of which can be inspected, laid up so that five solid plates to one joint shall be the proportion in each vertical section, and with six nickel steel bolts in each plate would make a structure as rigid as wrought iron and less liable to explode than any steel casting.
For this reason alone I recommend that the armature and not the magnets revolve although in this way some electrical advantages are sacrifices.
The units were built by Westinghouse with magnets revolving around the fixed armature.
d. The vibrations of the system.
Should the dynamo be rigidly attached to the turbine shaft and the time of torsional vibration of the system be that of revolution or of any periodic force acting on the coils the vibration might be so intense as to destroy the shaft altogether. Even a near approximation to the period of revolution, provided the time of torsional vibration is less than that of revolution, will make a vibration as the turbine gets up its speed.
In the present case with a heavy armature of large diameter there will be no trouble. A Rafford Coupling would partially cure the defect if it existed but I believe the weight and diameter of the dynamo should not be made too small even then. Steadiness of running demands considerable size and weight. Your engineers will however, attend to this.
Another kind of vibration comes from the action of the coils on the magnets. When only one current is taken from the machine the tremor may be intense at a very low period such as 5 or 10 per second and this would also occur in single phase motors. At a period of 30 to 50 the effect is too small to notice as the effect decreases as the square of the period increases.
The third variety of vibration due to unbalanced parts is too familiar to mention.
e. The frame.
Two principal styles of frame have been offered to us one with both bearings below the revolving armature or magnets as given in Brown's design.
Although the magnets form the revolving portion in Brown's design, it is evident that the form of frame he gives might be used with a revolving armature as well. In this case the armature and shaft could be quickly removed by the traveling crane and replaced by another while the first was repaired.
This would be a great advantage provided there were frequent breakdowns. As it is, the dynamos should give very little trouble, indeed no more trouble than the turbines.
In this case, therefore, the superior steadiness due to an upper bearing may be availed of as in the designs of the Oerlikon Co., the General Electric Co. and the Westinghouse Co.
In the designs of the first two, the upper bearing is held by a spider. The arms of this spider are straight in the Oerlikon designs and in the last one they are also horizontal thus holding the bearing rigidly against the lateral vibration and making an excellent and stable support.
The arms of the spider in the design of the General Electric Company, however, are curved in a vertical plane forming a weak and unstable support for the upper bearing. The upper bearing in the design of the Westinghouse Co., however, is supported by a solid cast iron dome rising to some height with windows in the side to allow men to enter. The great height of the dome allows the armature to be raised for repairs. Such a dome affords a noble and rigid support for the upper bearing quite equal to that in the Oerlikon design and vastly superior to the curved ribs in the General Electric design.
The lower bearing of the General Electric Company is supported by a spider with straight arms cast with the general frame. In this it is similar to the Oerlikon design. The details of the General Electric design are not given but it looks as if the collar on the shaft below could not pass up through the hole on account of the ball bearing. If the latter were made in parts and bolted together this might be accomplished.
The Westinghouse lower bearing is supported in the same manner as the other two with this exception: the spider can be removed leaving an opening about 8 ft, diameter for lowering or raising of the main shaft and its parts without removing the main magnets.
The Westinghouse plan is the only one having this important point.
In some of the Oerlikon and General Electric plans the lower bearing is not shown.
A photograph from the General Electric Company shows a lower bearing fitted to a beam imbedded in the brickwork. This seems to me a very poor arrangement as it is very necessary that the armature should run truly within the magnets and, for this reason alone should be rigidly supported by the frame. Again, a rigid beam with its ends in the masonry of the turbine well would probably interfere with the removal of the parts of the turbine and it's shaft. As I have not the details of the turbine I can only suggest this difficulty as having a probable existence.
The General Electric Company also presents the plan of a two story dynamo with the upper bearing sustained by a spider resting on tall pales of iron. Of course such a design is not to be considered seriously.
f. The bearings.
These should be long and carefully designed for adjustment and supply of oil.
In some of the designs of the General Electric Company the upper bearings are decidedly too short.
The bearings on the Westinghouse and Oerlikon designs are long and apparently carefully designed though I must leave the final criticism to Dr. Sellers.
g. Accessibility of Parts.
1st: The Bearings.
The upper bearing is equally accessible in all the plans although the mounting of the exciter above this bearing in the Westinghouse plan somewhat interferes with approach to it though not seriously. The lower bearing can also be approaches from below in all the designs.
2nd: The turbine shaft and well.
The Westinghouse plan is the only one which has the lower bearing supported on a removable spider which, when the armature is removed, can be taken away and leaves a clear opening of about 8 ft. diameter into the turbine well.
In all other cases the whole dynamo must be removed from its foundations.
As to the size of opening needed for lowering and raising the parts of the turbine I cannot say, not having the plans. A little change in the design of the Westinghouse Co. might possibly give sufficient room for this without removing the dynamo foundations.
3rd: The armature.
In Brown's plan the revolving parts can be removed entirely giving free access to the magnets and armature. Indeed new revolving parts could readily be put in while the old are being repaired. For a high potential machine this would be most valuable but for low potentials, repairs will be so seldom needed that this properly becomes less valuable.
Next to Brown's design comes the Westinghouse closely followed by the General Electric and Oerlikon Cos.
For low potentials possibly the armatures are sufficiently accessible in all the designs.
The facility of removal of the revolving parts differs greatly in the designs.
In this respect Brown's design stands preeminent.
In all the others the upper spider or dome must be removed together with the support of the lower bearing.
This the Oerlikon and Westinghouse Cos. have provided for.
In one of the General Electric plans there is a fly wheel just beneath the dynamo.
It is so supported by a collar on the shaft that it is impossible to remove it without removing the whole dynamo from its foundation. The armature can only be removed by the above process or by removing it from its shaft which is usually a difficult tedious and troublesome process even where special appliances are at hand.
In the design of the General Co. with lower bearing, judging only from the details that appear, the shaft with collar below cannot be removed at all. Whether this is a piece of carelessness or details are wanting, I cannot say, but am inclined to the former view.
4th: So many details are wanting that I cannot well judge of the accessibility of the other parts.
The ventilation of the armature has been provided for in the Oerlikon, Brown and General Electric designs. I see no provision for this in the Westinghouse designs. Possibly they consider that the superior strength of an armature built up without openings more than compensates for any gain from ventilation.
This is a point on which there might be great difference of opinion and I can scarcely decide. If an armature can be built to keep cool while solid, so much the better. If this cannot be done, let it be ventilated.
The guarantee as to heating will cover this point and it can be safely left to the maker.
The artificial stream of air proposed by the Oerlikon Go. will scarcely be necessary especially as the enclosing of the whole dynamo in a sheet iron jacket renders it less accessible and hides it from view when an accident happens.
i. Beauty of design.
In this respect the Westinghouse plan stands preeminent, the whole design showing graceful outlines and beauty where most of the others reveal no attempt to please the eye and several are almost repulsive from lack of artistic training.
j. Strains due to heating.
The armature when heated to 40 C. is expanded in diameter about 1/20 inch. When this takes place slowly the arms are also heated: when the heating is rapid, strains will be introduced into the armature and its arms. The Westinghouse Co. proposes to obviate this by shrinking the laminated armature over its supporting wheel. The success of this method is problematical.
B. The Electrical Design.
a. The armature in general,
This is now practically the same in all the designs, the only difference being in the shape of the conductor openings and in the revolution of the magnets or the conductors.
For electrical reasons the revolution of the magnet, is the best but, for mechanical reasons, the revolving armature is the safest as I have already shown.
b. The windings
The designs differ greatly in the number and shape of the openings and the number of conductors. The fewer the conductors and the larger the openings the more copper can be used in proportion to the insulation and with proper form of poles the current curve can be made very good even with very few conductors.
Furthermore, when the conductors are buried in the iron there are practically no eddy currents even in the largest conductors.
The shape of the conductor opening should be narrow and deep with the face cut away as in most of the designs.
The Oerlikon design with round bars is to be avoided.
The number of windings in each groove differs also. It is easy to obtain 1500 volts on a two phase dynamo with only one conductor in each groove.
Yet the Westinghouse Co. places two conductors in each groove to obtain only 800 volts.
The objection to two conductors in a groove is, in the first place, that more space is taken up by the insulation and so less copper can be placed in it; In the second place, repairs are more difficult as two sets of connections have to be broken and made again and one set of wires is apt to be on top of the other set.
I am decidedly of the opinion that the conductors should be large and few in number, being straight, flat bars of copper. The connections at the ends should be made by screwing other bars of copper to them so securely that no motion can take place and then soldering the joint. By this means every scientific requirement is satisfied and the facility for repair is far greater than with two wires in a groove.
In this respect the General Electric Co. plan seems to me to be the best although the details of their connections are absent.
It may be said, however, for the Westinghouse method that fewer soldered joints are needed and the flexible cable is more easily handled by the workmen. However, their method seems to leave no chance for connecting up the dynamo for giving two or more potentials.
c. The Curve of Electromotive Force.
The details of the shape of the poles are, in general, wanting, but enough remains to form some idea as to this matter.
For the transmission of power this is a most important subject and must be carefully studied in the present case.
The machines of Brown and the Westinghouse Co. show that some attention has been given to this matter while the Oerlikon and General Electric designs would give a poor result in this respect.
Indeed the General Electric Co. says that its curve is somewhat flat, their attention having been called to it by me, and yet they do not seem to mind it.
There is but one perfect form and that is the true sine form and all others indicate waste.
On this subject the Westinghouse Co. has made a very complete study and I consider them far in advance of the others in this respect and they could probably produce a dynamo giving the best current curves of any of the competitors.
d. The Regulation of the dynamo.
This is so intimately bound up with the way the dynamo is used and in all cases is so much a subject of experiment that I would not care to hazard an opinion on the relative value of the designs in this respect. It is extremely probable that there is little difference between them. An exact calculation of the self induction in all cases, together with the magnetization of the webs between the conductors and a few other factors might allow one to judge of the relative merits or the designs in this respect. The value of this process would be doubtful and I have not attempted it. I hope to work out a complete theory of this subject before long.
e. The material and lamination of the magnets.
The magnets should be made either of wrought iron or soft cast steel and not of cast iron. The Westinghouse Co. makes the magnets of laminated wrought iron cast into a cast iron or steel frame. The General Co. bolts the magnets to the frame and saws the poles up a little way to approximately laminate the ends.
Both constructions are capable of good results although the low period to be used at Niagara the heating of the field magnets will be greater than with a high period and the more perfect lamination of the Westinghouse Co, would probably give somewhat the best results.
f. The Insulation.
This is now usually of mica for the important parts and can well be left to the practical experience of the makers,
HEATING OF ARMATURES AND CHOICE OF DIAMETER OF ARMATURE.
In examining the designs I made a large number of calculations of the hysteresis and current heating. Finding the coefficient of heating (that is the heat per square c. m.) very nearly the same in very different designs, I made a general calculation to find the general loss so as to guide me in selecting the proper proportions and size of the dynamos. This led to some curious laws as follows:
Taking the cooling surface as only the inner and outer sides of the armature ring and not allowing the upper and lower side and for ventilation, I find the following:
A. The coefficient of hysteresis heating with constant magnetization and speed of turbine is independent of the number of poles and the vertical depth of the armature ring, but is directly proportional to the diameter of the armature.
B. The coefficient of current heating diminishes somewhat with increase of vertical depth but in a far greater ratio with increase of diameter.
It would seem from this that vertical depth adds very little to the efficiency or an armature because the hysteresis coefficient remains nearly constant and the coefficient of current heating is only slightly decreased.
Increase of diameter increases the coefficient of hysteresis heating in proportion to the diameter while it decreases the current heating as a very high power of the diameter depending on the change in size of the copper as the diameter increases.
From these laws dynamos of different diameters and all of the same horse power have the following properties:
Large diameter, great hysteresis heating and small current heating.
Small diameter small hysteresis heating and large current heating.
The calculation of the designs confirm these results, especially showing that great vertical depth is not needed in armatures. Thus the deep armatures of the Oerlikon Co. will work no cooler than the narrow armature of Brown of a slightly larger diameter.
In these large machines of 5000 horse power, the hysteresis is about equal to the current heating at a diameter about eight ft and a depth of 3 ft. These dimensions varying with many other factors, however.
By making the diameter 10 ft. the coefficient of hysteresis heating is increased about 25 per cent., but the coefficient of current heating is decreased more nearly in the proportion of 2 or 3 to 1. Hence the depth can be greatly decreased without heating the dynamo too much.
The first dimensions apply nearly to the General Electric design while the last is a little larger than Brown's design, the depth of the armature being only 23 in. against 36 for the General Electric design. The Westinghouse design comes between the two but very near to the Brown design.
The following figures show this result, those for the General Electric design being from the companies figures:
First number is hysteresis and second is current heating.
General Electric 25000 Watts. 25000 Watts.
Westinghouse 27000 1OOOO
Brown 31000. 6000
These figures show the above law of diameters but the calculations could only be made approximately on account of the lack of complete data.
However they are sufficient to allow a choice of diameter.
As far as we can judge from these figures and not allowing for ventilation of armature, all these dynamos will work very nearly with the same rise of temperature. At half load or no load the Edison dynamo would have some advantage but not even I think to counterbalance the increased resistance due to so small a diameter and great depth.
I am inclined to favor the dimensions of the Brown and Westinghouse machines as being the best.
The Oerlikon designs, as I stated before, have too great depth of armature.
CURVE OF CURRENT AND ELECTROMOTIVE FORCE.
This is most important for the transmission of power. A poor current curve causes greater heating in conductors especially the closed conductors of Tesla and multiphase motors and makes them work very poorly.
This subject is so new that it is but little understood. I find that the Westinghouse Co. is far in advance of the others in the study of this subject although even they have much to learn on it.
The General Electric Co. has made a complete error on the proper shape of the current curve.
The true shape should be as near a sine curve as possible.
The curve of the dynamo of the General Electric Co. is very flat and this is a feature very difficult to cure in a three phase machine.
It can be partially remedied by making the pole faces of the dynamo narrower but they need to be very narrow in the case of a three phase machine which considerably increases the hysteresis heating in the dynamo.
In small dynamos at a high period the curve gives little trouble, being nearly always a sine curve.
But in large dynamos and a low period the trouble will increase and will need serious attention.
The company best prepared to deal with this question is the Westinghouse Co. as they have already commenced to study it.
Throughout my report I have criticized the special features of the designs. In this portion I have collected the main points with a view to summing up the evidence.
Brown Boveri and Co.
In this dynamo the magnets revolve within a stationary armature. The potential is 3000 volts.
The principal features of this design are the light weight of the revolving parts and the frame, the whole being only 40 tons, and the peculiar distribution of the bearings, both being below the revolving magnets.
The peculiar bell shaped revolving portion is objectionable but is easily altered by lowering both bearings.
The great advantage of this design is the ease with which the revolving portion can be removed for repairs.
Were the armature revolving, this advantage would be greater as a new armature could be put in while the old was being repaired.
The light revolving parts seem to me objectionable as a fly wheel would probably be needed.
The light frame also seems objectionable as a heavy one is needed to take up the vibrations.
The reputation of Mr. Brown is so great that he would undoubtedly carry out the present project with success.
The objection to employing him rests in my mind upon three facts:
1st The patent difficulty, although this would apply most to the motors which might he obtained elsewhere or the patents avoided by transforming to continuous currents and using current motors for small powers.
2nd The price of his transformers are higher than they might be made for or obtained in this country.
3rd The great advantage to the company to be in amicable relations with one of the great electric companies here.
The Oerlikon Co.
The number of designs from this company is so great that, although I have examined them all, I shall treat them together. Dynamos both with revolving armatures and revolving magnets are shown.
The general features of these designs show great constructive ability and, although I see some features not very desirable, the main mechanical points are excellent. The electrical design, however, does not seem to me so good.
In the first place, the proportion of the parts does not seem so well designed as in the other cases, all of the Oerlikon plans being characterized by great vertical depth to the armature which I have shown in the portion treating of the heating of the armature to be useless. Indeed it is detrimental because it makes a machine with great self induction and poor regulation.
The conductors in most of the dynamos are round cylinders which are not so good as flat bars.
Then again no attention whatever has been paid to the curve of electromotive force which is very flat in most of the Oerlikon designs.
Outside of these criticisms the same remarks apply as to Brown's design.
Indeed the Company distinctly states that it will not guarantee freedom from patent difficulties.
General Electric Co.
The mechanical designs of this Company are by far the poorest of all that have been sent to me.
The two-story dynamo with the upper bearing sustained by a spider supported by tall poles in so repulsive to my mechanical ideas that I scarcely believe that it could have been presented seriously after their attention had, I believe, been called to the same faults in a previous design.
Again, in the design with the fly-wheel,- the armature can only be removed by taking it from its shaft, a difficult and troublesome operation especially as the rings for taking off the current have also to be removed. Indeed the armature cannot even be lifted a little for repairs.
The lower bearing is also somewhere below in the shaft which, is a very poor arrangement.
One of the photographs shows a lower bearing on a beam across the turbine well with its ends firmly imbedded in the masonry.
In al1 this no thought has been given to the facility of repairs to the dynamo and to the turbine or its shaft.
To get at the shaft or to remove the fly-wheel, the dynamo frame must be unbolted from its foundation and the frame raised from around the armature and fly-wheel. This leaves the latter upright in the air supported by one bearing below in a very weak position. The armature and fly-wheel are then removed. The turbine well is then cut in two by the fixed beam. Whether there is any room on either side to handle the parts or the turbine I cannot say, as I have not the designs of them. The whole process is most complicated, however.
In another design with ball bearing, it looks as if the shafts with collar below could never be removed as the collar would not slip through the ball and the latter cannot pass up through the frame. Nothing in the drawing or description indicates that the ball is split as no bolts are shown.
Again, I have criticized elsewhere the short upper bearing supported by spider with curved legs.
Altogether the mechanical portion of the plans seems to me crude and ill considered, indeed more the work of an amateur than that of an intelligent and able mechanical engineer.
The electrical designs are much better although I think very little attention has been given to the curve of electromotive force as the statements concerning it are conflicting.
The use of straight solid flat conductors in insulating tubes makes the best sort of conducting system easy to make and repair with the proportion of copper to insulation large.
The details of the connections are not given.
The proportions of the armature give greater depth and less diameter than the Brown and Westinghouse designs. In this respect I believe the proportions of the latter are better than the former.
The system offered by the General Co. is the three phase system. The motors are a direct infringement of the Tesla patents and could only be used at best by a successful piracy.
The line to Buffalo proposed by the General Co. consists of two lines of poles with switching stations. By using two lines only, the amount of copper must be duplicated as no repairs can be made on any pole with live wires on it. By using three lines only 1/2 more copper need be used as only 1 line out of three is out of use at once. The extra line of poles is but a slight expense compared with the savings of copper. The General Electric Co. proposes to expend over $200,000 for copper for 1OOOO H.P. while my estimate in another part of this report is only $100,000.
The period chosen by the Company, namely 41 2/3 allows arc and incandescent lighting to be obtained from the same type of dynamo without motor transformation. I consider this period superior to 33 1/3.
My general conclusions with respect to this Company are that much of their work and many of their plans for machines which are in use have been thoroughly tested are excellent. In the making of new designs, especially the mechanical portions, they seem to have a great lack of talent and I would hesitate most seriously about intrusting an untried scheme to their guidance. I believe they could carry out any design intrusted to them under the guidance of an expert electrician and mechanical engineer but that they would make some serious mistake if left to themselves and I feel this specially in the case of alternating current transmission of power in which field they have had practically no experience.
Furthermore they offer to us the three phase system, the principal motors of which are Tesla motors, the patent on which is held by another company.
The Westinghouse Company
The main points of the beautiful mechanical design presented by the Westinghouse Co. have already been gone over.
Attractive from its artistic beauty, its sterling qualities grow upon one the more it is studied.
It is the only one presented in which, after the removal of the armature, the spider sustaining the lower bearing can be removed, leaving an opening about 8 ft. diameter into the turbine well for raising and lowering pieces of the turbine or shaft.
In all other designs the well can only be opened by removing the whole dynamo from its foundations.
I see no errors of judgement by which the dynamo would be difficult to put together, take apart, or repair.
Both lower and upper bearings are rigidly supported so that the armature will run truly in the center of the magnets.
The proportions chosen for the armature seem to me very excellent. Avoiding the deep armature of the Oerlikon Co. they have designed one of very nearly the dimensions of Brown's design.
Altogether the design, from a mechanical standpoint, is preeminently the best.
From an electrical standpoint also the design is excellent, the dimensions being so chosen as to secure very good results in nearly all respects.
I believe, however, that the conductors should be changed to solid bars of copper and the machine arranged for giving either 800 or l0OO volts according as it is used on the transformers or on the local distribution. However, there is much to be said for the lower voltage used alone. The period, also, I believe should be changed to 41 2/3, so that the machines may be used for arc lighting, as the small difference between this and 33 1/3 is too small to affect the motors very appreciably.
I believe this Company and Mr. Stanley has selected the period of 33 1/3 in the following manner: For some un-explained reason, the period selected for lighting was originally made 133. One half or this or 66 is used by the Westinghouse Co. and Stanley for power transmission on a small scale. One half of this again gives 33 which they propose to use on a large scale for Niagara. To be sure they give some other reasons but I am confident that, if the period 41 2/3 were selected, they could easily adapt themselves to it. This would solve the problem of arc lighting in Buffalo by reducing the central station in Buffalo to a very small and simple affair and working the arc lights as well as the incandescent lights from transformers in the simplest possible manner. An immense increase of both is to be looked for from this simple system.
No injury will be done to the motor system by this slight increase and the transformers will be cheaper.
Simplicity is one or the most valuable features or any system especially such an enormous one as this.
Altogether I believe that the advantages of employing this Company are superior to those of employing any other, providing proper terms can be made with them.
THE PATENT QUESTION.
One of the principal guarantees on the apparatus should be with respect to patents. There is no trouble on the continuous current system, but it can scarcely be avoided on the alternating system. In the motors especially the patents are distributed among the different companies so that many of the motors and current transformers can scarcely be used without obtaining rights from different companies which it would be almost impossible to do.
Hence the system should be so chosen as to avoid trouble as far as possible, as nothing could compensate for it.
I am not in a position to advise your company in this matter, and can only throw out a few suggestions such as I understand the matter. My statements should be verified by other means, such as inquiries of the companies concerned.
Take the two-phase system.
I suppose the dynamo, transformers, wiring, and the use of synchronous motors to be free from patents.
The Tesla, motor patents belong to the Westinghouse Co., but their validity has been disputed. Elihu Thomson claims the combination of the magnets and closed coils which exist in this motor, while Tesla claims the moving pole. I suppose, however, that the Westinghouse Co. could ensure the use of this motor.
The Schuckardt current transformer and motor seems to be claimed by the General Electric Co. through Bradley's patent, though, while starting in the usual way, it comes under Tesla's patents. I am unable to say who can give the right to use this device. Fortunately there are several other devices to take its place. This machine is valuable and is used on the three phase as well as the two phase systems and it is unfortunate that it is so hampered by patents.
Take the three phase system.
Here the dynamo is probably free. If the current is conveyed away by six wires, this also is free. If however, only three wires are used as is usual on this system and which constitutes the greater part of its value, the device is claimed by the General Co. under Bradley's patent although there seems to be reason to doubt the validity of the patent.
A special form of the three phase transformer is held under German patents of which the Oerlikon Co. is the lessee.
The motors are on the same principle as the Tesla two phase motors and I see no way of getting around his claims, provided they are valid, except by acting the part of a pirate. Under all circumstances I believe there would be trouble.
If the above statement is true, the least trouble from patents would come from the employment of the Westinghouse Co. and using the two phase system or employing Brown and the two phase system so as to avoid the Tesla patent.
The so-called Ferranti Effect, "Wattless Current" etc.
This is caused by the electrostatic capacity of the wires and takes place principally when cables are used for conveying the alternating current to great distances. The effect increases with increase of the frequency up to a certain point after which it decreases, though, with the dimensions usual in such cases, it usually increases with the frequency. With certain relations between the resistance self induction frequency and static induction the effects can be made to vary considerably and some of them to vanish entirely.
This is one of the cases were the complication of the alternating system enters and where an electrical engineer, thoroughly acquainted with theory, is needed.
It is useless to say more about this at present.
So with respect to the next effect called by some "Wattless current" or current which passes in the wires, heating them and causing loss and yet producing no useful work. The more scientific expression is to say that, in this case, the current and electromotive force are not in the same phase.
Of like nature are the harmonic currents.
All these effects make the alternating system most difficult to use except in the simplest cases and I repeat that most careful and scientific engineering will be required where power is to be distributed and sold by the alternating system.
When the period is very high, the electric currents do not occupy the whole area of the conductors but only the surface. In this case there is an increased resistance to current and corresponding loss. In other words a given amount of copper does not go so far and the effect is nearly equivalent to an increase in the cost of copper. For a large horse power like 50O0, the low volt conductors must be large, and it may be well to inquire whether or not there will be trouble from this source, provided the frequency of 50 were selected. At this frequency there is no trouble with conductors of less size than 1 l/4 inch in diameter or1 l/2 inch for a period of 30. The electromotive force of the dynamos will probably be 600 volts or over, and, as the circuit is divided into two or more parts, each wire will carry 3000 amperes more or less, which is easily accommodated by two or three wires of the size mentioned or by proper copper strips of larger dimensions. Indeed I may say with confidence that there will absolutely no trouble from this source at the low frequency of 30 or even 50, although there would be at the highest frequency of 150.
I believe, however, that it would be better to use a dynamo of larger electromotive force, say, 1200 or 1500 volts in which case there would be no trouble at all.
The only effect in any case is to render the copper in the center of the conductors partially useless, and it can always be compensated for by using a little more copper, especially in the station connections.
As to he line to Buffalo there will be absolutely no trouble from this source as the high voltage makes the conductors very small.
Altogether no trouble need he feared in the whole system except one easily and quickly remedied.
1. I advise the use of alternating currents for the Buffalo transmission and as much of the local work as can be carried on by its aid with the use of motor transformers for obtaining a small amount of continuous current for railways, cranes etc.
As time advances and the need of a greater amount of continuous current is felt, it can be met by continuous current dynamos.
Where a supply of low potential continuous current is needed at a distance, it is to be met by transforming high potential alternating currents into continuous currents by motor transformers or their equivalent.
Where a large number of factories within a mile or two desire to run each separate machine or group of machines by a separate motor to avoid shafting, the need is best met by a continuous current dynamo, although the alternating system and Tesla motor will partially fill the need.
With a supply of both continuous and alternating current at the central station each want can be supplied in the best, possible manner as it arises.
This, I believe, will he the final outcome. At present let the most urgent necessity be satisfied by the alternating system.
2. I advise that the dynamo have a revolving armature, not revolving magnets, and that the armature weigh not less than 25 tons. That the diameter of the armature be about 10 ft. and its depth not more than 2 ft.
3. I am most positive and certain that the conductors should be solid, straight, flat copper bars, few in number and not the flexible cable winding of the Westinghouse Co.
4. The dynamo should be made to give either 800 or 1600 volts according to the connections, which should be capable of quick change. As this is a matter of economy and convenience only and as the working of the plant will be somewhat better at the lower voltage, a dynamo to give only 800 or 1OOO volts might be chosen.
5. I strongly advise a period of 41 2/3 with a second choice of 33 1/3 to be determined by further conference,
6. I consider the two phase and three phase systems of equal merit for they each have good and bad points of equal value.
7. The first two sets of transformers for the Buffalo transmission should be of large size, 1700 or 2500 h.p. according as the three or two phase systems are used; they shall be arranged to connect up for either 10,000 or 20,000 volts,
8. The potential for the Buffalo transmission should be 10,000 volts, to be changed to 20,000 as experience is obtained and there is a call for more power at Buffalo,
9. I believe a system of three lines of wooden poles, one of them being extra to allow for repairs should be used, with two or three switching stations to change the current from one line to the other. This is more economical and better than two lines as proposed by the General Electric Co.
10. I advise for 10,000 h.p. that copper to the value of about $100,000 be strung on the above three lines of wooden poles, more to be added as occasion demands. After some experience the advisability of other more solid construction can be determined.
II. I advise that the Westinghouse Co. be employed to do the work under the guidance of an intelligent electrical engineer since their plan for a dynamo is far the best in mechanical design and general dimensions, since the Company has the greatest experience in the practical use of the alternating system and since they seem to control the most important patents especially for the use of the Tesla motor At the same time I do not advise a blind acceptance of their system since all companies dislike to go outside their practice even to obtain something better. Their method of winding the armatures is certainly defective and a few solid bars with properly shaped poles is much better. Again, their period of 33 1/3 is obtained more from taking the arbitrary period of 133 and dividing by 4, according to their practice than from a complete study of the needs at Niagara. I believe the period 4l 2/3 to just take in arc lighting to be the best. These two minor points can be settled by discussion afterwards.
If the General Electric Company is selected, I believe it, must only be allowed to carry out, the making of the dynamo under the guidance of a competent mechanical engineer, and I believe, even then, that electrical mistakes will take place end that there will be great difficulty from the patents on motors. Their experience and knowledge of alternating current transmission is also very limited.
The plans of Brown Boveri and Co. are so meager that I can only speak of his dynamo and the price of transformers
I have already discussed the dynamo and find it has many advantages and some faults. That he is capable of doing the work at Niagara in an intelligent and excellent manner will be acknowledged by everybody. The price of his dynamo is very low, but of the transformers so great as to more than counterbalance the former. It is probable that this Company could put in a two phase plant as far as the dynamo, transformers and synchronous motors are concerned, but the Tesla motors must be purchased elsewhere. The need for small motors might also be met by transferring the alternating into continuous currents and using continuous current motors.
This system would probably be entirely independent of all patents and the future might develop on alternate current motor to replace the Tesla motor.
I believe this system to be entirely practical, although not quite so flexible as when the Tesla motor can be used.
The Oerlikon Company plans I have already considered. The electrical portion and the general dimensions do not seem to me so good as the others. Again, the three phase system is even more hampered than the two phase. I would have less confidence in this company for the electrical portion than either the Westinghouse Co. or Brown and Boverie Co., although their mechanical designs are excellent.