The principal advantages of steam turbines for generating electricity are so well known that they need only be mentioned here:
- Small floor space per Kw. capacity, reducing to a minimum the cost of real estate and buildings.
- Uniform angular velocity, thus facilitating the synchronizing and paralleling of alternators.
- Simplicity in operation and low expense for attendance.
- Entire freedom from vibration, and approximate noiselessness.
- Small oil consumption.
- High steam economy at all loads.
- High steam economy with rapidly fluctuating loads.
- Steam economy is not appreciably impaired by wear or lack of adjustment in long service.
- Adapted to high steam pressure and high superheat without practical difficulty and with consequent improvement in economy.
- Condensed water is kept entirely free from oil and can be returned to the boilers.
- Ability to use steam from any stage of the turbine for heating without the troubles that such use on a large scale brings with compound reciprocating engines.
[Engraving: 500 Kw. Direct Current Curtis Turbine-Generator: original size (6K) | 9x enlarged (47K)]
The steam turbines built by the General Electric Company are based on the inventions of Charles G. Curtis, developed by experimental worlk in Schenectady. Mr. Curtis' general idea is susceptible to varied application; machines of different forms have been built and experimental developments are constantly proceeding. Much of this experimental work is done in Building No. 11 with machines designed for the purpose and readily adaptable to a variety of conditions.
[Photo: Turbine Testing and Framing Shop (Building No. 20) Showing Turbine-Generators from 500 Kw. to 5000 Kw. Capacity: original size (28K) | 4x enlarged (88K)]
Over 250,000 H.P. of steam turbines, to be direct connected to electrical generators, are now on order. Among these are eight 5000 Kw. units for the Electric Companies of New York, Chicago and Boston. The New York Central & Hudson River R.R. has ordered eight units of the same size. The largest turbine yet manufactured has a capacity of 7500 H.P., but even larger ones are in prospect. The enormous demand for steam turbines has resulted in the construction of Building No. 86, devoted to their manufacture. The various floors and galleries of this building have a total floor space of nearly six acres. The different stages in turbine manufacture may be followed here and in Building No. 20.
The commercial steam turbines now being produced at Schenectady are all of the vertical shaft type, and range from 5000 Kw. to 500 Kw. capacity; turbines of smaller capacities, operating with shafts in a horizontal position, are being built at the Lynn Works of the General Electric Company, together with some 500 Kw. and 1500 Kw. vertical shaft machines.
[Engraving: 5000 Kw. Curtis Turbine-Generator: original size (14K) | 4x enlarged (48K)]
Most of the turbines now being built at Schenectady are of the four-stage type. In some of them the valves are operated by electro-magnets controlled by the governor, and others are so arranged that the governor operates the valves without the use of the magnets.
In the larger turbines, the buckets are recast gun metal finished to the proper surface and form. In the smaller machines buckets are cut from steel disks or rings by special machinery designed for the purpose. In machines of smaller diameter, operating at high speeds, steel is in many cases desirable for mechanical reasons.
The generators for steam turbines are necessarily designed and constructed with great care to meet the peculiar conditions of their service. The high speed imposes very great centrifugal strains, and a perfect and unchanging balance is essential. The speed of General Electric turbines is low, however, as compared with that of other steam turbines, making possible the adoption of generators of the most perfect electrical design; in fact, the turbine speeds have, generally speaking, been chosen with a view to obtaining ideal generating conditions. In this respect turbines of the Curtis type have an important advantage especially in the operation of direct current machines when such moderate speeds are particularly desirable, inasmuch as they insure low peripheral speeds for the armature and freedom from sparking or other commutator difficulties.