available+quantity

the quantity of goods available for sale at a given price, and the level of consumer need for those goods at a given price. The balance of supply and demand fluctuates as external economic factors such as the cost of materials and the level of competition in the marketplace influence the level of demand from consumers and the desire and ability of producers to supply the goods. Supply and demand is recognized as an economic principle, and is often referred to as the law of supply and demand.

SUBJECT AREA: Land transport, Railways and locomotives

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Fairlie worked on railways in Ireland and India, and established himself as a consulting engineer in London by the early 1860s. In 1864 he patented his design of locomotive: it was to be carried on two bogies and had a double boiler, the barrels extending in each direction from a central firebox. From smokeboxes at the outer ends, return tubes led to a single central chimney. At that time in British practice, locomotives of ever-increasing size were being carried on longer and longer rigid wheelbases, but often only one or two of their three or four pairs of wheels were powered. Bogies were little used and then only for carrying-wheels rather than driving-wheels: since their pivots were given no sideplay, they were of little value. Fairlie's design offered a powerful locomotive with a wheelbase which though long would be flexible; it would ride well and have all wheels driven and available for adhesion.

The first five double Fairlie locomotives were built by James Cross \& Co. of St Helens during 1865–7. None was particularly successful: the single central chimney of the original design had been replaced by two chimneys, one at each end of the locomotive, but the single central firebox was retained, so that exhaust up one chimney tended to draw cold air down the other. In 1870 the next double Fairlie, Little Wonder, was built for the Festiniog Railway, on which C.E. Spooner was pioneering steam trains of very narrow gauge. The order had gone to George England, but the locomotive was completed by his successor in business, the Fairlie Engine \& Steam Carriage Company, in which Fairlie and George England's son were the principal partners. Little Wonder was given two inner fireboxes separated by a water space and proved outstandingly successful. The spectacle of this locomotive hauling immensely long trains up grade, through the Festiniog Railway's sinuous curves, was demonstrated before engineers from many parts of the world and had lasting effect. Fairlie himself became a great protagonist of narrow-gauge railways and influenced their construction in many countries.

Towards the end of the 1860s, Fairlie was designing steam carriages or, as they would now be called, railcars, but only one was built before the death of George England Jr precipitated closure of the works in 1870. Fairlie's business became a design agency and his patent locomotives were built in large numbers under licence by many noted locomotive builders, for narrow, standard and broad gauges. Few operated in Britain, but many did in other lands; they were particularly successful in Mexico and Russia.

Many Fairlie locomotives were fitted with the radial valve gear invented by Egide Walschaert; Fairlie's role in the universal adoption of this valve gear was instrumental, for he introduced it to Britain in 1877 and fitted it to locomotives for New Zealand, whence it eventually spread worldwide. Earlier, in 1869, the Great Southern \& Western Railway of Ireland had built in its works the first "single Fairlie", a 0–4–4 tank engine carried on two bogies but with only one of them powered. This type, too, became popular during the last part of the nineteenth century. In the USA it was built in quantity by William Mason of Mason Machine Works, Taunton, Massachusetts, in preference to the double-ended type.

Double Fairlies may still be seen in operation on the Festiniog Railway; some of Fairlie's ideas were far ahead of their time, and modern diesel and electric locomotives are of the powered-bogie, double-ended type.

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параллельная система ИБП
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[Интент]

Parallel Operation: The system shall have the option to install up to four (4) UPSs in parallel configuration for redundancy or capacity.
1. The parallel UPS system shall be of the same design, voltage, and frequency. UPS modules of different size ratings shall be permitted to be paralleled together for purposes of increased capacity or UPS module redundancy. The UPSs in the parallel configuration shall not be required to have the same load capacity rating.
2. Parallel Capacity: With N+0 system-level redundancy, up to 2MW of load can be supported by the system.
3. Parallel Redundancy: With N+1 system-level redundancy, up to 1.5MW of load can be supported by the system, and only the UPS being replaced must be isolated from the source (bypass operation is not required for the entire system during the UPS replacement procedure).
4. Output control: A load sharing circuit shall be incorporated into the parallel control circuits to ensure that under no-load conditions, no circulating current exists between modules. This feature also allows each UPS to share equal amounts of the total critical load bus. The output voltage, output frequency, output phase angle, and output impedance of each module shall operate in uniformity to ensure correct load sharing. This control function shall not require any additional footprint and shall be an integral function of each UPS. The static bypass switches shall be connected in parallel.
5. Parallel System Controls: To avoid single points of failure, the UPS system shall have no single dedicated control system designed to control the operation of the parallel UPS system. Control of and direction of parallel UPSs shall take place via a master/slave relationship, where the first UPS to receive logic power asserts itself as a master. In the event of a master failure, a slave UPS shall take the role of master and assume the responsibility of the previous master UPS. Regardless of which UPS is master or slave, user changes to the system status, such as request for bypass, can be done from any UPS connected to the bus and all UPS on the bus shall transfer in simultaneously.
6. Communication: Communication between modules shall be connected so that the removal of any single cable shall not jeopardize the integrity of the parallel communication system. Load sharing communications shall be galvanically isolated for purposes of fault tolerance between UPS modules. A UPS module's influence over load sharing shall be inhibited in any mode where the UPS inverter is not supporting its output bus. Transfers to and from bypass can be initiated from any online UPS in the system.
7. Display: Each UPS multi-color LCD touch screen user interface shall be capable of using an active touch screen mimic bus to show the quantity of UPS(s) connected to the critical bus, as well as the general status of each UPS, such as circuit breaker status information. Any touchscreen display shall support the configuration of the [entire parallel] system and shall provide event and alarm data for all UPSs in the parallel configuration. A Virtual Display Application shall be available for download to the customer’s computer and shalll support remote monitoring of a complete system with up to 4 UPSs in parallel.
8. Battery runtime: Each UPS must have its own battery solution. The battery solution for the entire system can be a combination of standard and third-party batteries, but each UPS must use only one battery solution – either standard or third-party batteries.
9. Switchgear: A custom switchgear option shall be required for parallel operation.

[Schneider Electric]

Тематики

• источники и системы электропитания

EN

• parallel UPS system