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The utilization categories category for low-voltage switchgear defines the characteristic operating conditions for switchgear such as contactors, circuit-breakers, circuit-breaker-fuse units, contactor relays, etc. These devices are dimensioned for different electrical loads and for different operating conditions.
Circuit breakers with higher ratings can have adjustable trip settings, allowing fewer standardized products to be used, adjusted to the applicable precise ratings when installed. For example, a circuit breaker with a 400 ampere frame size might have its over-current detection threshold set only 300 amperes where that rating is appropriate.
Types used in commercial and industrial low-voltage distribution systems are rated to safely interrupt 200,000 amperes. The rating of power circuit breakers varies according to the application voltage; a circuit breaker that interrupts 50,000 amperes at 208 volts might be rated to interrupt only 10,000 amperes at 600 volts, for example.
Conversely, the 4000-series has "borrowed" from the 7400 series – such as the CD40193 and CD40161 being pin-for-pin functional replacements for 74C193 and 74C161. Older TTL parts made by manufacturers such as Signetics , Motorola , Mullard and Siemens may have different numeric prefix and numbering series entirely, such as in the European FJ ...
After the 1970s, vacuum switches began to replace the minimal-oil switches in medium-voltage switchgear. In the early 1980s, SF6 switches and breakers were also gradually replaced by vacuum technology in medium-voltage application. As of 2018, a vacuum circuit-breaker had reached 145 kV with a short-circuit rating of 200 kA. [4]
NX, formerly known as "Unigraphics", is an advanced high-end CAD/CAM/CAE, which has been owned since 2007 by Siemens Digital Industries Software. [1] [2] In 2000, Unigraphics purchased SDRC I-DEAS and began an effort to integrate aspects of both software packages into a single product which became Unigraphics NX or NX.
The Class 444 fleet was built at Siemens' Vienna plant. [10] [11] Before being shipped to Britain via the Channel Tunnel, the trains were extensively tested at Siemens' Wegberg-Wildenrath Test and Validation Centre in Germany. [10] This was an attempt to reduce the time taken for new trains to enter service, by ironing out any problems beforehand.
In 1957 Siemens demonstrated the first solid-state rectifier (solid-state rectifiers are now the standard for HVDC systems) however it was not until the early 1970s that this technology was used in commercial power systems. [18] In 1959 Westinghouse demonstrated the first circuit breaker that used SF 6 as the interrupting medium. [19]