High-Temperature Devices

High-temperature devices are defined as those devices that operate at a temperature exceeding 80 percent of the ignition temperature (expressed in Celsius) of the gas or vapor involved. The ignition temperature of natural gas usually is considered to be 900°F (482°C). Therefore, a device is... 

Electrical equipment can be mounted in various types of enclosures. A weather-tight enclosure normally has a gasket and does not allow air (and the moisture contained in the air) to enter the enclosure. Offshore, such an enclosure, if properly closed, will help protect the enclosed electrical equipment from, corrosion due to salt water spray. These types of enclosures can be used in Division 2 areas provided they do not enclose arcing, sparking or high temperature devices. 

The surface temperature of explosion-proof enclosures cannot exceed that of high-temperature devices, Equipment can be tested by nationally recognized testing laboratories and given one of 14 T ratings, as indicated in Table 17-2. This equipment may exceed the 80 percent rule."... 

Arcing contacts in Division 2 areas must be installed in explosion-proof enclosures, be immersed in oil, be hermetically sealed, or be non-incendive. High-temperature devices must be installed in explosion-proof enclosures. Fuses must be enclosed in explosion-proof enclosures unless the fuses are preceded by an explosion-proof, hermetically sealed, or oil-immersed switch and the fuses are used for overcurrent protection of instrument circuits not subject to overloading in normal use. 

Standard Open or Totally-Enclosed Fan-Cooled (TEFC) generators and motors are acceptable in Division 2 areas if they do not contain brushes or other arcing contacts or high-temperature devices. Three-phase TEFC motors are acceptable in Division 2 locations, but singlephase motors usually contain arcing devices and are not acceptable... 

Seals are required at entries by conduit or cable to explosion-proof enclosures containing arcing or high-temperature devices in Division 1 and Division 2 locations. It is not required to seal IM in. or smaller conduits into explosion-proof enclosures in Division 1 areas housing switches, circuit breakers, fuses, relays, etc., if their current-interrupting contacts are hermetically sealed or under oil (having a 2-in. minimum immersion for power contacts and 1-in. for control contacts). 

Except for conduit or cable entries into explosion-proof enclosures containing arcing or high-temperature devices (as described in Item I above), cables that will leak gas through the core at a rate of less than 0.007 ft /hr at 6 in. of water pressure need not be sealed if they are provided with a continuous gas/vapor-tight sheath. Cables with such a sheath that will transmit gas at or above this rate must be sealed if connected to process equipment that may cause a pressure of 6 in. of water at the cable end. 

Space heaters, particularly in electrical motors and generators which may be idle for significant periods of time, can also help prevent the accumulation of moisture. Space heaters installed in classified areas must operate at temperatures below high temperature devices. 

Gold has been mined and refined for many thousands of years, certainly before electric furnaces and other high-temperature devices were possible. The melting point of gold is 1064°C express this temperature in terms of the Kelvin and Fahrenheit scales. 

Thermionic converters are high temperature devices which utilize electron emission and collection with two electrodes at different temperatures to convert heat into electric power directly with no moving parts. Most thermionic converters operate with a plasma of positive ions in the interelectrode space to neutralize space charge and permit electron current flow. Both the plasma characteristics and the surface properties of the electrodes are controlled by the use of cesium vapor in thermionic diodes. 

All in all, SiC technology is progressing. A summary of contacts to the various polytypes is listed in TABLES 1 to 3. As mentioned above, the problem of reliable high temperature low resistance ohmic contacts is the most important problem to be solved. A second issue is the development of semi-insulating SiC for microwave and/or integrated circuits. SiC is now the prime candidate for commercial applications in high temperature devices and circuits and for devices and circuits operating in a harsh environment. 

M. Willander, M. Friesel, Q. Wahab, B. Straumal, Silicon carbide and diamond for high temperature device applications, J. Mater. Sci. Mater. Electron 17 (2006) 1—25. 

High-Temperature Devices Table 13.6 Operation temperature limits of piezoelectric materials 315... 

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