GE Mark VIe System Manual page 122

For all types of enclosure systems, it is important to highlight the potential effect of changes from the original design. GE
designed enclosure systems are engineered to maintain the Mark VIe system components within their specified temperature
ratings. Modifying the enclosure or adding additional equipment to the enclosure could potentially compromise the thermal
design.
While effective enclosure cooling can be accomplished in many ways, including active cooling like air conditioners,
thermoelectric coolers, or vortex coolers, most enclosures are air cooled using one of the following cooling systems. The
following are key points to consider when selecting one of these systems and are not intended to take the place of proper
enclosure thermal analyses.
5.4.2.1 Solid Door
Solid door enclosures are an occasional necessity where environmental conditions outside the enclosure are potentially
harmful to the enclosed equipment. Great care should be used in applying fully enclosed cabinets without supplemental
cooling, however, as relatively low power can result in significant internal temperature rises. For this reason, and because the
enclosure can also be susceptible to temperature rise due to unanticipated heat sources outside the enclosure, this type of
architecture is only recommended where additional analysis validates that thermal design requirements are met.
5.4.2.2 Free Convection Cooled
Free convection cooled ventilated enclosures are commonly used for control equipment and are suitable in many cases for
providing sufficient cooling air to internal equipment. The application of filters to the air vents is also a common practice and
can provide similar Ingress Protection (IP) rating to a solid door. It should be noted, however, that a filtered cabinet with
clogged filters will function like a solid door enclosure and can result in over-temperature conditions. For this reason, it is
recommended that the use of filters be limited to cases where the additional IP rating is required. In those cases, the filters
must be regularly maintained to ensure proper operation of the cooling system.
5.4.2.3 Fan Cooled
Fan cooled ventilated enclosures are typically used on enclosures where greater thermal margin is desired or where the
ambient temperature outside the enclosure is close to the operating temperature of the internal equipment. The fan cooled
enclosures can also be provided with filters to improve the IP rating of the enclosure. Again the filters should be regularly
maintained to ensure that the cooled system operates to its required capability. While fan cooled systems can ideally maintain
internal enclosure temperatures within a few degrees of the external temperature, care must still be used when applying these
systems to ensure that all components receive adequate cooling air. It is possible in forced cooling systems to have
components which experience greater temperature rises than they would in free convection if the component is located in an
area of poor circulation or recirculation.
122 GEH-6721_Vol_I_BP GEH-6721_Vol_I Mark VIe and Mark VIeS Control Systems Volume I
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