Last week we discussed some of the potential impacts of temperature and humidity on the operation and longevity of variable speed drives (VSD) and other motor control equipment. Providing the proper enclosure for the equipment is critical in ensuring you get the most from your investment. Let’s examine the various environmental conditions under which these electronic components might be installed and some methods for protecting against their deleterious effects.
At Joliet Technologies, we are frequently requested to assemble control cabinets for installation in diverse industrial and/or outdoor locations. We have also built panel assemblies for the off-shore oil industry, where the marine environment places extreme demands on the equipment. In designing these assemblies, we pay particular attention to the following:
Ambient temperature: as noted last week, drives and other control components are designed for operation within a temperature range. Typically, it is the upper end of that range, most often 40°C, that is of concern. Operating in an environment above that range places greater stresses on switching devices, potentially decreasing their operating life. If the ambient temperature surrounding the enclosure is sufficiently cooler than the drive enclosure, then either passive conduction or forced air ventilation will typically serve to maintain the drive temperature below upper limits, depending on the heat generated by the internal components and the effective heat transfer area (i.e., the surface area exposed to the air) of the enclosure. However, if the temperature differential between the surrounding air and the inside operating temperature of the cabinet is not adequate, and/or if the equipment dissipates a lot of heat during operation, active cooling is needed. Typically this takes the form of refrigerant cooling, although in some specialized low voltage and many medium voltage drive applications liquid cooling is used.
We can address higher temperature conditions in a number of ways. First, the enclosure size can be increased to provide increased surface area. The ability to do this depends on space constraints, costs, and the physical limitations of heat transfer. Second, one or more fans can be installed in the enclosure. These fans supplement the fan(s) installed within the drive by bringing cooler air into the cabinet from outside; this cooler air is then drawn across the electronics by the drive fan(s) and sent out of the cabinet through a filtered opening. Where more cooling is needed, an air conditioning package can be installed. These are often mounted on the side of the enclosure, and provision must be made to protect internal components from condensate leakage in case of drain tubing failure. Whether fan and filter package or air conditioning unit, the cooling equipment is specified to match the protection rating of the enclosure (e.g. NEMA 12 or IP54). Thermostatic controls can be provided separately or integral to the units to allow the controls to operate only when needed.
Dust and oil: In many industrial environments, airborne dust, oil droplets, and other typically inert airborne contaminants can be prevalent. Such contaminants can increase drive internal heating by “insulating” electrical components and increasing static pressure seen by the internal cooling fans). Also, build-up of dust and grime can result in electrical arcing between closely spaced components.
The drive may be protected from dust, dirt and/or oil by its manufactured enclosure, or a separate enclosure must be provided. If the former, the manufactured drive will typically have a Type 12 (UL/NEMA) or IP54 (IEC) rating for protection against dust and oil ingress. If needed, a separate cabinet would also be specified to provide the same protection. If a separate enclosure is used, provided it is properly rated the internal components can be an “open” or “chassis” type with limited or no physical protection of their own as long as personnel operating or maintaining the equipment are properly protected from inadvertent contact.
Moisture: The hazards of water on electrical components are well-known; what may not be as obvious are some of the sources of moisture. In addition to incidental contact from over-spray and the like, some industrial areas, particularly in the pharmaceutical and food sectors, require frequent wash-down of processing areas. In these cases, enclosures must be rated to prevent ingress of wind-blown or hose-directed (pressurized) water. Also, in areas where the drive enclosure is subject to wide temperature swings, such as when subjected to cold ambient temperatures and operating intermittently, condensation can form and cause internal corrosion or arcing.
For moisture protection in areas where water under some type of pressure is likely to hit the drive, Type 4/4x (NEMA) or IP65 (IEC) rated enclosures are suitable. Because ventilation/cooling methods for these types of enclosures can be problematic, drive manufacturers typically limit the sizes of their 4/4x rated drives to 10 – 20 horsepower, depending on supply voltage. However, suitably rated third-party cooling equipment can be provided for larger drives when installing them in a separate panel. Where subject to condensation, drives are typically provided with thermostatically-controlled cabinet heaters to prevent wide temperature swings.
Outdoor locations: Any or all of the above factors can be found in outdoor installations. Additional factors include the deteriorating effects of UV radiation, the temperature rise caused by exposure to sunlight, and greater susceptibility to lightning induced surges.
Drives located outdoors are typically installed in Type 3R (NEMA) or IP22 enclosures, with suitably rated heating and cooling equipment as needed. Manufacturers usually recommend that the drive cabinets not be exposed to direct sunlight; the temperature increase caused by direct exposure can be significant and will over-stress any reasonably sized cooling equipment. In areas with no available protected areas, shelters are recommended and, depending on their complexity, can be less costly than a damaged drive or even a new cooling unit. And even if the drive cabinet equipment is not damaged, some energy will be saved on an ongoing basis by reducing the temperatures the drive sees. When installing the cabinets in a manner to prevent direct exposure in temperate climates, attention should also be paid to seasonal changes in sun exposure as the angle of incidence changes throughout the year. Solar energy (termed “insolation”) charts can be found in several locations on the Internet to assist if needed.
If you have encountered challenging drive installation conditions, please feel free to share it with our readers in the Comments section. I’m sure there are as many unique situations as there are applications out there…