Temperature and humidity control of electrical panels for frequency converters

The temperature control of a frequency converter's electrical panel is a factor that, if overlooked, can cause significant problems in the equipment. It protects variable speed drives (VSDs) and other electronic equipment located inside the electrical panel. Often, in the configuration and commissioning of frequency inverters and other control components in electrical cabinets, is carried out in high-temperature and/or high-humidity environments. The drive's electronic components are rated to operate within given temperature and humidity ranges to ensure longevity and adequate current output, so there are real risks and cost implications associated with ignoring environmental limitations.

Temperature control of electrical panels for frequency converters

Although there is some variability from one manufacturer to another, frequency converters are generally derated, i.e. their rated amperage output is reduced, to operate between 40°C and 50°C. For example, some manufacturers specify that the output current should be reduced by 1% for every 1°C above 40°, bearing in mind that these units are not rated to operate above 50°. This is done to accommodate the increase in resistance at higher temperatures and to protect sensitive electronic components from excessive stress. Sometimes, the maximum rating of 50°C will be shown in the manufacturer's information as intended for «heavy duty» or «overload» use. This should not be confused with the overload capacity required for constant torque applications: higher load demands under constant torque use should be considered separately from any required temperature reduction. Manufacturers may provide power reduction curves for their frequency converters that provide the relevant details.

Even with the reduction in power, additional control is required to maintain the temperatures of the frequency converters at acceptable levels. This is largely because frequency converters generate a significant amount of heat while in operation.

Smaller units (e.g., less than 5 HP (3.7 kW)) are typically equipped with external heat sinks only, while larger units have one or more internal fans that are used to draw air over the electronics.

According to data from some manufacturers, a 100 HP (75kW) unit can dissipate 5100 Btu/h (1.5kW) or more under normal operating conditions. If that heat is contained within an electrical enclosure, the internal temperature can easily exceed temperature limits and cause premature drive failure. Frequency converter manufacturers provide very specific requirements for installation clearances and mounting methods to ensure that their units are adequately cooled. When converters are mounted on the wall or floor as stand-alone units, these methods may be all that is needed, but installation inside electrical panels often requires additional temperature control. This temperature control is usually provided by forced air ventilation or refrigerated cooling.

In cases where the ambient temperature is not excessive, fans can be installed on the walls or doors of the enclosure. Fans are sized to provide airflow according to manufacturers' recommendations, which take into account the heat dissipation of the unit and assume a maximum rated ambient temperature. Fans are also typically equipped with appropriate filters to protect the cabinet contents from dust and dirt; filter kits can be specified for indoor or outdoor use as needed.

For larger frequency converters, particularly when electrical panels are installed outdoors in hot climates, cooling with air conditioning equipment is required. It is not uncommon for a cooling capacity of 8,000 Btu (2.3 kWh) or more to be required inside the panel for a 100 HP (75 kW) converter and associated control components. Cooling requirements can also be affected by the location of the installation. For example, manufacturers recommend that drives and electrical panels for variable frequency drives not be installed in direct sunlight; if this cannot be avoided, then some type of shelter or sunshade is recommended. Simply locating the unit in a place protected from the sun during the hottest hours of the day can significantly reduce cooling demands; specific tools for calculating cooling demand can be found on the websites of various manufacturers of temperature control for electrical cabinets.

Humidity and condensation control in electrical panels for frequency converters

The operating ranges for most frequency converters range from 5% to 95% relative humidity (non-condensing), so in all but extreme cases, humidity is not a problem. However, electrical panels for variable frequency drives subject to wide temperature changes may be exposed to condensation. For example, an electrical panel mounted outdoors in a temperate climate may experience winter temperatures of 0 °C or below. This may not be a problem while the unit is running, but if it is turned off for an extended period of time, condensation can form on the internal components. This problem is usually solved by installing one or more heaters inside the electrical panel; the heaters are thermostatically controlled and are usually interlocked to operate according to the status of the drive.

If you currently have a temperature control application in electrical panels for specific or unusual frequency converters, please subscribe to our newsletter and receive updated information on the use and brands of frequency converters on the market that may be useful to you when implement frequency converters in industrial processes. There is a wealth of experience that can be applied to your problem, and at Tecnología para la Industria, we want to provide you with the information you need to make smart decisions about your electrical panels for frequency converters.