Low Voltage AC Drives Even More Efficient with Enclosure Cooling Systems


Variable Frequency Drives, also known as AC drives, are ubiquitous in applications utilizing electrical equipment. Their purpose in an electromechanical system is to control the speed and torque of an AC motor by changing the frequency and voltage of the input signal. They are used in applications that range from small compressors to large mill drives and industrial equipment.

While AC drives are commonly utilized for their energy saving potential, the exact amount of energy savings is based on the application. For example, in a centrifugal fan application, an AC drive can reduce energy costs ranging from 10 to 60 percent if the fan or pump is designed to operate between 40 to 80 percent of full speed, according to Siemens.

In addition to energy savings, AC drives also provide improved process control, higher operating efficiencies of motors, and reverse operations. If the application is suitable for a motor run on low voltage between 480 VAC and 600 VAC, then a low voltage AC drive may be taken advantage of to multiply the energy, efficiency and operational benefits of AC drives utilized at medium or high voltages. However, the benefits can quickly be diminished if heat wreaks havoc on the low voltage AC drive. While this is true for AC drives at any voltage, the focus of this article is on the impact of heat on low voltage AC drives.

Understanding Heat Dissipation in Low Voltage AC Drives

Modern low voltage AC drives operate with an efficiency in the range of 93% to 97% and are rated for operation below 40 °C (104 °F). A high temperature derating factor applies to VFD performance at temperatures beyond rated temperature. Most manufacturers suggest a temperature derating of 1% to 2% for every degree increase in temperature rise over 40 °C.

To understand how a VFD performs at higher temperature, consider a 3 kW VFD operating at 35 °C (95 °F) with an efficiency of 93% that produces a little over 200 W of waste heat inside a medium-sized enclosure. In the sealed enclosure with a total surface area of 42 square feet, this translates to an increase in enclosure temperature of 20 °F. With the VFD now operating at a temperature of 50 °C (124 °F), the derated efficiency is 73%. With over 25% of the power input to the drive being converted into heat, the enclosure temperature and the heat dissipated by the drive reinforce each other causing drive damage and even failure.

Benefits of an Enclosure Cooling System for Low Voltage AC Drives

In the league of electrical equipment, low voltage AC drives are considered highly efficient devices if they run at optimum conditions. The performance of AC drives depends on the phase of the supply voltage, altitude and temperature, although temperature is the most critical parameter.

AC drives installed and run in the temperature range specified by the manufacturer have better performance and a longer lifetime. Often, a reliable enclosure cooling system is sufficient to ensuring AC drives operate within proper temperature ranges. Installing an enclosure cooling system allows you to:

  • Control the operating temperature of a low voltage AC drive.
  • Minimize condensation inside an enclosure.
  • Prevent contaminants including dispersed oil and particulate matter, which is a common problem with natural ventilation, from entering the enclosure and damaging the low voltage AC drive
  • Optimize performance of a low voltage AC drive.

If you are thinking about investing in an enclosure cooling system to protect a low voltage AC drive, contact Thermal Edge for a free quote. We take pride in helping customers land the right product for their applications.