Temperature changes can have significant impacts on motors. It's crucial to understand which types of electric motors are more susceptible to extremes of cold, how to mitigate the issues that arise and possible alternatives. In some regions of Canada, the temperature can change by 20 degrees from day to night. Selecting the right motor will help maintain your performance in the cold and decrease potential motor downtime.
Permanent Magnet Motors
The function of a permanent magnet in an electric motor is to generate torque through a magnetic force. The magnetic force is what causes the motor to rotate. When permanent magnets are exposed to freezing temperatures, they can experience demagnetization, which reduces their ability to produce a magnetic force. For permanent magnet motors, such as DC motors and many types of synchronous AC motors, the motor performance suffers. Speed and torque are directly related to the magnetization level of the magnets.
The effects of demagnetization present most clearly when operating the motor at low voltage and high amps (low speed, high torque operation), where the motor may struggle to maintain performance.
The amount of demagnetization experienced by a motor depends on:
- The temperature
- What materials the magnet is made from
Rare earth magnets are more resilient to demagnetization than ferrite or ceramic types, but they are considerably more expensive. A lower-cost option is to install insulation on the motor (while keeping vents and openings clear to allow the motor to cool); however, this may not be enough, and a motor that uses only electromagnets may be a better choice.
Open Drip Proof (ODP) Motors
Open Drip Proof motors are more susceptible to the cold, as their large cooling vents readily allow moisture-laden air to move through the motor. When hot air from inside the motor comes in contact with the motor body's cold interior surface, it cools rapidly, causing condensation (water droplets) to form inside the motor. Condensation can have a severe impact on the critical components of the motor.
If left unchecked, moisture can quickly cause significant damage, rapidly deteriorating the motor windings and corroding metal components. For this reason, it's not recommended to use ODP motors in damp or humid environments, with the addition of cold temperatures, which increase the effects of condensation.
A good alternative is a Totally Enclosed Fan Cooled (TEFC) motor.
Totally Enclosed Fan Cooled Motors
These motors have a sealed, enclosed body that prevents free exchange of air between the interior and exterior of the motor, keeping moisture largely at bay. However, TEFC motors are not completely airtight. Repeated heating and cooling cycles will create pressure that draws small amounts of air and moisture inside, collecting over time.
To mitigate the problem, install a drain plug at the bottom of the motor. The drain plug needs to periodically open to allow any moisture inside the motor to escape before it causes internal damages. Additionally, a space heater may be used inside the motor, which prevents the temperature inside from falling below the point where condensation will form.
TEFC motors are often more costly than open motors but offer more protection against winter weather.
When selecting a motor for a hazardous location, first classify the location by confirming the class, division, group, and Auto-Ignition Temperature (AIT) of the hazardous materials.
Explosion-proof motorsare designed to contain an explosion of a specified hazardous gas inside the motor. Containing the explosion prevents the ignition of any flammable materials around the outside of the motor, protecting personnel, machines, and infrastructure within the vicinity.
In cold temperatures, an explosion creates a more significant temperature differential and produces a significantly greater pressure than it would in a warmer environment. The higher pressure can put stress on enclosures, seals, and flame paths that exceed the motor's ratings, creating a risk where the enclosure will fail to provide sufficient protection.
Explosion-proof motors have ratings for specific temperatures and environmental conditions. When in doubt, contact your trusted supplier to clarify details or seek more information.
The materials that a motor is made of influence how well it stands up to prolonged exposure to extreme cold temperatures. Many plastics and some metals are prone to become brittle and crack when exposed to freezing temperatures. Cooling fans, frames, brackets and even motor shafts are at greater risk due to forces and vibration they endure. Seals and gaskets are another potential weak point, with the soft elastomer materials hardening and cracking in freezing conditions.
Resilient metals such as bronze and steel are good alternatives for weaker metals such as grey iron, and silicon fares better in freezing temperatures than neoprene. If better materials are not an option, consider alternative motors that are designed to withstand colder temperatures.
Extreme cold temperatures can have several harmful effects on motors and their performance. Choosing the right motor for the job can result in massive savings by avoiding costly downtime and parts replacement and creating a safer and more productive work environment.