Electric Motor Cooling Methods

    Because of internal electrical and mechanical losses, all rotating electrical machines produce heat.  Losses are considerable during dynamic braking or startup. Additionally, losses typically rise as loading goes up. To transfer heat continuously to a cooling medium, like the air, a cooling system is required.

Typically, one or more fans installed on the rotor shaft of an AC induction motor circulate cooling air both internally and externally.  Fans are typically of the bi-directional type and made of a strong plastic material, aluminum, or steel to enable operation of the machine in either direction of rotation.  Additionally, cooling ribs are typically added to the motor's external frames to improve the surface area for heat radiation.

The standards IEC 34.6 and AS 1359.21 define the various techniques for cooling the rotating machines.

The most common version of AC motor is the totally enclosed fan cooled (TEFC) motor, which has cooling ribs running axially around the outside of the motor frame and an external forced cooling fan installed on the non-drive end (NDE) of the shaft.

These motors are engineered to maintain air flowing along the motor's surface along every inch of their length, which enhances cooling and promotes the ribs' inherent ability to clean themselves. For this reason, an air gap is typically allowed between the ribs and the fan cover.  To accomplish this, a space called an air gap is typically allowed between the ribs and the fan cover.

For internal cooling,  On smaller TEFC motors, the end rings are typically built with ribs to offer more air agitation for a uniform temperature distribution and to facilitate heat radiation from the end shields and frame.

In case of special operation, when typical TEFC induction motors are equipped with AC variable speed drives that are driven by VVVF converters, extra care must be taken.

->> The shaft-mounted fan's cooling performance is reduced during operation at speeds below its specified frequency of 50 Hz.  In order to provide appropriate cooling at low speeds for steady torque loads, it is occasionally required to install an independently powered forced cooling fan (IC 43).

->> On the other hand, the shaft-mounted fan performs well but may generate excessive noise when run continuously at high speeds over 50 Hz.

Once more, it could be wise to install a separately powered cooling fan.

IEC standards outline appropriate techniques for effectively cooling electric motors. According to the IEC 60034-6 standard, the three most popular motor cooling techniques have the following IC designation codes: The ICs 410, 411, and 418 are used.

IC 410: Totally Enclosed Non-Ventilated (TENV).  This type of motor has no external fans and is completely enclosed in a smooth or finned casing.  In this cooling approach, the electric motor is essentially cooled using free convection flow from the air.  This cooling technique is particularly appropriate for winches, cranes, and other devices that operate at continuous load for just a short time.

Fig: IC410

IC 411: Totally Enclosed Fan Cooled (TEFC).  The motor is completely enclosed in a smooth or finned housing. By this cooling technique a fan installed on the motor shaft cools the motor. This technique is the method used the most commonly in the industry to cool electric motors.  This is by far the most widely utilized and the industry standard for many different applications, including hydraulics, pumps, and fans.

Fig: IC411

IC 416: Totally Enclosed Force Ventilated (TEFV).  With this cooling technique, an airflow that normally originates from an externally attached fan cools the motor.  The motor is completely enclosed in a smooth or finned casing, and it includes a motorized axial fan that is installed externally and used to cool the motor.  This approach is typically employed in applications where variable-speed or low-speed motors with constant torque are in use.

Fig: IC416

IC418: Totally Enclosed Air Over (TEAO).  The motor has no external fan and is completely encased in a smooth or finned casing.  The motor is placed in the airstream produced by the drive itself. This technique is frequently applied to cooling towers, axial fans, and other HVAC applications.

Fig: IC418

IC611: The motor is equipped with a heat exchanger (air to air). There are two air circuits; one is external through the heat exchanger, and the other one is inside the motor armature. Two shaft-mounted fans work for each air circuit.

Fig: IC611

IC616: Air-to-air cooling with integral fan on motor's shaft inside stator and heat exchanger with open external circuit with force ventilation

Fig: IC616

IC666: Air-to-air cooling with a forced fan system inside the stator and a heat exchanger with an open external circuit with forced ventilation.

Fig: IC666

IC511: A fan on the motor shaft and open circuit piping in the motor's stator are used to cool the air pipe.

Fig: IC511

IC31W: Air-to-water cooling with inlet and outlet pipes or ducts for cooling water circulation.

Fig: IC31W

IC81W: Water-cooled heat exchanger and air-water cooling with integrated fan on motor shaft.

Fig: IC81W

IC86W: Air-water cooling with a force ventilation system inside the stator and a water-cooled heat exchanger.

Fig: IC86W

As demonstrated, various cooling techniques perform at particular kinds of applications.  However, there are many crucial factors to take into account when deciding how to cool your motor. Your application, the operating environment, the required lifetime, and other factors all play a role in choosing the best cooling technique. Additionally, if cooling is inadequate, you have the possibility of burning out the motor windings after only a few minutes of operation under unfortunate conditions.