Motor Cooling

Motor Cooling

Totally Enclosed Fan Cooled electric motors (TEFC) are air cooled motors provided with an external fan that is fitted on the electric motor’s own shaft or independently driven. It is also possible that the electric motor is installed in an air flow without a fan (TEAO, Totally Enclosed Air Over). The air necessary for cooling of the motor is usually provided by the driven equipment. The Totally Enclosed Non Ventilated electric motors (TENV) have no fan nor are they subject of forced cooling. There TENV motors are in particular used for short term duty cycle (i.e. S2-10min duty).

Electric motors with forced cooling (TEFC and TEAO) require approximately 25 to 30 cubic meters of cooling air per minute for 100 kW.

The following are the important features for effective electric motor cooling (this list is not exhaustive):

  • Blade shape
  • Drive mode
  • Noise generation
  • Energy consumption
  • Electric motor installation and maintenance

Blade shape

The simplest option is having the fan mounted directly on to the electric motor shaft. The rotating speed of the electric motor determines the speed of the fan. The required direction of rotation is usually not specified so the standard industrial electric motors are equipped with bi-directional fan with straight blades (radial fan) suitable for both directions of rotation (CW or CCW).

The drive mode

The fan can be directly driven by the electric motor and be fitted on the motor's own shaft for continuous use (S1 duty). If an electric motor is frequently switched on and off (for example at S4 duty), additional heat will be generated be by the motor, especially when there is a large moment of inertia attached to the motor’s shaft resulting in heavy start-up. Furthermore, an electric motor can not be cooled by a shaft fitted fan when stationary. Electric motor can be fitted with an independently driven fan (Totally Enclosed Force Ventilated), delivering cooling air for the duration of the motor's entire duty cycle. The force ventilation is suitable for a broad range of voltages. This runs from 230V 50Hz to 575V 60Hz, 3 phase; as indicated on force ventilation unit nameplate. An additional advantage when using this unit is its high protection class: IP66. This cooling method is often used when motors’ speed is controlled by frequency inverters, when a motor has to operate slowly at a relatively high torque. Note: If an electric motor runs at a half of the rated speed, the own fan borne by the motor’s shaft will deliver only 12.5% of the volume of the cooling air when compared with the air delivery at the motor’s rated speed.

Noise generation and energy consumption

The sound pressure level as well as energy consumption can be reduced by using uni-directional axial fans instead of radial fans. The reduction depends on the power and speed. The reduction effect at 6- and 8-pole electric motors (1,000 rpm and 750 rpm) is less significant.

Set-up and maintenance

When installing an electric motor it is important to ensure that the motor will have sufficient supply of cooling air. It is necessary to ensure that the air supply is not blocked in any way and in a dusty environment regular maintenance must be performed and motor cooling ribs cleaned in regular intervals!

Definition of terms

- CW = Clockwise (to the right when viewed from the drive end)
- CCW = Counter Clockwise (to the left when viewed from the drive end)
- TEFC = Totally Enclosed Fan Cooled / IC 411
- TEAO = Totally Enclosed Air Over / IC 418
- TENV = Totally Enclosed Non Ventilated / IC 410
- TEFV = Totally Enclosed Forced Ventilated / IC 416

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