The motor enclosure used in the wood-working industry is

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Examoogle · Accepted Answer

Totally enclosed fan cooled type

Explanation: In the wood-working industry, the air is heavily laden with fine wood dust and saw-dust, which are highly combustible and can cause severe damage if they penetrate the motor's internal electrical components. The Totally Enclosed Fan Cooled (TEFC) motor is chosen because it is designed with an enclosure that prevents the ingress of external dust, and its cooling is managed by an external fan blowing air over the outer frame, keeping the internal windings separate from the ambient environment.

Working Principle: The TEFC motor employs a robust frame that is physically sealed against the environment, preventing air circulation between the interior and exterior. Heat generated by the windings is conducted to the motor casing, and an external shaft-mounted fan forces ambient air over the fins of the casing to dissipate the heat without allowing the debris-filled ambient air to enter the motor housing.

Key Formulas: $P_{out} = \sqrt{3} V_L I_L \cos \phi \cdot \eta$ — Relation for power output in an induction motor where $\eta$ is efficiency.; $T \propto \frac{P}{\omega_s}$ — Torque relationship showing dependency on power and synchronous speed.

Key Points: TEFC motors are standard for environments with high contamination or abrasive dust.; The external cooling fins significantly increase the surface area for convective heat dissipation.; IP (Ingress Protection) ratings for TEFC motors are typically higher (IP54 or IP55).; Prevents fire hazards in woodworking due to the isolation of sparking parts from combustible dust.

Advantages: Complete protection against dust and moisture ingress.; Reliable operation in harsh industrial environments.; Low maintenance due to sealed internal components.

Disadvantages: Heavier and larger frame size compared to open-type motors.; Generally higher initial cost.; Potential for thermal issues if cooling fins are clogged with debris.

Applications: Wood-working and carpentry mills.; Cement plants and flour mills.; Chemical processing industries.

Additional Info: The 'Totally Enclosed' design ensures the windings are not affected by humidity or foreign particles.. Option C (Flame proof) is intended for explosive atmospheres (oil/gas), not just dusty wood environments.. Option D (Splash proof) only protects against vertically falling drops, which is insufficient for high dust concentration.

Answer: B is correct — Totally enclosed fan cooled (TEFC) motors prevent internal damage by isolating the stator and rotor from contaminated air using an external fan for heat dissipation.

Exam Tip: Always link the IP rating of the motor enclosure to the specific hazards of the industry, such as IP5X or IP6X for dusty environments like saw-mills.

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