Question 38 CEL02 - Chief Engineer - Limited (Alt)

The Correct Answer is D **Why Option D is Correct:** During periods of inactivity (storage or long standby), large electric motors are highly susceptible to damage from moisture. Changes in ambient temperature and humidity cause moisture to condense on the internal components, particularly the insulation and windings. This condensation significantly lowers the resistance of the insulation, which can lead to catastrophic electrical failures (shorts, ground faults) when the motor is restarted. Using **space heaters** (also known as "anti-condensation heaters" or "strip heaters") inside the motor casing or surrounding environment maintains the motor temperature slightly above the ambient dew point, effectively preventing the formation of condensation and preserving the integrity of the insulation. **Why the Other Options are Incorrect:** * **A) Spraying a solvent periodically to remove carbon dust.** Using solvents, especially aggressive ones, can damage the insulating varnish and materials used in the motor windings. While cleaning is necessary, it should be done carefully during scheduled maintenance, not periodically applied via spray during inactivity. * **B) Compressed air should be blown over areas where dust is deposited.** While compressed air is commonly used for cleaning motors, blowing it over windings while the motor is idle can force dust and abrasive particles deeper into the insulation layers or into the motor bearings, causing potential damage. Cleaning should be performed systematically and only when necessary. * **C) A thin layer of air-drying varnish should be applied on the windings.** Applying extra layers of varnish periodically is not a standard maintenance procedure during inactivity. The original varnish is intended to protect the windings. Applying additional varnish randomly or improperly can lead to uneven curing, cracking, overheating due to reduced heat dissipation, and ultimately compromise the existing insulation system. Varnish application is a specialized repair procedure, not routine inactivity maintenance.