Question 15

The Correct Answer is A. **Why option A is correct:** Option A, "periodic cleaning of the air filters or screens," is a fundamental and routine maintenance procedure for any large rotating electrical machine, such as a ship's service alternator. These screens prevent dust, dirt, and salt mist from entering the machine windings. If the filters are clogged, the alternator will overheat due to restricted airflow, leading to premature insulation failure and operational issues. Therefore, cleaning these filters is a scheduled, routine maintenance task. **Why the other options are incorrect:** * **B) megger testing of all rectifying diodes:** While diode testing is necessary if a fault is suspected or as part of a major overhaul, megger testing (high-voltage insulation resistance testing) is performed primarily on the windings and insulation, not on individual solid-state components like diodes. Diodes are typically checked for forward/reverse bias resistance using a multimeter or specialized tester, not routine meggering. This is not a standard routine maintenance task. * **C) lubricating exciter slip rings:** Modern ship service alternators are typically brushless (self-excited via rotating rectifiers). Brushless designs do not have exciter slip rings that require lubrication. Even if an older machine did have slip rings, they would be cleaned, not lubricated, as lubrication would interfere with the brush-to-ring electrical contact. * **D) changing the pedestal bearing insulation yearly:** Pedestal bearing insulation prevents shaft currents from damaging the bearings. While this insulation is vital and must be checked, it is designed to last many years and is not a consumable item that requires changing yearly as a routine maintenance task. Changing it is a corrective or planned major maintenance action, not an annual routine.