Question 7 QMED02 - Electrician-Refrigerating Engineer

The Correct Answer is B **Why Option B is Correct:** Routine AC motor maintenance is primarily focused on early detection of wear, insulation breakdown, or bearing failure, all of which often manifest as excessive heat. Taking temperature readings (usually of the motor casing and bearings) under normal operating load is a standard, quick, and non-intrusive procedure included in almost every routine maintenance checklist. It provides a baseline reference and immediately flags any developing issues (like friction from worn bearings or electrical resistance from deteriorating winding insulation) that cause abnormal temperature rises, allowing for timely intervention before catastrophic failure. **Why the Other Options are Incorrect:** * **A) rotor balance check:** Checking rotor balance is a specialized, time-consuming procedure typically performed only during major overhauls, after significant repairs (like replacing the rotor), or if excessive vibration is already detected. It is not generally part of routine, periodic maintenance. * **C) verifying RPM if a synchronous motor:** While synchronous motors are designed to run at a precise speed (synchronized with the line frequency), their speed rarely changes unless there is a severe system fault. Checking RPM is necessary for induction motors (to monitor slip) or during initial commissioning, but it's not a universally essential step for routine synchronous motor maintenance compared to critical checks like temperature and vibration. * **D) inspection of the motor's internals for loose rotor bars or field poles:** Inspecting internal components requires significant effort, often involving disassembly (removing end bells or the rotor itself). This level of inspection is reserved for scheduled major overhauls, predictive maintenance triggered by high vibration or performance issues, or failure analysis—it is too intrusive and time-consuming for routine maintenance rounds.