Answer :
- (a) Corrective Maintenance refers to the repair and restoration processes that are taken to fix any faults or breakdowns in equipment after they occur. This type of maintenance aims to return the equipment to a working state.
(b) Four benefits of corrective maintenance include:
- Minimized Downtime: Quickly addressing issues can reduce the time equipment is unusable.
- Cost Savings: Performing repairs can extend the lifespan of equipment, delaying the need for expensive replacements.
- Optimization of Resources: By focusing efforts on already broken equipment, rather than on equipment that doesn't need immediate attention, resources are better allocated.
- Increased Safety: Restoring proper function removes potential hazards posed by malfunctioning equipment.
(c) Five factors to consider when performing preventive maintenance:
- Equipment History: Understanding past issues and repairs can help predict future maintenance needs.
- Operating Conditions: Factors such as temperature, humidity, and usage rates can affect wear and tear.
- Manufacturer's Recommendations: Following guidelines from the equipment's manufacturer can optimize performance.
- Cost: Balancing the costs of maintenance against savings from preventing larger issues.
- Availability of Parts: Ensuring that necessary parts are on hand can affect schedule and planning.
(d) Five routine maintenance checks for a second-hand generator include:
Oil and Filter Changes: Ensuring clean oil and filters helps keep the engine running smoothly.
Battery Inspection: Checking the condition of the battery, including clean terminals and sufficient charge.
Fuel System: Ensuring there are no leaks and that the fuel is clean and sufficient.
Air Filter Inspection: Clean or replace air filters to maintain efficient airflow.
Cooling System: Check the coolant level and inspect hoses for any leaks or wear.
(a) Five likely faults in d.c generators:
Open Armature Coil: A break in the wires leading to an incomplete circuit.
Shorted Armature Coil: Reduced resistance due to wires touching or insulation failure.
Worn Brushes: Brushes that are overly worn can fail to contact the commutator properly.
Defective Commutator: Mechanical or electrical defects in the commutator.
Faulty Field Windings: Open or short-circuit conditions in field windings.
(b) Steps to repair the power plug:
- Identification: Identify which part of the plug or cord is faulty, ensuring the equipment is unplugged.
- Safety Precautions: Ensure that the device is disconnected from power, double-check with a voltage tester.
- Disassembly: Carefully open the plug to access internal wiring.
- Visual Inspection: Look for damaged, loose, or corroded connections or wires.
- Repair or Replacement: Reattach, repair, or replace the faulty parts and reassemble the plug.
(c) Five functional tests on a d.c motor after repair:
Motor Start Test: Verify the motor starts smoothly with no abnormal noises.
Load Test: Test the motor under load to ensure it performs as expected.
Speed Variation Test: Check that the motor runs at various speeds without issues.
Voltage and Current Measurements: Ensure voltage and current levels are within expected limits.
Vibration and Noise Test: Evaluate for any unusual vibrations or noise that could indicate persistent issues.
(a) Three reasons why fluorescent tube ends become black:
Electrode Degradation: Continuous heating of the electrodes can cause them to degrade and leave residue.
Mercury Migration: Movement of mercury vapor towards the ends leading to blackening.
Phosphor Coating Deterioration: Breakdown of the phosphor coating due to reactive gases.
(b) (i) Four merits of using mercury vapor lamps:
- High Efficiency: They convert more electricity into visible light.
- Long Life: They have a longer lifespan than many other lamps.
- Durability: Resistant to vibrations and mechanical shock.
- Bright White Light: Produces a natural-looking bright white light.
(ii) Three areas of application for mercury vapor lamps:
- Street Lighting: Commonly used for lighting streets and highways.
- Industrial Lighting: Used in factories and warehouses.
- Sports Facilities: Often utilized for lighting large sports arenas.
(c) (i) The stroboscopic effect refers to the visual phenomenon where moving objects appear stationary or slow-moving when illuminated by a series of short light pulses.
(ii) Three effects of the stroboscopic effect in a machine shop:
- Reduced Precision: Can lead to errors as moving machines may appear still.
- Safety Risks: Increases chances of accidents due to misjudgment of speeds.
- Visual Discomfort: Can cause eye strain and discomfort for workers.
(d) Two types of induction motors:
- Squirrel Cage Induction Motor: Known for its simplicity and ruggedness.
- Wound Rotor Induction Motor: Allows control over speed and torque by varying resistance.
