Safeguarding Your Power: A Guide to Industrial Alternator Preventive Maintenance

An industrial alternator is a robust piece of machinery that converts mechanical energy into electrical energy in the form of alternating current (AC). It operates through a rotating magnetic field that moves across stationary copper windings, generating electricity. To ensure these vital components operate reliably and efficiently, a structured preventive maintenance plan is essential. Regular maintenance not only reduces operating costs by preventing costly repairs but also prevents unexpected failures, maximizes reliability, and extends the alternator's service life.

A comprehensive maintenance schedule can be broadly categorized into two key areas: mechanical and electrical checks.

Mechanical Preventive Maintenance

Mechanical maintenance focuses on the physical components of the alternator, ensuring they are in good condition and functioning correctly.

1. Bearing Inspection & Lubrication

Proper lubrication of bearings is critical to prevent friction and wear.

Procedure:

1. For each bearing, locate the grease nipple, re-greasing label, and identify the bearing type.
2. Ensure the new grease is uncontaminated, with a consistent whitish-beige color and stiff texture.
3. Clean the grease gun nozzle, the grease nipple, and the grease exhaust.
4. Fit the grease gun to the nipple and apply the correct quantity of new grease.
5. Operate the alternator for at least 60 minutes, either on-load or off-load.
6. Clean the grease exhaust again. Inspect the expelled grease and compare it to the new grease. If the old grease is severely discolored or absent, the bearing should be replaced.

Maintenance Schedule:

2. Coupling & Alignment

Proper alignment and coupling are crucial for the smooth operation and longevity of the alternator.

Inspection Points:

• Mounting Points:
  • Inspect the generator set baseplate and mounting pads for any cracks or damage.
  • Check rubber anti-vibration mounts for signs of wear or deterioration.
  • Review historical vibration monitoring records to identify any increasing trends.
• One Bearing Coupling:
  • Remove the DE adaptor screen and cover to access the coupling.
  • Inspect coupling discs for damage such as cracks, distortion, or fretting at the disc holes. Replace if necessary.
  • Check and tighten the bolts securing the coupling disc to the engine flywheel, using the torque values specified by the engine manufacturer.
  • Reinstall the DE adaptor screen and drip-proof cover.

Maintenance Schedule:

3. Cooling System Check

An effective cooling system is vital to prevent the alternator from overheating.

Procedure:

1. Inspect the Fan Check for damaged vanes and cracks.
2. If Air Filters Are Fitted:
   • Remove air filters at the terminal box from their frames.
   • Wash and dry the air filters and gaskets to remove contaminant particles.
   • Inspect filters and gaskets for damage and replace them if necessary.
   • Reinstall the cleaned or new filters and gaskets.
3. Reinstall the Generator Set to prepare the unit for running.
4. Check Airflow to ensure air inlets and outlets are not blocked.

Maintenance Schedule:

4. Vibration Monitoring

Regular vibration monitoring can help detect potential issues before they become critical. The ideal position for monitoring the motor's vibration should be consistent.

Service Levels:

• Level 1: 250 hrs / 1 year
• Level 2: 1,000 hrs / 2 years
• Level 3: 3,000 hrs / 5 years
• Level 4: 30,000 hrs / 15 years

Electrical Preventive Maintenance

Electrical maintenance ensures the integrity and performance of the alternator's electrical systems.

1. Electrical Resistance and Insulation Resistance (IR) Testing

These tests are crucial for verifying the health of the alternator's windings and insulation.

Electrical Resistance Testing:

• Stop the alternator.
• Exciter Field (Stator): Disconnect F1 and F2 from the AVR and measure the resistance between them.
• Exciter Armature (Rotor): Disconnect rotor leads from the rectifier plate and measure the resistance.
• Main Field (Rotor): Disconnect DC leads from the rectifier plate and measure resistance (a micro-ohmmeter may be needed).
• Main Stator: Disconnect output leads and measure resistance between U1-V1, V1-W1, W2, U5-U6.
• PMG & Exciter Components: Disconnect leads and measure resistance between windings and earth.

Insulation Resistance Testing:

• Disconnect the relevant leads.
• Measure resistance between windings and earth.
• Repeat tests with and without the neutral-earth conductor.
• Record readings at intervals.
• If the reading is below the minimum required value, clean/dry and retest.

Service Levels for Insulation Resistance Tests: Pre-Commission, 250 hrs / 6 months, 1000 hrs / 1 year, 4000 hrs / 2 years, 12000 hrs / 3 years, 30000 hrs / 5 years.

2. AVR Inspection

The Automatic Voltage Regulator (AVR) is a critical component that requires regular checks.

Inspection Steps:

1. Remove the terminal box lid.
2. Check the tightness of fasteners securing the lid.
3. Verify that cables are firmly clamped at the terminal box gland.
4. Ensure all cables are anchored to prevent movement.
5. Inspect cables for any signs of damage.
6. Verify AVR accessories and control cables are correctly fitted.
7. If an anti-condensation heater is fitted, test its electrical resistance and insulation resistance.
8. Test the supply voltage to the anti-condensation heater.
9. Check that the AVR and accessories are clean, securely mounted, and cable connectors are firm.
10. For parallel operation, ensure synchronization control cables are securely connected.
11. Refit and secure the terminal box lid.

3. Rectifier Inspection

The rectifier assembly, including varistors and diodes, needs periodic testing and maintenance.

Test and Replace Varistors:

1. Inspect both varistors for signs of overheating, discoloration, or damage.
2. Check for loose connections due to vibration.
3. Discard any faulty or cracked varistors.
4. A serviceable varistor should show an open-circuit reading in both directions using a multimeter.
5. Replace the varistor if it is damaged.
6. Record the part number for correct replacement.
7. Reconnect all wires and leads securely.

Diode Testing and Replacement Procedure:

1. Disconnect the lead of one diode at the insulated terminal post.
2. Measure the voltage drop across the diode in the forward direction using a multimeter's diode test function. A healthy diode should have a forward voltage drop between 0.3–0.9 V.
3. Measure the resistance across the diode in the reverse direction using the 1000 VDC test voltage of an insulation tester. The reverse resistance should be below 20 MΩ.
4. If a diode is faulty (outside these ranges), remove all six diodes. They must be of the same type and manufacturer.
5. Apply a small amount of heat sink compound to the base of each new diode.
6. Check the polarity of each diode.
7. Screw each replacement diode into a threaded hole in the rectifier plate.
8. Apply a torque of 2.6–3.1 N·m (23–27.4 in-lb).
9. Replace both varistors with a matched pair.
10. Ensure all leads are secure and fasteners are tight.