Caterpillar SR4B Generator Set

⚠ The VR3 regulator is protected by a fuse(s) and a solid-state overcurrent protection. If a fuse becomes open, contact a Caterpillar dealer.

1. Remove the access panel of the generator.
2. Loosen the locknut on the voltage droop potentiometer (1).
3. Remove the protective screw from the voltage level potentiometer (2) and from the voltage gain potentiometer (3).
4. Turn the voltage droop potentiometer (1) counterclockwise to zero droop. Tighten the locknut.
5. Turn the voltage gain potentiometer (3) counterclockwise to zero, then to about 1/4 of full range of clockwise travel.
6. Perform required maintenance on the engine before you start the engine.
7. Start the engine and allow the engine to warm up.
8. Increase engine speed to full governed rated speed (high idle).
9. Set the no-load voltage with the voltage level potentiometer (2) or the voltage adjust rheostat.
10. Close the load circuit breaker and apply full load gradually. Adjust governor control to nameplate frequency or rated speed.
11. If the voltmeter reading increases above no-load voltage, turn the voltage gain potentiometer counterclockwise. If it decreases, turn it clockwise.
12. Remove the load. If necessary, adjust the voltage level potentiometer (2) to obtain desired voltage.
13. Apply the load. Repeat Steps 10 through 12 until the voltage at no load equals the voltage at full load.
14. Tighten the locknuts. Install the protective screws and the access panel of the generator.

⚠ Do not exceed half rated speed

⚠ Do not allow output to exceed nameplate rating

Tools: Digital Multimeter, 12 VDC Battery

1. Disconnect wires F1 and F2 from voltage regulator
2. Disconnect generator load
3. Connect 12 VDC battery to wires F1+ and F2-
4. Operate generator at half rated speed
5. Measure AC voltage across terminals T1-T2, T1-T3, T2-T3
6. Record voltages at half speed, then at ±10% speed variations
7. Verify minimum 85 VAC output at half speed
8. Verify speed changes produce proportional voltage changes

Tools: 6V-7070 Digital Multimeter, 146-4080 Digital Multimeter (RS-232)

1. Touch the red ohmmeter lead to the rectifier terminal marked '+'.
2. Touch the black ohmmeter lead to terminals AC1, AC2, and AC3; the meter should indicate an open circuit or high resistance.
3. Touch the black ohmmeter lead to the rectifier terminal marked '+'.
4. Touch the red ohmmeter lead to terminals AC1, AC2, and AC3; the meter should indicate a good diode or low resistance.
5. Touch the black ohmmeter lead to the rectifier terminal marked '-'.
6. Touch the red ohmmeter lead to terminals AC1, AC2, and AC3; the meter should indicate an open circuit or high resistance.
7. Touch the red ohmmeter lead to the rectifier terminal marked '-'.
8. Touch the black ohmmeter lead to terminals AC1, AC2, and AC3; the meter should indicate a good diode or low resistance.
9. If the meter does not indicate the expected result, the rectifier is bad. Replace the rectifier.

⚠ Shorted diode can damage exciter rotor

Tools: Digital Multimeter 6V-7070

1. Set digital multimeter to diode range and remove all leads
2. Test forward bias on each diode (black to positive, red to AC terminals)
3. Verify readings between 0.4 and 1.0
4. Test reverse bias (red to positive, black to AC terminals)
5. Verify overload (OL) readings on reverse bias
6. Replace rectifier block if any reading is outside specifications

Tools: Ohmmeter, Test Light

1. Using an ohmmeter, place the ohmmeter across the varistor. The resistance should be a minimum of 15000 ohms.
2. Disconnect either lead of the varistor (CR7).
3. Place the test light across the varistor.
4. Observe the results. The lamp should not light.
5. Reverse the test light.
6. Observe the results. The lamp should not light.
7. If the test light illuminates in either direction, there is a short in the varistor. Replace any faulty varistors with comparable operating characteristics.

⚠ Temperature affects resistance; test at room temperature only

⚠ Winding damage if outside specifications

Tools: Digital Multimeter, Milliohmmeter (Wheatstone Bridge)

1. Disconnect winding from other components before measuring
2. Measure armature windings with milliohmmeter (L2, L4, L5)
3. Measure field windings with multimeter (L1, L3)
4. Test at room temperature only
5. Compare measurements to specification values
6. Verify no continuity between windings or between winding and ground

Tools: Varnished cambric tape 5N-4685, Vinyl plastic tape 5N-4686, Cable straps

1. Fasten leads using flat plated washer under bolt and nut
2. Apply two layers of varnished cambric high voltage tape
3. Overlap tape 50% of width while wrapping
4. Extend tape 25 mm onto wire insulation on each side
5. Apply two layers of vinyl plastic tape over cambric tape
6. Extend vinyl tape 51 mm onto wire insulation on each side
7. Group all phase leads and secure with cable straps

Tools: Flat plated washers, Cable straps

1. When multiple leads attach to bus bar, place on alternate sides
2. Use flat plated washers under bolt head and nut
3. Group all generator phase leads together after connection
4. Tie phase leads together with cable straps
5. Maintain minimum 25 mm clearance between phase-to-phase connections

Tools: Grease fitting, 8F-9866 Grease gun

1. Remove either the louver assembly or the rear plate from the rear of the generator housing.
2. Remove the top grease pipe plug and remove the lower grease pipe plug.
3. Install a grease fitting in the grease pipe.
4. Grease the shielded ball bearings with 2S-3230 Bearing Lubricant (53.28 mL (1.8 ounces) to 59.20 mL (2.0 ounces)).
5. Wipe off the excess grease. Remove the top grease fitting. Install the plug.
6. Operate the generator for one hour to allow the grease to expand and force excess grease from the cavity.
7. Stop the engine. Install the plug in the bottom grease pipe and wipe off the excess grease.
8. Install the louver assembly or install the rear plate.

Tools: 8T-0900 Clamp on ammeter (1200 amperes), External Power Source, Rheostat

1. Make an external power source.
2. Disconnect F1+ and F2- from the voltage regulator. Disconnect the generator load. Connect generator output leads T0, T1, T2, and T3. Install the clamp-on ammeter on output lead T1.
3. Connect the rheostat at maximum resistance value. Connect the external power source to wires F1+ and F2-.
4. Start the generator set and run at idle speed.
5. Monitor the phase current. Gradually increase engine RPM until rated phase current or full generator set speed is obtained.
6. If more phase current is necessary, slowly turn the rheostat until the rated phase current is reached.
7. On an hourly basis, stop the drying procedure and check the insulation resistance. Repeat until the insulation resistance is acceptable.

⚠ Personal injury or death can result from high voltage.

Tools: Audio/visual proximity tester, Ground straps, DO NOT OPERATE warning tags

1. Stop the engine.
2. Attach a DO NOT OPERATE or similar warning tag to the engine prime mover starting circuit. Disconnect the engine starting circuit.
3. Disconnect the generator from the distribution system.
4. Lock out the circuit breaker. Attach a DO NOT OPERATE or similar warning tag to the circuit breaker. Verify all points of possible reverse power flow are locked out.
5. For power, sensing, and control circuitry, remove the transformer's fuses.
6. Attach a DO NOT OPERATE or similar warning tag to the generator excitation controls.
7. Remove the cover of the generator's terminal box.
8. Use an audio/visual proximity tester insulated for the proper voltage rating to verify the generator is de-energized.
9. Add ground straps to the conductors or terminals. During the entire work period, these ground straps must remain connected.

⚠ Personal injury or death can result from electrocution. The megohmmeter applies a high voltage; discharge the leads before touching.

Tools: 142-5055 Insulation Testing Gp, 9U-6003 Insulation Testing Gp

1. Take the generator out of service.
2. Visually inspect the generator for moisture. If moisture exists, do not perform this insulation test. Dry the unit first.
3. Inspect the installation. Determine the equipment that will be tested by the insulation tester.
4. Discharge the capacitance of the windings.
5. Disconnect T0 from ground.
6. Disconnect the regulator sensing lead wires: 20, 22, and 24.
7. Connect the insulation tester's RED lead to ground.
8. Connect the insulation tester's BLACK lead to T0.
9. For units 600 volts or less set the voltage to 500 Volts. For units more than 600 volts set the voltage to 1000 Volts.
10. Use the 30/60 Time Resistance Method: apply voltage and observe readings at 30 seconds and 60 seconds.
11. Record the 60 second reading corrected for temperature. Record temperature and humidity. Remove voltage.
12. Evaluate the readings by comparing the 60 second resistance reading with previous readings taken under similar conditions.
13. Switch the insulation tester to OFF to discharge the leads, then disconnect the insulation tester's leads.