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Table of Contents
Case Study
Resolving Overvoltage Issue in CAT 3512C Emergency Generator on Jack up drilling rig
Table of Contents
Background
Industry
Oil & Gas
Solution
Generator
Troubleshooting
Make & Model
CAT 3512C
Engine
Asset
Jack-up
Drilling Rig
Objective
To diagnose and resolve an overvoltage issue in the Emergency Generator that prevented the Circuit Breaker from closing during a blackout and to ensure operational readiness of Main Generator No.1 with a successful load trial.
Challenge / Problem Context
Emergency Generator started but its Circuit Breaker failed to close.
Customer observed an overvoltage issue during blackout conditions.
Emergency Generator could not be started for testing due to ongoing rig operations.
Loose PT (Potential Transformer) wire connection found in AVR input circuit.
AVR had been programmed using Main Generator No.1 settings, which caused compatibility issues.
Intermittent common alarms reported in Main Generator No.5.
Winding and insulation resistance needed to be verified to rule out internal faults.
What Did We Do?
Conducted a detailed safety and technical briefing onboard with the Chief Electrical Engineer and ET team.
Performed insulation resistance and winding resistance tests on the Main Stator, Main Rotor, Exciter Rotor and Stator, PMG Stator, and Diode Assembly—all results were satisfactory.
Identified a loose PT wire connection in the AVR input circuit and corrected it.
Bypassed the AVR and used external 12V DC excitation to test the alternator voltage at idle and rated RPM—results were stable and confirmed alternator health.
Reconnected the AVR and tested voltage output at both idle and rated RPM, confirming normal voltage of 600V AC.
Reviewed schematic drawings of the Circuit Breaker control circuit of Main Generator No.1 and conducted a successful load trial.
Investigated and resolved intermittent alarms in Main Generator No.5 by inspecting and reinstalling the harness for the lubricating oil and fuel pressure sensors.
Verified and documented the results of all diagnostic tests, including winding and insulation resistance measurements, and completed the report for customer validation.
Results That We Achieved
Resolved overvoltage issue by identifying and correcting a loose PT wire in the AVR circuit.
Validated alternator functionality with successful testing at idle and rated RPM, confirming 600V AC at full speed.
Confirmed AVR stability after reinstallation and eliminated risk of future overvoltage during operation.
Ensured operational readiness of Main Generator No.1 by successfully conducting a load trial with satisfactory performance.
Successfully completedCAT Generator Repair Services by resolving the overvoltage fault in the Emergency Generator’s AVR circuit.
