Uni-line Generator controls

Common issues

• Nuisance trip on reverse power or under/over frequency protection from incorrectly set relays after commissioning
• Loss of communication between controller and governor/AVR interface causing hunting or load-sharing instability
• Load-sharing imbalance between paralleled generators from degraded CAN bus wiring or termination
• Synchronizing failure (breaker will not close) from phase sequence or voltage-matching window errors
• Firmware/parameter mismatch after a controller replacement leading to incorrect protection curves
• Sensor/CT wiring faults producing false current or power readings
• Backup battery failure causing controller reset or loss of settings during a power dip

Inspection checklist

• Verify controller display readings against independent meters (voltage, frequency, current, power)
• Check load-sharing balance between paralleled generators under varying load
• Test protection functions (reverse power, over/under frequency, over/under voltage) against setpoints where practical
• Inspect CAN bus/communication wiring and terminating resistors
• Check backup battery condition and charging circuit
• Review event/alarm log for recurring trips or communication faults
• Confirm synchronizing (breaker close) sequence operates within the matching window
• Verify a current parameter backup exists and matches commissioning settings

Service intervals

Critical spares

• Backup battery for the controller
• Spare controller module or display unit of the same type, pre-programmed where possible
• CAN bus terminating resistors and connectors
• Current transformers matched to the installed rating
• Control circuit fuses

Safety

• Live testing on generator control/protection circuits carries electric shock risk - isolate and lock out where possible
• Incorrect parameter changes can defeat reverse power or overcurrent protection, risking equipment damage or fire
• Synchronizing errors can cause severe mechanical/electrical shock to the generator and its prime mover
• Arc flash risk when working in the switchboard/controller cabinet under load

Class survey

Class surveyors typically check protection function test records, synchronizing/load-sharing performance, and confirm the as-fitted parameter set matches the approved electrical protection coordination study.