A Live Grid Will Not Wait for the Generator

Before a generator breaker closes, the incoming machine must align with the energized bus. A mismatch can create severe electrical and mechanical stress.

1. Confirm Phase Sequence

The generator and grid must share the same three-phase rotation. Verify sequence during commissioning and after wiring changes before synchronizing.

2. Match Voltage Magnitude

Adjust generator excitation until terminal voltage is within the approved synchronizing window around bus voltage. A mismatch drives unwanted reactive current.

3. Bring Frequency Close

Use the prime-mover governor to bring generator frequency close to grid frequency. The remaining difference controls how quickly the phase angle moves.

4. Watch the Phase Angle

A synchroscope shows whether the incoming generator leads or lags the bus and how the angle changes. The target is the permitted closing window near alignment.

5. Allow for Breaker Closing Time

Breaker contacts do not move instantly. The synchronizer must issue its command early enough for the contacts to meet inside the approved phase-angle window.

6. Block an Unsafe Close

Synchronism-check protection should prevent closure when voltage, frequency or angle lies outside its settings. Do not bypass an unexplained block.

7. Verify the Connected Machine

After closure, confirm stable current, active power and reactive power. Synchronizing completes the connection; post-close monitoring confirms the result.

Sequence. Voltage. Frequency. Angle. Then Close.

Treat synchronization as an interlocked process, not a single switch action. Align the sources, account for breaker timing, and verify the machine afterward.