Here’s the full procedure for paralleling an incoming AC generator to another AC generator already connected to the main switchboard:
Preparation:
- Safety First: Ensure all personnel involved are qualified electricians wearing appropriate PPE (Personal Protective Equipment) like safety glasses, gloves, and properly rated footwear.
- Lockout/Tagout: Lock out and tag out both generators to prevent accidental energization during the paralleling process.
- Generator Inspection: Visually inspect the incoming generator for any signs of damage, loose connections, or leaks. Ensure all control panels and meters are functioning correctly.
- Synchronization Check:
- Voltage Matching: Verify that the voltage of the incoming generator matches the voltage of the running generator connected to the main switchboard. Use voltmeters on both generators to confirm they are within a specified tolerance (usually within 2-3%).
- Frequency Matching: Ensure the frequency of the incoming generator is very close to the frequency of the running generator. Utilize frequency meters on both generators to confirm they are synchronized within a small margin (usually within 0.1-0.2 Hz).
- Phase Sequence Matching: Verify that the phase sequence (order in which the voltage peaks occur) of the incoming generator matches the phase sequence of the running generator. This can be done using phase sequence meters or by employing synchronizing lamps/scopes (explained later).
Synchronization Process:
- Warm Up the Incoming Generator: Start the prime mover (engine, turbine) of the incoming generator and allow it to reach operating temperature and stable speed.
- Adjust Speed Governor: While monitoring the frequency meter, carefully adjust the speed governor of the incoming generator to match the frequency of the running generator. This is typically done through a control panel or governor linkage adjustments.
- Synchronization (Using Synchronizing Lamps/Scope):
- Connect Synchronizing Lamps: Connect synchronizing lamps (three incandescent lamps connected in a specific way) between corresponding phases of the incoming and running generators.
- Observe Lamp Flickering: As the frequencies of both generators approach synchronization, the flickering rate of the synchronizing lamps will slow down. They will appear to brighten and dim together when perfectly synchronized.
- Synchronizing Scope (Alternative): A synchronizing scope can be used as an alternative to lamps. It provides a visual representation of the phase difference between the two generators. Aim for a steady pattern on the scope to achieve synchronization.
- Close Circuit Breaker: Once the voltage, frequency, and phase sequence are synchronized as verified by the lamps/scope, close the circuit breaker connecting the incoming generator to the main switchboard. This action should be done smoothly and at the point of zero phase difference (indicated by a steady pattern on the lamps/scope).
Post-Synchronization Checks:
- Monitor Voltage and Frequency: Monitor the voltage and frequency readings on both generators and the main switchboard after paralleling. Ensure they remain stable within acceptable tolerances.
- Load Sharing: If desired, adjust the load sharing between the generators using their respective governor controls. This allows for optimized power distribution according to the overall load demand.
- Documentation: Record the paralleling process in a logbook, including date, time, generator readings, and any observations made.
Important Notes:
- This is a general guideline, and specific procedures might vary depending on the generator models, control systems, and facility safety protocols. Always refer to the manufacturer’s instructions and relevant electrical codes for the proper paralleling procedure for your specific equipment.
- Paralleling generators requires proper training and experience due to the risk of electrical faults and equipment damage if done incorrectly. It’s recommended to have a qualified electrician oversee the process, especially for critical applications.
Additional Considerations:
- Automatic Synchronizing Systems: Modern generator control systems can include automatic synchronizers that handle much of the synchronization process electronically, reducing manual intervention.
- Safety Interlocks: Safety interlocks can be implemented to prevent accidental paralleling if certain conditions, like voltage or frequency mismatch, are not met.
By following these steps and adhering to proper safety precautions, you can successfully parallel an incoming AC generator with an existing generator connected to the main switchboard.