Synchronizing Two Feeders in AC Grid Lines

In an alternating current (AC) power system, synchronizing two feeders is a critical process that ensures seamless power transfer between independent sources. Whether connecting a generator to the grid or paralleling two grid supplies, synchronization plays a pivotal role.

What Is Feeder Synchronization?

Feeder synchronization refers to the precise alignment of voltage, frequency, and phase between two AC power sources. When these parameters match, the feeders can be safely connected in parallel, allowing efficient load sharing and redundancy.

How Is Feeder Synchronization Achieved?

Several steps are involved in achieving feeder synchronization:

1. Voltage Matching:
   • The voltages of both feeders must be closely aligned. Any significant deviation can lead to undesirable transients during connection.
   • Synchronizers monitor voltage differences and ensure they fall within acceptable limits.
2. Frequency Alignment:
   • Frequency synchronization is crucial. The frequency of the incoming feeder (e.g., a generator) should match that of the existing grid.
   • Small variations are tolerable, but excessive differences can cause instability.
3. Phase Matching:
   • Phase synchronization ensures that the waveforms of both feeders are in phase.
   • Zero phase difference indicates perfect synchronization.

The Role of Synchronizers

Synchronizers are specialized devices used during the synchronization process. Here are the key points:

• Check Synchronizers:
  • These devices determine if two voltages are in synchronism or nearly so.
  • They provide volt-free contacts that control circuit breakers (CBs) to permit or block CB closing.
  • Check synchronizers prevent CB closure until safe synchronization conditions are met.
  • Programmable error limits define acceptable differences during comparison.
• Auto-Synchronizers:
  • Auto-synchronizers automate the synchronization process.
  • They actively adjust the generator’s speed (prime mover) to match grid frequency.
  • Auto-synchronizers ensure smoother transitions during paralleling.

When Will Two Feeders Synchronize?

Two feeders will synchronize under the following conditions:

1. Phase Synchronization:
   • When the phase angles of both feeders are zero (perfect alignment).
   • Phase sequence must also match to avoid reverse rotation.
2. Frequency Match:
   • The incoming feeder’s frequency matches the grid frequency.
   • Small frequency deviations are acceptable, but close alignment is ideal.

Common Methods for Feeder Synchronization

1. Manual Synchronization:
   • Operators manually adjust the generator’s speed to match grid frequency.
   • Voltmeters, frequency meters, and phase angle indicators aid the process.
2. Automatic Synchronization:
   • Auto-synchronizers continuously adjust the generator’s speed.
   • They monitor voltage, frequency, and phase, ensuring precise synchronization.
   • Auto-synchronization minimizes human error and speeds up the process.

Feeder synchronization ensures a harmonious connection between power sources, preventing disturbances and optimizing system performance. Whether it’s a generator joining the grid or parallel grid supplies, synchronization guarantees a smooth transition of power.