Parallel operation of alternators—also called synchronization—refers to connecting one alternator in parallel with another alternator or a common bus-bar (grid). In modern power systems, multiple 3-phase alternators operate together to share load efficiently and ensure reliable power supply.
🔗 Why Parallel Operation?
- Power demand on the grid often exceeds the capacity of a single alternator.
- Interconnected systems (e.g., national grids) combine capacities—for instance, 500 MW units contribute to a 50,000 MW grid.
When connected to a large network, an alternator is said to be tied to an infinite bus-bar—known for its stable voltage and frequency.
✅ Conditions for Synchronizing with Infinite Bus‐Bars
Before paralleling, the following four conditions must be satisfied:
- Voltage magnitude must match the bus-bar voltage.
- Frequency of the alternator must equal the grid’s frequency.
- Phase sequence (e.g., R‑Y‑B order) must be identical.
- Phase angle between alternator and bus-bar voltages must be zero.
🛠️ Synchronization Methods
1. Three-Lamp Method
Uses three lamps connected between corresponding phases of the alternator and bus-bar:
- One lamp (straight connection) dims or goes dark when voltages match.
- The other two (cross‐connected) become equally bright only when phase and frequency are matched—indicating readiness to close the switch.
2. Synchroscope Method
A synchroscope shows the relative speed (phase angle) between the alternator and bus-bar:
- Clockwise pointer → alternator runs faster
- Anti‑clockwise → slower
- Pointer at 12 o’clock → perfect synchronization → close the breaker.
⚡ Advantages of Parallel Operation
- Efficiency: Alternators operate closer to full-load efficiency by adding or removing units as demand changes.
- Continuity of service: If one unit fails, others continue supplying power.
- Flexible maintenance: Units can be taken offline for maintenance without disrupting supply.
- Future expansion: New alternators can be added to meet growing load without redesigning the entire system.
📊 Quick Comparison Table
| Feature | Benefit |
|---|---|
| Voltage/Frequency Matching | Avoids circulating currents and instability. |
| Phase Matching | Prevents power surges and mechanical stress. |
| Incremental Load Sharing | Optimizes performance and minimizes losses. |
📝 Final Thoughts
Parallel operation (synchronization) of alternators is key to modern power systems, enabling flexibility, reliability, and scalability. Whether using the lamp method or synchroscope, strict compliance with synchronization conditions is crucial.