Parallel Operation of the Alternators

Interconnection of Electric Power Systems

The interconnection of electric power systems is critical for economic efficiency, reliability, and parallel operation. Interconnecting AC power systems requires synchronous generators to operate in parallel, a practice commonly employed in generating stations where two or more generators are connected via transformers and transmission lines, forming a grid-connected network. Under normal operation, all generators and synchronous motors in an interconnected system maintain synchronism, enabling optimized operating efficiency and enhanced reliability through parallel configuration.

When load demand exceeds the capacity of connected units, additional generators are paralleled to carry the load; conversely, during low-demand periods, non-essential units are disconnected to maintain high-efficiency operation.

Reasons for Parallel Operation of Alternators

Alternators are operated in parallel for the following key advantages:

• Higher Load Capacity: Multiple alternators can supply larger loads than a single unit.

• Efficiency Optimization: During light loads, some alternators can be shut down, allowing remaining units to operate near full load for higher efficiency.

• Maintenance Flexibility: Scheduled maintenance or inspection of one machine does not disrupt supply, as other units maintain continuity.

• Reliability Assurance: Generator breakdowns do not cause power outages, as parallel units compensate.

• Scalability: Additional machines can be added without modifying the initial installation to meet growing load demands.

• Cost Reduction: Parallel operation lowers both operating costs and energy generation expenses.

• Supply Security: Ensures more reliable power supply and enables economical generation across the system.

Necessary Conditions for Parallel Operation of Alternators

Synchronous machines operate in parallel through a process called synchronizing, where a new unit (incoming machine) is connected to an existing system (running machines or infinite busbar). To ensure safe parallel operation, the following conditions must be met:

• Phase Sequence Matching: The phase sequence of the busbar voltages must align with that of the incoming machine.

• Phase Synchronization: The busbar voltages and the incoming machine’s terminal voltage must be in phase.

• Voltage Equality: The terminal voltage of the incoming machine must match the busbar voltage.

• Frequency Matching: The frequency of the incoming machine’s generated voltage must equal the busbar voltage frequency.