A synchronous generator is an electrical machine that converts the mechanical power of a spinning shaft into alternating current (AC) electrical power at a particular frequency determined by the speed at which the generator is spinning. In an AC electric power system, synchronization is the process of matching the frequency of a generator to all other synchronous generators on the system. An AC generator cannot deliver power to an electrical grid without causing a disturbance unless it is running at the same frequency as the network. And if two segments of a grid are disconnected, they cannot exchange AC power until they are brought back into synchronization. For this reason, grids that normally run disconnected from each other cannot exchange AC power without first going through a process to synchronize the exported power to the frequency of the importing grid. Non-synchronous sources of power such as solar photovoltaics and batteries are synchronized using power electronics.
When a synchronous generator is connected to the grid, the process of synchronization is required to ensure the generator is operating at the proper frequency. This process is also called paralleling the generator to the grid. This process comprises multiple steps:
- The generator is brought up to the synchronous speed while still disconnected from the grid
- The frequency as well as the relative phase of the generator and the grid are compared using instrumentation
- Necessary adjustments are made to the generator speed so that frequency and phase match precisely
- The electrical connection is established by closing the circuit breaker between the generator and the bus
- The power output of the generator is brought up to its desired level