Synchronisation of Alternators

Conditions for connecting an alternator in parallel with the grid.

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Before closing the breaker, the incoming machine must match the grid:

Voltage magnitude equal;
Frequency equal (in practice slightly higher);
Phase sequence the same;
Phase angle in step.

Methods: dark-lamp / bright-lamp methods, a synchroscope, or automatic synchronisers. Closing out of phase causes huge currents and torque that can damage the shaft and windings. Once synchronised, steam input controls the real power and excitation controls the reactive power.

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