A synchronous generator, also known as an alternator, is a device that converts mechanical energy into electrical energy by generating alternating current (AC). Maintaining synchronism with the AC power system is crucial to ensure that the generator's output voltage and frequency match those of the power grid. If a generator loses synchronism, it can lead to instability, power quality issues, and even system-wide failures. Here's how a synchronous generator maintains synchronism:
Rotational Synchronization: The generator's rotor, which contains a set of electromagnets, is mechanically connected to a prime mover (such as a steam turbine, gas turbine, or hydroelectric turbine). The prime mover provides the mechanical energy needed to turn the rotor. This rotation creates a rotating magnetic field within the generator.
Stator Winding Interaction: The stator, the stationary part of the generator, contains a set of stationary windings. These windings are connected to the external electrical circuit and the power grid. As the rotor's magnetic field rotates, it induces a voltage in the stator windings, following Faraday's law of electromagnetic induction.
AC Voltage Generation: The interaction between the rotating magnetic field of the rotor and the stationary stator windings causes the stator windings to produce an alternating voltage. This voltage is the generator's output voltage and is typically three-phase AC.
Matching Frequency and Voltage: For synchronism to be maintained, the frequency and voltage of the generated AC output must match the frequency and voltage of the power grid. The grid operates at a specific frequency (such as 50 Hz or 60 Hz) and voltage level. The generator's prime mover is controlled to maintain a constant rotational speed, ensuring that the generated frequency closely matches the grid frequency.
Automatic Voltage Regulator (AVR): To regulate the generator's output voltage and ensure it matches the grid voltage, synchronous generators use an Automatic Voltage Regulator (AVR). The AVR monitors the generator's output voltage and adjusts the field current supplied to the rotor's electromagnets. This, in turn, adjusts the strength of the magnetic field, affecting the generator's output voltage. The AVR responds to changes in load and other conditions to maintain voltage stability.
Governor Control: The prime mover's governor system controls the mechanical input to the generator. If the grid frequency starts to deviate from the desired frequency due to changes in load, the governor adjusts the prime mover's speed to correct the frequency and maintain synchronism.
By carefully controlling the prime mover's speed and adjusting the generator's field current through the AVR, a synchronous generator can continuously adjust its output frequency and voltage to match those of the power grid. This synchronization process ensures the stable and reliable operation of the entire interconnected power system.