Short Answer:

A synchronous machine contributes to system stability by maintaining synchronism with the power system during normal and disturbed conditions. It provides inertia, supports voltage regulation, and supplies or absorbs reactive power, helping to balance the system’s frequency and voltage.

During faults or sudden load changes, the mechanical and electrical interactions in a synchronous machine help stabilize rotor angles and maintain power flow. Its ability to store and exchange kinetic energy makes it essential for maintaining transient, voltage, and frequency stability in the grid.

Detailed Explanation:

Contribution of synchronous machine to system stability

Synchronous machines, especially synchronous generators, are central components in power systems. Their stable operation is crucial for keeping the entire grid synchronized. System stability depends on how well these machines respond to disturbances, such as faults, load changes, or generator disconnection.

Synchronous machines interact with the system both mechanically and electrically. Their mechanical rotation provides inertia, which resists sudden changes in speed or frequency. Electrically, they manage reactive power and maintain terminal voltage through their excitation systems.

Together, these features allow synchronous machines to absorb disturbances and support recovery, making them key players in ensuring the system stays stable and reliable.

Key ways a synchronous machine supports system stability

1. Rotor angle (transient) stability:
   • When a fault occurs or the load suddenly changes, the rotor angle of the generator may shift.
   • The synchronous machine responds by adjusting power output based on the rotor motion.
   • The internal torque created by the magnetic field helps the rotor slow down or speed up appropriately, allowing it to regain synchronism.
2. Inertia contribution:
   • Synchronous machines have rotating masses (rotors) that store kinetic energy.
   • This inertia resists sudden changes in system frequency and damps frequency oscillations after disturbances.
   • Inertia slows down the rate of change of frequency (RoCoF), giving time for control systems to react.
3. Voltage stability and reactive power control:
   • Through excitation control, synchronous machines regulate their terminal voltage.
   • They supply or absorb reactive power to support voltage levels across the network.
   • During voltage dips, they increase excitation to boost voltage; during high voltage, they absorb reactive power to stabilize the system.
4. Frequency stability:
   • Synchronous machines participate in primary frequency control through speed governors.
   • When frequency drops due to imbalance, the machine increases its output; when frequency rises, it reduces power output.
   • This balances active power in the system and helps restore frequency to normal.
5. Damping power system oscillations:
   • Using devices like Power System Stabilizers (PSS) connected to the AVR, synchronous machines help damp small signal oscillations, improving small signal stability.
   • This ensures better coordination among machines and avoids slow oscillations that can grow uncontrollably.

Long-term importance

• In traditional grids, synchronous machines dominate and provide natural stability.
• With increasing integration of inverter-based renewables, the loss of synchronous machines is becoming a challenge.
• Efforts are being made to replicate their stabilizing effects using synthetic inertia and advanced control systems.

Conclusion:

A synchronous machine contributes significantly to system stability by offering inertia, rotor angle correction, voltage regulation, and frequency control. Its mechanical and electrical properties make it a vital part of a stable and responsive power system. Without synchronous machines, maintaining grid stability during disturbances would be much more difficult.