What is hunting in synchronous machine?

Hunting or Synchronizing power is an undesirable phenomenon that occurs in synchronous machines (generators or motors) during the process of synchronization. It refers to the oscillation or rocking of the rotor around its equilibrium position when it is subjected to alternating currents.

To understand hunting, let's consider a synchronous generator attempting to synchronize with the power grid. When the generator's voltage and frequency match the grid's, it is said to be in synchronism. However, if the generator's frequency differs from the grid's, a phenomenon known as "hunting" occurs.

During hunting, the generator's rotor oscillates back and forth around its equilibrium position due to the interaction between its magnetic field and the rotating magnetic field of the grid. The oscillations can cause the generator's voltage and frequency to fluctuate, leading to instability in the power system.

Here are the main factors that contribute to hunting:

Load Variation: Sudden changes in the electrical load on the synchronous machine can cause its speed to fluctuate. This variation in speed can lead to oscillations and result in hunting.

Inertia: The moment of inertia of the rotating mass (rotor) of the synchronous machine plays a crucial role in hunting. A machine with a high moment of inertia is more resistant to hunting than one with a low moment of inertia.

System Stiffness: The stiffness of the power system, which refers to its ability to resist changes in frequency, also influences hunting. A weak power system (with low system stiffness) is more prone to hunting than a strong power system (with high system stiffness).

Hunting can have several negative effects:

Generator Damage: Severe hunting can cause mechanical stress on the generator's shaft and bearings, leading to damage and reduced lifespan.

Voltage and Frequency Fluctuations: Hunting can cause the generator's voltage and frequency to oscillate, affecting other equipment connected to the power system and potentially disrupting sensitive loads.

System Instability: Hunting can lead to instability in the power system, causing generators and other devices to trip offline and potentially resulting in a blackout.

To mitigate hunting, power system engineers use various techniques such as high-speed synchronizing relays, synchronizing torques, and voltage regulators to ensure smooth synchronization and minimize oscillations in the system.