What is hunting in governors

Short Answer:

Hunting in governors refers to the continuous and rapid fluctuation of engine speed above and below the mean speed due to over-sensitivity of the governor. When a governor is too sensitive, it makes excessive corrections to small speed changes, causing the engine to oscillate instead of running smoothly.

This repeated variation in speed reduces efficiency and may cause mechanical damage. Hunting must be minimized by properly balancing sensitivity, stability, and damping in the governor mechanism.

Detailed Explanation :

Hunting in Governors

Hunting in governors is a mechanical phenomenon that occurs when the governor continuously fluctuates between high and low speeds around the mean speed. It happens because of over-correction made by a highly sensitive governor in response to even a slight variation in engine speed. Instead of quickly settling to the steady-state speed, the engine speed keeps oscillating. This repetitive rise and fall in speed is called hunting.

When the engine load suddenly changes, the governor detects the speed variation and adjusts the fuel or steam supply to bring the speed back to normal. However, if the governor is too sensitive, it may reduce or increase the supply more than required. As a result, the engine speed first drops below and then rises above the mean speed repeatedly. This cycle of fluctuation continues until proper damping is introduced.

Causes of Hunting

  1. Over-sensitivity of the governor: When the governor is designed to react to even very small speed changes, it overcompensates the control action, causing oscillations.
  2. Lack of damping or friction: In the absence of sufficient damping (resistance to motion), the governor balls and sleeve keep moving rapidly up and down without settling.
  3. Sudden change in engine load: A quick increase or decrease in load causes a sudden variation in speed that the governor cannot stabilize immediately.
  4. Incorrect design of controlling mechanism: Poor balancing of the governor mechanism or improper spring tension in spring-loaded governors can lead to hunting.
  5. Delay in control response: In some mechanical systems, there is a time lag between the detection of speed change and the corrective action, which leads to overshooting and hunting.

Effects of Hunting

  • Continuous fluctuations in engine speed lead to uneven operation and vibration.
  • It causes wear and tear of mechanical components like bearings and shafts due to repeated acceleration and deceleration.
  • The efficiency of the engine or machine reduces because of unstable working conditions.
  • It can damage delicate parts of the governor and the connected fuel control system.
  • In power generation units, it causes unstable voltage and frequency output.

Prevention and Control of Hunting

To avoid hunting, several techniques are used to improve governor performance:

  1. Proper Damping: Frictional or hydraulic damping is provided to absorb excess energy and bring the governor to rest quickly.
  2. Balanced Sensitivity: The governor should neither be too sensitive nor too insensitive. Optimum sensitivity ensures that the governor responds accurately without overshooting.
  3. Stable Design: Proper design of linkages, springs, and rotating masses ensures smooth operation.
  4. Gradual Load Variation: Sudden load changes should be avoided to maintain steady speed.
  5. Use of Flywheel: In some cases, a flywheel is used along with the governor to stabilize fluctuations in speed.

Hunting can be analyzed using the governor’s characteristic curve, which shows the relationship between speed and controlling force. A stable governor must have a gradual change in controlling force with speed. If the controlling force changes too sharply, it increases the risk of hunting.

In modern engines, electronic governors or control systems use feedback mechanisms to detect and correct speed changes smoothly, thus eliminating the hunting effect almost completely.

Conclusion:

Hunting in governors is the continuous oscillation of engine speed around the mean value due to over-sensitivity and lack of damping. It leads to unstable operation and mechanical wear. By providing adequate damping, proper sensitivity, and stable design, hunting can be minimized, ensuring smooth and efficient engine performance.