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Examoogle • User • info@examoogle.com • EE-2024-8821
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The effect of speed governor dead band is that
Governor becomes dead
Increase or decrease in the speed occurs before position of control valve changes
Speed becomes constant
None of above
Increase or decrease in the speed occurs before position of control valve changes
Quick Summary: The dead band of a speed governor is the range of speed variation within which the governor does not respond. Consequently, the control valve remains stationary even if the system frequency or speed fluctuates slightly.
The dead band of a speed governor is the range of speed variation within which the governor does not respond. Consequently, the control valve remains stationary even if the system frequency or speed fluctuates slightly.
Ndead=±21(ΔN) — Typical range of speed variation within which the valve position remains constant
The dead band is primarily caused by mechanical friction, backlash, and clearances in the governor linkage mechanism. Until the speed deviation exceeds a specific threshold defined by the sensitivity of the mechanical components, the error signal is insufficient to overcome static friction (stiction) to move the pilot valve.
Dead band is an undesirable but inevitable characteristic of mechanical governors due to friction.
It limits the sensitivity of the primary frequency control loop.
Higher dead band leads to poorer frequency regulation in a power system.
Modern electronic (digital) governors have negligible dead bands compared to mechanical types.
Prevents excessive 'hunting' or continuous oscillation of control valves due to minor noise
Reduces wear on mechanical actuator components
Causes steady-state frequency errors
Reduces the effectiveness of Load Frequency Control (LFC)
Increases the settling time during small load disturbances
Thermal power plant steam turbines
Hydroelectric generator speed control
The dead band is often expressed as a percentage of the rated speed, typically in the range of 0.05% to 0.1%.
Option A is incorrect because the governor is not 'dead' or broken; it is simply insensitive to small signals.
Option C is incorrect because the speed does not become constant; rather, the control mechanism fails to correct the speed error.
B is correct — It refers to the range of speed deviation over which the governor mechanism fails to initiate a corrective action on the control valve due to internal mechanical friction.
In Control Systems, dead band is a type of 'non-linearity' that creates a localized region of zero gain, impacting the system's ability to achieve precise tracking.