What is Free governor mode of operation FGMO

What is Free governor mode of operation FGMO
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What is Free governor mode of operation FGMO ? In short “FGMO” is a primary method for operating governors in power plants that automatically adjusts electrical power generation in response to changes in the frequency of the electricity grid. Its goal is to maintain a stable grid frequency, which is crucial for reliable power delivery.

Here’s how it works: FGMO

  • A governor in a power plant monitors the grid frequency.
  • If the frequency starts to drop (because demand for electricity is high), the governor automatically increases the power output of the plant.
  • Conversely, if the frequency goes up (because demand is low), the governor reduces power output.

FGMO Summative explanation

  1. Regulation/droop characteristics: FGMO entails that the governor of a power plant is free to govern its regulation/droop characteristics. This primary regulation is autonomous and an inherent property of turbine governing system.
  2. Stabilize frequency: The governing system senses the change in frequency and adjusts the control valve of working fluid so that mechanical power matches with the changed load. This automatic adjustment by the governor helps stabilize frequency.
  3. Droop Settings: In FGMO, the governor droop is set between 4-6% for thermal plants and 2-3% for hydro plants. Droop determines how much the plant output changes for a given change in frequency.
  4. Governor Parameters: Other governor parameters like deadband and limiters are also set to prevent too much change in output for small frequency deviations or large frequency swings.
  5. Grid Enhancement: Overall, FGMO improved frequency stability, reduced energy losses, and increased reliability in the Bangladesh grid. Minimal investments to activate governors had major benefits.

Frequency regulation

Control modePrimary controlSecondary controlTertiary Control
Used meansGovernorAGC Manual set pointSpinning, Non spinning reserve
Method of controlAutomaticAuto and ManuallyManually
Control placeLocallyCentrally
Control signalLocal sensorLocal sensor or system operator
Activation timeImmediatelyDepends on Power system
An Endeavor of Frequency Regulation by Free Governor Mode of
Operation in Bangladesh Power System

What is Free governor mode of operation FGMO

The speed governors installed on generators have a droop setting, usually around 5%. This droop setting determines how much the generator output will change for a given change in frequency.

Key Elements of FGMO

There are several key elements that enable effective FGMO:

  • No Deadbands – The governors respond across the entire normal frequency range from 47.5 Hz to 51.5 Hz without any deadbands or limits.
  • 105% Overload Capability – The generator load limiter is set to allow temporary overloading of up to 105% during low frequencies.
  • Primary Response – Generators instantly adjust their outputs in response to frequency changes. This primary response is sustained for 5 minutes.
  • Secondary Response – After the initial response, the generator slowly ramps back to its original setpoint over 5-10 minutes.
  • Monitoring – System operators closely monitor the response of generators to ensure adequate FGMO action.

Why is FGMO Important for Grid Stability?

FGMO provides the first stage of fast, automatic response to system disturbances. It helps:

  • Arrest large frequency swings following faults or load changes
  • Reduce the magnitude of frequency deviations
  • Avoid under-frequency load shedding
  • Prevent cascade tripping of generators
  • Increase overall system stiffness and stability

Without FGMO, frequency excursions can be much more severe following contingencies. FGMO acts as a vital stabilizing mechanism before slower secondary control actions are activated.

How does Droop Speed Control help in maintaining grid stability

Droop speed control is a method of regulating the output of a generator in response to changes in the grid frequency. It helps in maintaining grid stability by providing primary regulation, which is the instantaneous and automatic adjustment of generation to match the load demand. According to the web page context, some of the benefits of droop speed control are:

  • Reduced frequency fluctuations: Droop speed control reduces the rapid and large variations of frequency that occur due to load changes, unit trippings, or grid disturbances. This improves the quality and reliability of power supply and prevents damage to equipment and appliances.
  • Increased system stiffness: Droop speed control increases the system stiffness, which is the ratio of change in power to change in frequency. A higher system stiffness means that the frequency is less sensitive to power imbalances and can recover faster from disturbances. This enhances the security and stability of the grid and avoids grid collapse.
  • Avoided tripping of generators: Droop speed control allows the generators to vary their output within a certain range (usually 5% to 10%) depending on the frequency deviation. This prevents the generators from tripping on high or low frequency, which could worsen the situation and lead to cascading failures.
  • Frequency linked dispatch: Droop speed control enables the generators to follow the frequency linked dispatch guidelines, which are the rules for adjusting the set points of generators based on the frequency and the variable cost of generation. This helps in optimizing the economic operation of the grid and minimizing the unscheduled interchange of power.


Bangladesh Power System Reliability and Efficiency Improvement Project final report 4 May 2017


Report of the Committee on Free Governor Mode Operation of Generating Units

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