FGMO: What you should know about it

What is FGMO mode of operation?

Free Governor Mode Operation: The mode of governor operation which compensates the change in frequency by changing the generation is called Free Governor Mode Operation(FGMO). In a word, FGMO is the variation of generation according to the frequency.

The parameters of FGMO

    👉 Droop

    👉 Dead band

    👉 Load limiter

    👉 Ramp rate 

    👉 Amount of load under FGMO

Droop

It is the amount of speed (or frequency) change, which causes the change in generation from minimum to maximum.

Droop defines the relationship between changes in grid frequency and the corresponding adjustments in generator output. It is expressed as a percentage, indicating the required frequency change to effect a full-load change in generator output. For instance, a 5% droop means a 5% frequency deviation results in a 100% change in generator output. In FGMO, droop settings typically range between 4-6% for thermal plants and 2-3% for hydro plants.

Dead Band

The limit of frequency inside which the FGMO do not respond is called the dead band. If the dead band is not set, that means kept zero, then every moment the load will continue to change as the frequency is never possible to keep at it's rated value.

The dead band refers to a frequency range within which the governor does not respond to frequency changes, preventing unnecessary adjustments for minor fluctuations. In FGMO, minimizing or eliminating the dead band is crucial to ensure continuous sensitivity to frequency variations. According to the National Grid Code, governors should operate without deliberate dead bands to maintain grid stability

Ramp Rate

The variation of generation with respect to time is known as Ramp rate. It is mainly dependent on the ability of turbine. Higher the ramp rate, good for power system/grid but hurmful for turbine. Lower the ramp rate, good for machine or turbine but it is not good for system/grid. 

The ramp rate determines the speed at which a generator can increase or decrease its output. In FGMO, after an initial response to a frequency change, generators should return to their original set points gradually, typically at a ramp rate of 1% of output per minute. This controlled adjustment allows system operators to implement other control actions, such as load shedding, to maintain grid stability.

 Load Limiter

The upper limit and the lower limit of generation of the machine need to be fixed. The load of the generator varies from the set value according to the setting of droop and frequency deviation, but the load limiter will restrict the generation within it's set value.

The load limiter sets the maximum output a generator can achieve, preventing overloading and potential damage. In FGMO, load limiters are typically set at 105% of the generator's rated capacity, allowing temporary overloads during frequency drops to support grid stability. This setting enables generators to sustain increased output for short durations, typically around five minutes, during low-frequency events.

Total load under FGMO

The generation will vary according to frequency deviation and droop set. If the frequency deviation is more, then the load of machine may vary in high amount from it's set value even from 0% to 100% load. So it's required to set the limit of amount, it will vary from the load set value. 

The proportion of total generation capacity operating under FGMO significantly impacts grid stability. A higher percentage of generators in FGMO enhances the system's ability to respond to frequency deviations. For example, in the Western Region of India, implementing FGMO across approximately 10,000 MW of generation capacity increased system stiffness, improving the grid's resilience to frequency fluctuations

Understanding and appropriately configuring these parameters are vital for the effective operation of FGMO, ensuring that power systems can promptly and efficiently respond to frequency changes, thereby maintaining grid stability and reliability.