FGMO: What you should know about it

What is the FGMO mode of operation?

Free Governor Mode Operation- The mode of governor operation that compensates for 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.

This mode allows for greater flexibility and stability in power systems, especially during fluctuations in load demand. By adjusting output in response to frequency changes, FGMO helps maintain a balanced and reliable electricity supply.

This adaptability is crucial for preventing system overloads and ensuring that consumers receive a consistent power supply. Additionally, FGMO can enhance the overall efficiency of the power grid by optimizing generation resources in real-time.

The parameters of FGMO

    👉 Droop

    👉 Deadband

    👉 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 cause a full-load change in generator output. For instance, a 5% droop means that 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 within which the FGMO does not respond is called the dead band. If the dead band is not set, that means it is kept at zero, then every moment the load will continue to change as the frequency is never possible to keep at its 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.

This approach helps in achieving a more responsive control system, allowing for quicker adjustments to maintain the desired frequency. As a result, grid operators can better manage supply and demand, reducing the risk of outages and improving overall reliability.

Ramp Rate

The variation of generation with respect to time is known as ramp rate. It is mainly dependent on the turbine's ability. The higher the ramp rate, the better for the power system/grid but the more harmful for the turbine. Lowering the ramp rate is beneficial for the machine or turbine, but it is not beneficial for the 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.

Maintaining this balance is crucial, as sudden fluctuations in generator output can lead to frequency instability, risking blackouts. By adhering to these ramp rate guidelines, operators can ensure a more reliable and resilient power grid.

 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 its 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 the machine may vary by a high amount from its set value, even from 0% to 100% load. So it's required to set the limit of the 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.