As per CERC guidelines, thermal generating sets with a capacity of more than 200 MW should be under Restricted Governing Mode of Operation.

In the RGMO, floating frequency concept is used in which the frequency set point is allowed to float between 49 to 50.5 Hz. Load corrections are made whenever the frequency changes from floating frequency set point. This change is limited to _+5% of machine rating. The load change so made is sustained for approximately 6 minutes (dynamic time delay.

However small changes upto +_0.03 Hz are ignored for load corrections. The set point is generated from the actual speed with a time delay of upto 2 minutes. When the frequency changes by more than +_0.03 Hz, a HOLD signal is generated (for a period of minimum of 3 minutes to a maximum of 6 minutes proportional to the frequency change) and forces the set point remain steady.

When the generator frequency is lowering from 50.2 Hz, load rise has to be effected upto 5% as per the droop characteristics of the set. When the generator frequency is lowering towards 50.2 Hz from a higher frequency, the load correction signal is blocked.

When the frequency rises from 50.2 Hz to a higher value, load reduction signal is released upto 5% as per the droop characteristics. When the frequency is lowering below 49 Hz or above 50.5 Hz, the load change will be as per the existing droop settings.

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