Explain AGC and the three levels: primary, secondary, tertiary control.

Explain AGC and the three levels: primary, secondary, tertiary control.

• A. Primary control provides fast automatic frequency response via governors; secondary control (AGC) automatically adjusts tie-line power flows to restore frequency; tertiary control optimizes economic dispatch and reserves.
• B. Primary control sets economic dispatch; secondary handles protection; tertiary manages voltage regulation.
• C. Primary and secondary controls are identical in function; tertiary control is passive.
• D. AGC consists of two levels only: primary and secondary.

Answer: (C)

Automatic Generation Control coordinates how much power is being produced to keep the whole system stable in frequency and to match the planned power exchanges between areas. It works through three levels that operate on different timescales and with different goals. Primary control is the immediate, local response. When the system frequency changes, turbine governors at each generator react automatically and almost instantaneously to counter that deviation. This fast, decentralized action uses droop characteristics so generators share the load changes fairly. It dampens swings and helps keep frequency from drifting further, but by itself it doesn’t hold the frequency exactly at the nominal value or correct long-term imbalances. Secondary control, often called Automatic Generation Control, is a centralized layer that continuously monitors the actual system frequency and the power flow between control areas (the tie-lines). It computes an area control error, which combines frequency deviation and any mismatch in scheduled tie-line power. Using this information, it adjusts selected generator outputs in a coordinated way to bring the frequency back to its nominal value and to restore the tie-line flows to their scheduled values. This produces a zero steady-state error and typically operates on a timescale of seconds to minutes, with integral action to eliminate residual errors. Tertiary control covers the slower, economic and strategic adjustments. It involves re-optimizing generation dispatch to minimize system cost while maintaining adequate reserves and reliability. Tertiary control can re-dispatch units, update schedules, and plan for future conditions, helping the system prepare for disturbances and changes in demand or resource availability over longer periods (hours to days). In short, primary control provides fast stabilization, secondary control (AGC) corrects frequency and tie-line deviations to nominal values, and tertiary control optimizes economic operation and reserves on longer timescales.

Automatic Generation Control coordinates how much power is being produced to keep the whole system stable in frequency and to match the planned power exchanges between areas. It works through three levels that operate on different timescales and with different goals.

Primary control is the immediate, local response. When the system frequency changes, turbine governors at each generator react automatically and almost instantaneously to counter that deviation. This fast, decentralized action uses droop characteristics so generators share the load changes fairly. It dampens swings and helps keep frequency from drifting further, but by itself it doesn’t hold the frequency exactly at the nominal value or correct long-term imbalances.

Secondary control, often called Automatic Generation Control, is a centralized layer that continuously monitors the actual system frequency and the power flow between control areas (the tie-lines). It computes an area control error, which combines frequency deviation and any mismatch in scheduled tie-line power. Using this information, it adjusts selected generator outputs in a coordinated way to bring the frequency back to its nominal value and to restore the tie-line flows to their scheduled values. This produces a zero steady-state error and typically operates on a timescale of seconds to minutes, with integral action to eliminate residual errors.

Tertiary control covers the slower, economic and strategic adjustments. It involves re-optimizing generation dispatch to minimize system cost while maintaining adequate reserves and reliability. Tertiary control can re-dispatch units, update schedules, and plan for future conditions, helping the system prepare for disturbances and changes in demand or resource availability over longer periods (hours to days).

In short, primary control provides fast stabilization, secondary control (AGC) corrects frequency and tie-line deviations to nominal values, and tertiary control optimizes economic operation and reserves on longer timescales.