Dispatch

Dispatch is the real-time process of directing generators to produce specific amounts of power so that total generation continuously matches system demand plus transmission losses, while respecting network constraints and maintaining reliability margins. It is the operational heartbeat of any power system.

Key Aspects of Dispatch:

• Time Scales: Dispatch operates across multiple time scales, from automatic generation control (AGC) signals every 2–4 seconds for frequency regulation, to 5-minute economic dispatch intervals in organized markets, to 15-minute or hourly re-dispatch cycles in bilateral systems.
• Generation-Load Balance: At every instant, total generation must equal total load plus losses. Any mismatch causes system frequency to deviate from nominal (50 or 60 Hz), with excess generation raising frequency and deficit lowering it.
• Market Integration: In liberalized electricity markets, dispatch is tightly coupled with market clearing: generators submit bids, the market operator clears the market based on merit order, and the resulting schedules become dispatch instructions subject to security constraints.
• Security Constraints: Dispatch must respect thermal limits on transmission lines, voltage limits at buses, and stability margins. Security-constrained dispatch (SCD) modifies the pure economic solution to ensure the system remains secure even after credible contingencies (N-1 criterion).
• Renewable Integration: The growth of variable renewable energy (wind and solar) has made dispatch more complex, requiring faster ramping from conventional units, more frequent re-dispatch, and coordination with energy storage and demand response to manage variability and uncertainty.