Optimum dispatch is the state that

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The power system is in prior to any contingency

Explanation: Optimum dispatch refers to the operational state of a power system where all generating units are synchronized and scheduled to meet the load demand at the lowest possible cost, under the assumption that the system is operating under normal (secure) conditions prior to any contingency. It ensures that the incremental costs of all generators are balanced according to the coordination equation while respecting physical constraints.

Working Principle: The principle of optimum dispatch is based on the Equal Incremental Cost criterion. Mathematically, for a lossless system, we set $\frac{dF_i}{dP_i} = \lambda$ for all units, where $F_i$ is the fuel cost and $P_i$ is the power output. This state is maintained as long as the system remains in a 'pre-contingency' state, meaning no component has failed and the transmission lines are operating within their security limits.

Key Formulas: $\frac{dF_i}{dP_i} = \lambda$ — The coordination equation for optimum economic dispatch in a lossless system.; $\sum_{i=1}^{n} P_i = P_D + P_L$ — The system power balance constraint, where $P_L$ is transmission loss.

Key Points: Optimum dispatch aims to minimize the total operational cost of generation.; It requires the incremental cost of all committed units to be equal to a system-wide lambda ($\lambda$).; Security-constrained economic dispatch (SCED) extends this to maintain operations during contingencies.; The pre-contingency state is essential to ensure that the system has enough headroom to handle sudden outages.

Advantages: Minimizes fuel consumption and operational expenditure.; Improves system efficiency by balancing generation effectively.

Disadvantages: Requires high computational overhead for real-time adjustments.; Ignores potential emergency scenarios if strictly limited to pre-contingency analysis.

Applications: Load Dispatch Centers (LDC) operation.; Automated Generation Control (AGC) systems.

Additional Info: The state described in option B refers to the 'Secure' state within the security assessment hierarchy (Secure, Alert, Emergency, In-extremis, Restorative).. Option A is vague, while Option C describes an economic goal rather than a security operational state.. Economic Dispatch is specifically the process of allocating generation to meet load at minimum cost, assuming standard operating limits.

Answer: B is correct — Optimum dispatch is the economic and technical state of the power system while operating in a secure, pre-contingency condition.

Exam Tip: Always remember that economic dispatch is essentially a constrained optimization problem where the objective function is the cost curve and constraints include power balance and generator limits.

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