Optimum dispatch state is

Question

Examoogle · Accepted Answer

Not secure

Explanation: In power system operation, the 'Optimum Dispatch' (Economic Load Dispatch) state is focused solely on minimizing the total cost of generation by adjusting the power output of generators, often at the expense of security margins. Because it prioritizes cost optimization over the static security constraints (N-1 criteria), it is inherently 'Not Secure' compared to a state that explicitly incorporates security constraints.

Working Principle: The Economic Load Dispatch (ELD) problem involves solving $\min F = \sum C_i(P_i)$ subject to $\sum P_i = P_D + P_{loss}$. This optimization often pushes the system toward boundary constraints (e.g., thermal limits or bus voltage limits) to maximize efficiency, thereby leaving the system vulnerable to contingency events, which renders the state 'Not Secure' in terms of operational reliability.

Key Formulas: $F_T = \sum_{i=1}^{n} (a_i P_i^2 + b_i P_i + c_i)$ — Total generation cost function; $\frac{dC_i}{dP_i} = \lambda$ — Coordination equation for optimum dispatch

Key Points: Optimum dispatch focuses on economic efficiency ($\min$ cost).; Security-constrained dispatch incorporates system reliability margins.; The transition to optimum dispatch often utilizes the full capacity of generators.; System security and economic efficiency are typically inversely related in unconstrained models.

Advantages: Minimal fuel expenditure; Maximized thermal efficiency of plant units

Disadvantages: High vulnerability to contingency failure; Low operational reserve margins

Applications: Energy management system (EMS) optimization; Long-term generation scheduling

Additional Info: A state is considered secure if all equipment is within limits and no violation occurs under N-1 contingencies.. Option A is incorrect because optimum dispatch does not guarantee security.. Option B is vague; security is typically treated as a binary or probabilistic threshold.

Answer: C is correct — An optimum dispatch state prioritizes cost minimization, which often ignores the security margins required to handle contingencies, thus classifying it as 'Not secure'.

Exam Tip: Always remember that in power systems, there is a fundamental trade-off between the 'Economic Dispatch' (cost-focused) and 'Security-Constrained Economic Dispatch' (SCED) (reliability-focused).

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