Results and Discussions – AC Scenario

This test case is focused on studying the performance of the developed decision making framework in the AC scenarios. For demonstration purposes, the probabilistic ACOPF-based optimization problem is solved with inclusion of the predicted wind and load data at hour 20. Similar to previous case study, the possibility of at most 5 TLS actions in an hour is assumed. A total of 80 optimal solutions are obtained each of which would differently impact the objectives [see Figure 26 - Figure 29] (Stage 1).

Figure 26 to Figure 29 illustrates how the optimal TLS candidates for economic gains would affect the other objectives. According to Figure 26, as the number of optimal TLS actions increases, the higher percentage of economic saving would be realized. The minimum and maximum cost saving would be in the amount of k$43.376 and k$958.982, respectively, in case of 1-line and 5-line TLS actions. Figure 27 demonstrates that the system instability risk may improve up to 61.53% compared to the base case for a 3-line switch candidate while it degrades the most up to -218.01% for a 5-line TLS option.

Among all the optimal topology control candidates found, the maximum improvement in network losses and system EDNS index would be 30.7% and 200.29%, respectively [see

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Figure 26. Impact of ACOPF-based optimal TLS candidates on system dispatch cost.

Figure 27. Impact of ACOPF-based optimal TLS candidates on system instability risk.

Figure 28. Impact of ACOPF-based optimal TLS candidates on network losses.

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Figure 29. Impact of ACOPF-based optimal TLS candidates on system EDNS – IRAN 400kV Transmission Grid.

Figure 28 and Figure 29]. However, the resulting optimal TLS candidates may adversely affect these two system performance indicators up to -153.99% and -21.48%, for a 5-line and 3-line TLS actions, respectively. All the 80 TLS candidates are then screened in the developed AC feasibility check platform (while assumed to be stable due to the lack of dynamic data). The search space for the developed multi-objective decision making framework contains the survived 74 optimal TLS plans among which the final solution would be selected for implementation. The optimal Pareto fronts, demonstrative of the compromise between various objectives of interest for the non-dominant solutions, are obtained through NSGA-II application with 100 iterations and the results are demonstrated in Figure 30 -Figure 33.

The range of the optimal dispatch cost (corresponding to the optimal TLS candidates in the Pareto fronts) varies between M$4.221 and M$5.137 reflecting a total of 17.4% and 1.18% cost savings respectively (Stage 2). Similarly, the selected non-

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Figure 30. Non-dominant ACOPF-based solutions of the multi-objective problem:

Trade-off between the generation dispatch cost and system instability risk.

Figure 31. Non-dominant ACOPF-based solutions of the multi-objective problem:

Trade-off between the generation dispatch cost and system EDNS.

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Figure 32. Non-dominant ACOPF-based solutions of the multi-objective problem:

Trade-off between the generation dispatch cost and network losses.

Figure 33. Non-dominant ACOPF-based solutions of the multi-objective problem:

Trade-off between the network losses and system instability risk.

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dominant solutions in the Pareto fronts would lead to improvements in the system EDNS reliability index ranging from 265MW/yr. to 407MW/yr.

The fuzzy satisfying method is applied on the non-dominant solutions and the results for various satisfaction levels (corresponding to various objectives reflecting the operator expertise and judgments) are tabulated in Table 8 (Stage 3). The final decisions for implementing the optimal TLS candidates can be made for various selections of satisfaction levels for each objective (see Table 8). For instance, one can compare the first and second rows of the table, where an increase in _d3 is realized. As a result, the final solution for TLS implementation has been changed from a 2-line TLS plan with M$4.97 dispatch cost (and higher reliability) to another involving 3-line TLS actions with an overall economic value of M$4.89 (and a lower reliability performance), all compared to the system base case condition.

Table 8. Operator Satisfaction Levels and Final Optimal ACOPF-based TLS Solutions:

IRAN 400kV Transmission Grid

Satisfaction Levels Objective Function Value Final Switching

103 4.6 Conclusions

This Section offers the following contributions:

 New multi-objective optimization decision making paradigm for adoption of network topology control in economic scenarios is proposed.

 Several critical and contradictory/competing objectives for TLS implementation taking into account both ISO’s and TSO’s requirements are incorporated and quantified.

 Probabilistic nature of the involved uncertainties (e.g., renewable generation and variable loads) is efficiently modeled through the 2-PEM technique.

 The proposed probabilistic multi-objective decision making framework is handled via a robust elicits optimization technique, i.e., NSGA-II, following by the fuzzy satisfying method to account for the TSO’s preference and practical experiences.

 The impact of optimal transmission line switching (TLS) on power system requisite performance measures (e.g., generation dispatch cost, network losses, system LOLP and EDNS reliability indicators, as well as the instability risk) is numerically demonstrated. As hypostatized before, different TLS solutions may migrate the grid to new operating conditions with different levels of mentioned performance characteristics. This, hence, verified the need for the proposed all-inclusive decision support tool for TLS implementation decision making.

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 The performance of the suggested multi-objective optimization framework for topology control decision making is thoroughly investigated through two case studies where uncertainties of load and renewables are probabilistically handled.

 While several DCOPF- or ACOPF-based topology control plans (involving one or multiple TLS actions) may be suggested at a given hour for economic gains, it is demonstrated that the proposed decision making framework can efficiently recognize the final plan for reliable implementation.

The presented framework provides the TSOs with the tradeoffs between various objectives (system reliability, system stability, network loss, and system economics) when deciding on TLS adoption in bulk power grids. This suggested decision support tool will further help the decision makers to more reliably select the optimal TLS plans for final implementation.

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5 CIRCUIT BREAKER HEALTH ASSESSMENT: THE KEY TO RELIABLE