Gas Network's Impact on Power System Voltage Security

Abstract : Due to the energy linkage between electricity and gas networks, assessing the voltage security of the electricity system without considering the practical constraints of both systems, may lead to unrealistic values of loading margins (LM). This work proposes a model for investigating the impact of gas networks on the voltage security of electric transmission networks. The overall objective is to maximize the LM of the electricity network while satisfying all relevant constraints in both gas and electricity networks such as hourly line pack of gas pipelines, reactive power capability limits of generators, and complementarity constraints representing the generators active/reactive power limits based on the capability curves, power flow equations at both current operation, and security limit points. Three (small, medium, and large) case studies are presented as the applications of the proposed model for LM maximization in power systems that are highly coupled with gas networks. The obtained results corroborate the impact of both gas and electrical networks operation constraints such as voltage and reactive power limits, nodal gas pressure limits, gas network loading as well as the line pack phenomenon of gas pipelines on the LM of power systems.
 ? Power flow analysis is very important in planning stages of new networks or addition to existing ones like adding new generator sites, meeting increase load demand and locating new transmission sites. ? The load flow solution gives the nodal voltages and phase angles and hence the power injection at all the buses and power flows through interconnecting power channels. ? Grid congestion is often associated with a cascading collapse leading to a major blackout. Such a collapse is characterized by a self-sustaining sequence of line outages followed by a topology breakup of the network.
 ? These curves are generated by running many power flow cases using conventional methods. ? While such procedures can be automated, they are time-consuming and do not readily provide all information required to determine the causes of stability problems. ? The GBI allows to monitor if a contingency poses a voltage stability issue. Then ABI and SBI indexes can be used within the DSA tool to derive rules for operators, which can be built using decision trees. ? The value of the new method in synthesizing the information is highlighted by calculating a data synthesis factor that is compared with the previous method.
 • The proposed approach was implemented using a 12-bus simplified distribution network. The results of the study indicate that initiating events and possible cascading chains may be identified, ranked and visualized. • Based on the active or reactive branch flows from a solved power flow or state estimation computation, the proposed method organizes the busses and branches of the network into homogeneous groups according to a few concepts which are introduced below. • It is helpful in determining the best location as well as optimal capacity of proposed generating station, substation and new lines. • It determines the voltage of the buses. The voltage level at the certain buses must be kept within the closed tolerances.
 ? The paper investigates the method’s performance during pre- and post- contingency states and accuracy comparisons are made with the previous method. ? Static methods are usually very efficient but they neither account for post contingency control actions that depend on the system’s evolution, nor do they capture more complex instability mechanisms. ? Thus, making the proposed method computational more efficient than the previous one. ? The proposed method obtains time-series from dynamic simulations subject to sequential load changes that are then used as input to a voltage stability estimation method.

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