Sakshi Pahwa

Abruptness of cascade failures in power grids.

Electric power-systems are one of the most important critical infrastructures. In recent years, they have been exposed to extreme stress due to the increasing demand, the introduction of distributed renewable energy sources, and the development of extensive interconnections. We investigate the phenomenon of abrupt breakdown of an electric power-system under two scenarios: load growth (mimicking the ever-increasing customer demand) and power fluctuations (mimicking the effects of renewable sources). Our results on real, realistic and synthetic networks indicate that increasing the system size causes breakdowns to become more abrupt; in fact, mapping the system to a solvable statistical-physics model indicates the occurrence of a first order transition in the large size limit. Such an enhancement for the systemic risk failures (black-outs) with increasing network size is an effect that should be considered in the current projects aiming to integrate national power-grids into “super-grids”.

Topological analysis of the power grid and mitigation strategies against cascading failures

This paper presents a complex systems overview of a power grid network. In recent years, concerns about the robustness of the power grid have grown because of several cascading outages in different parts of the world. In this paper, cascading effect has been simulated on three different networks, the IEEE 300 bus test system, the IEEE 118 bus test system, and the WSCC 179 bus equivalent model. Power Degradation has been discussed as a measure to estimate the damage to the network, in terms of load loss and node loss. A network generator has been developed to generate graphs with characteristics similar to the IEEE standard networks and the generated graphs are then compared with the standard networks to show the effect of topology in determining the robustness of a power grid. Three mitigation strategies, Homogeneous Load Reduction, Targeted Range-Based Load Reduction, and Use of Distributed Renewable Sources in combination with Islanding, have been suggested. The Homogeneous Load Reduction is the simplest to implement but the Targeted Range-Based Load Reduction is the most effective strategy.

Load shedding strategies for preventing cascading failures in power grid

Abstract Load shedding has always been a commonly adopted method in emergency situations to maintain power system reliability. Several load-reduction strategies have been suggested in the past, but most are complex and not scalable. This article proposes and thoroughly investigates three load-shedding strategies to prevent cascading failures in the power grid. The first strategy is a baseline case called the homogeneous load-shedding strategy. It homogeneously reduces load in all of the buses of the system. This strategy is extremely simple and fast, and these properties motivate its use in some specific scenarios in spite of its inefficiencies. Next, to accurately find the location and amount of load shedding, a polynomial complexity optimization formulation is proposed, which is much more efficient in overall load shedding in the system. A novel tree heuristic is proposed to overcome the drawbacks of the optimization, namely fairness and scalability. The tree heuristic is linear and very simple to implement. In general, it gives close to optimal results. The results of the tree strategy are compared with that of another existing heuristic, and it is found that the tree performs equal to or better than the existing heuristic for all cases.

Cascade Failures and Distributed Generation in Power Grids

Power grids are nowadays experiencing a transformation due to the introduction of distributed generation based on renewable sources. At difference with classical distributed generation, where local power sources mitigate anomalous user consumption peaks, renewable sources introduce in the grid intrinsically erratic power inputs. By introducing a simple schematic (but realistic) model for power grids with stochastic distributed generation, we study the effects of erratic sources on the robustness of several IEEE power grid test networks with up to 2 × 10³ buses. We find that increasing the penetration of erratic sources causes the grid to fail with a sharp transition. We compare such results with the case of failures caused by the natural increasing power demand.

A simulative analysis of the robustness of Smart Grid communication networks

The need for reliable and quick communication in the power grid is growing and becoming very critical. With the Smart Grid initiative, an increasing number of intelligent devices, such as smart meters and new sensors, are being added to the grid. As these new devices are added, the traffic demand on the communication network increases. This can cause issues like longer delay, dropped packets, and equipment failure. The power grid relies on this data to function properly. The power grid will lose reliability and will not be able to provide customers with power without correct and timely data. The current communication network architecture needs to be evaluated and improved. In this paper, a simulator program has been developed to study the communication network. The simulation model is written in C++ and models the components of the network. The simulation results provide insight on how to design the network in order for the system to be robust from failures. We will use the simulation model to evaluate the interdependency between the communication network and the power grid in the future.

A complex networks approach for sizing and siting of distributed generators in the distribution system

The use of distributed energy is gaining more importance with the advent of the smart grid, challenges of power transfer over long distances and the need to be secure and independent in energy production. In this paper, we present an analytical method, using electrical centrality, to determine the locations and sizes of distributed generators to be placed in the distribution system. Electrical centrality is a metric used in the topological analysis of power systems, that differentiates the electrical structure of the system from its topological structure. It uses the Zbus matrix of the distribution system to determine which nodes are electrically more central to the system and indicates them as the best locations for the placement of distributed generators, with the size of the generator related to the centrality of the node but decided by exhaustive search. It is assumed that all the generation is supplied through distributed generators. We obtain the results for the 12-, 33-, and 69-node distribution systems using this method. The results indicate that the locations indicated by electrical centrality are either the end nodes or nodes closer to the end nodes in the different branches of the networks. Generally, the end nodes are the ones where the voltage drops. As a result, this placement of distributed generators definitely corrects the voltage profile. This placement successfully makes the overall system losses very small as is seen from the optimal power flow solution obtained before and after the distributed generator placement.

Electrical Networks: An Introduction

A world without electricity is beyond our imagination. Starting from the prehistoric times, man has made much progress in every walk of life. We have become accustomed to getting everything at the flick of a switch, touch of a button, or turn of a knob. While we have become so used to enjoying the benefits of electricity, it is not easy to imagine how electricity travels from its source to our homes and offices. It sometimes has to cover large distances through a complex network of transmission lines and power substations to provide us the facilities and entertainment that we take for granted. This network which transports electricity from the source to the consumers is called the electrical network. The electrical network is a collective term for different components such as transformers, transmission lines, substations, and different stages and sub-networks devoted to generation, transmission, and distribution. Sometimes, there may be sub-transmission and secondary distribution networks too. A simple schematic of an electric network is shown in Fig. 8.1. In the past decade, analysis of the electrical power system as a complex network has been an evolving and challenging topic of research.

Power Grids, Smart Grids and Complex Networks

We present some possible Complex Networks approaches to study and understand Power Grids and to improve them into Smart Grids . We first sketch the general properties of the Electric System with an attention to the effects of Distributed Generation. We then analyse the effects of renewable power sources on Voltage Controllability. Afterwords, we study the impact of electric line overloads on the nature of Blackouts. Finally, we discuss the possibility of implementing Self Healing capabilities into Power Grids through the use of Routing Protocols.