Benjamin A. Carreras

The Impact of Distributed Generation on Power Transmission Grid Dynamics

In this paper we investigate the impact of the introduction of distributed generation on the robustness of the power transmission grid using a dynamic model of the power transmission system (OPA). It is found that with different fractions and distributions of distributed generation, varied dynamics are possible. An important parameter is found to be the ratio of the variability of the distributed generation to the generation capacity margin. Somewhat counter-intuitively, in some of these cases the robustness of the transmission grid can be degraded with the potential for an increased risk of large failures with increased distributed generation if not done carefully.

The dynamics of the formation of the edge particle transport barrier at TJ-II

A large set of discharges with both spontaneous and forced confinement transitions at low electron density is studied at the stellarator TJ-II in different magnetic configurations. By means of a Bayesian technique, using reflectometry and interferometry, electron density profiles are reconstructed in the outer half of the plasma. A scanning heavy ion beam probe delivers information on the global evolution of the plasma potential. Langmuir probes are used to measure long-range correlations. Together, a comprehensive picture is obtained of the evolution of various key global plasma profiles and parameters across forward and backward transitions associated with the formation of an edge sheared flow layer. The impact of low-order rationals on the transition is elucidated.

MHD mode activity and the velocity shear layer at TJ-II

Low-frequency MHD mode activity was studied at the TJ-II stellarator. A spatiotemporal Fourier technique was used to resolve frequency-degenerate modes. By means of this technique, several MHD modes could be identified in discharges with a spontaneous confinement transition in different but similar magnetic configurations. The configurations differed mainly with respect to the radial position of the rational surfaces, thus allowing the reconstruction of a poloidal mode rotation profile based on the mode activity, which was found to be consistent with earlier work. The detected mode spectrum also provided an explanation for the bicoherence observed in one of the configurations after the confinement transition. Both the mode spectrum and the velocity profile were closely reproduced by nonlinear resistive MHD calculations in simplified geometry. As a consequence, the magnetic Reynolds stress is hypothesized to play an important role in the establishment of the velocity shear layer in TJ-II and the concomitant confinement transition.

A dynamical model for plasma confinement transitions

A three-equation model describing the evolution of the turbulence level, averaged shear flow and sheared zonal flow is analyzed using topological properties of the asymptotic solutions. An exploration in parameter space is done, identifying the attractor sets, which are fixed points and limit cycles. Then a more detailed analysis of all Morse sets is conducted using topological-combinatorial computations. This model allows the description of different types of transitions to improved plasma confinement regimes.

Extraction of intermittent waveforms associated with the zonal flow at the transition leading to the edge shear flow layer

A new technique for the detection of (very) low-frequency oscillations with significant long-range correlation is presented. The technique is applied to Langmuir probe data obtained at the TJ-II stellarator in discharges with spontaneous confinement transitions with and without electrode biasing. A succession of low-frequency and very low-frequency oscillations is observed, preceding the confinement transition.

Dynamics of an Economics Model for Generation Coupled to the OPA Power Transmission Model

In this paper we explore the interaction between a dynamic model of the power transmission system (OPA) and a simple economic model of power generation development. Despite the simplicity of this economic model, complex dynamics both in the economics (prices, market share etc) and in the transmission system characteristics (blackouts, reliability etc) are found. Depending on the values of the control parameters (the price enhancement factor, the critical margin and the Minimal Acceptable Rate of Return) the system can be in various states with vastly differing properties. These states are characterized by power law tails in the failure sizes in one limit and exponential tails with extremely high frequency of failures in the other limit. At least some of these control parameters can be thought of as regulatory based and could therefore be directly influenced by reliability considerations.

The interplay of network structure and dispatch solutions in power grid cascading failures

For a given minimum cost of the electricity dispatch, multiple equivalent dispatch solutions may exist. We explore the sensitivity of networks to these dispatch solutions and their impact on the vulnerability of the network to cascading failure blackouts. It is shown that, depending on the heterogeneity of the network structure, the blackout statistics can be sensitive to the dispatch solution chosen, with the clustering coefficient of the network being a key ingredient. We also investigate mechanisms or configurations that decrease discrepancies that can occur between the different dispatch solutions.

Self-organized criticality: An interplay between stable and turbulent regimes of multiple anodic double layers in glow discharge plasma

The role of self-organized criticality (SOC) in the transformation of multiple anodic double layers (MADLs) from the stable to turbulent regime has been investigated experimentally as the system approaches towards critical behavior. The experiment was performed in a modified glow discharge plasma setup, and the initial stable state of MADL comprising three concentric perceptible layers was produced when the drift velocity of electrons towards the anode exceeds the electron thermal velocity (νd ≥ 1.3νte). The macroscopic arrangement of both positive and negative charges in opposite layers of MADL is attributed to the self-organization scenario. Beyond νd ≥ 3νte, MADL begins to collapse and approaches critical and supercritical states through layer reduction which continue till the last remaining layer of the double layer is transformed into a highly unstable radiant anode glow. The avalanche resulting from the collapse of MADL leads to the rise of turbulence in the system. Long-range correlations, a key si...

The Impact of Local Power Balance and Link Reliability on Blackout Risk in Heterogeneous Power Transmission Grids

Many critical infrastructures such as the power transmission grid are heterogeneous both in their basic structure and in some of their underlying characteristics, This heterogeneity can be good for system robustness if it reduces the spread of failures or bad if it adds risk or vulnerability to the system. In this paper we investigate the effect of heterogeneity in the strength of the links between parts of the system network structures, as well as the balance of local generation and demand, on the robustness of the power transmission grid using the OPA complex system model of the power transmission system. It is found that increasing or decreasing the reliability of the links between parts of the grid changes the likelihood of different size failures with neither being optimal for all sizes. Furthermore, imbalances between load and generation in the local regions further degrades the system reliability.

Lambda-Gaga: Toward a New Metric for the Complex System State of the Electrical Grid

The power transmission grid, as well as many other complex critical infrastructure systems, display characteristics of a critical or near critical complex system with the risk of large cascading failures. Understanding this risk and its relation to the system state as it evolves, could allow for a more realistic risk assessment over time and even for mitigation or at least preparation if in a high risk state. In order to facilitate this type of analysis in the context of the power grid as a complex system, we develop a new measure of the complex system state, the generalized autonomous generational average Lambda-gaga, which correlates with the risk. The Lambda-gaga measure is an extension of the standard cascading propagation measure lambda but avoids the contamination of that measure by small events.