25 research outputs found
Random load fluctuations and collapse probability of a power system operating near codimension 1 saddle-node bifurcation
For a power system operating in the vicinity of the power transfer limit of
its transmission system, effect of stochastic fluctuations of power loads can
become critical as a sufficiently strong such fluctuation may activate voltage
instability and lead to a large scale collapse of the system. Considering the
effect of these stochastic fluctuations near a codimension 1 saddle-node
bifurcation, we explicitly calculate the autocorrelation function of the state
vector and show how its behavior explains the phenomenon of critical
slowing-down often observed for power systems on the threshold of blackout. We
also estimate the collapse probability/mean clearing time for the power system
and construct a new indicator function signaling the proximity to a large scale
collapse. The new indicator function is easy to estimate in real time using PMU
data feeds as well as SCADA information about fluctuations of power load on the
nodes of the power grid. We discuss control strategies leading to the
minimization of the collapse probability.Comment: 5 pages, 1 figure, submission to IEEE PES General Meeting 201
Critical slowing-down as indicator of approach to the loss of stability
We consider stochastic electro-mechanical dynamics of an overdamped power
system in the vicinity of the saddle-node bifurcation associated with the loss
of global stability such as voltage collapse or phase angle instability.
Fluctuations of the system state vector are driven by random variations of
loads and intermittent renewable generation. In the vicinity of collapse the
power system experiences so-called phenomenon of critical slowing-down
characterized by slowing and simultaneous amplification of the system state
vector fluctuations. In generic case of a co-dimension 1 bifurcation
corresponding to the threshold of instability it is possible to extract a
single mode of the system state vector responsible for this phenomenon. We
characterize stochastic fluctuations of the system state vector using the
formal perturbative expansion over the lowest (real) eigenvalue of the system
power flow Jacobian and verify the resulting expressions for correlation
functions of the state vector by direct numerical simulations. We conclude that
the onset of critical slowing-down is a good marker of approach to the
threshold of global instability. It can be straightforwardly detected from the
analysis of single-node autostructure and autocorrelation functions of system
state variables and thus does not require full observability of the grid.Comment: Shorter version submitted to IEEE SmartGridComm 2014; 6 pages, 4
figures, discussion of autostructure functions adde
Equation of state and Beginning of Thermalization After Preheating
We study the out-of-equilibrium nonlinear dynamics of fields after
post-inflationary preheating. During preheating, the energy in the homogeneous
inflaton is exponentially rapidly transfered into highly occupied
out-of-equilibrium inhomogeneous modes, which subsequently evolve towards
equilibrium. The infrared modes excited during preheating evolve towards a
saturated distribution long before thermalization completes. We compute the
equation of state during and immediately after preheating. It rapidly evolves
towards radiation domination long before the actual thermal equilibrium is
established. The exact time of this transition is a non-monotonic function of
the coupling between the inflaton and the decay products, and it varies only
very weakly (around 10^(-35) s) as this coupling changes over several orders of
magnitude. This result is applied to refine the relation between the number of
efoldings N and the physical wavelength of perturbations generated during
inflation. We also discuss the implications for the theory of modulated
perturbations from preheating. We finally argue that many questions of the
thermal history of the universe should be addressed in terms of
pre-thermalization, illustrating this point with a calculation of perturbative
production of gravitinos immediately after chaotic inflation. We also highlight
the effects of three-legs inflaton interactions on the dynamics of preheating
and thermalization in an expanding universe.Comment: 15 pages, 13 figure
The Enhancement of Asphalt Concrete Surface Rigidity Based on Application of Shungite-Bitumen Binder
Physical interaction of organic binder depends on bituminous film ability to absorb the mineral particles on the surface. The thick film formation begins with the bitumen amalgamation with mineral powder grains and finishes during the processes of application, seal arrangement and cooling down of asphalt concrete. Active surface centers are on every mineral material and they supply their reactive ability and interaction with bitumen. For proving experimentally and to study the physical and mechanical properties in real operation conditions that were arranged, the blanket was arranged from stone-mastic asphalt with shungite bituminous binder of 500 m long. The monitoring conducted during 3 years indicates that asphalt concrete with shungite binder is subjected to calibration to a lesser degree in comparison with asphalt concrete based on standard powder. For operation reliability of nonrigid road base, it is necessary to estimate and prognosticate asphalt concrete fatigue properties in a blanket. The characterized property appears in such a way that the effect of loads which is significantly smaller than the destructive ones leads to the gradual degradation of fatigue and destruction of the blanket. The results proved that asphalt concrete with shungite bituminous binders has higher operation characteristics
Surprising phenomena in a rich new class of inflationary models
We report on a new class of fast-roll inflationary models. In a huge part of
its parameter space, inflationary perturbations exhibit quite unusual phenomena
such as scalar and tensor modes freezing out at widely different times, as well
as scalar modes reentering the horizon during inflation. In another, narrower
range of parameters, this class of models agrees with observations. One
specific point in parameter space is characterized by extraordinary behavior of
the scalar perturbations. Freeze-out of scalar perturbations as well as
particle production at horizon crossing are absent. Also the behavior of the
perturbations around this quasi-de Sitter background is dual to a quantum field
theory in flat space-time. Finally, the form of the primordial power spectrum
is determined by the interaction between different modes of scalar
perturbations.Comment: 12 pages, 5 figures, 1 table, references + comments added, errors
corrected, conclusions unchanged, version published in JCA