Effect of small disturbances on Inter-connected system

Nature Physics, 2013

An imperative condition for the functioning of a power-grid network is that its power generators remain synchronized. Disturbances can prompt desynchronization, which is a process that has been involved in large power outages. Here we derive a condition under which the desired synchronous state of a power grid is stable, and use this condition to identify tunable parameters of the generators that are determinants of spontaneous synchronization. Our analysis gives rise to an approach to specify parameter assignments that can enhance synchronization of any given network, which we demonstrate for a selection of both test systems and real power grids. Because our results concern spontaneous synchronization, they are relevant both for reducing dependence on conventional control devices, thus offering an additional layer of protection given that most power outages involve equipment or operational errors, and for contributing to the development of "smart grids" that can recover from failures in real time.

Physical Review E

Dynamical simulation of the cascade failures on the EU and USA high-voltage power grids has been done via solving the second-order Kuramoto equation. We show that synchronization transition happens by increasing the global coupling parameter K with metasatble states depending on the initial conditions so that hysteresis loops occur. We provide analytic results for the time dependence of frequency spread in the large K approximation and by comparing it with numerics of d = 2, 3 lattices, we find agreement in the case of ordered initial conditions. However, different powerlaw (PL) tails occur, when the fluctuations are strong. After thermalizing the systems we allow a single line cut failure and follow the subsequent overloads with respect to threshold values T. The PDFs p(N f) of the cascade failures exhibit PL tails near the synchronization transition point Kc. Near Kc the exponents of the PL-s for the US power grid vary with T as 1.4 ≤ τ ≤ 2.1, in agreement with the empirical blackout statistics, while on the EU power grid we find somewhat steeper PL-s characterized by 1.4 ≤ τ ≤ 2.4. Below Kc we find signatures of T-dependent PL-s, caused by frustrated synchronization, reminiscent of Griffiths effects. Here we also observe stability growth following the blackout cascades, similar to intentional islanding, but for K > Kc this does not happen. For T < Tc, bumps appear in the PDFs with large mean values, known as "dragon king" blackout events. We also analyze the delaying/stabilizing effects of instantaneous feedback or increased dissipation and show how local synchronization behaves on geographic maps.

Applied Sciences

In a constantly and rapidly changing global environment, one of the main priority tasks for every country is preserving, maintaining, and operating an independent and individually robust and stable energy system. This paper aims at researching electrical power systems’ (EPSs) behavior during desynchronization from a synchronous area, its stability in islanded mode, and its synchronization. The analysis of EPS behavior was accomplished utilizing numerical simulations in a widely used programming/simulation package. The sudden tripping of the EPS into an isolated island mode with known generation and load values was simulated, analyzed, and discussed. We investigated the behavior of an isolated EPS in the case of the loss of a certain amount of active power, and determined the maximum power that must be available to ensure the reliable operation of the isolated EPS and the power reserve that must be maintained to prevent the EPS from triggering UFLS. The simulation of the synchronizat...

Engineering review, 2016

The connection of distributed sources and their impact on distribution grid has been the subject of intensive research in the last two decades. Creating a favorable environment for the production of electrical energy from renewable energy sources in many countries around the world made an evident increase in electrical energy production from renewable sources. Connecting these generators to distribution grid is not always an easy task, and often, in cases of inadequate analysis and poor choice of ways of connecting these sources, can have a negative impact on the quality of electrical energy in local distribution grids. In this paper, using a realistic test system, the focus of research is to identify the behavior of group synchronous generators connected to the medium-voltage distribution grid in &quot;cascade&quot; manner. The s elected test system presents the real power distribution system of the Municipality of Gornji Vakuf-Uskoplje, to which six synchronous generators are conn...

In the paper there is presented a set of signals used for modeling disturbances in power system. Such a set can be useful in testing new algorithms. There is also given a description of the disturbances. In the second part authors examine the ability of the wavelet transform approach to detect and extract feature from different disturbances superimposed on power line voltage.

2003

Dispersed generation (DG) from renewable resources and mini-cogeneration in public MV and LV distribution networks has so far been a small part of total installed capacity of power systems. This situation has justified the requirement in the Technical Standards in force in various countries that DG must be automatically disconnected at the occurrence of faults or abnormal operation conditions of the public network. A massive installation of DG is currently encouraged. If this target will be achieved, the automatic disconnection of large amounts of DG in an area initiated by network short circuits would drastically reduce the expected benefits of DG. The paper investigates the possibility of keeping DG in service during network disturbances, in particular: • Assumptions are made on possible future extensive applications of DG in regional networks (primary sources; power ratings; locations; type of interfacing with MV-LV lines; dispatchability). • Dynamic simulations of distribution networks with adequate models of DG using various interfacings (synchronous generators (SGs); asynchronous generators (AGs); static power converters (SPCs)) are set up. • Results of parametric analyses are presented for a significant case study and conditions to be fulfilled are identified for avoiding or minimizing disconnection of DG during short circuits in HV, MV and LV networks. Simulations are made with PSAF program for the comprehensive study of DG interfaced with SGs, AGs, and SPCs. The ATP-EMTP is used for the analysis of special transients. Results show that it is possible to ride through the network faults by keeping in service DG and loads except SGs connected to faulty distribution lines.

Successful operation of a power system depends largely on the engineer's ability to provide reliable and uninterrupted service to the loads. The reliability of the power supply implies much more than merely being available. Ideally, the loads must be fed at constant voltage and frequency at all times. The first requirement of reliable service is to keep the synchronous generators running in parallel and with adequate capacity to meet the load demand [1]. Synchronous machines do not easily fall out of step under normal conditions. If a machine tends to speed up or slow down, synchronizing forces tend to keep it in step. Conditions do arise, however, such as a fault on the network, failure in a piece of equipment, sudden application of a major load such as a steel mill, or loss of a line or generating unit., in which operation is such that the synchronizing forces for one or more machines may not be adequate, and small impacts in the system may cause these machines to lose synchronism [3]. A second requirement of reliable electrical service is to maintain the integrity of the power network. The high-voltage transmission system connects the generating stations and the load centers. Interruptions in this network may hinder the flow of power to the load. This usually requires a study of large geographical areas since almost all power systems are interconnected with neighboring systems. Random changes in load are taking place at all times, with subsequent adjustments of generation [1]. We may look at any of these as a change from one equilibrium state to another. Synchronism frequently may be lost in that transition period, or growing oscillations may occur over a transmission line, eventually leading to its tripping. These problems must be studied by the power system engineer and fall under the heading "power system stability”.

Proceedings of the Annual Hawaii International Conference on System Sciences, 2022

This paper presents some of the stability considerations for an ac interconnection of the North American Eastern and Western electric grids. Except for a brief time around 1970, the North American Eastern and Western grids have operated asynchronously, with only small power transfers possible through a few back-to-back HVDC ties. This paper provides results from a study showing that an ac interconnection may be possible with only modest changes to the existing transmission grid. The paper's main focus is on the dynamic aspects of such an interconnection. The paper also shows how newer visualization techniques can be leveraged to show the results of larger-scale, long duration dynamic simulations. Results are given for a 110,000-bus model of the actual North American electric grid and an 82,000-bus synthetic grid.

The energy transition towards increased electric power production from renewable energy (RE) resources creates new challenges to ensure the stability of power grids. In conventional power grids voltage fluctuations can be controlled locally. Here, we explore whether the energy transition changes this situation. We study systematically the transients of voltage amplitude, phase and frequency deviations due to local contingencies in dependence on system inertia, heterogeneity and topology. The 3rd order dynamic power grid model is studied numerically and analytically and compared with real grid simulations for the Nigerian (330 kV) power grid and other grid models, using DigSILENT PowerFactory software. We provide a quantitative analysis of the parametric dependence of the velocity with which a disturbance propagates throughout the grid, and of the period of oscillations of the frequency and voltage transients. We find beating patterns in the transients which we iden...