It has been over two decades since the publication of pioneer works about the power transformer diagnostics based on monitoring of their acoustic fingerprints. Since then, there has been great ...progress in this field and the methods used are as complex as ever. Any unnecessary intervention on a power transformer implies its temporary disconnection from the power grid. The inability to supply electricity to the customer means not only financial loss for the utility but also generates a non-material loss, e.g., the loss of reputation to the customer. Faster, more accurate, more reliable, and less invasive diagnosis is the main reason behind development and improvement in this field. The main goal of this paper is to categorize and review state-of-the art of vibro-acoustic diagnostic methods for power transformers. This paper opens with a brief note about continuous condition monitoring, after which we overview the causes of transformer vibrations as well as the collection and preprocessing of diagnostic data. Then, we review and categorize works related to the acoustic condition assessment of power transformers considering both: feature extraction in the time, frequency, time-frequency domain, and mathematical modeling and system identification of dynamic systems.
System integrity protection schemes (SIPS) are schemes that can, under potentially hazardous conditions, prevent a complete blackout of endangered parts of an electrical power system (EPS). The main ...objective of SIPS is to monitor the state of the power transmission network in real time and to react in emergency cases. This paper explores the use of phasor measurement unit (PMU) technology for the development of SIPS as a part of wide-area monitoring, protection, and control (WAMPAC) systems. A new SIPS development method is described using the experience from the real-time operation. The developed optimal bus-splitting scheme identifies potential actions that can eliminate or reduce power system overloads and protect the integrity of the power system. An optimal bus-splitting scheme based on a DC power flow model and PMU measurements is given as an example and is explained and tested on an IEEE 14 bus test system. Conducted simulations indicate that the described SIPS methodology supported by the PMU measurements can mitigate potential overloads of the observed network part.
The share of renewable energy sources interfaced to the bulk power system through power electronic devices is continuously increasing. As a result, the power systems of the future face challenges of ...stability and reduced inertia and, to maintain the stability of the low-inertia systems, various concepts of grid-forming converter control schemes have been introduced, which enable converters to behave similarly to traditional synchronous machines. As the research in this area is gaining in importance, the sheer amount of papers with models for different kinds of simulations and the complexity of control algorithms may be daunting for newcomers in this field to understand them and to start modeling such devices. Moreover, different control schemes are often erroneously used interchangeably which adds to the confusion. This papers aims to give a clear understanding of the above aspects by explaining details of modeling and initialization of grid-forming converter control schemes for power system fundamental frequency dynamic simulations (root-mean-square or RMS simulations) by using an example of a virtual synchronous machine (VSM). Starting from comparison of traditional systems and systems with a high share of converters and continuing with a functional overview of virtual inertia based converters in modern power systems, a step-by-step initialization of the static and dynamic model is given, focusing on RMS simulations. Finally, selected simulation examples are shown which illustrate main characteristics of virtual synchronous machines and their comparison to real synchronous machines. The presented dynamic model is made freely available in DIgSILENT PowerFactory format.
In wide area monitoring, protection, and control (WAMPAC) systems, angle stability of transmission network is monitored using data from phasor measurement units (PMU) placed on transmission lines. ...Based on this PMU data stream advanced algorithm for out-of-step condition detection and early warning issuing is developed. The algorithm based on theoretical background described in this paper is backed up by the data and results from corresponding simulations done in Matlab environment. Presented results aim to provide the insights of the potential benefits, such as fast and efficient detection and reaction to angle instability, this algorithm can have on the improvement of the power system protection. Accordingly, suggestion is given how the developed algorithm can be implemented in protection segments of the WAMPAC systems in the transmission system operator control centers.
More and more countries and utilities are trying to develop smart grid projects to make transformation of their power infrastructure towards future grids with increased share of renewable energy ...production and near zero emissions. The intermittent nature of solar and wind power can in general cause large problems for power system control. Parallel to this process, the aging of existing infrastructure also imposes requirements to utility budgets in the form of a need for large capital investments in reconstruction or maintenance of key equipment. Synchrophasor and other synchronized measurement technologies are setting themselves as one of the solutions for larger wind power integration. With that aim, in this paper one possible solution for wind power control through data mining algorithms used on a large quantity of data gathered from phasor measurement units (PMU) is described. Developed model and algorithm are tested on an IEEE 14 bus test system as well as on real measurements made on wind power plants currently in operation. One such wind power plant is connected to the distribution grid and the other one to the transmission grid. Results are analyzed and compared.
This paper presents a high-level overview of the integration of renewable energy sources (RES), primarily wind and solar, into the electric power system (EPS) in Croatia. It presents transmission ...system integration aspects for the particular case of this country. It explains the current situation and technical characteristics of the current conventional generation units and currently installed wind energy capacities. Based on the current situation future development scenario is determined and used to evaluate the impacts of the wide-scale integration of renewables. Grid connections aspects, power balancing, market participation, and inertia reduction aspects are considered. Furthermore, some specifics of both solar and wind integration are discussed identifying problems and potential solutions. Primarily through the provision of the inertial response of both solar and wind and through better forecasting of wind production. Finally, the outlook for the Croatian power system is given, that will most probably double its RES capacity in the coming 3-year period and a certain level of investments and changes of current operational practices will need to be provided.
•Impact of DFIG operating point on virtual inertial response from cut-in to cut-out.•Virtual inertial response multidimensional sensitivity analysis to DFIG parameters.•Inertial response sensitivity ...to initial conditions depends on the MPPT algorithm.•Some DFIG elements can be neglected in inertial response dynamics, while some can’t.
Power converter technology partially or fully electrically decouples the wind energy source from the grid which results in the decrease of system inertia. However, when those units participate in virtual inertial response their electromechanical dynamics become coupled to the grid electromechanical modes. To date, there were no comprehensive studies on how do different elements and parameters of a wind energy conversion system (WECS) impact its virtual inertial response provision. This is important from the standpoint of understanding the expected wind farm response during frequency containment process as well as from the standpoint of developing better inertial response controllers. In this paper we have investigated how do operating point, line-side and machine-side converter, phase-locked loop and pitch angle control impact the inertial response of the total power controlled type III WECS (DFIG) which is one of the most common wind turbine topologies used today. We show that the operating point, pitch angle control and outer loop of the machine-side converter have a visible impact on strength of the inertial response, while other elements do not and some can even be neglected in inertial response studies.
The paper analyses the coordinated hydro-wind power generation considering joint bidding in the electricity market. The impact of mutual bidding strategies on market prices, traded volumes, and ...revenues has been quantified. The coordination assumes that hydro power generation is scheduled mainly to compensate the differences between actual and planned wind power outputs. The potential of this coordination in achieving and utilizing of market power is explored. The market equilibrium of asymmetric generation companies is analyzed using a game theory approach. The assumed market situation is imperfect competition and non-cooperative game. A numerical approximation of the asymmetric supply function equilibrium is used to model this game. An introduced novelty is the application of an asymmetric supply function equilibrium approximation for coordinated hydro-wind power generation. The model is tested using real input data from the Croatian power system.
System integrity protection schemes (SIPS) supported by phasor measurement unit (PMU) technology are based on the concept of collecting information from remote stations, sending the information to a ...central concentrator that executes a decision-making algorithm and initiates specialized actions to prevent the spread of system disturbance. This paper gives application of overload mitigation SIPS. Described protection scheme is based on a mixed integer linear programming (MILP) optimization of the DC power flow model whose objective is to maximize total load on the observed part of the network. Inaccuracy of the used DC model and the actual state is replaced by using the PMU technology. In this way, the influence of reactive power that is ignored in the DC model power flow model calculation is replaced in real-time with real synchronized measurements. Described SIPS is tested on IEEE 14 busbar test system. Conducted simulations indicate that developed optimization algorithm can mitigate potential element overloads with extremely high accuracy by using load shedding methods. Example on real part of Croatian power transmission network is given at the end of paper. This specific analysis demonstrates benefits of using SIPS based on synchro phasors in real world.
Wind power generation has reached a significant share in power systems worldwide and will continue to increase. As the converter-connected generation reduces the grid inertia, more and more interest ...has been given to exploiting the kinetic energy and controllability of variable-speed wind turbine generators (VSWTGs) for frequency support. Consequently, the grid frequency dynamics are changing. Thus, it is necessary to include the frequency response of wind power plants in the system frequency response (SFR) model. A novel approach to low-order SFR modelling of a future power system with a high share of frequency-support-capable VSWTGs has been presented. Low-order model of VSWTGs with primary frequency response and natural inertial response has been developed considering different wind turbine operating regimes and compared to the non-linear model for validation. Low-order model has been presented in a symbolic transfer function form. Model accuracy has been discussed and the impact of VSWTG parameters on frequency response has been analysed. The developed model facilitates studying power system frequency dynamics by avoiding the need for modelling complex VSWTG systems, while retaining a satisfying level of accuracy.
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