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![Failure modes for transmission transformers in ZTZ-Service in 2000 − 2005. [12]](profile/Lina-Bertling-Tjernberg/publication/251779839/figure/fig1/AS:393308946878470@1470783568854/Failure-modes-for-transmission-transformers-in-ZTZ-Service-in-2000-2005-12.png)
![Figure 5: Failure modes for transformers on 20 − 100 MVA. [14]](profile/Lina-Bertling-Tjernberg/publication/251779839/figure/fig2/AS:393308951072768@1470783569228/Failure-modes-for-transformers-on-20-100-MVA-14_Q320.jpg)
![Figure 6: Failure modes for transformers above 100 MVA. [14]](profile/Lina-Bertling-Tjernberg/publication/251779839/figure/fig3/AS:393308951072769@1470783569254/Failure-modes-for-transformers-above-100-MVA-14_Q320.jpg)
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... Although the failure rate of an individual transformer is affected by factors such as the region, operation time, and statistical methods, the transformers' failure rates have similar changing trends over time [48], [49]. The trend in the individual transformer failure rates should be consistent with the statistical data of the failure rate that is observed from multiple transformers. ...
Evaluating the real-time failure rate of transformers can effectively guide the planning of maintenance and reduce their failure risk. This paper proposed a novel transformer failure rate model that considers the impact of maintenance based on daily oil chromatographic monitoring data mining. Firstly, to ensure the quality of the modeling data, an improved k-nearest neighbor (KNN) algorithm based on genetic algorithm (GA) is proposed to repair the missing monitoring data. The repaired data is then mapped to the equivalent state duration (ESD) by the M-BPNN proposed, which is used to modify the multistate Markov process of transformers so as to quantify the impact of maintenance on failure rate. Considering the changing characteristics of the dissolved gases' content in the short period, the ESD is further merged in sequential periods to obtain the merged equivalent state duration (MESD). Finally, an analytical function of the transformer failure rate with respect to the MESD is obtained. Case studies on a typical substation demonstrate that the proposed approach has the ability to characterize the impact of maintenance and the actual failure rate, thereby improving the accuracy of the substation reliability assessment.
... Consequently, the incorrect diagnostic inference can be obtained. In order to avoid this situation the expert estimates method is used, where the experts with great experience in electrical equipment diagnostics evaluate the obtained diagnosis correctness by informal criteria [13]. ...
The power transformers state analysis based on different DGA approaches is presented in the paper. The DGA results interpretation complexity in modern information analytical systems of the high voltage equipment technical state assessment was revealed. The necessity of information analytical systems training and self-training principles was justified. Applying these principles for new data and formalized expert knowledge extraction will improve estimates quality.
... Under asset management, maintenance of physical components and policies forms the crucial part. Literature survey shows that there have been explicit studies on maintenance of various power system components, that is, power transformers [4][5][6][7][8], overhead lines and cables [4,8,9], protection devices [8][9][10] and wind-farm components [9,11,12]. Maintenance strategies like corrective maintenance [3,9], preventive maintenance [3,9,13] and Reliability-Centered Maintenance (RCM) [13][14][15] have been explicitly studied. ...
Asset management is one of the key components in a transforming electric power industry. Electric power
industry is undergoing significant changes due to technical, socio-economical and environmental
developments. Also, due to restructuring and deregulation, the focus has been on transmission and
distribution assets that include transmission lines, power transformers, protection devices, substation
equipment and support structures. This study aims to provide a detailed exposure to asset management
classification, various interesting maintenance methods and theories developed. The work encompasses the
issue of data management in recent years. Due to the use of various smart metering devices, large amounts of information is being collected. The advent of data mining techniques has changed the asset management
scenario and it has been covered in this survey paper. In the end, it also discusses various risk assessment
techniques in asset management developed and used for academic research and industries. It is accompanied with survey results from pan-European TSOs on various aspects in asset management.
... As seen from the above classification, maintenance forms the crucial part of AM. Literature survey shows there have been explicit studies on maintenance of various power system components, like power transformers, overhead lines, cables, and protection devices [95][96][97][98][99][100][101][102][103]. With the integration of RES, wind farms have been extensively studied from AM point of view in [96,97,[104][105][106][107]. ...
In the planning and operation of power systems, actions are taken in different processes and time-horizons. The purpose of these actions is to secure a high reliability level. Although the three main processes (grid development, asset management and system operation) are described in literature, there has been no explicit study on the time-horizons (long-term, mid-term and short-term) and actual time-scale (decades, years, months, etc.) that these processes focus on. This paper aims at making a review of the various activities performed by Transmission System Operators (TSOs) while reviewing the concept of each time-horizon and methodologies developed in literature. As decisions taken in different time-horizons can influence each other, the interactions and overlapping are discussed.
... Grid components, such as feeders and transformers, have a load rating that is typically defined as an apparent power rating or current rating. If the load rating of these components is exceeded, accelerated ageing occurs, which reduces their technical lifetime [76]- [77]. This might increase the exploitation costs of the distribution system, when the technical lifetime of the system assets is reduced below the economic and strategic lifetime [76], because the grid components have to be replaced earlier than initially planned. ...
... If the load rating of these components is exceeded, accelerated ageing occurs, which reduces their technical lifetime [76]- [77]. This might increase the exploitation costs of the distribution system, when the technical lifetime of the system assets is reduced below the economic and strategic lifetime [76], because the grid components have to be replaced earlier than initially planned. Therefore, to a certain extent, such ratings are not hard real-time constraints, but represent an additional cost, because the component has to be replaced sooner than initially planned. ...
... Otra fuente de sobreinducción consiste en los valores inferiores de frecuencia presentes en la red, para los cuales naturalmente no ha sido diseñado el transformador. Otro factor que influye en el incremento de la temperatura en estos equipos, consiste en el envejecimiento del aceite, ya que cada vez que el transformador se sobrecarga con relación a su funcionamiento nominal, existe sobrecalentamiento, y por lo tanto reducción en su ciclo de vida [5]. Con el objetivo de mantener controlada esta variable para así garantizar el correcto funcionamiento del transformador, es de vital importancia implementar un sistema de instrumentación confiable, capaz de proporcionar la cantidad de datos suficiente como para proceder a ejecutar operaciones de control. ...
En este documento se presenta el desarrollo de un prototipo para el monitoreo remoto de la temperatura presente en transformadores de distribución. El sistema opera con dos señales de entrada, una proveniente de la temperatura existente en la parte interna del transformador, y otra correspondiente a la medición del valor ambiente. Posteriormente, las señales pasan a una etapa de acondicionamiento por medio de amplificadores operacionales, para finalmente ser transmitidas mediante módulos de radiofrecuencia. En el receptor, se realiza la visualización de los valores correspondientes en una pantalla de cristal líquido. El sistema se instaló en uno de los transformadores de distribución del laboratorio de máquinas eléctricas de la Universidad Tecnológica de Pereira, realizando 20 mediciones de temperatura con el sistema de medición y con el equipo patrón, a diferentes horas del día y con diferentes cargabilidades para el transformador, obteniéndose un error máximo del 3,09%.
... Grid components, such as feeders and transformers, have a load rating that is typically defined as an apparent power rating or current rating. If the load rating of these components is exceeded, accelerated ageing occurs, which reduces their technical lifetime [76]- [77]. This might increase the exploitation costs of the distribution system, when the technical lifetime of the system assets is reduced below the economic and strategic lifetime [76], because the grid components have to be replaced earlier than initially planned. ...
... If the load rating of these components is exceeded, accelerated ageing occurs, which reduces their technical lifetime [76]- [77]. This might increase the exploitation costs of the distribution system, when the technical lifetime of the system assets is reduced below the economic and strategic lifetime [76], because the grid components have to be replaced earlier than initially planned. Therefore, to a certain extent, such ratings are not hard real-time constraints, but represent an additional cost, because the component has to be replaced sooner than initially planned. ...
The number of plug-in electric vehicles (PEVs) on the road is growing significantly, which allows to reduce the consumption of greenhouse gas emitting fossil fuels, such as gasoline and diesel. This is due to the increased primary energy efficiency of electrically powered vehicles compared to conventional vehicles on the one hand, and the primary fuel flexibility for electricity generation on the other hand. The absence of tailpipe emissions reduces the local concentrations of harmful pollutants, which is benefits human health. PEVs are able to charge at every location that offers a suitable grid connection opportunity, e.g., at home and the workplace. The typical long standstill times at these locations and the low average daily driven distances allow low-power charging to fulfill the majority of the mobility needs, thereby keeping the charging infrastructure investments low.
As the number of PEVs on the road increases, the grid impact of PEV charging is observed more widely, e.g., altered grid load profiles, increased peak power, and increased voltage magnitude deviations. Therefore, an extensive amount of research is conducted on coordinated charging strategies that have the objective to mitigate the grid impact of PEV charging. Typically, large-scale coordination mechanisms are being investigated, which require a sufficiently high large-scale PEV penetration rate to be effective. However, due to the clustering of PEV users, high local concentrations may occur prior to a high widespread PEV penetration. Therefore, certain distribution grids will already be impacted in the near-term future. More specifically, the residential low voltage (LV) grid impact may be challenging, due to the simultaneity between PEV charging and residential electricity consumption.
This dissertation investigates several local PEV charging strategies that have the objective to mitigate the distribution grid impact with a minimal amount of external input. Two active power control strategies for PEV charging are assessed separately and in combination: voltage-dependent charging and standstill time-based charging. The former strategy does not need require any input, as the voltage magnitude is measured anyway within the onboard charger. The latter strategy only requires the next departure time, so that the charging power rating can be reduced as much as possible, while still being fully charged for the next trip.
Besides the abovementioned active power control strategies, reactive power control is also investigated, i.e., reactive power current injections during PEV charging. Certain PEV charger topologies allow for the injection of reactive power flows into the grid, so this capability could be enabled. The advantage compared to the active power control strategies is that, given an appropriate sizing of the PEV charger, this grid-supportive measure does not impact the user comfort, because the active power flow is not altered. Reactive current injection does not require any external inputs, because it is merely a power factor set point of the onboard PEV charger.
Finally, the distribution grid impact and sizing requirements of fast charging infrastructure is assessed. Opposed to plug-in hybrid electric vehicles (PHEVs), all of the required propulsion energy for battery electric vehicles (BEVs) must be delivered by the onboard battery. Therefore, fast charging is indispensable for long-distance driving, so that recharging does not take excessively long. Because slow and fast charging are complementary charging options, different slow charging strategies are taken into account when the fast charge requirements are assessed. Furthermore, different representative LV grid topologies are taken into account, as well as the medium voltage (MV) grid topology to which the different LV grids and the fast charging infrastructure are connected.
The proposed local active and reactive power control strategies allow to substantially mitigate the distribution grid impact of PEV charging, with limited adaptations compared to their current implementation. The active power control strategies could be implemented on all of the currently used onboard PEV chargers. The reactive power control strategies can be implemented on onboard PEV chargers with a full-bridge IGBT rectifier topologies, as used for several PEVs. The distribution grid impact of the slow charging control strategies is more significant than the presence of fast charging infrastructure. Therefore, it the limited additional distribution grid impact of fast charging infrastructure can even be compensated for by implementing the proposed control strategies for slow charging.
... On one hand, factors causing transformer failure are many, and some failure theory is not clear enough to consider them into the model reasonably. According to the transformer failure statistics[23][24][25], lots of transformer failures result from abnormal working conditions, which primarily includes abnormal overload, external short circuit, and lightening. Therefore, these three types of abnormal working conditions are included in the model. ...
In order to diagnose transformer fault efficiently and accurately, a dynamic integrated fault diagnosis method based on Bayesian network is proposed in this paper. First, an integrated fault diagnosis model is established based on the causal relationship among abnormal working conditions, failure modes, and failure symptoms of transformers, aimed at obtaining the most possible failure mode. And then considering the evidence input into the diagnosis model is gradually acquired and the fault diagnosis process in reality is multistep, a dynamic fault diagnosis mechanism is proposed based on the integrated fault diagnosis model. Different from the existing one-step diagnosis mechanism, it includes a multistep evidence-selection process, which gives the most effective diagnostic test to be performed in next step. Therefore, it can reduce unnecessary diagnostic tests and improve the accuracy and efficiency of diagnosis. Finally, the dynamic integrated fault diagnosis method is applied to actual cases, and the validity of this method is verified.
... The tank should be inspected for oil leaks, excessive corrosion, dents, and other signs of rough handling. Internal arcing in an oil-filled transformer can instantly vaporize surrounding oil, which can lead to high gas pressures that may rupture the tank (Franzén & Bertling, 2007). ...
Power transformers are critical equipment of the electric power transmission system, because they adjust the electric voltage to a suitable level on each stage of the power transmission from generation station to the end user. Reliability modeling of power transformers is very important for the electric grid design and risk assessment. In this paper, we propose a reliability model of power transformers with maintenance outage incorporated. The power transformer is divided into two groups of components described by different Markov state space models. Both types of state space models are combined to implement the whole power transformer modeling. Reliability indices such as probabilities of full, derated, and zero capacity as well as system unavailability are derived, and numerical evaluation of selected indices is presented with respect to different parameters. The developed models and analysis method are expected to serve as a useful component for the electric grid system design, assessment, and operation.
... Numerous approaches have been applied to power transformer condition monitoring and failure rate modeling. Some of these approaches use sophisticated modeling while others use simplistic rules of the thumb [17], [18]. Perhaps the most promising research results come from the Electric Power Research Institute (EPRI) [19]- [22]. ...
... The inclusion of N-1 contingency constraints guarantees that the system can still tolerate the loss of any single component (generating unit or transmission component) while scheduling the transformers for maintenance. The objective function of the model, which has to be minimized, consists of energy production cost as well as startup and shutdown costs of generating units: (17) The objective function (17) is subjected to prevailing generating units' operating constraints, transmission network DC power flow constraints in normal and N-1 contingency states, as well as specific transformers' maintenance constraints, formulated as follows: In the above formulation, the single outage of generating units and transmission components in contingency is modeled, respectively, by vectors of binary parameters and . The elements of these two vectors are binary numbers, with 1 denoting the availability of components, and 0 otherwise. ...
The emergence of smart grid technologies in terms of advanced communication infrastructure, embedded intelligence, diagnostics and monitoring capabilities offers new opportunities for improved transmission asset management strategies (TAMS). Accordingly, power system operators are currently looking for analytics that can make use of transmission asset condition monitors and data already available to make better-informed decisions. This two-part paper introduces a two-stage maintenance scheduler for power transmission assets. Part I begins with the motivation for TAMS and then continues with a two-stage maintenance management model that incorporates joint midterm and short-term maintenance. The first stage involves a midterm asset maintenance scheduler that explicitly considers the asset condition dynamics in terms of failure rate. The second stage introduces a short-term maintenance scheduler with N-1 reliability that schedules the output of the midterm maintenance scheduler in the short run. The midterm and short-term stages are completely decoupled schemes to make the problem computationally tractable. For the sake of exposition here, we focus on the maintenance of grid transformers. The proposed methodology is general, however, and can be extended to other network equipments as well. The characteristics of the proposed model and its benefits are investigated in Part II through several case studies.
