Showing papers by "Vattenfall published in 2018"

Burden on hydropower units for short-term balancing of renewable power systems

Abstract: There is a general need to change hydropower operational regimes to balance the growing contribution of variable renewable energy sources in power systems. Quantifying the burden on generation equipment is increasingly uncertain and difficult. Here, we propose a framework combining technical and economic indicators to analyze primary frequency control (PFC) on a timescale of seconds. We develop a model integrating hydraulic, mechanical, and electrical subsystems to characterize efficiency loss, wear and fatigue, regulation mileage, and frequency quality. We evaluate burden relief strategies under three idealized remuneration schemes for PFC, inspired by those used in Sweden, the USA, and China, respectively. We show how burden and compensation vary under future scenarios of renewable power systems. Our framework can be used by producers to develop favorable operation strategies that reduce burden and increase economic value, and by transmission system operators to provide insights on the relation between incentive structures and regulating performance.

The regional heterogeneity of household recycling: a spatial-econometric analysis of Swedish plastic packing waste

Abstract: Environmental policy is often formulated at the national level, but the primary responsibilities for policy implementation, monitoring and compliance are often assigned to local actors (e.g., municipalities). This paper investigates the regional heterogeneity of household plastic waste collection among Swedish municipalities, and how collection rates have been influenced by local waste management policies, geographical conditions and socio-economic characteristics. This is achieved by employing spatial econometric methods and cross-sectional data for 282 Swedish municipalities. The results confirm the presence of spatial correlation. Furthermore, municipalities that employ weight-based waste management fees generally experience higher collection rates. The presence of curbside recycling and a high intensity of recycling drop-off stations, i.e., policy measures that help improve the infrastructural conditions for household recycling, also help explain why some municipalities perform better than others. However, the correlations between packaging waste collection and a number of important regional cost variables, such as the distance to the recycling industry, urbanization rate and population density, turn out both statistically and economically insignificant. An important explanation for this could be that the Swedish producer responsibility scheme has offered regionally differentiated (and fixed) monetary compensations to local collection entrepreneurs, and these have typically been higher in high-cost regions. This implies that plastic packaging waste collection in Sweden has been performed in a spatially cost-ineffective manner.

Optimal wind farm cable routing: Modeling branches and offshore transformer modules

Abstract: Many EU countries aim at reducing fossil fuels in the near future, hence an efficient production of green energy is very important to reach this goal. In this paper we address the optimization of cable connections between turbines in an offshore wind park. Different versions of the problem have been studied in the recent literature. As turbines are becoming still more customized, it is important to be able to evaluate the impact of new technologies with a flexible optimization tool for scenario evaluation. In a previous joint project with Vattenfall BA Wind (a global leader in energy production) we have studied and modelled the main constraints arising in practical cases. Building on that model, in the present paper, we address new technological features that have been recently proposed by Vattenfall’s experts. We show how some new features can be modelled and solved using a Mixed-Integer Linear Programming paradigm. We report and discuss computational results on the performance of our new models on a set of real-world instances provided by Vattenfall.

Impact Assessment of Remote Control and Preventive Maintenance on the Failure Rate of a Disconnector Population

Abstract: This paper presents the impact of different explanatory variables, such as remote control availability and conducted preventive maintenance, among others, on failure statistics of a disconnector population in Sweden using the proportional hazard model To do so, 2191 work orders were analyzed, which included 1626 disconnectors and 278 major failures Here, the results show that the remote control availability for disconnectors—an example of such smart-grid technology—has a negative effect on the failure rate, whereas preventive maintenance has a positive impact It is also shown that the disconnector age is not significant and that certain disconnector types have a significant and positive correlation toward failures when compared to other disconnector types The results increase the understanding of disconnector failures to improve asset management

Allocation of Frequency Control Reserves and Its Impact on Wear and Tear on a Hydropower Fleet

Abstract: Power systems are making a transition from purely technical, centrally planned systems to market based, decentralized systems. The need for balancing power and frequency control reserves are increasing, partially due to variable renewable production, which gives an opportunity for new incomes but also a challenge in terms of changed modes of operation with risk for reduced lifetime for controllable power plants. This paper investigates how the allocation of a sold volume of frequency control reserves within a large hydropower production fleet can affect the costs of providing primary and secondary reserves, in terms of its impact on wear and fatigue, production losses, and the quality of the delivered frequency control. The results show that for primary control, low static gain in the governors results in poor quality and a large amount of load cycles of the units. High static gain, on the other hand, increases the production losses. The control work of the fleet can be reduced by using a proper balance of primary and secondary control gain on each unit, although the intuitive results from linear models exaggerate this effect. Automatic secondary control improves the system frequency quality but also increases the wear.

REDWIN – REDucing cost in offshore WINd by integrated structural and geotechnical design

Abstract: The cost of offshore wind energy production has to be reduced continuously to improve its competitiveness compared to other energy sources. To contribute to this goal, a 4-year research project REDWIN – REDucing cost of offshore WINd by structural and geotechnical integrated design – is currently ongoing, addressing the challenge of integrating the geotechnical discipline in the design process. The project aims to develop foundation and soil models to be used in dynamic time-domain analyses of offshore wind turbine structures. A library of models has been developed for representation of the most common foundation types. The models can be applied to different ground conditions by site-specific model input. To make the models applicable for practical usage, it has been important to balance the need for computational effectiveness against the need for accuracy. Studies so far indicate that the foundation models improve the accuracy in the integrated analyses.

Assessment of Explanatory Variables on the Failure Rate of Circuit Breakers Using the Proportional Hazard Model

Abstract: This paper utilises the proportional hazard model to understand and quantify the impact of explanatory variables on the failure rate of circuit breakers (CB). Particularly, 4496 work orders with 2622 high voltage CBs are investigated with an occurrence of 281 major failures. Different explanatory variables such as CB type, manufacturer, preventive maintenance (PM), and others are gathered to quantify their significance and magnitude of their effect. The results present that PM has a positive impact, the number of operations within the last year a negative impact, and age has a small but negative impact on the failure rate. The CB type is not significant in all analyses which can be explained by examining the PM and age of these CB types. This paper contributes to the understanding of how explantatory variables impact the failure rate which is essential for power system asset management.

Transient Air-Water Flow and Air Demand following an Opening Outlet Gate

Abstract: In Sweden, the dam-safety guidelines call for an overhaul of many existing bottom outlets. During the opening of an outlet gate, understanding the transient air-water flowis essential for its safe ...

Modelling of Recurrent Circuit Breaker Failures with Regression Models for Count Data

Abstract: High voltage circuit breaker (CB) are of fundamental importance to protect and operate the power system. To improve their performance and to better predict failures, it is necessary to understand the effect of covariates such as preventive maintenance, age, voltage level, and the CB type. A straightforward approach is to investigate recurrent failures with regression models for count data. In this paper, several regression models are developed to estimate the impact of the aforementioned covariates to predict the recurrence of failures. The results show that age has a significant and negative impact, preventive maintenance before the first failure has a positive impact, and that the voltage level has a negative impact. Moreover, the Poisson, Negative Binomial, and zero-inflated models are compared. The comparison shows that the Negative Binomial model has the best fit to the studied recurrent failure data.

Performance of lubricating oils for wind turbine gear boxes and bearings

Abstract: In this study, the friction and wear properties of six different new and used wind turbine gear oils (ISO VG 320), with different base oil formulations and additives packages, were investigated. Fo ...

Chemical interaction between sea-salt and tellurium, between 300 and 1180 K.

Abstract: As an emergency action during the Fukushima accident, seawater was used to maintain cooling. To evaluate the effect of the salt on fission-products, sodium chloride, and tellurium were heated together using different ratios in different atmospheres (inert or oxidizing) using thermogravimetric analysis. The experiment under inert conditions showed no indication of interaction. However, under oxidizing conditions an interaction for all samples was observed that prevented an otherwise observed mass increase of the tellurium reference. The change in the appearance of the samples at increasing temperatures was studied by heating them in a furnace.

Effects of Void Ratio and Hydraulic Gradient on Permeability and Suffusion of Glacial Till Cores

Abstract: Dams with core of broadly graded glacial moraines (tills) exhibit signs of internal erosion by suffusion to a larger extent than dams constructed with other types of materials, as reported by Sherard (1979). Garner and Fannin (2010) indicated that internal erosion initiates when an unfavorable combination of soil material, stress conditions and hydraulic load occur. A laboratory program, carried out at Lulea University of Technology (LTU), aims to study the effects of void ratio and hydraulic gradient on the initiation of suffusion of glacial till. It consists of suffusion tests conducted in permeameters with an inner diameter 101.6 mm and a height of 115 mm. Results show, as expected, that the hydraulic conductivity is lower with lower void ratio. Nevertheless, as the hydraulic gradient increases, the hydraulic conductivity reaches steady values. Changes in the hydraulic conductivity suggest variation in the initial void ratio due to detachment of the finer particles from the soil matrix. These fine particles start clogging the lower layers, therefore the rate of water flow decreases and so does the hydraulic conductivity. The hydraulic gradient for which the hydraulic conductivity reaches steady values is considered as the upper limit without suffusion evolved.

Digital Business Outcomes: Digital Innovation and Its Contribution to Corporate Development

Abstract: Nowadays, IT is an important component of a company’s value chain. However, it has to face the latent suspicion of being ‘too expensive anyway’ as the management is constantly demanding cost savings. Furthermore, the modern role of IT also requires the implementation of innovative tasks to maintain sustainability for companies. From this, one can derive IT’s task to translate its services and its technical and legal framework conditions into business language. The purpose of this article is to show the broad scope of IT in the value chain of today’s companies. With this, we are moving away from a purely financial perspective and explicitly include organizational and process‐related improvements. By the example of the relatively advanced implementation of IT strategy at Vattenfall, VOICE shows with a flagship project the versatility of IT’s value contribution.

Modelling creep in concrete cylinders subjected to different relative humidity levels–the VeRCoRs 2018 benchmark

Abstract: In this study, a multiphysics model is presented that predicts creep in three months old concrete cylinders subjected to drying. The model includes concrete hydration, and a moisture transport model with relative humidity as the driving potential. These parameters are important to include in order to simulate creep. The model was implemented in the finite element software COMSOL Multiphysics. The calculated axial deformation of the cylinder was compared with measurements performed on an experimental set-up. The model was found to be able to predict the axial deformations with reasonable accuracy. This study is a part of the VeRCoRs 2018 benchmark provided by the Electricite de France, EDF.

Adaptive Cyber-Security Scheme Incorporating QoS Requirements for WAMC Applications

Abstract: Smart Grid integrates power systems and communication systems to support intelligent control and operation applications. The inputs of those applications are normally measured data collected anywhere in the system and they are transmitted over Wide Area Networks (WAN). Challenges associated with Quality of Service (QoS) and cyber-security in the delivery of these data need to be addressed. In most research work in Smart Grid, QoS and cyber-security are considered separately. However, there is tension between the two: in order to maintain a certain level of QoS security might have to be compromised. The relationship is not, however, deterministic as both QoS and the performance of cyber-security countermeasures may vary over time. To address such challenges, this paper proposes a novel adaptive cyber-security scheme. It quantifies experts opinions of available cyber-security algorithms into a metric called security coverage. Then security coverage is adaptively optimized, by switching cyber-security algorithms, depending on observed data link QoS performance. The scheme is validated with simulation studies on a typical Wide Area Monitoring Control (WAMC) application, power oscillation damping control. The proposed adaptive cyber-security scheme is generally applicable to Smart Grid or power system applications that face varying communication performance during operation.