Power quality issues of 3MW direct-driven PMSG wind turbine

This paper presents power quality issues of a grid connected wind generation system with a MW-class direct-driven permanent magnet synchronous generator (PMSG). A variable speed wind turbine model was simulated and developed with the simulation tool of PSCAD/EMTDC. The model includes a wind turbine with one mass-model drive train model, a PMSG model and a full-scale voltage source back to back PWM converter. The converter controller model is employed in the dq-synchronous rotating reference frame and applied to both generator and grid sides. To achieve maximum power point tracking, a tip speed ratio method is applied in machine side, whereas DC voltage control is applied in grid side to achieve constant DC voltage. Due to wind fluctuation and power oscillation as a result of wind shear and tower shadow effects (3p), there will be a fluctuation in the output power and voltage. The concerned power quality issues in this work are Harmonics, power fluctuation and flicker emission. The measurements will be carried out under different wind speed and circumstances

Smart grid interoperability use cases for extending electricity storage modeling within the IEC Common Information Model

Copyright @ 2012 IEEEThe IEC Common Information Model (CIM) is recognized as a core standard, supporting electricity transmission system interoperability. Packages of UML classes make up its domain ontology to enable a standardised abstraction of network topology and proprietary power system models. Since the early days of its design, the CIM has grown to reflect the widening scope and detail of utility information use cases as the desire to interoperate between a greater number of systems has increased. The cyber-physical nature of the smart grid places even greater demand upon the CIM to model future scenarios for power system operation and management that are starting to arise. Recent developments of modern electricity networks have begun to implement electricity storage (ES) technologies to provide ancillary balancing services, useful to grid integration of large-scale renewable energy systems. In response to this we investigate modeling of grid-scale electricity storage, by drawing on information use cases for future smart grid operational scenarios at National Grid, the GB Transmission System Operator. We find current structures within the CIM do not accommodate the informational requirements associated with novel ES systems and propose extensions to address this requirement.This study is supported by the UK National Grid and Brunel Universit

Transient stability analysis using potential energy indices for determining critical generator sets

In this paper, we propose the enhancement of existing power system stability analysis techniques through the use of a proposed set of potential energy indices, applied for observing the separation of generators into critical sets during transient events. This proposed potential-energy-based description of system transient stability behavior permits the formation of a critical generator cutset, which is then used in a quantitative single machine equivalent (SIME) energy-function analysis of system stability. The derivation of the method will show that the proposed potential energy indices do not rely on a detailed representation of the network model, making the indices suitable for use in a variety of applications. This method enhances the current capabilities of SIME analysis for pre-fault offline stability studies, but may also be useful for near-real-time stability analysis, owing to the lack of dependence of the proposed potential energy indices on the network parameters. The ability to utilize the proposed indices without the need for network parameters or fault location information, typically obtained from updated SCADA data, potentially allows the proposed method to be applied for real-time stability analysis utilizing only PMU input data

Choice of State Estimation Solution Process for Medium Voltage Distribution Systems

As distribution networks are turning into active systems, enhanced observability and continuous monitoring becomes essential for effective management and control. The state estimation (SE) tool is therefore now considered as the core component in future distribution management systems. The development of a novel distribution system SE tool is required to accommodate small to very large networks, operable with limited real time measurements and able to execute the computation of large volumes of data in a limited time frame. In this context, the paper investigates the computation time and voltage estimation qualities of three different SE optimization solution methods in order to evaluate their effectiveness as potential distribution SE candidate solutions

A vertex-based finite volume method applied to non-linear material problems in computational solid mechanics

A vertex-based finite volume (FV) method is presented for the computational solution of quasi-static solid mechanics problems involving material non-linearity and infinitesimal strains. The problems are analysed numerically with fully unstructured meshes that consist of a variety of two- and three-dimensional element types. A detailed comparison between the vertex-based FV and the standard Galerkin FE methods is provided with regard to discretization, solution accuracy and computational efficiency. For some problem classes a direct equivalence of the two methods is demonstrated, both theoretically and numerically. However, for other problems some interesting advantages and disadvantages of the FV formulation over the Galerkin FE method are highlighted

Maximum dive depths of eight New Zealand Procellariiformes, including Pterodroma species

Lightweight capillary tube depth gauges were attached to eight petrel species breeding at New Zealand colonies during the period 1998-2008. This paper presents the first information on the diving ability of Pterodroma petrels.Grey-faced Petrels, Pterodroma macroptera gouldi, recorded maximum dives down to 23 m. Males (6.3 ± 6.3 m SD) dived deeper on average than females (3.6 2.5 m) during the incubation period but not significantly so (P=0.06). Breeding birds dived significantly deeper on average than non-breeders, and breeding males dived significantly deeper on average than non-breeding males. The two small Pterodroma species sampled, Pterodroma pycrofti and Pterodroma nigripennis, only exhibited shallow dives down to 2 m but sample sizes were small. Sooty Shearwaters, Puffinus griseus, had mean maximum dive depths of 42.7 ± 23.7 m, with males (53.0 ± 17.3 m) diving significantly deeper on average than females (20.1 ± 20.4 m) during the incubation period. One male Sooty Shearwater dived to nearly 93 m, the deepest dive so far recorded in the order Procellariiformes. Flesh-footed Shearwaters, Puffinus carneipes, dived to 28 m, with a mean maximum dive depth of 13.6 ± 7.9 m. Hutton's Shearwaters, Puffinus huttoni, had a mean maximum dive depth of 23.0 ± 8.5 m (range 11.1-36.6 m). A single Fluttering Shearwater, Puffinus gavia, recovered with a dive gauge had dived to 29 m. Mean maximum dives made by Common Diving-Petrels, Pelecanoides urinatrix, of 10.9 ± 6.1 m (range 6.9-22.2 m) were shallower than results reported from other sites but may have been biased by gauge failures. Capillary gauges provide the best means we have at present to understand the diving capability ofsmall seabirds. While studies elsewhere have shown these gauges may overestimate diving performance by about 10-15%, other factors identified in this study indicate that sometimes diving performance will be underestimated using this simple technique

A study of publish/subscribe systems for real-time grid monitoring

Monitoring and controlling a large number of geographically distributed scientific instruments is a challenging task. Some operations on these instruments require real-time (or quasi real-time) response which make it even more difficult. In this paper, we describe the requirements of distributed monitoring for a possible future electrical power grid based on real-time extensions to grid computing. We examine several standards and publish/subscribe middleware candidates, some of which were specially designed and developed for grid monitoring. We analyze their architecture and functionality, and discuss the advantages and disadvantages. We report on a series of tests to measure their real-time performance and scalability

Performance evaluation of MPLS-enabled communications infrastructure for wide area monitoring systems

In order to obtain the transient power system measurement information, Wide Area Monitoring Systems (WAMS) should be able to collect Phasor Measurement Unit (PMU) data in a timely manner. Therefore along with the continual deployment of PMUs in Great Britain (GB) transmission system substations, a high performance communications infrastructure is becoming essential with regard to the establishment of reliable WAMS. This paper focuses mainly on evaluating the performance of the real-time WAMS communication infrastructure when Multi-Protocol Label Switching (MPLS) capability is added to a conventional IP network. Furthermore, PMU communications from geographically distributed substations to a Phasor Data Concentrator (PDC) are investigated over different transport protocols. Using OPNET Modeler, simulations are performed based on the existing WAMS infrastructure as installed on the GB transmission system. The simulation results are analyzed in detail in order to fully determine the different characteristics of communication delays between PMUs and PDC

A critical comparison of approaches to resource name management within the IEC common information model

Copyright @ 2012 IEEEElectricity network resources are frequently identified within different power systems by inhomogeneous names and identities due to the legacy of their administration by different utility business domains. The IEC 61970 Common Information Model (CIM) enables network modeling to reflect the reality of multiple names for unique network resources. However this issue presents a serious challenge to the integrity of a shared CIM repository that has the task of maintaining a resource manifest, linking network resources to master identities, when unique network resources may have multiple names and identities derived from different power system models and other power system applications. The current approach, using CIM 15, is to manage multiple resource names within a singular CIM namespace utilizing the CIM “IdentifiedObject” and “Name” classes. We compare this approach to one using additional namespaces relating to different power systems, similar to the practice used in CIM extensions, in order to more clearly identify the genealogy of a network resource, provide faster model import times and a simpler means of supporting the relationship between multiple resource names and identities and a master resource identity.This study is supported by the UK National Grid and Brunel University

Towards scalable end-to-end QoS provision for VoIP applications

The growth of the Internet and the development of its new applications have increased the demand for providing a certain level of resource assurance and service support. The concept of ensuring quality of service (QoS) has been introduced in order to provide the support and assurance for these services. Different QoS mechanisms, such as integrated services (IntServ) and differentiated services (DiffServ), have been developed and introduced to provide different levels of QoS provision. However, IntServ can suffer from scalability issues that make it infeasible for large-scale network implementations. On the other hand, the aggregated-based per-flow technique of DiffServ does not provide such an end-to-end QoS guarantee. Recently, the IETF have proposed a new QoS architecture that implements IntServ over DiffServ in order to provide an end-to-end QoS for scalable networks. Hence, it became possible to provide and support a certain level of QoS for some delay sensitive and bandwidth-demanding applications such as voice over Internet Protocol (VoIP). With regard to VoIP applications, delay, jitter and packet loss are crucial issues that have to be taken into consideration for any VoIP system design and such parameters need a distinct level of QoS support