Kenneth S. Smith

Smart Grid technology review within the Transmission and Distribution sector

Electricity networks operators must operate their network with a high degree of efficiency and reliability. Presently the drivers for lower-carbon electricity generation technologies are high, and to accommodate such technologies (e.g. large-scale wind power), significant changes have to be made to the way that Transmission and Distribution (T&D) networks are designed and operated. The Smart Grid concept has been introduced to highlight alternative, automated technologies that may bring significant benefits to the T&D networks. This paper summarizes smart grid technologies within the T&D sector that in terms of technology readiness are superior to other technologies, and are expected to be deployed in the near future. This paper summarizes the drivers behind development of the smart grid, then by introducing some smart grid technologies, their potential applications and benefits are discussed. The engineering challenges which may prevent large scale deployment of smart grid technologies is discussed

Designing Passive Harmonic Filters for an Aluminum Smelting Plant

This paper presents the results of harmonic analysis and harmonic filter design for a grid-connected aluminum smelting plant. Harmonic-penetration-analysis studies are carried out to determine the system resonance frequencies and the individual and total harmonic voltage distortions for a wide range of possible system operating conditions including scenarios with N-1 and N-2 generation, an outage of a harmonic filter, and an outage of a rectifier transformer. A conceptual harmonic-filter-design procedure for the filters required for the smelting plant is presented. The suitability and robustness of the proposed harmonic filter configuration in terms of the filters component current and voltage ratings and corresponding rms values are investigated.

Transformer Inrush Currents

This article presents the harmonic analysis of transformer inrush currents in offshore power systems. Offshore production facilities interconnected by subsea cables are becoming increasingly common, either as new projects or as extensions to existing facilities. Interconnection via a subsea cable introduces a significant shunt capacitance to the source power system, giving rise to low natural or resonant frequency. One source of harmonic currents is the system transformer. When initially energized, the transformer may draw a transient inrush current that contains all harmonic components. If one of the harmonic components in the inrush current is close to the resonant frequency of the power system depending upon the damping levels, a sustained overvoltage may be produced. This has recently caused operational problems on a number of newly interconnected offshore systems. Analysis tools and methodologies are presented in this article that can be used during detailed engineering design to assess the likelihood of such dangerous events and to identify whether mitigation is required, long before the problems are encountered during system commissioning.

Step on the gas

This article has described the electrical power system studies that are necessary to ensure the correct and reliable operation of a large LNG plant. The features of typical LNG plants have been described and the required operational constraints on such systems discussed. The software analysis tools used for such system studies and the methodologies adopted to ensure that the proposed design meets the FEED requirements are discussed. The key performance criteria to be checked by load-flow, fault level, motor-starting, transient and dynamic stability and harmonic penetration studies are highlighted, with typical results from actual studies used to illustrate these points. The examples demonstrate that an iterative approach is required, as changes to satisfy one performance criteria may have a detrimental impact on another equally important criteria.

Assessment and enhancement of grid fault-induced torsional oscillations for induction generator-based wind turbines

This paper investigates the torsional levels of the Doubly-fed Induction Generator (DFIG) and the Fixed Speed Induction Generator (FSIG) initiated by network faults. The inclusion of the turbine-generator mutual damping is investigated for the DFIG, and FSIG. For the DFIG the significance of a detailed representation of the grid-side input filter and the DC-link capacitor are studied. A method is proposed to mitigate the torsional oscillations of the turbine-generator shaft system using a Minor Control Loop (MCL) strategy. PSCAD-EMTDC studies demonstrate that the proposed controller can alleviate the risk of torsional oscillations. A conventional Power System Stabilizer (PSS) requires identification of four parameters, however the proposed controller requires only two parameters (MCL gain and washout time constant).

Electrical Network Design Studies for Natural Gas Liquefaction Plants

The process requirements of liquefied natural gas (LNG) plants demand a high level of reliability from the supporting electrical power system. Extensive power system studies are required to confirm that the proposed electrical system meets the stringent design requirements. This paper outlines the load-flow, short-circuit, transient-stability and harmonic studies typically undertaken as part of the front end engineering design (FEED) of such a system. Studies confirm the rating of key equipment in the system SLD, ensure that the proposed circuit breaker ratings are adequate and confirm that the dynamic performance of the system is satisfactory. Studies are repeated as the design process proceeds to ensure the delivery of a reliable power system

Electrical Network Studies for Industrial/Petrochemical Plants

Extensive power system studies are required to confirm that the proposed electrical systems for new build industrial and petrochemical plants satisfy stringent design requirements. This paper outlines the load-flow, short-circuit, transient-stability and harmonic studies typically undertaken as part of the Front End Engineering Design (FEED) of such a system. These are illustrated using as an example an LNG liquefaction plant. Studies confirm the rating of key equipment in the system SLD, ensure that circuit breaker ratings are adequate and confirm that the dynamic performance of the system is satisfactory. Studies are repeated as the design process proceeds to ensure the delivery of a reliable power system

Islanded vs. grid connected LNG plants

Liquefied Natural Gas (LNG) Plants are conventionally supplied using onsite generation. This paper outlines alternative design concepts which utilize a public grid to partially or fully supply the process loads. The results obtained from the power system studies for such alternative design concepts as typically undertaken as part of the Front End Engineering Design (FEED) to ensure design requirements are met, are compared to the conventional islanded network configuration. The key differentiators in the results of the system analysis are outlined with a view to establish the merits of each design and to ensure the delivery of a reliable power system as the design process proceeds.

Investigation of a cascaded tripping incident

This paper investigates an incident that occurred in a grid connected aluminum smelting plant that resulted in cascaded tripping of power plant parts and eventual system instability. The incident was initiated by tripping of an interconnector due to the operation of its directional over-current relay. The results of the power system simulation studies are described to explain the transient performance of the system during the incident. Having identified the main area of the electrical system weakness, an under frequency load shedding scheme is designed and implemented in practice to maintain the system stability during the most severe loss of generation scenarios. The paper demonstrates how using a detailed dynamic simulation of the electrical network can be used to assist with post event analysis, and provides additional insight into the dynamic performance of the system which cannot be obtained using only SCADA or PMS data. The good correlation between measured and simulated data confirms the veracity of the model and gives confidence in the proposed under frequency load shedding scheme.

Designing Harmonic Filters for an Aluminum Smelting Plant

This paper presents the results of harmonic analysis and harmonic filter design for a grid connected aluminum smelting plant. Harmonic analysis studies are carried out to detect the system resonance frequencies and determine individual and total harmonic voltage distortion for a wide range of possible system operating conditions including scenarios with N-1 and N-2 generation, an outage of a harmonic filter, and an outage of a rectifier transformer. A conceptual harmonic filter design procedure for the filters required for the smelting plant is presented. The suitability and robustness of the proposed harmonic filter configuration in terms of the filters components current and voltage ratings, and corresponding r.m.s. values is investigated.