Voltage and power quality improvement strategy for a DFIG wind turbine during variable wind conditions

This paper presents a voltage and power quality enhancement scheme for a doubly-fed induction generator (DFIG) wind farm during variable wind conditions. The wind profiles were derived considering the measured data at a DFIG wind farm located in Northern Ireland (NI). The aggregated DFIG wind farm model was validated using measured data at a wind farm during variable generation. The voltage control strategy was developed considering the X/R ratio of the wind farm feeder which connects the wind farm and the grid. The performance of the proposed strategy was evaluated for different X/R ratios, and wind profiles with different characteristics. The impact of flicker propagation along the wind farm feeder and effectiveness of the proposed strategy is also evaluated with consumer loads connected to the wind farm feeder. It is shown that voltage variability and short-term flicker severity is significantly reduced following implementation of the novel strategy described.

Modelling and Control of a Variable-Speed Switched Reluctance Generator based Wind Turbine

This paper studies the system modelling and control aspects of switched reluctance generator (SRG) based variable speed wind turbines. A control system is implemented to provide proper operation of the SRG as well as power tracking capabilities for varying wind speeds. The control system for the grid side inverter that will allow the SRG to properly generate power to the system is also presented. Studies are presented of both the SRG and inverter control systems capabilities during a balanced three-phase fault. The paper will demonstrate that the SRG based wind turbine presents a feasible variable wind speed solution with good fault response capabilities.

Inter-Area Power Oscillation Frequency Mode with Wind Turbine Generator in Irish Power System using PMU Data

Two case studies are presented in this paper to demonstrate the impact of different power system operation conditions on the power oscillation frequency modes in the Irish power system. A simplified 2 area equivalent of the Irish power system has been used in this paper, where area 1 represents the Republic of Ireland power system and area 2 represents the Northern Ireland power system.

The potential power oscillation frequency modes on the interconnector during different operation conditions have been analysed in this paper. The main objective of this paper is to analyse the influence of different operation conditions involving wind turbine generator (WTG) penetration on power oscillation frequency modes using phasor measurement unit (PMU) data.

Fast Fourier transform (FFT) analysis was performed to identify the frequency oscillation mode while correlation coefficient analysis was used to determine the source of the frequency oscillation. The results show that WTG, particularly fixed speed induction generation (FSIG), gives significant contribution to inter-area power oscillation frequency modes during high WTG operation.

Tip Leakage Flow and Heat Transfer on Turbine Stage Tip and Casing: Effect of Unsteady Stator-Rotor Interactions

Unsteady simulations were performed to investigate time dependent behaviors of the leakage flow structures and heat transfer on the rotor blade tip and casing in a single stage gas turbine engine. This paper mainly illustrates the unsteady nature of the leakage flow and heat transfer, particularly, that caused by the stator–rotor interactions. In order to obtain time-accurate results, the effects of varying the number of time steps, sub iterations, and the number of vane passing periods was firstly examined. The effect of tip clearance height and rotor speeds was also examined. The results showed periodic patterns of the tip leakage flow and heat transfer rate distribution for each vane passing. The relative position of the vane and vane trailing edge shock with respect to time alters the flow conditions in the rotor domain, and results in significant variations in the tip leakage flow structures and heat transfer rate distributions. It is observed that the trailing edge shock phenomenon results in a critical heat transfer region on the blade tip and casing. Consequently, the turbine blade tip and casing are subjected to large fluctuations of Nusselt number (about Nu = 2000 to 6000 and about Nu = 1000 to 10000, respectively) at a high frequency (coinciding with the rotor speed).

From Francis Hutcheson to James McCosh: Irish Presbyterians and Defining the Scottish Philosophy in the Nineteenth Century

This article examines the disputes amongst Irish Presbyterians about the teaching of moral philosophy by Professor John Ferrie in the college department of the Royal Belfast Academical Institution in the early nineteenth century and the substantive philosophical and theological issues that were raised. These issues have largely been ignored by Irish historians, but a discussion of them is of general relevance to historians of ideas as they illuminate a series of broader questions about the definition and development of Scottish philosophy. These are represented in the move from two philosophers who had strong connections with Irish Presbyterianism—Francis Hutcheson, the early eighteenth-century moral sense philosopher and theological moderate from County Down, and James McCosh, nineteenth-century exponent of modified Common Sense philosophy at Queen's College Belfast and a committed evangelical. In particular, this article addresses three important themes—the definition and character of ‘the Scottish philosophy’, the relationship between evangelicalism and Common Sense philosophy, and the process of development and adaptation that occurred in eighteenth-century Scottish thought during the first half of the nineteenth century.

Conjugate Heat Transfer Analysis of an Internally Cooled Gas Turbine Vane

A conjugate heat transfer (CHT) method was used to perform the aerothermal analysis of an internally cooled turbine vane, and was validated against experimental and empirical data.
Firstly, validation of the method with regard to internal cooling was done by reproducing heat transfer test data in a channel with pin fin heat augmenters, under steady constant wall temperature. The computed Nusselt numbers for the two tested configurations (full length circular pin fins attached to both walls and partial pin fins attached to one wall only) showed good agreement with the measurements. Sensitivity to mesh density was evaluated under this simplified case in order to establish mesh requirements for the analysis of the full component.
Secondly, the CHT method was applied onto a turbine vane test case from an actual engine. The predicted vane airfoil metal temperature was compared to the measured thermal paint data and the in-house empirical predictions. The CHT results agreed well with the thermal paint data and showed better prediction than the current empirical modeling approach.

Unsteady tip leakage characteristics and heat transfer on turbine blade tip and casing

An unsteady numerical investigation was performed to examine time dependent behaviors of the tip leakage flow structures and heat transfer on the rotor blade tip and casing in a single stage gas turbine engine. A transonic, high-pressure
turbine stage was modeled and simulated using a stage pressure ratio of 3.2. The rotor’s tip clearance was 1.2 mm in height (3% of the rotor span) and its speed was set at 9500 rpm. Periodic flow is observed for each vane passing period. Tip leakage flow as well as heat transfer data showed highly time dependent behaviors. A stator trailing edge shock appears as the turbine stage is operating at transonic conditions. The shock alters the flow condition in the rotor section, namely, the tip leakage flow structures and heat transfer rate distributions. The instantaneous Nusselt number distributions are compared to the time averaged and steady-state results. The same patterns in tip leakage flow
structures and heat transfer rate distributions were observed in both unsteady and steady simulations. However, the unsteady simulation captured the locally time-dependent high heat transfer phenomena caused by the unsteady interaction with the upstream vane trailing-edge shock and the passing wake.

A Numerical Study of Inlet Geometry for a Low Inertia Mixed Flow Turbocharger Turbine

Mixed flow turbines can offer improvements over typical radial turbines used in automotive turbochargers, with regards to transient performance and low velocity ratio efficiency. Turbine rotor mass dominates the rotating inertia of the turbocharger, and any reductions of mass in the outer radii of the wheel, including the rotor back-disk, can significantly reduce this inertia and improve the acceleration of the assembly. Off-design, low velocity ratio conditions are typified by highly tangential flow at the rotor inlet and a non-zero inlet blade angle is preferred for such operating conditions. This is achievable in a Mixed Flow Turbine without increasing bending stresses within the rotor blade, which is beneficial in high speed and high inlet temperature turbine design. A range of mixed flow turbine rotors was designed with varying cone angle and inlet blade angle and each was assessed at a number of operating points. These rotors were based on an existing radial flow turbine, and both the hub and shroud contours and exducer geometry were maintained. The inertia of each rotor was also considered. The results indicated that there was a trade-off between efficiency and inertia for the rotors and certain designs may be beneficial for the transient performance of downsized, turbocharged engines.

Effect of turbine inlet temperature on blade tip leakage flow and heat transfer

One of the most critical gas turbine engine components, rotor blade tip and casing, are exposed to high thermal load. It becomes a significant design challenge to protect the turbine materials from this severe situation. As a result of geometric complexity and experimental limitations, Computational Fluid Dynamics (CFD) tools have been used to predict blade tip leakage flow aerodynamics and heat transfer at typical engine operating conditions. In this paper, the effect of turbine inlet temperature on the tip leakage flow structure and heat transfer has been studied numerically. Uniform low (LTIT: 444 K) and high (HTIT: 800 K) turbine inlet temperature have been considered. The results showed the higher turbine inlet temperature yields the higher velocity and temperature variations in the leakage flow aerodynamics and heat transfer. For a given turbine geometry and on-design operating conditions, the turbine power output can be increased by 1.48 times, when the turbine inlet temperature increases 1.80 times. Whereas the averaged heat fluxes on the casing and the blade tip become 2.71 and 2.82 times larger, respectively. Therefore, about 2.8 times larger cooling capacity is required to keep the same turbine material temperature. Furthermore, the maximum heat flux on the blade tip of high turbine inlet temperature case reaches up to 3.348 times larger than that of LTIT case. The effect of the interaction of stator and rotor on heat transfer features is also explored using unsteady simulations.

Field testing a full-scale tidal turbine Part 2: In-line Wake Effects

Recent research has shown that higher ambient turbulence leads to better wake recovery, so turbines could be installed in closer proximity in real tidal flows than might be assumed from typical towing tank tests that do not take into account turbulent inflow conditions. The standard tools to assess flow velocities in field conditions are Doppler based sonar devices, such as Acoustic Doppler Profilers (ADPs) or Acoustic Doppler Velocimeters (ADVs). The use of these devices poses some challenges when assessing the wake of a tidal turbine. While ADPs allow the three-dimensional measurement of a velocity profile over a distance, the data is calculated as a mean of three diverging beams and with low temporal resolution. ADVs can measure with higher sampling frequency but only at a single point in the flow. During the MaRINET testing of the SCHOTTELSIT turbine at the QUB tidal test site in Portaferry, Northern Ireland, ADP and ADV measurements were successfully tested.Two methods were employed for measuring the wake: firstly, with a rigidly mounted ADP and secondly, with a submerged ADV which was streamed behind the turbine. This paper presents the experimental set-up and results and discusses limitations and challenges of the two methods used.

Field Testing a Full-Scale Tidal Turbine Part 3: Acoustic Characteristics

Like any new technology, tidal power converters are being assessed for potential environmental impacts. Similar to wind power, where noise emissions have led to some regulations and limitations on consented installation sites, noise emissions of these new tidal devices attract considerable attention, especially due to the possible interaction with the marine fauna. However, the effect of turbine noise cannot be assessed as a stand-alone issue, but must be investigated in the context of the natural background noise in high flow environments. Noise measurements are also believed to be a useful tool for monitoring the operating conditions and health of equipment. While underwater noise measurements are not trivial to perform, this non-intrusive mon- itoring method could prove to be very cost effective. This paper presents sound measurements performed on the SCHOTTEL Instream Turbine as part of the MaRINET testing campaign at the QUB tidal test site in Portaferry during the summer of 2014. This paper demonstrates a comparison of the turbine noise emissions with the normal background noise at the test site and presents possible applications as a monitoring system.

A Numerical and Experimental Assessment of the Use of a Turbine Utilizing Splitter Blades for an Automotive Variable Geometry Turbocharger

Automotive manufacturers require improved part load engine performance to further improve fuel economy. For a swing vane VGS (Variable Geometry Stator) turbine this means a more closed stator vane, to deal with the low MFRs (Mass Flow Rates), high PRs (Pressure Ratios) and low rotor rotational speeds. During these conditions the turbine is operating at low velocity ratios. As more energy is available at high pressure ratios and during lower turbocharger rotational speeds, a turbine which is efficient at these conditions is desirable. Another key aspect for automotive manufacturers is engine responsiveness. High inertia designs result in “turbo lag” which means an increased time before the target boost pressure is reached. Therefore, designs with improved performance at low velocity ratios, reduced inertia or an increased swallowing capacity are the current targets for turbocharger manufacturers.

To try to meet these design targets a CFD (Computational Fluid Dynamics) study was performed on a turbine wheel using splitter blades. A number of parameters were investigated. These included splitter blade merdional length, blade number and blade angle distribution.

The numerical study was performed on a scaled automotive VGS. Three different stator vane positions have been analysed. A single passage CFD model was developed and used to provide information on the flow features affecting performance in both the stator vanes and turbine.

Following the CFD investigation the design with the best compromise in terms of performance, inertia and increased MFP (Mass Flow Parameter) was selected for manufacture and testing. Tests were performed on a scaled, low temperature turbine test rig. The aerodynamic flow path of the gas stand was the same as that investigated during the CFD. The test results revealed a design which had similar performance at the closed stator vane positions when compared to the baseline wheel. At the maximum MFR stator vane condition a drop of −0.6% pts in efficiency was seen. However, 5.5% increase in MFP was obtained with the additional benefit of a drop in rotor inertia of 3.7%, compared to the baseline wheel.