• Energy Research
• other engineering and technologies close
• GB close
• BE close

This paper presents a literature survey on the subject of voltage stability analysis of power systems. The survey describes several published methods and techniques used to determine voltage stability indices. These indices predict proximity to voltage instability and collapse problems. The Q-V and P-V curves; singular value decomposition; modal analysis; test function; reduced determinant; loading margin by multiple power flow solutions; local load margins; thevenin/load impedance; and energy function are the methods which have been decribed in the paper. The methods described are based on the original work that first proposed them. They are based on the power-flow system model, where the variation of real and reactive powers are assumed to be the main parameters driving the system to voltage instability. Some of the described methods were applied on the IEEE 30-bus power system.

Even with state of the art forecasting methods, the short-term generation of wind farms cannot be predicted with a high degree of accuracy. In a market situation, these forecasting errors lead to commercial risk through imbalance costs when advance contracting. This situation is one that needs to be addressed due to the steady increase in the amount of grid connected wind generation, combined with the rise of deregulated, market orientated electricity systems. In the presence of imbalance prices and uncertain generation, a method is required to determine the optimum level of contract energy to be sold on the advance markets. Such a method is presented here using Markov probabilities for a wind farm and demonstrates substantial reductions in the imbalance costs. The effect of market closure delays and forecasting window lengths are also shown.

In this paper a novel generalised modelling framework for multi-energy systems containing storage elements is combined with a multi-objective model predictive control. The control objective is to both minimise the economic cost of importing energy into the system as well as providing the service of smoothing the profile of the electrical energy imported thus levelling the load and reducing peak demand. The capabilities of the approach are demonstrated by its application to a representative case study based on two buildings at the University of Manchester. Results show that model predictive control is capable of simultaneously addressing minimisation of economic cost as well as smoothing the electrical energy import.

Abstract In this paper, the possibility of applying a Power System Stabilizer (PSS) via the governor-turbine system of a generating unit is studied for both single-machine and multimachine power systems. The results of analysis and simulation show that the conventional exciter-based PSS can be used in conjunction with the modern high-speed governor to suppress low-frequency oscillations in power systems. This arrangement of stabilizer possesses better robustness to the changes of power system operating conditions. Furthermore, in the environment of a multimachine power system, the control of PSS on the governor of every generator can be locally synthesized to stabilize the whole system, PSS design becomes much easier and simpler.

Abstract The housing growth programme could offer an opportunity for accelerating the deployment of decentralised renewable energy systems (DRES) in the UK. The Government hopes to leverage private sector investment into DRES as part of new housing projects. The aim of this paper is to assess whether current regulatory and funding frameworks are sufficient to achieve this. The question is explored by drawing on the experience of developers, local authorities, energy utilities and service companies operating in the largest housing growth region in the UK–Thames Gateway. Their experience suggests that the current low intervention approach will be insufficient to generate the shift required in both industries. In order to be more successful economic and regulatory instruments should focus on producers (house-builders and energy providers) rather than consumers (households). Tighter regulation is needed to ensure that producers have a responsibility to install DRES as part of new developments, to enable connection to the grid, to ensure a sustained financial return from investment and revenue is spent on the expansion of new renewable energy infrastructure. This regulatory framework must be under-pinned by substantial funds focused on producers. Greater intervention is needed if DRES is to be included in new housing development.

Abstract A new method for providing ventilation in large enclosures, which utilizes the principle of ‘selective withdrawal’ of contaminants while ensuring energy-efficiency and allowing a better use of space, is presented in this study. The concept is based on dividing the enclosed space ventilation-wise into separate zones using a combination of horizontal partitions by stratification and vertical partitions by temporary walls. This gives a high degree of flexibility in the use of available space. The relative influence of all the parameters on the flow patterns inside an enclosure is discussed in order to identify the design parameters that should be controlled to apply the technique successfully. An experimental study in a scale model was conducted, which provided a better understanding of the physical processes that occur in such enclosures. The influence of exhaust location on the flow field was studied in particular. It was found that by controlling the position of exhaust the stratification effects are enhanced and maintained at a desired level in order to achieve a successful utilization of the selective ventilation system.

Biomethane production from processed industrial food waste (IFW) in admixture with sewage sludge (primary and waste activated sludge: PS and WAS) was evaluated at a range of C:N ratios using a standard biochemical methane potential (BMP) test. IFW alone had a C:N of 30 whereas for WAS it was 5.4 and thus the C:N ratio of the blends fell in that range. Increasing the IFW content in mix improves the methane potential by increasing both the cumulative biogas production and the rate of methane production. Optimum methane yield 239 mL/g VSremoved occurred at a C:N ratio of 15 which was achieved with a blend containing 11 percent (w/w) IFW. As the fraction of IFW in the blend increased, volatile solids (VS) destruction was increased and this led to a reduction in methane yield and amount of production. The highest destruction of volatile solids of 93 percent was achieved at C:N of 20 followed by C:N 30 and 15. A shortened BMP test is adequate for evaluating optimum admixtures.

Rotating stall and surge are flow instabilities contributing to the acoustic noise generated in centrifugal compressors at low mass flow rates. Their acoustic generation mechanisms are exposed employing compressible Large Eddy Sim- ulations (LES). The LES data are used for calculating the dominant acoustic sources emerging at low mass flow rates. They give the inhomogeneous char- acter of the Ffowcs Williams and Hawkings (FW-H) wave equation. The blade loading term associated with the unsteady pressure loads developed on solid surfaces (dipole in character) is found to be the major contributor to the aerodynamically generated noise at low mass flow rates. The acoustic source due to the velocity variations and compressibility effects (quadrupole in character) as well as the acoustic source caused by the displacement of the fluid due to the accelerations of the solid surfaces (monopole in character) were found to be not as dominant. We show that the acoustic source associated with surge is generated by the pressure oscillation, which is governed by the tip leakage flow. The vortical structures of rotating stall are interacting with the impeller. These manipulate the flow incidence angles and cause thereby unsteady blade loading towards the discharge. A low-pressure sink between 4 and 6 o’clock causes a halving of the perturbation frequencies at low mass flow rates operat- ing conditions. From two point space-time cross correlation analysis based on circumferential velocity in the diffuser it was found that the rotating stall cell propagation speed increases locally in the low pressure zone under the volute tongue. It was also found that rotating stall can coexist with surge operat- ing condition, but the feature is then seen to operate over a broader frequency interval.