Meshing radial networks at 11kV

This project evaluates the benefits of meshing existing 11kV radial networks in order to reduce losses and maximise the connection of low carbon distributed generation. These networks are often arranged as radial feeders with normally-open links between two of the feeders; the link is closed only to enable continuity of supply to an isolated portion of a feeder following a fault on the network. However, this link could also be closed permanently thus operating the network as a meshed topology under non-faulted conditions. The study will look at loss savings and the addition of distributed generation on a typical network under three different scenarios; traditional radial feeders, fixed meshed network and a dynamic meshed network. The networks are compared in terms of feeder losses, capacity, voltage regulation and fault levels

Improve the Flexibility of Power Distribution Network by Using Back-to-back Voltage Source Converter

Employing increasing distributed generations (DGs) into existing distribution networks is an inevitable trend of the development of modern electric power systems because of the benefits including the environmentally friendly generation, higher efficiency and improved flexibility and reliability. However, high DG penetration level could pose various issues among which the voltage violation and fault level increase are the most concerned. According to the current situation of UK distribution networks, voltage violation is likely to be the first constraint to be met when DG penetration level is increased to certain level. Therefore, compensators are considered to be implemented to regulate the voltage. The reactive power compensators that widely used in transmission systems appear less effective in distribution networks thus active power compensation is desired. Soft-open points (SOPs) are power-electronic devices used replacing the normally-open points which can control active power transfer between two feeders and/or provide reactive power compensation. The back-to-back voltage source converter (B2B-VSC) is preferred as the SOP because of its capability of restricting fault current despite that it has higher power loss and associated capital cost. Two types of controller are developed for the B2B-VSC-based SOP: one is based on the PI control theory and the other is based on the concept of synchronverters. For the former type, the controller design is introduced comprehensively including system modelling and parameters selection. The precise selection of the damping ratio for nonstandard second-order system is derived, and a technique of resetting integrator in output voltage controller loop to achieve fast and smooth islanding transition is proposed. For the latter type, modifications are made to adapt the synchronverter idea to the application of an SOP. Simulations and experiments are carried out to validate the controller designs and both the controllers are verified to be able to provide sufficient performance on voltage regulation, fault current restriction and independent load supply in island mode. In general, the controller based on PI control theory has better performance in fault condition thanks to the current control loop, and the controller based on synchronverter owns better reliability because it does not require additional detections and signal switches inside the controller. At last, the use of an SOP in a dynamic load dominated network after the loss of mains is further investigated. Torque-speed characteristic is used to analyse the influence of the VSC’s filter impedance on the stability margin of an induction motor. Though the filter impedance can significantly decrease the stability margin, the output impedance of the VSC can be mitigated by properly designing the output voltage controller. Simulation and experiment are carried out to validate the analyses and controller design. The results show that the VSC is capable of supplying an induction motor in island mode

A systematic review for computer based observational techniques for assessing exposure to risk factors for work-related musculoskeletal disorders

The objective of this review are to systematically examine the existing techniques of computer based observational method for assessing Work-related musculoskeletal disorders (WMSDs) and analysed them to the needs of different potential users. Articles related are searched and collected from scientific database starting from 1977 to 2016. Seven methods are identified for computer based observational techniques and from these methods, only three methods have been evaluated as the intra-observer reliability and five methods are evaluated as interobserver reliability where the average results are moderate to good agreement. For concurrent validity, five methods have been evaluated with moderate agreement. Some of the risk factors that related with WMSDs are; physical, psychosocial, work organization and individual factors. In addition, these existing techniques did not fulfil the criteria of reliability and validity testing during the development of these methods

A Review and Synthesis of the Outcomes from Low Carbon Networks Fund Projects

The Low Carbon Networks Fund (LCNF) was established by Ofgem in 2009 with an objective to “help Distribution Network Operators (DNOs) understand how they provide security of supply at value for money and facilitate transition to the low carbon economy”. The £500m fund operated in a tiered format, funding small scale projects as Tier 1 and running a Tier 2 annual competitive process to fund a smaller number of large projects. By 31st March 2015, forty Tier 1 projects and twenty-three Tier 2 projects had been approved with project budgets totalling £29.5m and £220.3m respectively. The LCNF governance arrangements state that projects should focus on the trialling of: new equipment (more specifically, that unproven in GB), novel arrangements or applications of existing equipment, novel operational practices, or novel commercial arrangements. The requirement that learning gained from projects could be disseminated was a key feature of the LCNF. The motivation for the review reported here was a recognition that significant learning and data had been generated from a large volume of project activity but, with so many individual reports published, that it was difficult for outside observers to identify clear messages with respect to the innovations investigated under the programme. This review is therefore intended to identify, categorise and synthesise the learning outcomes published by LCNF projects up to December 2015

A methodology for optimal placement of distributed generation on meshed networks to reduce power losses for time variant loads.

Master of Science in Power and Energy. University of KwaZulu-Natal, Durban, 2015.In the 21st century, humanity’s thirst for an energy intensive lifestyle has led to the saturated expansion of the modern day power system. As the power system expands, centralised generation philosophies are rapidly being constrained due to increased technical losses. The inability to balance technical, economic and environmental conventional generation needs place further strain on the power system. This constraint has catalysed the emergence of decentralized renewable energy sources. Distributed generation supplements the electrical needs of a rapidly expanding demand for energy and minimises the adverse environmental impact of fossil fuel power stations. Distributed Generation is defined as electric power generation units connected close to load centres. Distributed generation can be classified according to rating, purpose, technology, environmental impact, mode of operation and penetration. Optimally connected distributed generation have many advantages over classically supplied power systems. Such as reduced power losses, improve voltage support and reliability to the system. Deferring network upgrades by relieving congestion and reducing greenhouse gas emission being some of the benefits of integrated distributed generation. This research delivers an optimal placement method of solar photovoltaic distributed generation on a 56 bus utility network to reduce power losses. Critical electrical factors for optimal placement of distributed generation to reduce power losses are defined. A practical loss optimization technique for optimal placement of distributed generation on meshed networks is defined. The technique follows an approach of ranking, profiling, activating, evaluating and finally selecting the optimally placed distributed resources. The importance of reactive power compensation is examined when integrating distributed generation onto meshed networks. Pre and post distributed solar photovoltaic generation placement shows the worsening phase angles leading to poorer power factors. The research demonstrates the impact of penetration and concentration of distributed generation on power system losses. Highly concentrated placement of non-dispatched distributed generation units lead to increase in power losses. Results conclude that the placement of distributed generation for loss reduction on a meshed power system is optimally located to match load-profiled centres. This research is significant as power utility engineers can now benefit from a wider range of skills to assess the impact of DG connections

Distribution Network Reconfiguration Considering Security-Constraint and Multi-DG Configurations

YesThis paper proposes a novel method for distribution network reconfiguration considering security-constraints and multi-configuration of renewable distributed generators (DG). The objective of the proposed method is to minimize the total operational cost using security constrained optimal power flow (SCOPF). The impact of multi-configuration of renewable DGs in a meshed network is investigated. In this work, lines were added to the radial distribution network to analyse the network power flow in different network configurations. The added lines were connected to the closest generator bus which offered least operating cost. A 16-bus UK generic distribution system (UKGDS) was used to model the efficiency of the proposed method. The obtained results in multi-DG configuration ensure the security of the network in N-1 contingency criteria

Alternative design strategies of distribution systems

In contrast with traditional approaches based either on the analysis of a small specific area or on idealistic networks, the proposed methodology determines optimal network design policies by evaluating alternative planning strategies on statistically similar networks. The position of consumers influences the amount of equipment used to serve them. Therefore, simple geometric models or randomly placed points used in previous researches are not adequate. Using an algorithm based on fractal theory, realistic consumer sets are generated in terms of their position, type and demand to allow statistical evaluation of the cost of different design policies. In order to systematically deal with the problem of determining justifiable network investments, the concept of economically adapted distribution network was investigated and applied in the context of a loss-inclusive design promoting efficient investment policies from an overall social perspective. The network’s components are optimized, after yearly load flow calculations, based on the minimum life-cycle cost methodology, balancing annuitised capital investments and maintenance costs against the cost of system operation. Evaluating the cost of each particular design over statistically similar networks allows statistically significant conclusions to be drawn. The main results include the optimal number of substations for typical urban and rural LV, HV and EHV distribution systems, network costs (investment, purchasing and maintenance) and losses as well as the sensitivity of optimal network design to future energy prices and cost of equipment. The impact of the increasing amount of microgeneration on networks has not been fully addressed to date. There have not been clustering problems in existing networks as a result of customers choosing to install microgenerators, either as a new device or as a replacement of a previous heating system. The operation of microgeneration connected to the distribution network can cause statutory voltage limits, recommended voltage unbalance levels and switchgear fault ratings to be exceeded. However, there are a range of distribution network designs and operating practices and thus the impact will vary accordingly. The operation of distribution networks is approached considering the existence of single or three-phase loads and microgeneration. This would however cause the network to be unbalanced and hence, traditional methods that consider a three-phase balanced system would provide misleading results. Every residential daily load’s behaviour shows rapid shifts from “load valleys” to high peaks due to the random and frequent “switch on/off” of appliances. Modelling each load individually will reveal problematic operating conditions which were not considered when using a smooth load profile. Thus, each and every domestic load was represented by a different load profile and the impact on losses was evaluated. Relating losses, voltages, currents and load unbalance ratio leads to conclusions about the way how to optimise the network with DG. The aim was to investigate and develop methodology for evaluation of the long-term loss-inclusive optimal network design strategies and to determine the effect of the penetration of microgeneration, such as CHP and PV, in realistic distribution networks and optimal network planning. The need for reinforcement of network components will depend on the level of generation and on the extent to which reverse power flows occurs. In most parts of the network, microgeneration exports will not be sufficient to result in any need for network investment. However, if the network was to be planned accounting with DG, capital investment scenarios are presented and compared to existing networks trying to accommodate clusters of microgeneration