Search

Conservation voltage reduction (CVR) has been traditionally applied adopting moderate settings at primary substations and when distributed generation was uncommon. However, as new infrastructure is deployed across European-style medium voltage (MV) and low voltage (LV) networks, driven by increasing photovoltaic (PV) penetration levels, the opportunity arises to develop more advanced CVR schemes. This paper proposes a centralized, three-phase AC optimal power flow (OPF)-based CVR scheme that, using monitoring, on-load tap changers and capacitors across MV and LV, actively manages voltages to minimize energy consumption, even with high PV penetration, while considering MV–LV constraints. To tackle scalability issues brought by discrete variables, a two-stage approach is proposed to solve the OPF as a non-linear programming problem (relaxing integer variables). A process that continuously checks customer voltages is adopted to trigger the optimization only when needed. Moreover, CVR benefits are not only quantified at a network level but also for customers, providing useful insights to policy makers. The proposed control is assessed using a realistic, unbalanced U.K. residential MV–LV network (2,400+ customers) with high PV penetration, and 1-min resolution time-varying profiles and load models. Results demonstrate that the proposed control effectively coordinates voltage regulation in MV and LV levels throughout the day, minimizing energy imports for all customers. [ABSTRACT FROM AUTHOR]

This two-part paper surveys the frequency and voltage control ancillary services in power systems from various parts of the world. In this second part, essential economic features that must be taken into account when designing markets for ancillary services are first discussed. The methods adopted in eight different systems (Australia, France, Germany, Great Britain, New Zealand, PJM, Spain, and Sweden) for trading frequency and voltage control ancillary services are then compared. Lastly, new indicators for comparing volumes and costs of ancillary services across systems are proposed and calculated for the systems included in this survey. The companion paper surveys the technical features of these ancillary services. [ABSTRACT FROM AUTHOR]

The decommissioning of synchronous generators, and their replacement by decoupled renewable power plants, has a significant impact on the transient stability performance of a power system. This paper concerns with an investigation of the degree of transient stability enhancement that can be achieved in power systems with high shares (e.g., around 75%) of wind generation. It is considered that the wind generators can work either under the principle of current control or under the principle of fast local voltage control. In both cases, a power–angle modulation (PAM) controller is superimposed on the current control loops of the grid side converters of the wind generators. The investigation of the degree of enhancement takes into account different approaches of the tuning of PAM. It considers a simple approach in the form of parametric sensitivity, and also a sophisticated approach in the form of a formal optimization problem. Besides, the paper gives insight on what is a suitable objective function of the optimization problem, which entails the best performance of PAM. The whole investigation is conducted based on a synthetic model of the Great Britain (GB) system [ABSTRACT FROM AUTHOR]

Although district heat network schemes provide a pragmatic solution for reducing the environmental impact of urban energy systems, there are additional benefits that could arise from servicing electric vehicles. Using the electricity generated on-site to power electric vehicles can make district heating networks more economically feasible, while also increasing environmental benefits. This paper explores the potential integration of electric vehicle charging into large-scale district heating networks with the aim of increasing the value of the generated electricity and thereby improving the financial feasibility of such systems. A modelling approach is presented composed of a diverse range of distributed technologies that considers residential and commercial electric vehicle charging demands via agent-based modelling. An existing district heating network system in London was taken as a case study. The energy system was modelled as a mixed integer linear program and optimised for either profit maximisation or carbon dioxide emissions minimisation. Commercial electric vehicles provided the best alternative to increase revenue streams by about 11% against the current system configuration with emissions effectively unchanged. The research indicates that district heating network systems need to carefully analyse opportunities for transport electrification in order to improve the integration, and sustainability, of urban energy systems. • Framing of a modern district energy system as a mixed integer linear program. • Agent-based modelling used to simulate electric vehicle charging demands. • Electric vehicle charging in a district heating network simulated for a London area. • District heating integration with electric vehicles improves revenues by 11%. [ABSTRACT FROM AUTHOR]

This study describes the power conversion and control solution used in the electrical power take-off of a 35 kW test rig developed to investigate a linear, direct drive, air-cored, tubular, permanent magnet generator for an offshore wave energy device. The solution proposed is to collect the power extracted directly from individual coils of the generator, which have different induced voltages and cannot easily be connected into a small number of phases. Local energy storage is integrated into the system to smooth the electrical output power and reduce the rating of the downstream inverter for grid interfacing. The solution is demonstrated by analysis, backed up by simulation and test results. This shows the potential and limitations of the proposed conversion technology solution. [ABSTRACT FROM AUTHOR]

This paper points out the need for static synchronous compensators (STATCOMs) used in conjunction with wind parks. It describes the principles of operation of a medium voltage STATCOM and presents operational experiences based on installations in Great Britain and in Canada. Furthermore, value adding additional functions of a STATCOM are named. [ABSTRACT FROM AUTHOR]

• Severe PV ramping at high penetration could cause voltage instability in presence of Induction motor loads. • Replacement of Induction motor by Variable Speed Drive (VSD) loads enhances voltage stability of distribution network. • Enhanced stability with VSD is studied theoretically with Q-V analysis and with time simulations. • Minimum IM replacement by VSD is determined for realistic distribution network at various PV penetration levels. The Photovoltaic (PV) sources have become the most popular renewable energy resources as it is modular and are deployed quickly. However, the distributed PVs are highly volatile and can have high ramping characteristics where the ramping can go up to 90% of its capacity in about 20 s due to events such as the passing of fast-moving clouds. This kind of PV ramps with high magnitudes can lead to voltage instability in distribution networks that are usually dominated by Induction motor (IM) loads. This paper explains the mechanism of such an instability analytically using Q-V analysis with distribution feeder and IM load characteristics. Highlighting the gradual replacement of IM loads by Variable Speed Drive (VSD) loads due to energy efficiency policies, the paper demonstrates the enhanced voltage stability under VSD loads by both time simulation and analytical approach. Furthermore, the analysis is extended to a realistic distribution network namely, United Kingdom General Distribution System (UKGDS) and extensive case studies are conducted to analyze the voltage stability during PV ramping events at various load compositions of IMs and VSDs. Moreover, the minimum VSD penetration level required to avert the voltage instability at various PV penetration levels have also been determined. [ABSTRACT FROM AUTHOR]

Recent long term planning studies have demonstrated the important role of variable renewables (VRE) in decarbonising our energy system. However, cost-optimising models do not capture the visual impact of VREs on the landscape which can act to undermine their public acceptability. Here, we use crowd-sourced scenicness data to derive spatially explicit wind energy capacity potentials for three scenarios of public sensitivity to this visual impact. We then use these scenarios in a cost-optimising model of Great Britain's power system to assess their impact on the cost and design of the electricity system in 2050. Our results show that total system costs can increase by up to 14.2% when public sensitivity to visual impact is high compared to low. It is thus essential for policy makers to consider these cost implications and to find mechanisms to ameliorate the visual impact of onshore wind in local communities. [ABSTRACT FROM AUTHOR]

This paper investigates the possible options for achieving a substantial reduction in a substation footprint using air-insulated switchgear as a more environmentally-friendly alternative to gas-insulated substations that use SF6 gas. Adopting a new approach to surge arrester location and numbers, International Electrotechnical Commission (IEC) minimum clearances can be successfully selected instead of the maximum clearances as currently adopted by many utilities, as is the case in the UK. In addition, innovative alternative compact busbar arrangements using vertical and delta configurations have been proposed by the authors. A further opportunity for compaction is offered by the application of compact and integrated technology offered from several manufacturers. The full overvoltage control within the entire substation under any surge condition is a key aspect of the feasibility of this type of substation. This work demonstrates that the new design option can be an attractive alternative for future substation configuration with minimum footprint. [ABSTRACT FROM AUTHOR]

The issue of congestion management in distribution networks by considering a methodology for generation curtailment due to voltage constraints is addressed. The curtailment is based on the contribution of generators to the constraints as quantified by voltage-sensitivity factors. It has been shown that generation curtailment following a simple proportionality rule is not efficient and some alternatives, which give a more efficient outcome, have been proposed. Influence of network losses on the curtailment rules has also been shown. The considerations have been illustrated using two simple 11 kV networks. [ABSTRACT FROM AUTHOR]

• A simultaneous DSR event for the refrigeration systems in three retail stores. • DSR event of the store trials facilitates energy savings and the planned load shed. • The aggregated loads facilitate 97.3% and 27% of load shed at start and during DSR. • The synchronised return to operation post DSR drops the line voltage by 1%. • A pressure offset at the beginning of a DSR improves the performance of the system. The paper considers the impact of Demand Side Response events on the supply power profile and energy efficiency of widely distributed aggregated loads applied across commercial refrigeration systems. Responses to secondary grid frequency static DSR events are investigated. Experimental trials are conducted on a system of refrigerators representing a small retail store, and subsequently on the refrigerators of an operational superstore in the UK. Energy consumption and energy savings during 3 h of operation pre- and post-secondary DSR, are discussed. In addition, a simultaneous secondary DSR event is realised across three operational retail stores located in different geographical regions of the UK. A Simulink model for a 3Φ power network is used to investigate the impact of a synchronised return to normal operation of the aggregated refrigeration systems post DSR on the local power network. Results show ∼1% drop in line voltage due to the synchronised return to operation. Analysis of energy consumption shows that DSR events can facilitate energy savings of between 3.8% and 9.3% compared to normal operation. This is a result of the refrigerators operating more efficiently during and shortly after the DSR. The use of aggregated refrigeration loads can contribute to the necessary load-shed by 97.3% at the beginning of DSR and 27% during the 30 minutes of a DSR, based on results from a simultaneous DSR event carried out on three retail stores. [ABSTRACT FROM AUTHOR]

• The proposed STCD scheme coordinates all generator OLTC's tap changing actions under security and optimization rules for achieving uniform grid voltage and maintaining grid voltage stability. • Optimization rules are applied to determine most effective tap changing actions for individual OLTCs using static data "volts change per tap" and avoid grid unnecessary MVar circulation. • Security rules are applied to calculate secured tap change limits for individual OLTCs maintaining sufficient safety margin for all individual generators with various reactive power output levels. • The proposed STCD schemes is effective in securely regulating grid voltage to target values and economically managing reactive sharings amongst the generators; this is verified in the real GB southeast coast grid model. To regulate transmission network voltage within statutory limits, transmission system operators (TSO) can issue instructions to the grid synchronized generators to simultaneously change their transformer tap positions, and these instructions are normally preceded by advance notice and executed at the required time. This operation action is known as "Simultaneous Tap Change Dispatch" (STCD). This paper presents a security and optimization rule-based generator Simultaneous Tap Change Dispatch (STCD) scheme, which aims to maintain system wide-area voltage stability through effective and fast voltage regulation, and to minimize the total amount of reactive power utilization; thus, indirectly reduces the line losses. Technical implementation of the proposed STCD is discussed, and the costs of MVar utilization by the STCD is compared with the employment of new shunt reactors. The proposed STCD scheme is validated in a DIgSILENT Power Factory platform to simulate a real regional system model in Great Britain (GB). And, the effectiveness of STCD scheme in transmission voltage regulation, generator MVar optimization, and operational security are verified by comparing to the baseline (a system with uncoordinated schemes). [ABSTRACT FROM AUTHOR]

In the absence of phase transposition, overhead lines are a major source of unbalance in both currents and voltages on the transmission system. In the England and Wales (E&W) transmission system, the individual circuits are phased such that the average unbalance produced is minimized. The main negative phase-sequence (NPS) voltages on the transmission system arise at loop-in points for generation and load connection under an outage condition of one of the connection circuits and where there is a large NPS voltage induction from the parallel circuit. If not limited, excessive unbalance can cause system incidents and lead to damage of power system equipment. [ABSTRACT FROM AUTHOR]