Voltage control in LV networks: An initial investigation

The installation of small-scale photovoltaic (PV) systems in European low voltage (LV) networks is continuously increasing given the attractive incentives adopted by countries such as the UK and Germany. In many cases, these installations are clustered in the same feeder or LV network, potentially resulting in voltage rise issues. To address this in a flexible way, here it is proposed the real-time intelligent control of LV on-load tap changer (OLTC)-fitted transformers to regulate voltages at the LV feeders. The performance of the proposed control logic is investigated adopting remote voltage monitoring of the end points as well as estimated values. The proposed control logic is applied to a real UK LV network considering one-minute simulations for a day. The results of both the monitoring and estimation-based approaches are compared for different PV penetrations. The control logic with remote monitoring successfully kept voltages of customers within the EN50160 standard. A strong performance was also shown when using estimated values. This highlights the potential applicability of such an approach

On the effects of monitoring and control settings on voltage control in PV-rich LV networks

(accepted) Adopting on-load tap changer (OLTC)-fitted transformers in low voltage (LV) networks can be a potential solution to counteract voltage rise caused by high penetrations of residential photovoltaic (PV) systems. To efficiently control the OLTC network monitoring might be considered. This work assesses the performance of a proposed OLTC control logic considering different remote monitoring schemes and control cycles. A Monte Carlo-based time-series analysis is applied to a real UK residential LV network considering different uneven PV penetrations per feeder. Results show that the adoption of monitoring only at the end of each feeder can provide a satisfactory performance of customer voltages (BS EN50160 compliant). Additionally, the proposed control logic with a 30-minute control cycle can reduce the number of tap changes whilst producing a good voltage performance. The results can help distribution network operators determining the most adequate control approaches for OLTC-fitted transformers in future LV networks

Strategies for Design of Future Distribution Networks

The role and economics of future distribution network design are fundamentally changing. One of the key elements of network design that is yet to be incorporated in the design is consideration of network losses given the increased energy costs coupled with a significant fall in price of distribution network equipment. In addition, the climate change challenge has focussed attention on energy efficiency and initiatives to potentially electrify heat and transport sectors. This thesis investigates the implications of alternative options for operation and design of distribution networks under various future development scenarios. To achieve this, a fractal-based distribution network model has been developed and implemented. In particular, the model allows for the creation of representative networks with various topological features, which is comparable with those of real distribution networks of similar topologies. The validity of the model has been demonstrated through the investigation of various alternative design options for Coventry network. Furthermore, relevant techniques have been developed for network assessment, allowing for the quantification of the impact of distributed energy resources on the distribution network performance and investment. The research findings suggest that losses will be a major driving factor for distribution network design. Such design should bring long-term economic and environment benefits, if compared with the historic peak-load driven design. The analyses from this research also suggest that three voltage level design (by phasing out the 33kV level) is likely to be more cost-effective in urban areas, while rural areas has potential voltage drop problem and suffer poor reliability performance from such design, making it economically unattractive. Finally, significant benefits of optimising demand response have been identified and quantified for different levels of penetrations of electric vehicles and heat pumps in the GB electricity distribution network

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

The effect of the van Staden wind farm on the power quality of the rural distribution network

Connection of wind farms to weak networks with a typically low X/R and short circuit ratio could result in a larger variation of voltage for corresponding variation in wind farm generation output. This variation in voltage could negatively affect the quality of electrical power in the vicinity of the connected wind farm. The analysis was based on actual on-site measurement data at individual consumers’ point of supply and the effect of the Van Stadens Wind Farm integration as seen by the consumers can be determined. It was found through statistical and correlative analysis that the voltage quality measured at the test sites were not negatively affected by the presence of generation at the Metrowind Van Stadens Wind Farm. The voltage was found to be more negatively affected by the load current drawn by the consumer at the test site and that it is foremost when the loading current was higher. No definitive evidence of an increase in voltage harmonics due to generation output or loading current was found. At two sites it was however found that the 7th order harmonic is eliminated or reduced by an increase in the generation of the wind farm above approximately 20% of maximum output. Power Factory simulations, using the Quasi Dynamic simulation tool, was performed to validate the voltage findings of the on-site power quality measurements and two things were clear from the simulations. Firstly the voltage at the point of connection has a strong negative correlation with the consumer loading current and means that the voltage will usually decrease with an increase in the loading current and vice versa. Secondly, as with the analysis of the on-site measurement results, it can be said that when current is low, then the generation output of the wind farm will have a proportional effect on the voltage. From the findings of the on-site measurements it was concluded that the wind farm did not have a negative effect on the test site consumers in the vicinity and the Power factory simulations confirmed the conclusions on the voltage analysis. It was also concluded that the local consumer load current has a larger effect on the local measured voltage than the generation output of the wind farm

Time domain analysis of switching transient fields in high voltage substations

Switching operations of circuit breakers and disconnect switches generate transient currents propagating along the substation busbars. At the moment of switching, the busbars temporarily acts as antennae radiating transient electromagnetic fields within the substations. The radiated fields may interfere and disrupt normal operations of electronic equipment used within the substation for measurement, control and communication purposes. Hence there is the need to fully characterise the substation electromagnetic environment as early as the design stage of substation planning and operation to ensure safe operations of the electronic equipment. This paper deals with the computation of transient electromagnetic fields due to switching within a high voltage air-insulated substation (AIS) using the finite difference time domain (FDTD) metho

Voltage dip performance analysis.

Thesis (M.Sc.)-University of KwaZulu-Natal, Durban, 2009.The power quality performance of South African utilities has been regulated through the application of NRS 048-2 standard. The earliest edition of the power quality standard (NRS 048- 2:1996) defines compatibility levels for voltage dips in the form of annual dip limits for each voltage dip type. Actual measured utility dip performance has consistently resulted in higher dip numbers than the limits imposed in the standard. On the other hand, the dip limits were considered to be less restrictive by industrial customers. The revised power quality standard addresses the difficulties in managing voltage dip performance based on dip limits as specified in the first edition of NRS 048-2. This new philosophy does not define dip limits; instead, utilities are required to develop specific strategies to manage dip performance according to customer requirements. This research work develops an alternative approach to the management of dip performance as opposed to the application of dip limits. The study analyses measured voltage dip records for a steel-processing plant and a pulp and paper plant. The supply network for each plant is modelled to define dip influence zones as a function of fault locations. The principal results of this study are critical circuits, causes of dips, dip influence zones and the key elements of the proposed approach in communicating dip performance. The optimised approach was presented to and adopted by the customers involved

An analysis of the reliability of the 22kV distribution network of the Nelson Mandela Bay Municipality

This dissertation is a systematic study of the 22kV Nelson Mandela Bay Municipality (NMBM) electricity power distribution network reliability evaluation and improvements to be applied. Reliability evaluation of electric power systems has traditionally been an integral part of planning and operation. Changes in the electricity utility, coupled with aging electrical apparatus, create a need for more realistic techniques for power system reliability modelling. This work presents a reliability evaluation technique that combines set literature and evaluation criteria. In analysing system reliability, this research takes into account the reasons for many outages and voltage dips and seeks to find mitigating approaches that are financially justified. The study analyses the power system in terms of the methodology developed, using power system reliability techniques, power quality evaluation, protection analyses and evaluating the network against maintenance interventions and programs, manpower availability and weather conditions contributing to the outages. In evaluating the power system various techniques are used to determine if the power network operates within the NRS standards, namely, reliability calculations, testing of protection equipment, interrogation of power quality instruments and modeling the network on Digsilent. This study will look at all the important factors influencing power system reliability, analysing the network in terms of the methodology and recommend improvements