GenAVC – an Active Voltage Control scheme - has been successfully trialled to assist in the connection of distributed generation in the EDF Energy network. The GenAVC scheme has enabled the connection of an additional 1 MW of generation which would have otherwise required substantial network reinforcement.
In addition Senergy Econnect has developed a software tool to assist planners in assessing whether GenAVC can mitigate voltage rise problems associated with distributed generation without the need for network reinforcement.
Horton Quarry Landfill site in West Sussex had an existing 2 MW generator which was restricted to an output of 1.8 MW and experienced occasional nuisance tripping due to over-voltage. The site was producing excess gas which had to be flared off, therefore an application was submitted to EDF Energy to add an additional 1 MW of generation.
Initial network assessments indicated that this was not possible without substantial network reinforcement which would have made the project economically unviable. Alternative options were sought and an IFI (Innovation Funding Incentive) project was set up to trial Senergy Econnect’s GenAVC.
A problem commonly associated with distributed generation is that it causes voltage rises on the network which led to EDF exceeding its statutory limits.
A traditional feeder will see a volt drop along it due to the impedance of the cables as shown by the red feeder and associated trace in figure 1.
If a generator is introduced then this results in a change in power flow – less current flows out of the primary substation and therefore there is less volt drop along the cable. The voltage at the point of connection of the generation is increased and can rise above allowed limits. This is shown by the blue feeder and associated trace in figure 1.
GenAVC is designed to overcome the problems of overvoltage associated with generation. It takes voltage and current measurements at the primary substation and the generator substation which means it knows exactly what the generator is doing at any point in time.
Usually the generator is a considerable distance from the primary substation and therefore some form of communications link is needed between the two points. There are various options for doing this but at Horton Quarry a BT leased line is used. The Remote Terminal Unit then sends information back to the primary substation where GenAVC uses state estimation techniques to calculate the voltage at all points on the network. It can then send a control signal to the existing AVC scheme telling it whether to increase or decrease the voltage. A block diagram of this is shown in figure 2.
The effect of GenAVC is shown in figure 3 – the voltage at the primary substation is lowered to ensure that, at the point of generation it is below the maximum statutory limits but at other points on the network it is above the minimum statutory limits.
GenAVC does not replace the existing AVC scheme, it simply ‘piggy backs’ onto it and modifies the control signal. As such it is not complicated to install and is relatively compact. The installations at Steyning and at Horton Quarry are shown in figure 4.
The performance of GenAVC has been positive. (see figure 5). The first trace shows the voltage at the primary substation (dark green) and the voltage at the generator (light green). 1.06 is the maximum permitted voltage and it is evident that this is reached at periods of low demand. Once this happens, GenAVC acts to reduce the voltage at the primary substation. This is shown in the second trace which indicates to what extent GenAVC is influencing the existing AVC scheme. Similarly, at periods of high demand, other points on the network reach the lower limits and GenAVC acts to increase the voltage at the primary substation. The third trace shows the output of the existing generation (2 MW) and the fourth shows the output of the new generation (1 MW).
The IFI project also developed a web-based software tool which allows planners to make an initial assessment as to whether GenAVC can help with a particular network. The user has to input network data such as impedances, primary voltage and feeder currents for a 12 month period and the software will then produce an output giving an estimate of the remaining ‘headroom’ available on the network if GenAVC was employed, an example of which is shown in figure 6.
The green line represents the additional generation which the user has requested to add and this should be read off from the scale on the right hand side (around 1 MW). The red line shows the available voltage head room on the network, read off in per unit values from the left hand side and MW values from the right hand side. In this instance GenAVC can solve the voltage issues for the majority of the time and is likely to be an economic solution. Results will vary in each individual situation.
EDF Energy and Senergy Econnect will continue to monitor the system over the coming months, and expect to see GenAVC’s successful performance continue.
Senergy Econnect is a specialist in the grid connection of renewable energy and delivers solutions to renewable energy projects around the world. Involved in more than 50% of all wind MW commissioned in Great Britain, the company has a track-record in providing solutions to challenging grid integration opportunities with expertise in a wide range of generation technologies in onshore and offshore wind, marine renewables, hydro, natural, coal-seam and landfill gas, wind/diesel hybrids, biomass, waste to energy, solar thermal and PV (also known as solar power energy) and geo-thermal.
Senergy Econnect has developed solutions in transmission networks, distribution networks and system operations, to support the growing penetration and integration of renewable energy generation.
The company is part of Senergy, a diversified energy services business that operates around the world in the oil and gas and renewable energy industries. Senergy focuses on adding value and minimising risk for clients through the application of commercial and technical innovation.
|About the authors: |
Dr Vincent Thornley has 15 years’ experience in the power systems industry, involved in all aspects of research, development, manufacture and marketing of power system control, protection and automation products. His early career was spent with Reyrolle, designers and manufacturers of relays for the worldwide protection and control market. In recent years he has been particularly focused on voltage control of electrical networks and the effects of distributed generation, which led to completion of an engineering doctorate with the University of Manchester. Since then he has been Products Manager with Senergy Econnect, leading the development and commercialisation of the company's Smart Grid and Demand Side Management products. David Reid joined EDF Energy Networks in 2004 immediately after graduating from Sussex University with an MEng in Electrical and Electronic Engineering. He completed the company’s 18 month graduate training programme before moving in to distribution planning which involved planning the maintenance and improvement of the 11kV and LV networks. Whilst in this position he was responsible for determining points of connection for new load and new generation which is how he became involved with the GenAVC project. He is now in a project management position, involved with the design and construction of major projects such as new primary and grid substations.