The Low Carbon Hub

Why we did the Lincolnshire Low Carbon Hub

Project description

An Introduction to the Problem

Distribution networks at all voltage levels, from 132,000V down to 415V, have predominately been designed for demand connections and to operate passively. This passive design philosophy has historically been the most appropriate and cost effective method to operate distribution networks since the difference between minimum and maximum network demands hasn’t been significant. When network reinforcement is required, for a proposed increase in either demand or generation, this has largely been achieved through installing new overhead lines (OHL) and / or underground cables.

However, due to the increasing connection of distributed generation, large areas are becoming generation dominated and, at times when the generated energy exceeds demand, power is exported from the distribution network back into the transmission network. This can cause problems on both the distribution and transmission networks which restrict further generation connections.

An Introduction to the Lincolnshire Low Carbon Hub

The Low Carbon Hub for East Lincolnshire was designed to test a variety of new and innovative techniques for integrating significant amounts of low carbon generation on to electricity distribution networks, in an effort to avoid the costs and other issues that would normally be associated with more conventional methods of network reinforcement.

Lincolnshire, being on the east coast, makes it suitable for a wide range of renewable generation types. These include onshore and offshore wind farms, large scale solar Photo Voltaic (PV) and energy from bio crops. However, many generators cannot connect to the distribution network closest to them due to the effects their connection would have on the operation of the existing network. These generators thus tend to require long, new underground cable installations to connect them to more robust sections of the network. This is inevitably a very expensive solution that frequently destroys the business case for the generator. However, Western Power Distribution (WPD) continued to receive a high volume of connection enquiries from developers throughout the life of the LCH – a situation that strengthened the justification for this project.

Through the Low Carbon Hub, the project sought to explore how the existing electricity network could be developed ahead of need and thus deliver low carbon electricity to customers at a significantly reduced cost in comparison to conventional reinforcement.

The project developed the six complementary project techniques detailed in Figure 1, demonstrating them and a telecommunications system in east Lincolnshire to increase effective network capacity and facilitate additional generation connections. To help with this objective, the project received £3m of funding from Ofgem’s Low Carbon Networks Fund Tier 2. 

• Why did we undertake the Low Carbon Hub?

  Lincolnshire, being on the East coast makes it suitable for a wide range of renewable generation types, these include onshore and offshore wind farms, large scale solar Photo Voltaic (PV) and energy from bio crops.  A number of operational Distributed Generation sites are already connected in East Lincolnshire.  When applications for new generation connections are modelled, the long, relatively high impedance circuits, low minimum demands and existing DG means new connections often require significant network reinforcement.

  Over the last 5+ years many generation developers have requested connections, however, often these are either very expensive or would be delayed for many years whilst conventional network reinforcement is carried out.

  In an effort to reduce generation connection costs and speed up connections, WPD is demonstrating new technologies and operating procedures.  We have also been working with Distributed Generation customers to develop and demonstrate new “Alternative” commercial arrangements, offered alongside the conventional connections currently being offered.  This provides the customer with additional choice.

  This project aimed to find new novel network solutions to make connections to the system simpler by adding network flexibility.

  The issues in East Lincolnshire are now becoming more prevalent across increasing number of locations across the UK; The Low Carbon Hub is very replicable as the new techniques could be used to solve many of the issues now being seen in other areas on 132,000V, 33,000V and 11,000V networks.

• How the Low Carbon Hub benefits customers

  The Low Carbon Hub has six main techniques to allow more generation to connect to and existing electricity network. Network enhancements, Commercial agreements, Dynamic Voltage Control, 33kV active network ring, Flexible AC Transmission System (FACTs) Device, Dynamic systems ratings.

  The six techniques have been be used together in the Low carbon Hub; however we have shown that the techniques can be used in different permeations to allow the connection of distributed generators to the existing network.

  These techniques when used together have increased the network’s thermal capacity and improved voltage control whilst maintaining network security. 

• What we did in Lincolnshire

  New commercial agreements

  The Low Carbon Hub project (LCH) has demonstrated how Distribution Network Operators (DNO) and generation developers can enter into new innovative commercial arrangements, now referred to as Alternative Connections Agreements. These agreements can unlock additional generation capacity if the generator is willing to operate in a suitable reactive power control mode and to constrain active power export when required. Western Power Distribution (WPD) has been offering cost-effective HV and EHV Alternative Connection Agreements in East Lincolnshire since February 2014 as an alternative to the high cost of conventional network reinforcement. Six Alternative Connections have been accepted, allowing the connection of 48.8MVA of additional new connections at an estimated cost saving of £42m.
   

  For the new commercial agreements method to succeed, the project also required hardware –an Active Network Management (ANM) scheme to monitor key network points and to constrain the power export of Alternative DG Connections at times when, otherwise, the network would operate outside of its design and statutory limits. The ANM scheme has been installed and integrated into WPD’s Network Management Software (NMS). This can facilitate the cost effective connection of generation by preventing the less likely, but extreme, system operation scenarios that trigger network reinforcement. 

  Finally, the project required new network planning skills to understand the impact of Alternative Connections on the network under both normal and abnormal network conditions. Two new constraint analysis software tools were thus specified, designed, tested and used by WPD planners as part of the project. These planning tools provide greater visibility of the network power flows after Alternative Connections have been made. WPD notes that DG developers also need to understand whether an Alternative Connection is suitable for them by performing their own due diligence on the connection and likely future constraints.

  33kV active network ring

  

  The creation of the ‘active network ring’ allows the network to run with greater controllability. This is possible through increased visibility of power flows and voltage profiles. The arrangement allows the system to be reconfigured, based on the real time status of the network, to optimise system capacity under system stress, which involved installation of new network equipment. Extensive network construction and reconfiguring was carried out at 6 substations to allow two network feeders to be meshed.

  This arrangement also increases power flow route diversity, with the associated benefits to system availability and losses reduction.

  Network enhancements

  

  One of the LCH methods was to ascertain what additional functionality should be either designed or built into networks to reduce the costs of connecting future generation. In this trial, key overhead lines (OHL) that were already being replaced for asset condition reasons were given enhanced capacity specifications, and 300mm2 Hard Drawn Aluminium (HDA) conductors were fitted in place of the original 150mm2 steel reinforced aluminium conductor (ACSR). 10.2km of 33kV network was rebuilt with the larger design standard.

  This double cross-sectional area offered half the circuit resistance.  Reducing the circuit resistance in this way, unlocked additional network capacity for both conventional and alternative connections, and reduced technical losses.

  The project required low latency, high bandwidth telecommunications links between primary substations for network protection and other data requirements. All suitable technologies were investigated and reported on in a review of the available wired and wireless communications media.1 Fibre and microwave comms networks were installed as part of the project.
  1. Click here to view the report. 

  Dynamic system ratings

  

  The LCH built on the work of the Skegness 132kV Dynamic Line Rating project in the Registered Power Zone (RPZ) which delivered cheaper connections to the offshore wind farms, giving Western Power Distribution Policy for dynamically rating 132kV tower lines. The LCH has developed a method of dynamically rating 33kV OHLs.

  This approach uses new code within the NMS to calculate maximum operating limits for the 33kV OHL based on real time electrical output of wind farms instead of using multiple weather stations.

  The method converts the electrical output from multiple turbines into the wind speed at the nacelle height using turbine manufacturer's data. The wind speed at the OHL height is then estimated using the wind shear power law. Finally the wind speed data is incorporated into the Dynamic Line rating algorithm to better estimate the actual maximum circuit rating, thus making best use of all the available information.

  Dynamic Voltage Control

  

  Dynamic Voltage Control (DVC) algorithm, has been incorporated within WPD’s Network Management Software (NMS). It optimises the network voltage using key voltage and current measurement points across the East Lincolnshire network. Both existing Automatic Voltage Control (AVC) relays at Skegness Grid Substation and communications infrastructure have been modified to accept automated remote target voltage changes directly from the NMS. The DVC method can optimise the voltage profile very effectively balancing both demand and generation requirements to unlock capacity.

  This element of the LCH project even manages to create an effective data monitoring point where there is no instrument transformer. At Horncastle Primary substation, the DVC requires a 33kV primary voltage measurement.  Since there is no 33kV VT, an equivalent signal is being derived from measured values for the 11kV voltage, the real and reactive power through the transformer, its tap position and the transformer’s physical characteristics.

  Flexible AC Transmission System (FACT) Device

  

  One of the factors that would unlock further network capacity is an improved control of power factor and network voltage. One method of controlling these parameters is to provide (source or sink) shunt compensation through an appropriate shunt-connected device.

  One such device is a DStatcom, so the LCH project procured a 3.75MVAr DStatcom for this purpose. It was connected in parallel with the electricity network at Trusthorpe to improve the control, locally, the power factor and network voltage. Through this LCH project the solution was demonstrated for the first time in mainland UK at 33kV. The DStatcom can control the network voltage (boosting the voltage by 3% and bucking the voltage by as much as 5%) and can reduce network losses by balancing circuit reactive power flows.

• Project outcomes

  Active Network Management

  After a successful demonstration, Active Network Management will continue to be rolled out by WPD across all four WPD licence areas with 11 new zones opened by 2023. Each will use the Alternative Connection agreements developed as part of this project. An extensive internal implementation programme is required to make an ANM rollout possible.

  A DNO constraint analysis tool is an essential aspect of Alternative Connections for both the DNO and DG developer. The project has built and demonstrated how a constraint estimation tool can be used to study Alternative Connections under both normal and abnormal network configurations, how a generation developer can be provided with the necessary information to evaluate likely constraints, understand the risk and suitability of accepting an alternative connection.

  33kV Active Network Ring

  The project has shown the 33kV active ring method is less appropriate than ANM for roll-out due to the high costs and effort associated with delivery, and the low net benefit. It is expected that, for simple meshing scenarios, benefits could be achieved by adapting the existing network more cost effectively. For more complex meshing scenarios, an offline rebuild would be most appropriate solution. Further work is required to understand when it is appropriate to mesh simple 33kV sections.

  The project aimed to show how the existing network could be altered rather than rebuilt to enhance capacity. The learning has shown that if the delivery timescales are short and significant works are required on site, the quickest solution is the construction of an offline build as demonstrated at Trusthorpe primary substation. This approach also reduces network risk as the majority of the construction can be carried out away from high voltage network and whilst the existing network is still in service. The use of a hybrid of existing air insulated assets and new gas insulated switchboards connected with cables has to be carefully managed to prevent the operation of sites being too complex. This was carefully managed within WPD’s existing design policies.

  Network Enhancements

  Certain assets, such as 33kV OHLs in ANM areas, should be enhanced ahead of need where there is a clear indication the functionality will be utilised in the future. The installation of a larger conductor reduces the resistance of the circuit; the reactance of the replacement circuit remains similar to the original circuit. The replacement conductor reduced the effects of voltage drop and voltage rise and reduces network losses.

  It can be challenging to secure landowner permission if trying to replace an OHL with shorter span lengths. As this was achieved with a new OHL H pole design with an equivalent span of 145m. This can be used again for similar future scenarios.

  Dynamic System Ratings

  We have learnt how an algorithm can be scripted within WPD’s NMS using Wind Farm output as a proxy for wind speed.  Dynamic Line Ratings must take into account all the assets in a circuit such as cables, circuit breakers, disconnectors and current transformers which cannot be dynamically rated based on weather conditions, their ratings are fixed. In East Lincolnshire, the 33kV OHLs can typically be dynamically rated up to 113% of the static winter rating. Any further increase would require cables and current transformers to be up rated. The DLR must also apply the safety factors that are required to account for any sheltering of a line. Both natural and manmade structures can cause sheltering and change over a relatively short time period.

  Dynamic Voltage Control

  Networks voltage profiles can be optimised by using centralised network intelligence. A control algorithm can be located within a NMS with remote target voltages applied to AVCs using an algorithm to determine whether the network voltage can be safely adjusted taking into account both the present demand and generation conditions. Further work is required to make this a more robust and failsafe method before roll out across a wide area.

  Transferring an AVC relay across to DNP3 control will unlock additional functionality in the relay; however this requires numerous changes across the business outside of a trial.

  An AVC relay can be cost effectively used to provide a steady state voltage measurement where there isn’t a voltage transformer.

  Flexible AC Transmission System (FACT) Device

  A DStatcom, a FACTs device, is very effective at controlling voltage, especially during network outages to remain within statutory limits. On relatively weak networks, at the ends of feeders, or at relatively long electrical distances from the voltage controlling substation, it is particularly effective.

  • When the DStatcom is operating at 100% capacitive mode (exporting reactive power) the voltage is boosted by 3%.
  • When the DStatcom is operating at 100% reactive mode (importing reactive power) the voltage is reduced by 5%.

  Where there are both voltage rise and drop issues, Statcoms will increasingly be used in key distribution locations to improve voltage control and to facilitate further generation connections. The WPD DStatcom complies with WPD’s noise policies, however unless additional noise mitigations are put in place – the audible noise generated by a DStatcom is likely to limit their use in substations in close proximity to customers.

• Documents and links

  Registration Form

  Closedown Report