Demonstration project 5 Network-enhanced flexibility (NETFLEX)

Main findings

TSOs can plan the network more boldly by monitoring it more accurately and by controlling it more tightly while delivering the same level of reliability:

  • The Dynamic Line Rating (DLR) forecaster enables to plan in average 10-15% higher transmission capacities thanks to an accurate monitoring of overhead line sag and local wind forecast.
  • The Smart Controller enables to coordinate multiple Phase-Shifting Transformers and HVDC links to impact on the flows on some critical branches and to route electricity when it is needed and where capacity is left.
  • In order to achieve the same level of reliability, the DLR forecaster can use a more ambitious policy as the Smart Controller enables compensating for over-estimations.
  • The Smart Controller also enables to enhance wind penetration thanks to more coordinated actions on multiple Power Flow Controlling devices (PFCs).
  • Damping can be reliably forecasted based on flows and injections.

Project description

The variability of wind generation creates quicker and more significant changes in the flows of electricity through the transmission network than conventional fuels. Grid reinforcements are needed to connect and integrate more wind by managing variations from wind output while keeping the same level of security of supply. Furthermore the upgrading and installation of new overhead lines and underground cables takes time. More flexible solutions are needed to cope with these variations in a timely and cost-effective way.

The goal of NETFLEX is to demonstrate that network flexibility enables more power to be transported to where it is needed without compromising operational security. It shows how a more accurate monitoring and enhancement of grid control allows TSOs to plan and operate the networks more boldly.

Dynamic Line Rating (DLR) devices like Ampacimons (www.ampacimon.com) can be installed quickly on overhead lines to provide accurate measurements of the capacity of the transmission system in real time as well as forecast up to two days ahead with a warranty of no clearance violation. Real time measurements from Ampacimon enable defining the confi-dence interval and choosing the appropriate level of risk. This capacity depends on wind conditions and is very sensitive at low wind speeds (0-5 m/s). Integrating this capacity into network operations requires reliable weather-based forecasts.

Power Flow Controlling devices (PFCs) like Phase-Shifting Transformers (PST) and High Voltage Direct Current (HVDC) links provide the means for changing and distributing flows locally, through 'corridors'. But several PFCs together would influence flows over a broader area and free up more system capacity. To do so, a more sophisticated and coordinated controller was developed: a smart controller.

Phasor Measurement Units (PMU) and Wide Area Monitoring Systems (WAMS) provide real time information about system dynamics. Because these dynamics are closely related to the intrinsic features of power plants, loads and dispersed generations – and not only the transmission grid - it becomes more and more complicated to simulate them. As a consequence, planning more accurately and possibly closer to stability limits, involved finding a solution for accurately forecasting stability, which was a real challenge.

Results in detail

The demo team successfully developed a reliable DLR-forecaster which forecasts one and two days ahead and delivers an average gain of 10-15% over the seasonal ratings (with 98% confidence). Ampaci-mons measurements and weather forecasts were integrated using a risk-based approach.

The project team developed a smart controller to optimise the use of PFCs for directing flows to lines which still have capacity. The controller takes conventional security criteria (N-1) into consideration and smooth the operation of PFCs while alleviating congestions. It also assesses wind deviations the system can cope with. By comparing wind deviations and the uncertainties on wind forecasts, operators can estimate which part of the remaining margin can be allocated to the market and which part must be preserved for security purposes. Tests showed that it could enable the integration of more wind power into the existing system.

To monitor and improve system stability, a damping forecaster was developed. Based on the forecasted flows and injections from some large power plants, the damping ratio of the system's dominant inter-area modes is forecast in a reliable way. The analyses have shown that the existing PFCs do not have a significant impact on the damping ratio. Hence, their use for improving damping is rather limited. On the other hand, increasing capacities through PFCs does not come at the expense of a decreased damping.

Together, the Ampacimons, the PFCs, the PMUs, the WAMS, the DLR-forecaster, the damping-forecaster and the smart controller will allow more audacious forecasting thanks to a more accurate monitoring of capacities and stability, and a tighter control over the flows. Further investigations are underway in order to identify how to increase damping both in real time and in operational planning.

A full deployment of Ampacimons and their integration into SCADAs and EMS, and the full implementation of a smart controller of existing PFCs in Central Western Europe would generate substantial economic benefits (up to 250 million EUR per year) by lowering overall generation costs for the region.

Enhancing network flexibility means the grid can be used to transport more power. It is a better way to use existing assets. It does not create permanent physical capacity as such. It allows network operators to close the gap between grid congestion and the effective commissioning of new transmission assets that takes between five and 10 years, thus effectively allowing the integration of more variable generation, in particular wind power (correlation with the cooling), with existing network assets.