Spotlight on: Turbines Flexibility and Network Codes

22 January 2019

In this exclusive interview, Luca Guenzi (Solar Turbines) and Maxime Buquet (GE Power), co-chairs of the EUTurbines Task Force Grid Code since 2011, give an insight in the association’s network code (NC) related work. The two experts elaborate on the relevance of NC for turbines and power plants, presenting the different codes and EUTurbines’ position – including the recently published statement on frequency requirements.

Why are Turbines flexibility and Network Codes (NC) high on EUTurbines’ agenda?

NC basically define the technical conditions for a power generating unit to connected to the electrical network. Power grids, or networks, are sensitive machineries, matching on a second-to-second basis the delicate balance between demand and production needs.

Turbines are a core provider of flexibility in today’s EU grids, as one of the most agile, low-carbon technologies. They are in the front-line to provide so called “ancillary services”, having the technical capability to make the grid efficient and robust. As such, they provide multiple solutions, ranging from power-on-demand, to voltage controls, or providing the ability to re-start dead segments of the grid. Overall, these services help the grid to deliver sustainable, efficient, and dispatchable electrons.

Can you explain the nature and relevance of grid codes for Gas and Steam turbines?

As said earlier, a grid code is a set of rules and requirements that must be met for connecting generating plants and loads to the electrical system. With an evolving grid mix and different needs, the national grid codes in all EU Member States are under revision – to align them to the European Network Codes. As EU Regulations, they are binding pieces of legislation.

Gas and Steam Turbines owners are often connected to a power grid, and, as such, must meet its technical requirements based on the power exported – often tied to local regulations, complying to grid codes is obligatory.

It is critical to identify and define the requirements as exact as possible: too loose, the electrical system could fail; too stringent requirements would lead to unnecessary infrastructure and operation costs, which would result in increased electricity costs. Additionally, the requirements shall also consider future trends in generation technology and electricity use.

What is EUTurbines’ involvement in the NC process?

The EUTurbines TF Grid Code has been providing views and commented upon Connection Codes mainly, with a vested interest into the NC Requirements for Generators (RfG). The TF provided in depth and wide-ranging technical experience, sharing the unprecedented world-wide knowledge of our EUTurbines grid experts. We are very proud and grateful for the technical collaboration among our different domain knowledge specialists, thanks to the commitment and engagement of all our TF members! 

With the transposition of the EU framework at national level, EUTurbines has become a Member of the Grid Connection and System Operation European Stakeholder Committees (ESCs) to monitor and support the integration of the new requirements at national level. EUTurbines constructively proposed modifications in the draft rules, and supported several initiatives over transparency, such as the creation of an active library and its content. It now allows to efficiently track progress in individual Member States. EUTurbines and other Industry Associations have also been key advocates for the creation of Implementation Guidance Documents (IGDs), whose aim to define “how” to transpose the Regulation in practical terms.

We are also involved with CENELEC (European Committee for Electrotechnical Standardization) activities, contributing drafting technical harmonised standards aligned with the new regulation.

Lastly, our members have been providing technical expertise and feedback to ad-hoc European expert groups (EG). The aim is to ensure that the turbines industry is involved in the process of drafting fair and pragmatic requirements in terms of Cost Benefit Analyses (CBA), Compliance Demonstration, as well as to deliver the promising solutions for the EU electricity sector associated to Energy Storage systems and Mixed Technology Power Plants.

Which is currently the area of most relevance for EUTurbines?

Without a doubt, the frequency related requirements. We have been very active on this topic. For Gas and Steam Turbines, frequency related requirements can have an important impact on the generating unit design, its lifecycle and its overall costs.

The fear of some stakeholders that the future energy mix will lead to an unstable electrical system resulted in a discussion of new and burdensome requirements for generation units, that are sometimes difficult to justify. It is important that those requirements fit the specificities and capabilities of each technology to be efficient, including turbine technologies – which are an essential and integral part of the grid –; this is not always necessarily the case.

The EUTurbines TF Grid Code team therefore considered that it was time to prepare a statement addressing some specific requirements that can become unnecessarily impacting; if not properly addressed during the implementation at national level. With it, we explain the challenges of some of the proposed requirements and propose several recommendations for the codes’ national implementation.

What are the specific elements to be highlighted in this discussion?

As EUTurbines, we have focused on the following areas: (a) Maximum Admissible active power reduction at low frequencies, (b) Requirements for frequency limits and (c) Rate of change of frequency (RoCoF).

Gas Turbines Power Output is often impacted by rotational speed, which basically means grid frequency. When the frequency falls, the power output may just naturally decrease. In the RfG NC, the Gas Turbines intrinsic behaviour is partly addressed when system operators request to define the characteristics associated to a defined temperature – considering the technical limitations of the generating unit technology. EUTurbines position is that the manufacturer can provide information about the turbine’s intrinsic behaviour, so that the system operator can plan how to properly deal with such phenomena.

The Requirements for frequency limits defined in the NC are already more demanding than what is outlined in the current product standard. EUTurbines recommends not extending the limits in the NC, which have been used as the basis for the current technology design, unless there is a clear need to do so. Extending the limits means impacting the life cycle of the units and it also can have an impact on the design of the generator, as it would exceed the values in the product standards.

Finally, the RoCoF is a requirement typically associated with the inertia on the grid. Today, RoCoF is associated to a time window and the fast RoCoFs are expected to happen in a very short time window (100-200ms). Gas Turbines are expected to handle a high RoCoF on such short period of time. Considering a longer time window, the expected RoCoF aligns with the present requirements between 0.5 and 1 Hz/s. There is still some confusion on how this requirement is defined, and we therefore addressed it in our position paper.

What is the EUTurbines core recommendation for the evolution of grid requirements in the future?

When referring to national implementation of the NC requirements, we recommend the technical committees to take in consideration the technology-specific behaviour and to seek our competence and support for clarifications and input. Equipment manufacturers have to comply with all rules and requirements throughout the entire process – including with national differences. It is therefore important that we are involved in the discussions: as manufacturers of turbines, we are highly technically qualified stakeholders that can greatly contribute to the discussions about frequency requirements and capabilities.

What is next for the EUTurbines Grid Code Task Force?

We presented our input at the ESCs. While we received positive feedback during the discussion, our recommendations have not yet been integrated in the IGDs. Since the NC implementation is ongoing, we plan to distribute the information to the different national committees. We will continue to defend our technology specificities and support the development of the new requirements participating to the different technical committees, making available our expertise.

We should not forget that turbines provide the “heart beat” of most grids. Their excellent dynamic behaviour and technical growth margin make them indisputable assets in the future energy mix, with an increasing share of variable renewables.

There is no discussion to sunset our Grid Task Force. With ever-evolving power grids, well-set requirements and innovative generation solutions are paramount. New opportunities related to the arrival of power electronics, embedded storage, flexibility and renewable gases are exciting. Turbines do not lack options to provide new solutions for the grids in the future!

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