Grid Codes were originally developed for centralized grids, not the more distributed networks that are rapidly evolving. How quickly should grid codes evolve without jeopardizing grid security?
Wherever there’s a grid, there’s a grid code
In the energy sector, we probably all know a few people who find these complex and highly technical sets of documents as thrilling as a great novel. For the rest of us, the grid code does what it’s meant to do: keep our lights on by ensuring that equipment and systems connected to the grid are compliant with the code. While grid codes are essential to the safe and reliable operation of a grid, the fact is that the codes were established to meet the needs of centralized grids. Regardless of the fuel – coal, gas or nuclear – the common denominator was scale. A relatively few large plants could provide all the power needed and balance demand with supply by managing output and bringing more or fewer plants online.
These large generators also provided inertia on the system, contributing to system stability, based on the kinetic energy of synchronized machines at the heart of big power plants. These “synchronous” generators have a natural response to moderate frequency changes caused by fluctuations in supply and demand and enable the system to remain stable following an unplanned fault. This is because system inertia controls the Rate of Change of Frequency (RoCoF). The larger the inertia, the slower the change of frequency in the system during load/generation imbalance. Renewables, such as wind and solar, don’t provide these synchronized spinning masses. But, allied to battery energy storage systems (BESS) and other energy storage technologies, they do have the capability to provide rapid reactive response to fluctuations in voltage and frequency through their controllers. PSC’s Steve Nutt and Carlos Ferrandon talk more about this in their recent blog post.
The grid as we know it is changing
With the growth of renewables and the reduction of large generation plants such as coal and nuclear, we’re entering new territory. The grid is becoming increasingly distributed, so we have to change our thinking about how we balance the grid as effectively, efficiently and as safely as we have achieved up to now. One example of this evolution is the UK grid code modification that came into effect in February 2022. Modification GC0137 enables grid forming connectors to be connected to the GB grid for the first time. This means that BESS and renewables can now provide “synthetic inertia” and frequency support to the UK grid similar to traditional synchronous generators. While the idea itself is far from new, the acceptance of the idea and its incorporation into the UK’s grid code is a major change. Although this modification does not mandate that new inverter-connected generation includes grid forming technology, market changes may seek to capitalize on these changes. In fact, National Grid ESO is already investigating the potential for a stability market in the UK, with results due to be released soon.
The modification to the UK grid code doesn’t mean, of course, that old methodologies are replaced overnight. Grids everywhere are in transition and grid codes need to adapt. The transition needs to be managed in a way that maintains security and operability and enables the public to continue to enjoy the knowledge that when they flick a switch, the lights come on, the heating works, their food can be cooked, and their cars can be charged. As the UK’s ESO, the National Grid, said in their announcement of the adoption of GC0137, “Whilst we acknowledge that GC0137 will have no immediate impact on system stability, we consider GC0137 to be a vital step in transitioning to carbon-neutral system operation.” The pace of technology change, however, begs the question: are grid codes evolving quickly enough? Could change be introduced more rapidly? Are grid codes in their current form actually stifling innovation? This modification to the code was first proposed in December 2019. So, to go live in 2022 is actually quite speedy given the scale of what’s involved and the risk of getting it wrong. The grid is a complex system and is critical to our way of life. It is not something that should change without thorough planning to avoid unforeseen consequences.
Mission-criticality warrants thorough planning and testing
To build confidence in innovative enhancements of grid codes, we need to model the network and its response to incidents. This sounds simple enough given the power of modern computing and AI technologies. However, modeling for a system as complex and dynamic as a grid is crucial. Conventional network models are constructs that can use data to analyze a wide range of ‘what if’ scenarios. But, as always in the field of data analysis, the validity of the result depends on the quality of the data inputs. Interactions between the control systems of machines connected to the grid will be particularly important to ensure instability does not occur. This can require more detailed electromagnetic transient (EMT) models in software such as PSCAD. Additionally, digital twinning could offer a robust way of testing the impact of technological innovations on a grid. In their report ‘Digital Twins for Energy’ (Sept 2021), TechUK – a trade association for digital technology companies – said: “An energy sector-wide approach to accelerating the development, adoption and diffusion of connected digital twins will support enhanced strategic planning, drive performance optimization of critical energy infrastructures, and enhance the UK’s resilience in the face of unprecedented levels of uncertainty and complexity.” Digital twins use live data in a digital replica of the grid, so we can see in real-time – and with real data – exactly what the effects of new technology might be without risk to the actual grid. Clearly, major modifications to grid codes – such as the National Grid’s GC0137 – are essential as the shape of grids develops. It’s also essential that, however tempting it may be to act quickly, the stability of the grid is supported by thorough analysis and any necessary testing before major changes are implemented. So while the pace of change is accelerating, it’s important not to change too quickly without exhaustive analysis and realistic testing to mitigate risk.
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