Power Systems Protection

It has been truly busy time, diving deep into the causes and dynamics of the Iberian blackout last week. After all, I wanted to take a step back and compile the most frequent technical questions I’ve received, along with my personal answers based on experience and system technology perspective. I think this recent grid event raised some important lessons for power system stability in high-renewable grids. Here’s a simplified closer look, question by question: Q1: Did renewables cause the blackout? Cannot say directly. But with ~60% solar and ~10% wind generation at the time, the grid had low inertia due to inverter-based sources. This lack of synchronous inertia left the system vulnerable actually. That means as a disturbance occurred, the frequency deviation was sharper and faster, overwhelming protection systems before corrective action could stabilize the grid. Q2: Why is inertia so critical? Inertia from synchronous generators acts instantly with the frequency deviation, slowing down frequency changes by releasing kinetic energy. Without inertia, frequency falls faster and deeper, reducing reaction time for controls and risking cascading trips. Q3: Would more thermal or hydro have prevented it? Very likely yess, because synchronous thermal and hydro plants don’t just supply inertia; they provide short-circuit strength crucial for fault clearing and relay operation. Their presence also improves voltage stability and mitigates frequency oscillations. Without these stabilizers, a high-inverter grid faces higher risk during disturbances. Q4: Can batteries (BESS) or fast frequency response (FFR) replace inertia? Unfortunately not fully (or very very less than imagined / expected). Because BESS and FFR react after(!) a frequency deviation occurs; inertia works with(!) the deviation, inherently delaying the drop. While grid-forming inverters and synthetic inertia are promising technologies, they cannot (yet) replicate the instantaneous stabilizing effect of physical rotating mass at system scale. Q5: What’s the way forward for high-renewable grids? I think a robust future grid actually should have a balance. In that scenario, renewables deliver clean energy; synchronous thermal, hydro, and pumped storage provide inertia and grid strength; grid-forming inverters enhance stability but cannot entirely replace synchronous inertia. After all as a short summary, I can clearly state that decarbonization doesn’t mean eliminating inertia; it means integrating renewables with inertia-providing resources to ensure frequency stability, fault tolerance and protection system performance. The Iberian event echoes lessons from Europe’s Jan 8, 2021 grid split. Let’s never forget, inertia remains the backbone of a stable 50 Hz synchronous grid☘️

For the last part of my Energy Resilience series, we have to talk about the worst-case scenario – when the lights actually go out. Earlier this year we saw that happen in Spain and Portugal. A major blackout left millions without power. Trains stopped, shops couldn’t take card payments, hospitals and factories switched to backup. A wake-up call that modern life depends on electricity in ways we often forget until it is gone.   This is what happens when grids are pushed to the edge by fast-moving disturbances or extreme conditions. A couple of years ago, South Australia experienced a state-wide blackout after severe weather took out multiple transmission lines. Investigations showed the system lacked enough inertia to stay stable through the shock. Part of the solution was to install synchronous condensers – giant flywheels that give the grid “weight” and stability. Siemens Energy delivered two of them as part of the response. Not the only measure of course – adapting regulation is also essential – but it showed something important: without resilience in the system, recovery is slow and uncertain. So what do we actually need if we want a fast ramp-up after a major incident? From my perspective, it comes down to three things. 1️⃣ Standardize before the crisis: When parts fail, every minute spent interpreting drawings or debating specifications is a minute the lights stay out. Standard equipment and uniform processes mean teams can move quickly because they are working with tools they already know. Recovery begins long before the fault happens. 2️⃣ Design power plants with failure in mind: A fast restart depends on assets built to recover quickly, not just run efficiently. That means black-start capability, smart redundancy where it matters and systems that can restart without waiting for the wider grid. In the U.S. for example we supported a power plant with a battery system that enables multiple restart attempts within one hour – resilience designed into the plant itself. 3️⃣ No improvisation in the dark: A blackout is the worst moment to negotiate who does what. Good restoration plans spell out which assets come back first, how to stabilize small sections of the grid and when to reconnect them safely. Regular drills with operators, authorities and major customers turn these plans into routine rather than theory. These steps matter because in any major incident skilled people are often the scarcest resource – grid operators, field crews and technical specialists. That is why preparation matters so much. Clear roles, common standards and trusted partnerships mean limited teams can do more in less time. Because when the worst happens what people remember is how long it stayed dark. I hope you have found this mini-series useful. I know social media is often about speed and short takes but sometimes – especially on important topics like this – I find it worthwhile digging into the detail together.✍️ I’d be interested to hear if you agree.

⚡ The official report on the Iberian blackout confirms it was mainly a voltage instability event. The system had already experienced "intense voltage fluctuations" in the days before the incident. Wide-area oscillations prompted the system operator to increase grid meshing and reduce exports to France. These measures, unfortunately, decreased line flows, which paradoxically raised voltages due to the line charging effect, causing power plants to trip on over-voltage. This triggered a cascading failure, worsened by some plants tripping improperly before voltage limits were reached. The main conclusion from the report is a "lack of voltage control resources"; either they were poorly scheduled, or those allocated failed to provide sufficient power, despite an overall adequate generating capacity.   🔦 For the voltage control to be effective, it is important to consider the difference between high R/X and low R/X ratio systems. In high-voltage grids (transmission networks), which typically have a low R/X ratio, voltage magnitude is primarily sensitive to reactive power. Here, the voltage drop can be approximated by ignoring resistance and focusing on the reactive component. This is why traditional grid operators use reactive power to regulate voltage in these systems. Conversely, in low voltage (LV) systems and distribution networks, the high R/X ratio means voltage magnitude is more sensitive to active power injection. In these systems, the effect of resistance is significant, and the voltage drop approximation includes both active and reactive components. For instance, a PV plant can regulate voltage by reducing active power injection or providing negative reactive power, as per standards like IEEE 1547-2018. If reactive power alone is insufficient, active power control, which involves elements such as heat pumps, electric vehicles (EVs), or battery storage, may be necessary.   🪫 A notable point from the Iberian blackout report is the recommendation to "allow asynchronous installations to apply power electronics solutions to manage voltage fluctuations." This indicates that the voltage control capabilities of inverter-based resources (IBRs) were not fully utilised. Although IBRs offer considerable potential, challenges persist, particularly for real-time smart inverter Volt/Var Control (VVC). These include susceptibility to control instability caused by incorrect parameter selection, as smart inverter settings are sensitive to feeder configuration and operating conditions. An inappropriate droop (slope) setting can lead to control instability or voltage oscillations. There is an inherent trade-off between maintaining control stability and achieving accurate set-point tracking, which can cause voltage violations. Additionally, the non-adaptability of droop VVC to changing conditions can hinder deployment. #blackout #renewables #gridmodernization #powerelectronics #gridforming #voltage #cleanenergy

"One of the key ways to make energy systems more reliable is by maximizing flexibility — improving how well the system can adapt in real time to changes in supply and demand. The more flexible the system, the better it can handle sudden demand spikes in the event of extreme weather, such as cold snaps or heat waves, or respond to supply disruptions such as plant outages. Improving flexibility includes upgrading aging infrastructure. Much of the U.S. grid was built decades ago under different demand patterns. Modernizing the grid — by updating substations and transmission equipment, deploying advanced sensors and incorporating advanced transmission technologies (ATTs), for example — can reduce failure rates during extreme heat and cold. These technologies help operators detect problems quicker, reroute power if equipment is damaged and restore service fast. Modernization not only improves reliability but also reduces expensive emergency interventions and lowers long-term maintenance costs. Increasing grid capacity, both through deployment of ATTs and building regional and interregional transmission lines, can reduce the risk of a local weather event turning into a widespread outage. Creating a more interconnected grid allows regions to share power during shortages. Having this greater transmission capacity also help keep prices down by allowing lower-cost electricity to reach areas facing higher demand. Demand-side management options can help ease pressure on the system during extreme weather events. These include encouraging customers and large users to reduce or shift electricity use during peak periods in exchange for lower bills or leveraging distributed energy resources to help prevent shortages. Systems that rely too much on a single fuel are more vulnerable to disruption. Diversification across energy sources and technologies helps reduce the risk of issues related to fuel shortages, infrastructure failures and localized weather impacts. Finally, policy is also critical. It’s vital that incentives are properly aligned with modern needs for flexibility and preparedness. This can help utilities make system investments that really work in extreme weather and minimize costs to consumers in both the short and the long run." Kelly Lefler World Resources Institute https://lnkd.in/e5syqXQp

For most of the last century, generators stabilised the grid as a by-product of producing energy. Today, we are building assets that stabilise the grid without producing energy at all. That shift identifies the binding constraint. Electricity system transition is no longer constrained by renewable resource availability. It is constrained by deliverability and operability. In inverter-dominated systems under rapid load growth, the binding constraints are: - transmission and major substation capacity - system strength, fault levels, frequency and voltage control - connection and commissioning throughput - secure operation under worst-day conditions - execution pace across networks and system services Generation capacity remains necessary. On its own, it no longer delivers firm supply or supports large new loads. Historically, synchronous generators supplied energy and stability together. Inertia, fault current, voltage support, and controllability were implicit. As synchronous plant retires, these services must be provided explicitly. Stability shifts from physics-led to control-led. System behaviour becomes more sensitive to modelling accuracy, protection coordination, control settings, and real-time visibility. Curtailment is not excess energy. It is a deliverability or security constraint. When transmission and substations lag generation, congestion and curtailment rise. Independent analysis shows that delay increases prices and emissions by extending reliance on higher-cost thermal generation. Distribution networks are no longer passive. They now host distributed generation, storage, EV charging, and large loads at the edge of transmission. Voltage control, protection coordination, hosting capacity, and connection throughput now constrain both decarbonisation and industrial growth. Firming is a hard requirement. Batteries provide fast frequency response and contingency arrest. They do not provide multi-day energy and do not replace networks or system strength in weak grids. Demand response reduces peaks. It cannot be relied upon for system-wide security under stress. Execution speed is critical. Slow delivery increases congestion duration, curtailment exposure, reserve requirements, and reliance on ageing plant. These effects flow directly into costs, emissions, and reliability. This is why electricity bills can rise even when average wholesale prices fall. Costs are driven by peak demand, contingencies, and security, not average energy. Large digital and industrial loads are transmission-scale, continuous, and failure-intolerant. They increase contingency size and correlation risk. At that scale, loads do not connect to the grid, they shape it. Supporting growth requires time-to-power, transmission and substation capacity in load corridors, explicit system strength and fault levels, operable firming under worst-day conditions, scalable connection and commissioning, and early procurement of long lead time HV equipment. #energy

Grid-Forming Inverters: A Comparative Study of Different Control Strategies ----------------------------------------------------------------------------------- As grid-forming inverters (GFMIs) are anticipated to play a leading role in future power systems, comprehensive understanding of their dynamics and control strategies becomes essential. Our recent article delves deep into this, offering a comparative study including: 1)      Detailing the control structures and tuning of four different control strategies for GFMIs (Droop, VSG, Compensated Generalized VSG, and Adaptive VSG). 2)      Conducting extensive frequency domain analysis employing impedance-based stability analysis, exploring various scenarios (SCR variations, Xg/Rg variations, operating point variations, dynamics of virtual impedance, and dynamics of inner current and voltage loops). 3)      Validating the frequency domain analysis through EMT simulations. 4)      Testing against external grid disturbances (frequency deviations, phase shifts, and voltage sags) in both strong and weak grid connections.   For more information: Article Title: Grid-Forming Inverters: A Comparative Study of Different Control Strategies in Frequency and Time Domains. Authors: Nabil Mohammed, Harith Udawatte, Weihua Zhou, Professor David Hill, Behrooz Bahrani. Journal: IEEE Open Journal of the Industrial Electronics Society. Links [Open Access]: https://lnkd.in/gE_fgJ6F ; https://lnkd.in/gMz-S4KE .   Special thanks to the Australian Renewable Energy Agency (ARENA) and the Australian Research Council for funding this work.   #powerelectronics #forminginverters #renewableenergy #gridintegration #sustainability #energytransition

Grid-forming control to achieve a 100% power electronics interfaced power transmission systems by Taoufik Qoria -”Nouvelles lois de contrˆole pour former des r´eseaux de transport avec 100% d’´electronique de puissance” ´ECOLE DOCTORALE SCIENCES ET M´ETIERS DE L’ING´ENIEUR L2EP - Campus de Lille  Abstract: The rapid development of intermittent renewable generation and HVDC links yields an important increase of the penetration rate of power electronic converters in the transmission systems. Today, power converters have the main function of injecting power into the main grid, while relying on synchronous machines that guaranty all system needs. This operation mode of power converters is called "Grid-following". Grid-following converters have several limitations: their inability to operate in a standalone mode, their stability issues under weak-grids and faulty conditions and their negative side effect on the system inertia.To meet these challenges, the grid-forming control is a good solution to respond to the system needs and allow a stable and safe operation of power system with high penetration rate of power electronic converters, up to a 100%. Firstly, three grid-forming control strategies are proposed to guarantee four main features: voltage control, power control, inertia emulation and frequency support. The system dynamics and robustness based on each control have been analyzed and discussed. Then, depending on the converter topology, the connection with the AC grid may require additional filters and control loops. In this thesis, two converter topologies have been considered (2-Level VSC and VSC-MMC) and the implementation associated with each one has been discussed. Finally, the questions of the grid-forming converters protection against overcurrent and their post-fault synchronization have been investigated, and then a hybrid current limitation and resynchronization algorithms have been proposed to enhance the transient stability of the system. At the end, an experimental test bench has been developed to confirm the theoretical approach.  VIEW FULL THESIS: https://lnkd.in/dcTJU-9v

Grid Control Series: How grid frequency stays stable even when power consumption fluctuates. Curious? Let me explain below! 👇 This will be the first post of the grid control series which will cover grid control methods, why they are needed and what are the challenges within the actual energy transformation. One key aspect of each power grid system is a stable frequency. But how is it ensured that the frequency remains stable even when continuous load changes occur within the grid? The frequency of the power system depends directly on differences between the generated power and the consumed power. It can be imagined as a scale that, when there is an imbalance ➡️ the frequency will decrease if consumption is bigger than generation ➡️ the frequency will increase if consumption is lower than generation ➡️ Traditional Power Systems: In traditional power systems (Large power plants) the following mechanisms stabilize the frequency of the grid: 1️⃣ Dynamic load fluctuations are absorbed to a certain extent by the inertia of rotating masses and their stored kinetic energy. This natural inertia resists rapid frequency changes. 2️⃣ Frequency deviations are further stabilized by the provision of controllable reserve power, which is traded on the reserve power market. 3️⃣ For larger frequency deviations (e.g., ±200 mHz in Germany), inherent system functions of the power controllers like P(f) come into play. These are specified in standards (e.g., VDE AR-N-4110) in Germany and must be provided by every generation unit. ➡️ Modern Grid Approaches with Renewable Energies: As renewable and inverter-based generation increases, physical inertia decreases as they typically don't provide mechanical inertia like traditional generators. However, modern grid forming inverters combined with battery storage systems are able to emulate the inertia and thus, to stabilize the grid on dynamic load changes (1️⃣) by: ✅ Virtual Synchronous Machines (VSM) ✅ Virtual Inertia Emulation ✅ Droop Control In addtion, as in traditional approaches they are also able to participate in the reserve power market (2️⃣) as well to provide frequency control mechanisms like P(f) (3️⃣). This allows modern grids to maintain frequency stability even in low-inertia conditions. What are your main challenges in designing and controlling renewable energy systems in modern grids? #ControlSystemEngineering #GridStability #ActivePowerControl #InertiaEmulation #RenewableEnergy #PowerSystems #Simulation

⚡ Capacitor Banks in Power Systems – The Silent Hero of Grid Stability 👉 The Capacitor Bank As electrical engineers, we often focus on transformers, generators, and protection relays — but capacitor banks quietly play a critical role in maintaining system reliability and reducing operational costs. Let’s break it down. 🔹 Why Do We Need Capacitor Banks? Most industrial and utility loads (motors, pumps, compressors, HVAC, induction furnaces) are inductive in nature. Inductive loads: Consume Reactive Power (kVAR) Lower the Power Factor Increase current flow Cause voltage drops Increase system losses (I²R losses) Attract penalties from utilities Capacitor banks provide leading reactive power, which compensates the lagging reactive power of inductive loads. ✅ Result? Improved power factor Reduced line losses Improved voltage profile Increased system capacity Lower electricity bills 🔹 Types of Capacitor Banks Used in Power Systems 1️⃣ Low Voltage (LV) Capacitor Banks Installed in industries Typically 415V / 480V systems Automatic Power Factor Correction (APFC panels) Controlled through contactors or thyristors 2️⃣ Medium Voltage (MV) Capacitor Banks 6.6kV / 11kV / 33kV systems Installed at substations Switched via vacuum circuit breakers Often protected with unbalance relays 3️⃣ High Voltage (HV) Capacitor Banks 132kV and above Used in transmission systems Improve voltage stability over long lines 🔹 Protection of Capacitor Banks – Critical for Reliability Capacitor banks are sensitive equipment and require proper protection: 🔸 Overcurrent protection 🔸 Unbalance protection 🔸 Overvoltage protection 🔸 Inrush current control (reactors) 🔸 Harmonic filtering (detuned reactors) In systems with harmonic distortion (VFDs, UPS, converters), detuned capacitor banks are essential to avoid resonance conditions. 🔹 Real-World Impact in Power Plants & Substations From my experience in power generation environments: ✔ Proper reactive power management reduces transformer overloading ✔ Voltage regulation improves generator stability ✔ System losses significantly decrease ✔ Grid compliance becomes easier Capacitor banks are not just cost-saving devices — they are strategic grid assets #ElectricalEngineering #PowerSystems #CapacitorBank #PowerFactor #ReactivePower #GridStability #Substation #EnergyManagement #PowerPlant #ElectricalProtection #Transmission #Distribution #SmartGrid #RenewableEnergy #EngineeringLife #HighVoltage #IndustrialEngineering #EnergyEfficiency

If you are an early-stage researcher who wants to dive into the grid-forming (#GFM) inverter world, we have created a step-by-step tutorial based on #UNIFI’s GFM reference design— as part of UNIFI’s educational initiative. ⚙️Written in easy-to-follow language, this tutorial walks you through: ✅ The control architecture of GFM inverters ✅ How to pick control gains for outer voltage and inner current loops ✅ LCL filter design basics ✅ How current limiters work and why they matter ⚙️This tutorial also comes with hands-on guidance for navigating UNIFI’s open-source GitHub repository, which contains everything you need to build your first GFM inverter: ✅ Simulation models (both average and EMT models) ✅ PCB design files ✅ Embedded control code for running hardware ✅ Detailed documentation for single-phase and three-phase GFM hardware—covering all the bits and pieces: component selection, thermal considerations, sensing-circuit design, and more! Starting from scratch, building a working GFM inverter setup can take years. With this tutorial and the resources in UNIFI’s repository, you can skip most of the setup headaches—saving 1–2 years of work! 🔗If you’re ready to get started, check out the tutorial and explore the repository—links in the first comment. Rahul Mallik Weiqian Cai Kamakshi Tatkare Jakob Triemstra Cuauhtemoc Macias