Reliability Assessment in Power Systems

The new NERC Long-Term Reliability Assessment (LTRA) has just dropped, and it’s alarming. Here are some quick highlights: 👉 13 out of 23 regions are at elevated or high risk. 👉 5 of these regions are at High Risk, all in the U.S. (PJM, MISO, ERCOT, WECC-Northwest, and WECC-Basin). 👉 High Risk means “shortfalls may occur at normal peak conditions." 👉 Resource and transmission additions are not keeping pace with retirements and load growth, despite efforts to expedite new resources. 👉 Data centers account for most of the load growth anticipated over the next 10 years. 👉 Most new builds consist of solar and battery storage, which “are inverter-based and weather-dependent resources that increase the complexity of planning and operating a reliable grid.” 👉 Fossil-fuel retirements are “reducing the amount of generation that has fuel on site and impacting the system’s ability to respond to spikes in demand.” 👉 Thermal generation is increasingly natural-gas dominant, making it important to “ensure that regional natural gas infrastructure can reliably serve the needs of BPS generators.” 👉 The combination of a shift toward heavy reliance on weather-based resources and reduced fuel diversity “increases risks of supply shortfalls during winter months.” NERC recommends grid planners and operators: ✅ Expedite resource additions. ✅ Be flexible with resource retirements and extend the service of units whose retirement would increase reliability risks. ✅ Improve the siting and permitting process for development. ✅ Improve planning and coordination. ✅ Ensure essential reliability services (ERS) are maintained as more conventional resources are replaced with intermittent wind and solar. While much of this mirrors the 2024 LTRA—generator retirements, insufficient replacement capacity, and the need for expedited resources and transmission—the major difference is that NERC has elevated five regions to High Risk that were not in the 2024 report. Three of these regions—PJM, MISO, and ERCOT—represent three of the four largest RTOs in the country by population served. With the inclusion of the WECC regions, this means nearly half of the country now falls into High Risk of shortfalls under normal conditions in the near future. Full Report: https://lnkd.in/gM6YCv7B

NTP Study insight 6. I’ve focused on the economic and #decarbonization benefits of #transmission in the previous posts but maintaining #reliability in future system designs was a core principle of the National Transmission Planning (NTP) study. Reliability indicators were analyzed using resource adequacy, production cost, and power flow models. Using probabilistic models with multiple weather years of data, we found that all scenarios—including those with up to 90% variable #wind and #solar generation—are designed to meet an adequacy target of 10 ppm in normalized expected unserved energy. For context, this 10 ppm level is roughly equivalent to about ~5-min of complete load shedding per year or 9% load-shedding for one hour per year. In fact, most scenarios were adequate down to ~1 ppm. Transmission helps to achieve adequacy at low costs, especially with interregional coordination, as described in insight 3. Transmission is used bidirectionally, where one region’s needs are met by neighboring resources during some periods of the year and vice versa during other periods thereby reducing overall capacity needs. This bidirectional use of transmission and low levels of dropped load are observed with detailed unit commitment and dispatch modeling of “nodal” models of the grid. Developing such nodal models is an incredibly complex process but the NTP team managed to do so in a rigorous way that ultimately enabled the production cost simulations and power flow analyses. The figure shows an example of such a nodal representation of a 90% decarbonized and (most likely) reliable U.S. grid. The DOE report can be found here: https://lnkd.in/gNtd5N5f Patrick Brown and Jessica Kuna led the resource adequacy analysis. Jarrad Wright and Leonardo Rese and many other excellent “engineers-in-the-loop” from National Renewable Energy Laboratory and Pacific Northwest National Laboratory were instrumental in the nodal analyses.

Last year Sagnik Basumallik and I wrote a paper on the challenges large loads pose to grid reliability and some potential solutions to mitigate these challenges. Our paper - “Reliability Challenges and Solutions for Large Load Integration in Bulk Power Systems,” was accepted for IEEE T&D 2026! We started this effort after working on the first NERC LLTF white paper and this paper built on our experience there. In this paper we expanded on that work with event reviews and identified possible mitigation options for the risks these loads pose to the bulk power system. In the paper we analyzed the impact to the grid from several events where large loads tripped in response to normal system faults, and oscillations originating from large loads across the AEP, Dominion, EirGrid, and ERCOT systems. Then we identified the following causes of events that have been seen and developed a taxonomy of root causes per their source - hardware or software. These causes included: ⚡️Fault-Induced Customer Initiated Load Reduction/Tripping ⚡️Oscillations due to Instability in Electronic Controllers ⚡️Oscillations due to Outdated Firmware Settings ⚡️Transients due to Regular, Cyclical Fluctuations in Data Center Digital Processes ⚡️Coordinated Customer Initiated Load Reduction After the event reviews we looked at what possible mitigations could address the reliability challenges that we identified. Facility side mitigations included: UPS and power supply controller changes to manage oscillations along with hardware updates for voltage ride-through support, coordination with transmission protection schemes, and grid forming loads. Grid side mitigations included E-STATCOMs, better dynamic modeling, improved monitoring capabilities, and market services. Future work is still needed however on large load dynamic modeling, improved monitoring such as point on wave monitoring, and large load characterization. You can read the preprint version of the paper here: https://lnkd.in/gKsJTRz6

How reliable is my electrical system? I find this to be a fascinating question as it can be a very hard thing to nail down. Everyone can come to terms with what increases or decreases reliability. A backup or redundant relay allows for a zone to clear if the primary relay failed but provides added exposure to false trips from the backup due to settings errors or relay failure (microprocessor-based relays generally won't trip if an internal fault is detected). A facility with a second independent source and a means to transfer load from one source to the other will provide additional reliability. As any reliability engineer knows, the math exists for calculating various reliability numbers even if good data is hard to come by. For components in series, the reliability for each component would multiply together. For example, if you had two components with 90% reliability in series, the expected reliability would be the multiplication of the reliabilities. R1 * R2 = 81%. The two components in the series reduce the expected reliability to 81%. I think the thing to note from this is a device with poor reliability drags down the system incredibly. Now, if these components had parallel reliability where both of them needed to fail for a process fault, the reliability in parallel would be 1 - (the products of 1 - Rn). For R1 and R2 in this case: Reliability = 1 - (1 - R1)(1 - R2) = .99. The backup device or system offered 9% more reliability. When it comes to microprocessor relays, they generally have very high reliability, but what it is would be dependent on their condition and age. An older relay is more prone to failing over some time. Its bathtub mortality curve tends to start rising around year 16, with the main mode of failure being the failure of electrolytic capacitors in its power supply. This means that after the relays have been running long enough to pass there infant failures on the left-hand side of the tub curve, the reliability gains are mostly towards its end of life when reliability starts to decline. One thing that is kind of interesting about this is that some relay schemes for ultra-critical situations sometimes have three relays in parallel and set up a voting scheme. The voting scheme requires two relays to fail or misoperate. This guards in a different way because a voting scheme will also prevent both failures to operate and misoperations. Parallel devices will help prevent failure to operate but also contribute to the likelihood of a misoperation. For example, if a parallel system was set up with 3 90% devices rather than a voting system, the reliability would be 99.9%. In a voting scheme, those three devices would have a reliability less than 97.2% but would have a much lower likelihood of misoperation. It is kind of a trade-off. Do you want a system that is biased toward operating or guarding more against misoperations? Depends on your process. #utilities #renewables #energystorage #electricalengineering

𝗜𝗺𝗽𝗼𝗿𝘁𝗮𝗻𝘁 𝗠𝗮𝗶𝗻𝘁𝗲𝗻𝗮𝗻𝗰𝗲 𝗠𝗮𝘁𝗿𝗶𝗰𝘀 Power system reliability is an important aspect of the grid that impacts electricity security and dependability. Electrical equipment may fail unexpectedly or unplanned. In some instances, it is shut down for planned or routine maintenance. In any instance, have we planned for any redundancy if there is a failure? This brief post demonstrates key reliability metrics with a simple example. 𝟭. 𝗔𝗰𝘁𝗶𝘃𝗲 𝗳𝗮𝗶𝗹𝘂𝗿𝗲 𝗿𝗮𝘁𝗲 (λ𝗔): The number of failures per year is known as the active failure rate. It informs us of the chances of a device failing within a period. This information is important because it helps plant or facility management understand the number of failures expected within a year. A higher λA means that the equipment is unreliable and would have to be shut down for more maintenance work. Downtime increases with an increase in the active failure rate. 𝟮. 𝗠𝗲𝗮𝗻 𝗧𝗶𝗺𝗲 𝗧𝗼 𝗥𝗲𝗽𝗮𝗶𝗿 (𝗠𝗧𝗧𝗥):  This is the average number of hours spent repairing damaged or failed equipment and restoring it to normalcy. This is important because it tells management how long a maintenance crew will take to fix a failed device and restore normal operations. 𝟯. 𝗠𝗲𝗮𝗻 𝗧𝗶𝗺𝗲 𝗧𝗼 𝗙𝗮𝗶𝗹𝘂𝗿𝗲 (𝗠𝗧𝗧𝗙):  It is the average time a device works as expected before it runs into a failure. This key metric is relevant because it helps you to know how reliable a system or equipment is before it is likely to fail. A higher number shows that the systems will take longer before failing. 𝟰. 𝗠𝗲𝗮𝗻 𝗥𝗲𝗽𝗮𝗶𝗿 𝗥𝗮𝘁𝗲 (μ): It is the average number of repairs per year. A lower number is preferable because it shows fewer failures.  𝟱. 𝗙𝗼𝗿𝗰𝗲𝗱 𝗢𝘂𝘁𝗮𝗴𝗲 𝗥𝗮𝘁𝗲 (𝗙𝗢𝗥):  This determines an equipment's unavailability. The lower the failure rate, the better for a system's reliability. Continuous operations will be expected, reducing downtime and increasing ROI. Power outages are expensive, making reliability a key metric for power systems security and the economics of nations or enterprises. A power transformer is used as an example in this illustration. For further details on the power system's design of reliability, refer to IEEE Standard 493, also known as the Gold Book - "IEEE Recommended Practice for the Design of Reliable Industrial and Commercial Power Systems"

**🚨 Ensuring Reliability in 115kV GIS: The CT Loop Test 🚨** When it comes to high-voltage systems like 115kV Gas Insulated Switchgear (GIS), precision and reliability are non-negotiable. One of the most critical tests to ensure this is the **CT (Current Transformer) Loop Test**. Current Transformers play a vital role in protection and metering, and any fault in their operation can lead to catastrophic failures. The CT Loop Test is a comprehensive procedure designed to verify the integrity, accuracy, and safety of CT circuits. ### **What does the CT Loop Test involve?** 1️⃣ **Visual Inspection**: Checking for damage, loose connections, and proper labeling. 2️⃣ **Insulation Resistance Test**: Ensuring no short circuits or ground faults. 3️⃣ **Polarity Check**: Confirming correct polarity for accurate relay operation. 4️⃣ **CT Ratio Test**: Validating the transformation ratio for precise current measurement. 5️⃣ **Burden Test**: Ensuring the connected load is within the CT’s rated capacity. 6️⃣ **Loop Resistance Measurement**: Verifying the integrity of the entire secondary circuit. ### **Why is this test so important?** - **Safety**: Prevents incorrect operation of protection relays, reducing the risk of equipment damage or outages. - **Accuracy**: Ensures metering and protection devices receive correct current values. - **Reliability**: Identifies potential issues before they escalate, ensuring uninterrupted power supply. #PowerSystems #ElectricalEngineering #GIS #Reliability #SafetyFirst #CTLoopTest #HighVoltage #EnergySector #Engineering