Managing Transformer Switching Surges

𝗜𝗻𝗱𝗲𝗽𝗲𝗻𝗱𝗲𝗻𝘁 𝗦𝗶𝗻𝗴𝗹𝗲-𝗣𝗼𝗹𝗲 𝗣𝗼𝗪 𝗖𝗼𝗻𝘁𝗿𝗼𝗹: 𝗔 𝗧𝗿𝘂𝗹𝘆 𝗡𝗼𝘃𝗲𝗹 𝗣𝗶𝗲𝗰𝗲 𝗼𝗳 𝗪𝗼𝗿𝗸 Over the past months, alongside my daily responsibilities, I decided to develop a fully functional advanced controller and write a paper about it and it is a piece of work I am genuinely proud of. I developed and validated an 𝗶𝗻𝗱𝗲𝗽𝗲𝗻𝗱𝗲𝗻𝘁 𝘀𝗶𝗻𝗴𝗹𝗲-𝗽𝗼𝗹𝗲 𝗣𝗼𝗶𝗻𝘁-𝗼𝗻-𝗪𝗮𝘃𝗲 (𝗣𝗼𝗪) 𝘀𝘄𝗶𝘁𝗰𝗵𝗶𝗻𝗴 𝗰𝗼𝗻𝘁𝗿𝗼𝗹𝗹𝗲𝗿 for transformer inrush current mitigation, implemented and tested in 𝗠𝗔𝗧𝗟𝗔𝗕/𝗦𝗶𝗺𝘂𝗹𝗶𝗻𝗸 using detailed EMTs, including parallel transformer energization through a 50-km subsea cable network. 𝗜𝗺𝗽𝗼𝗿𝘁𝗮𝗻𝘁𝗹𝘆, this work was generated 𝗽𝘂𝗿𝗲𝗹𝘆 𝗳𝗿𝗼𝗺 𝗺𝘆 𝗼𝘄𝗻 𝗶𝗱𝗲𝗮𝘀 𝗮𝗻𝗱 𝗲𝗻𝗴𝗶𝗻𝗲𝗲𝗿𝗶𝗻𝗴 𝗲𝘅𝗽𝗲𝗿𝗶𝗲𝗻𝗰𝗲. I did not follow or replicate any existing research paper or methodology; I did not base the controller on academic references. The concept, logic, and implementation were created independently and shaped only by practical system challenges. 𝗧𝗼 𝘁𝗵𝗲 𝗯𝗲𝘀𝘁 𝗼𝗳 𝗺𝘆 𝗸𝗻𝗼𝘄𝗹𝗲𝗱𝗴𝗲, this work represents one of the very few practical, implementation-ready PoW control strategies that: • Operates 𝗶𝗻𝗱𝗲𝗽𝗲𝗻𝗱𝗲𝗻𝘁𝗹𝘆 𝗽𝗲𝗿 𝗽𝗼𝗹𝗲 • Directly addresses 𝗿𝗲𝘀𝗶𝗱𝘂𝗮𝗹 𝗳𝗹𝘂𝘅 during closing and opening • Maintains stability during 𝗽𝗮𝗿𝗮𝗹𝗹𝗲𝗹 𝘁𝗿𝗮𝗻𝘀𝗳𝗼𝗿𝗺𝗲𝗿 𝗼𝗽𝗲𝗿𝗮𝘁𝗶𝗼𝗻 • Validated using 𝗿𝗲𝗮𝗹𝗶𝘀𝘁𝗶𝗰 𝗘𝗠𝗧 𝗺𝗼𝗱𝗲𝗹𝗶𝗻𝗴 rather than simplified waveforms This combination is rarely presented in the literature, and I consider it one of my 𝗯𝗲𝘀𝘁 𝗽𝗿𝗼𝗳𝗲𝘀𝘀𝗶𝗼𝗻𝗮𝗹 𝘄𝗼𝗿𝗸𝘀 𝘀𝗼 𝗳𝗮𝗿, a true personal masterpiece developed from industry practice rather than an academic laboratory. 𝗞𝗲𝘆 𝗮𝗰𝗵𝗶𝗲𝘃𝗲𝗺𝗲𝗻𝘁𝘀 𝗶𝗻𝗰𝗹𝘂𝗱𝗲: • > 𝟵𝟬% 𝗿𝗲𝗱𝘂𝗰𝘁𝗶𝗼𝗻 𝗶𝗻 𝗽𝗲𝗮𝗸 𝗶𝗻𝗿𝘂𝘀𝗵 𝗰𝘂𝗿𝗿𝗲𝗻𝘁 • Suppression of RMS current to practical limits • Mitigation of PCC voltage dips • Elimination of flux asymmetry • Strong performance during 𝗽𝗮𝗿𝗮𝗹𝗹𝗲𝗹 𝗲𝗻𝗲𝗿𝗴𝗶𝘇𝗮𝘁𝗶𝗼𝗻 • Clear benchmarking of 𝗭𝗲𝗿𝗼-𝗖𝗿𝗼𝘀𝘀 𝘃𝘀 𝗣𝗼𝗪 𝗰𝗼𝗻𝘁𝗿𝗼𝗹 All of this was developed 𝘄𝗶𝘁𝗵𝗼𝘂𝘁 a PhD program, 𝘄𝗶𝘁𝗵𝗼𝘂𝘁 a university laboratory, and 𝘄𝗶𝘁𝗵𝗼𝘂𝘁 academic supervision, purely from professional experience, curiosity. Although the second IEEE submission was not accepted, the journey confirmed that: • Novel research is not exclusive to universities • Independent engineers can deliver 𝘀𝘁𝗮𝘁𝗲-𝗼𝗳-𝘁𝗵𝗲-𝗮𝗿𝘁 technical work • Innovation grows from curiosity and persistence To engineers working in industry rather than academia: You do not need a title to innovate at a high level. Passion, patience, and curiosity can produce 𝗺𝗮𝘀𝘁𝗲𝗿𝗽𝗶𝗲𝗰𝗲-𝗹𝗲𝘃𝗲𝗹 𝘄𝗼𝗿𝗸. 𝗜𝗻𝗻𝗼𝘃𝗮𝘁𝗶𝗼𝗻 𝗯𝗲𝗹𝗼𝗻𝗴𝘀 𝘁𝗼 𝗲𝘃𝗲𝗿𝘆𝗼𝗻𝗲. #powersystemsengineering #PoWcontroller #Zerocrosscontroller #Transformerenergization

Should you consider using Controlled Switching Device (also know as CSD or Point on Wave (PoW)) in your substation projects? What is it? Why is it important? What are the benefits of using it, and why has it become a standard feature in the latest Wind Farms, BESS, and Solar Farm substation projects? At its core, a CSD is all about precision. It’s the art and science of perfectly timing when a circuit breaker opens or closes, relative to the phase angle of the current or voltage waveform. Imagine the electrical waveform as a wave in the ocean. If you jump on it at the right moment, you ride smoothly. If you mistime it, you crash - hard. CSD ensures we "ride" the wave perfectly, minimizing those rough "crashes," or in technical terms, electrical transients. When we open or close a circuit breaker, especially on high voltage systems, it can create electrical transients. These are like sudden jolts in the system that can cause a range of problems - from equipment stress and failures to issues with power quality and even protective relays misoperations. Controlled switching helps us avoid these issues by using intelligent electronic controls to carefully time the circuit breaker's operations. By monitoring the phase angle of the voltage or current waveform, the technology determines the perfect moment to open or close the breaker, typically around the zero crossing points of the waveform. The results? Reduced arcing, minimized transients, and a smoother overall operation. I've personally used CSD in wind farms and BESS projects, where it plays a big role in maintaining system stability and protecting equipment. It significantly helps to reduce transformer inrush currents, minimizing the mechanical and thermal stress, protecting them from potential damage. This leads to longer equipment lifespan, fewer maintenance issues, and enhanced overall system stability. It normally takes a power transformer’s residual flux into account for seamless energizations and some models work with both single-pole and 3‑pole simultaneous operation switching devices. It's worth mentioning that this technology is not only used to mitigate transformer inrush currents. It has a large range of applications, including the switching of capacitor banks, filters, shunt reactors, transmission lines, and cables as well! If your projects demand top-tier power quality and robust equipment protection, especially in HV substations, CSD can be a great solution. However, as with any advanced tool, its value lies in understanding when and where to apply it for maximum impact. By leveraging CST in the right scenarios, you can significantly enhance system reliability, extend equipment lifespan, and ensure smooth operations in even the most challenging environments. What are your thoughts? Have you used Controlled Switching Devices in your projects? Tell us more about it, leave your comment! #PowerEngineering #ControlledSwitching #PointOnWave #HighVoltage #RenewableEnergy

Conceptual: —————— When a transformer is energized (or re-energized), the magnetizing current exhibits a surge of (transient) current, referred to as inrush current. The inrush current can lead to a large voltage dip where the magnitude of the voltage dip will depend on the source impedance. The protective relays (such as differential/overcurrent) if they are not set properly, they could trip due to inrush current. When the source to the transformer is switched off, the transformer core remains magnetized. Graph 1: ———— Represents a hypothetical B-H curve (not to scale). B: flux density (Tesla). H: magnetic field intensity (A/m). H*leng=N*I=mmf. leng: mean length of core magnetic path I: current N: number of turns mmf: magnetomotive force (Ampere.turn) When the source to the transformer is reduced to 0, flux density does not go to 0, depicted as B_r, which is residual flux density. Some flux (~50-90%) will remain in the core when/if the transformer is de-energized. Graph 2: ————- Point 1: when the source to the transformer is switched off. Point 2: when the transformer is re-energized. Current is shown in red solid line. The current waveform is distorted due to harmonics. Dotted line shows the case of current if it was not turned off. Flux is shown in blue solid line. The dotted line shows the case if flux continued flowing (no current interruption). Voltage waveform is not shown. ———————————————————- Which option(s) would be appropriate? ———————————————————- (1) Inrush current could be avoided if it was practical to energize the transformer when the voltage waveform corresponds to the flux density in the core (B_r)—residual flux. (2) Inrush current could be avoided if an applied excitation current equal to +/- H_c (coercive force), which would demagnetize the core by forcing the residual flux to 0 before energization. (3) It is better to energize a transformer from the high voltage side. Core form transformer windings are concentric. The high voltage winding is the outer and further from the core, making the high voltage winding to have a higher inductance. (4) Inrush current is only limited by the air-core inductance of the energized winding. When the core is saturated, the energized winding becomes like an air-core inductor (relative permeability=1). (5) Inrush current contains harmonic components, mostly 2nd order harmonic. Relays use 2nd order harmonic restraint to avoid mis-operation due to inrush current. (6) If a transformer is already online and a second transformer near it is energized, the online transformer can be exposed to ‘sympathetic’ inrush from the energization of a transformer as current flows through the path between the two transformers. (7) When a transformer is energized, there is no electromotive force (emf) in the energized winding to limit current. As the back emf builds up, the inrush current goes away. But until the back emf is built up, a surge of current will flow. (8) Other.

POW #Relay: Point-on-Wave (controlled switching equipment) is used in GIS (Gas-Insulated #Substations) to optimize #circuit_breaker operations and minimize switching-related transients. Which is crucial in to ensure smooth, reliable, and efficient CB operations while reducing electrical stresses, improving power quality, and extending equipment lifespan. *Advantages* : 1. Reduction of Switching Transients and VFTO (Very Fast Transient Overvoltages)   > GIS substations are prone to VFTO due to their compact design and metallic enclosures. > POW relays ensure that breakers operate at precise moments in the AC waveform to reduce these transients, protecting insulation and connected equipment.   2. Minimization of Inrush and Outrush Currents         > When energizing or de-energizing transformers, reactors, or capacitor banks, uncontrolled switching can lead to high inrush or outrush currents.          > Controlled switching reduces these effects by closing or opening the breaker at the optimal waveform point.   3. Extension of Equipment Lifespan             > Circuit breakers in GIS substations operate under high system voltages and currents. Repeated transient stress can degrade breaker contacts.             > By reducing switching surges, POW relays enhance the reliability and longevity of breakers, transformers, and other GIS components.   4. Improved Power Quality and Stability               > Switching transients can cause voltage fluctuations, harmonics, and system instability.             > Controlled switching ensures smooth operations, improving overall power quality and network stability.   5. Reduction of Breaker Restrike and Reignition Events               > Uncontrolled opening of circuit breakers can lead to restrikes or reignitions, causing insulation damage.             > POW relays help in controlled opening at zero current, minimizing the chances of restrikes.   6. Protection of Sensitive Equipment               > GIS substations often feed critical loads such as industrial plants, hospitals, and data centers.             > Reducing transients and inrush currents ensures stable operation and protection of sensitive downstream equipment.   *Applications* in GIS Substations: 1> Transmission line switching (OHL & cable feeders) 2> Transformer switching (reducing inrush currents) 3> Reactor switching (limiting transient overvoltages) 4> Capacitor bank switching (avoiding voltage spikes)

🚨 Understanding Transformer Inrush Current: What You Need to Know! ⚡️🔌 When you energize a transformer, it can draw a surge of 5 to 15 times its normal operating current-this is called inrush current. This brief but powerful spike happens because the transformer’s magnetic core suddenly magnetizes and can saturate, causing a massive current flow. Why does this matter? 👉 It can cause nuisance tripping of breakers 👉 Stress transformer windings and insulation 👉 Introduce harmonics that affect power quality Key Causes: - Core saturation - Residual magnetism - Point in the AC cycle when energized How to manage it? ✅ Controlled switching at voltage zero-crossings ✅ Pre-insertion resistors or NTC thermistors ✅ Time delay relays to avoid false trips ✅ Soft-start circuits for gradual voltage ramp-up Managing inrush current means smoother operations, better power quality, and longer transformer life! 💡🔧 #PowerEngineering #Transformers #ElectricalEngineering #InrushCurrent #EnergyManagement #ElectricalSafety #PowerSystems #EngineeringTips #ElectricPower #RenewableEnergy #SmartGrid #IndustrialAutomation #TechInsights #ElectricalMaintenance