Electrical Engineering Circuit Analysis

[ ⛳ Reverse Current & Over-voltage Protection ] 🤩 Learn How to Design a Reverse Current With Over-Voltage Protection Use a Comparator, a Zener diode, MOSFETs and few resistors ✨ 🤔 How does this circuit work? This circuit is based on a comparator and a P-Ch MOSFET. In order to turn "on" the P-Channel MOSFET, the gate must be brought "Low" below VBATT. To accomplish this, the comparator's Inverting input is tied to the battery side of the MOSFET to set the output low during forward current. R3 limits the gate current should there be any transients and should be a low value to allow the peak currents needed to drive the MOSFET gate capacitance. R2 provides the pull-down needed when the comparator output goes high-Z during power-off to ensure the gate is pulled to zero volts to turn off the MOSFET. The SHDN pin can be utilized to add Overvotlage Protection (OVP) by adding a second MOSFET, zener diode and resistor. When the SHDN pin is pulled 1.35 V above V-, the comparator is placed in shutdown. During shutdown, the comparator output goes Hi-Z and R2 pulls the gate and source together to turn off the MOSFET (VGS = 0 V). RPD pulls the SHDN pin low while the Zener diode is not conducting (< VZ). When ZD1 reaches its breakdown voltage and starts conducting, it will pull RPD up to a voltage calculated to place >1.35 V on the shutdown pin. 📌 Circuit Reference based on Texas Instruments p/n: TLV1805 comparator https://lnkd.in/eJwMK9Cj For this application, we need to choose a comparator with the following: ☑ with rail-to-rail input common mode range to enable high-side current sensing. ☑ with a push-pull output stage to efficiently drive the p-channel MOSFET. ☑ with low input offset voltage to optimize accuracy. 📌 Ideally, I'd consider using p/n: TPS25942A e-fuse by Texas Instruments https://lnkd.in/eHeaycV7 which comes equipped with: ✅ Adjustable current limit ✅ Current monitoring ✅ Inrush current control ✅ Overvoltage protection ✅ Power good signal ✅ Reverse current blocking ✅ Short circuit protection ✅ Thermal shutdown. #circuitdesign #analogdesign #electronics #hardwaredesign #pcbdesign

Episode 3.1 – Testing of Power Transformers ⚡ Power transformers are the heart of substations — but just like the human heart, you don’t rely on “looks” alone. You test it to be sure it’s healthy and reliable before putting it into service. I’ve learned that most transformer failures could have been avoided if tests were done properly, recorded carefully, and interpreted correctly. Testing is not just about “numbers” — it’s about listening to what the transformer is trying to tell you. In this episode, we’ll discuss the most important transformer tests, their procedures, testing sets used, and what the results mean. 1. Insulation Resistance (IR) Test Purpose: To check the condition of insulation between windings and winding-to-earth. Helps detect moisture, dirt, or insulation deterioration. Instruments: 5 kV Digital Megger (Insulation Tester). Wiring/Connections: LV & HV windings tested separately against earth, and between HV ↔ LV windings. For example: HV–Earth LV–Earth HV–LV Procedure: 1. Disconnect transformer from system (completely isolated). 2. Short all terminals of HV together, and similarly LV together. 3. Apply 5 kV DC between HV group and Earth, then LV group and Earth, and finally between HV and LV. 4. Record IR at 15 sec, 60 sec, and 10 min. Result Interpretation: A high IR (>1000 MΩ) is good. If IR is low → moisture or insulation breakdown. The Polarization Index (PI = IR at 10 min / IR at 1 min) should be > 2. < 1.5 → insulation deterioration or moisture present. 👉 Field Tip: Once during monsoon, I got unusually low IR readings at a 132/11 kV transformer. It turned out the silica gel in the breather was fully pink — the oil had absorbed moisture. Replacing silica and re-filtering the oil restored IR. ⚡ we will deep dive into each test so this series will be a bit lengthy but it will give you the pure essence of each test about the instruments. Please guys give feedback so that i can improve the quality of content. if anything you want to know or for any suggestion you're more than welcome 🤗

Have you ever tried to coordinate feeder relays with the substation transformer overcurrent elements and felt the math didn’t quite line up? It happens because the current seen on the transformer high side is not the same as what the feeder relays measure on the low side. The transformer’s turns ratio and winding configuration reshape the fault current before it reaches the high-side device. Here’s the step-by-step logic I personally use when checking coordination: 1) Understand the transformer connection A common North American distribution substation transformer is high side Delta / low side Yg. Don't forget: the Delta blocks zero sequence current from passing to the high side. 2) Know what each relay is measuring • Low-side feeder relays (phase/ground) measure positive, negative, and zero sequence current on the low-voltage base. • High-side phase overcurrent sees only positive and negative sequence current for a low-side line-to-ground fault because the delta traps I0. 3) Compare currents for the same fault For a single-line-to-ground fault on the feeder: • Feeder current: I(feeder) = I1 + I2 + I0 • High-side current: I(high side) = I1 + I2 • The feeder device responds to the full residual current, while the transformer protection is blind to I0. 4) Identify the tightest point of coordination Surprisingly, it’s not the LG fault. The toughest case is a LL fault near the substation: • Feeder side 50/51P sees about 87 % of the current it would see for a 3ϕ fault. • High-side transformer 50/51P sees nearly the full 3ϕ current because the delta winding passes positive and negative sequence unchanged. If you coordinate the feeder phase time-overcurrent 50/51P pickup and curve to clear before the high-side 50/51P for this LL case, you’ll generally maintain margin for all other fault types (including LG and 3ϕ faults). 5) Verify with actual curves Time-current curves on the low-side feeder relays and the high-side transformer protection must be compared using the converted current magnitudes each will experience. Only then can you be sure the feeder clears before the transformer trips for downstream faults. Real systems complicate this: zero-sequence compensation on feeder relays, different CT ratios, and relay curve shapes can all shift coordination. Questions for the community: • Have you seen feeders miscoordinate because someone forgot the delta blocks zero sequence? • Any lessons from real faults where the high-side transformer protection tripped first? I’d like to hear how others are refining these checks with today’s digital relays and modeling tools (ASPEN Inc., CYME, ETAP Software, EasyPower Software, SKM, etc). Comment or share your experience (or share this post if you found it valuable)!

𝑰𝒎𝒑𝒆𝒅𝒂𝒏𝒄𝒆 𝑩𝒂𝒏𝒅𝒘𝒊𝒅𝒕𝒉 𝑶𝒑𝒕𝒊𝒎𝒊𝒛𝒂𝒕𝒊𝒐𝒏 𝑼𝒔𝒊𝒏𝒈 𝑺𝒎𝒊𝒕𝒉 𝑪𝒉𝒂𝒓𝒕 𝒂𝒏𝒅 𝑴𝒂𝒕𝒄𝒉𝒊𝒏𝒈 𝑵𝒆𝒕𝒘𝒐𝒓𝒌𝒔: In high-frequency RF systems, especially at mmWave and THz bands, impedance matching isn’t just about maximum power transfer at a single frequency, it’s about achieving efficient power delivery across a desired bandwidth. Bandwidth optimization through Smith Chart engineering and matching networks remains a cornerstone in antenna design, RFICs, and filter integration. 1. Reflection Coefficient & VSWR Basics: - The reflection coefficient is given by: -> γ = (Z_in − Z_0) / (Z_in + Z_0) - Return loss: -> RL = −20log|γ| - Voltage Standing Wave Ratio (VSWR): -> VSWR = (1 + |γ|) / (1 − |γ|) - For wideband matching, |S11| < −10 dB is typically the design target. 2. Bandwidth Definition and Q Relationship: - Fractional bandwidth: -> FBW = (f_high − f_low)/f_center - Quality factor approximation: -> Q = f_center / BW = π/−2ln|Γ| - A narrow Q leads to broader bandwidth. Lowering the antenna's Q by using lossy or broadband materials may improve match but impact radiation efficiency. - Bode-Fano Criterion for capacitive loads: -> ∫ log(1/|Γ(ω)|) dω ≤ π / (R × C) where R = real load resistance, C = reactive component → This sets the theoretical bound on bandwidth vs. reflection. 3. Using the Smith Chart for Matching: - The Smith Chart visualizes complex impedance transformation and provides insight into: → Constant resistance and reactance circles → Normalized admittance transformation - Impedance arcs can be rotated using: → Series inductors/capacitors (clockwise/counter-clockwise) → Shunt stubs for creating resonance at target points - Transmission line transformation: -> Z_in = Z_0 × (Z_L + jZ_0tan(βl)) / (Z_0 + jZ_Ltan(βl)) - (useful for microstrip implementations) 4. Matching Network Strategies: - L-Section Matching: Matches between resistive loads using one series and one shunt element, effective for narrowband. - π and T Networks: Multi-element matching suitable for high-Q or mismatched loads. - Stub Matching: Quarter-wavelength open or shorted stubs used in microstrip layouts. - Double-Stub and Triple-Stub Tuners: Useful when load changes with frequency. - LC Ladder and Transformer Matching: Ideal for power amplifiers and broadband filter stages. 5. Real-World Application Examples: - 5G Antennas: Require multiband impedance optimization for 3.5 GHz and 28 GHz bands using Smith chart-assisted multi-resonant designs. - THz Rectennas: Matching efficiency crucial due to high losses; narrowband filters are designed directly on Smith Chart. - RF Front-Ends: Broadband LNAs use LC matching + transmission line techniques to maintain gain flatness. - UWB Devices: Use stepped impedance transformers and tapered lines to match antennas over GHz-wide bandwidths. #SmithChart #ImpedanceMatching #RFDesign #BandwidthOptimization #MatchingNetworks #5G #THz #RFEngineering #PhDResearch #AntennaDesign

Why Transformers Trip on Energization and How Point-on-Wave Switching Prevents It Transformer inrush is an odd phenomenon because it isn’t the same every time a transformer is energized. It’s not unusual to hear stories of someone switching in a transformer that occasionally trips on overcurrent, but most of the time energizes without any issue. The reason this happens is that two main factors determine the maximum inrush current: residual core magnetization from when it was last de-energized (remanence) and the point on the voltage waveform where it’s energized. The residual core magnetization depends on when, phase-wise, the transformer was de-energized and on its loading at that moment. Since all three phases are 120 degrees apart, it’s impossible to de-energize each phase so that all three legs have zero remanence. The best you can do is de-energize when the transformer is under volted or loaded, which minimizes core excitation and results in less residual magnetization. The phase angle at which the transformer is energized plays a big role in how severe inrush will be, as it determines whether the magnetic flux stays contained within the core. If the flux cannot be contained, it leaks out into the oil and tank walls. The grid then “sees” a much smaller reactance, and a large inrush current flows because the primary and secondary windings are no longer efficiently coupled through the flux. A core contains magnetic flux when there are still iron domains not yet aligned with the magnetic field. Once all the domains are aligned north-south with the field, the core no longer acts as a preferred path for flux, forcing it to branch out into the tank and oil. This is saturation and is what ultimately causes large inrush currents. Transformer inrush occurs when the magnetic flux tries to align all the iron domains in one direction and the core can no longer contain it. If someone energizes the transformer at a point on the waveform that aligns with the existing residual magnetization, the resulting flux adds to the existing polarity causing large inrush current due to saturation. If they energize 180 degrees out of phase with the existing magnetization, the flux has a lot of iron domains to rotate before saturating the core. That’s why some transformers “trip once in a blue moon” on energization. The protection settings may be too tight to account for the occasional alignment between remanence and phase angle of energization. How POV switch mitigates inrush by smartly taking the remanence into consideration to determine when to switch in each phase , potentially 180 deg out of phase with iron domain alignment, so that the core doesn’t saturate. #utilities #renewables #energystorage #datacenters #electricalengineering

When electronic devices operate, they draw power from a DC power source, such as a battery or a power supply unit. However, these power sources can introduce unwanted noise and fluctuations into the DC voltage, especially at higher frequencies. This noise can come from various sources, including switching circuits, electromagnetic interference, or even fluctuations in the power grid. Bypass capacitors are strategically placed across the power supply rails of electronic circuits. These capacitors act as energy reservoirs that can quickly charge and discharge in response to changes in voltage. When high-frequency noise appears on the power supply line, the bypass capacitor effectively provides a low-impedance path for these AC signals, allowing them to bypass the sensitive components of the circuit. At the same time, the bypass capacitor presents a high impedance to the DC voltage, ensuring that the steady-state power supply remains unaffected. The effectiveness of a bypass capacitor in filtering out noise depends on several factors, including its capacitance value, the equivalent series resistance (ESR), and the inductance of the capacitor, as well as the impedance of the circuit it's connected to. Generally, smaller capacitance values are more effective at filtering higher frequencies, while larger capacitance values are better suited for filtering lower frequencies. By providing a low-impedance path for high-frequency noise, bypass capacitors help maintain a stable and clean DC voltage at the point of use within the circuit. This is crucial for the proper operation of sensitive components, such as integrated circuits, microcontrollers, and other electronic devices, ensuring their reliability and performance while minimizing electromagnetic interference and noise-induced errors. #bypass_capacitor #filter #EMI #NOISE

Transformer Testing Used equipment: 1.1 Insulation Resistance Test (Megger Test) • Purpose: Checks insulation health between windings and ground. • Instrument Used: Megger (Insulation Resistance Tester) • Test Voltage: • LV Winding: 500V – 1000V • HV Winding: 2500V – 5000V 1.2 Transformer Turns Ratio (TTR) Test • Purpose: Ensures correct turn ratio between primary and secondary. • Instrument Used: TTR Meter (Transformer Turns Ratio Tester) • Acceptable Range: ±0.5% of design ratio 1.3 Winding Resistance Test • Purpose: Measures resistance of windings to detect loose connections or damage. • Instrument Used: Micro-Ohmmeter / DC Resistance Tester • Test Current: 1A – 10A DC 1.4 Vector Group Test • Purpose: Confirms correct vector group and phase displacement. • Instrument Used: Phase Angle Meter & TTR Meter 1.5 No-Load Loss and Current Test • Purpose: Measures core losses at rated voltage. • Instrument Used: • Power Analyzer • Voltmeter & Ammeter 1.6 Load Loss and Impedance Test • Purpose: Measures copper losses and impedance voltage. • Instrument Used: • Power Analyzer • High-Voltage Source 1.7 Oil Dielectric Strength Test • Purpose: Checks insulation quality of transformer oil. • Instrument Used: BDV (Breakdown Voltage) Tester • Standard Value: Minimum 30 kV for new oil 1.8 Magnetic Balance Test • Purpose: Ensures uniform flux distribution in three-phase transformers. • Instrument Used: Multimeter & Variac (Variable Voltage Supply) 2. Type Tests (Performed on One Unit per Batch) 2.1 Short Circuit Test (Dynamic & Thermal Stability Test) • Purpose: Verifies the transformer’s ability to withstand fault conditions. • Instrument Used: High-Power Short Circuit Test Setup 2.2 Lightning Impulse Test • Purpose: Simulates lightning strikes to check dielectric strength. • Instrument Used: • Impulse Generator • Oscilloscope 2.3 Temperature Rise Test • Purpose: Measures winding and oil temperature rise during full load. • Instrument Used: • Thermocouples • IR Camera 3. Special Tests (As per Customer Request) 3.1 Partial Discharge Test • Purpose: Detects internal insulation defects. • Instrument Used: Partial Discharge Detector 3.2 Sweep Frequency Response Analysis (SFRA) Test • Purpose: Detects winding displacement or mechanical deformation. • Instrument Used: SFRA Analyzer 3.3 Frequency Response Analysis (FRA) Test • Purpose: Checks mechanical integrity of windings. • Instrument Used: Frequency Response Analyzer #power #Transformer #Testing #Maintenance #IFAS #MV

🔎 Is Your Transformer Insulation Aging Silently? It might look healthy on the outside — but deep inside, the insulation could be silently breaking down. 🧪 That’s where the Tan Delta Test steps in. A simple yet powerful diagnostic that tells you how well your transformer insulation is holding up — without opening it up. ⚡ But what is Tan Delta, really? Also called the Dissipation Factor Test, it measures the dielectric losses in a transformer's insulation system — losses that increase due to: 🔸 Moisture 🔸 Contamination 🔸 Aging of paper or oil 🔸 Internal partial discharges 🎯 Think of insulation as a capacitor. Perfect insulation → Purely capacitive (zero loss) Aging insulation → More leakage = More resistive current 🧮 Tan delta = Ratio of leakage (resistive) current to capacitive current 📉 The lower the tan delta, the healthier your insulation. 🔧 How the Tan Delta Test Works (in 4 simple steps): 1️⃣ Isolate the transformer and ground the neutral 2️⃣ Connect tan delta test kit across the bushings 3️⃣ Apply test voltage (2kV to 10kV) 4️⃣ Measure tan δ and capacitance at various voltage levels 📌 Rising tan delta at higher voltages signals weak spots in insulation. 📊 Interpreting the Results: ✅ < 0.5% — Healthy ⚠️ 0.5% to 1% — Monitor 🚨 > 1% — Action Needed! 🔁 Always compare with factory or historical test results to identify trends. 💡 What It Can Reveal: ✔ Moisture ingress ✔ Insulation aging ✔ Contaminated oil ✔ Partial discharge ✔ Hidden insulation failure risks 📏 Follow Industry Standards: 🛠️ IEC 60076-3 🛠️ Regular testing during commissioning, major repairs, and routine diagnostics 🧠 Tan Delta testing is like a health scan for your transformer's insulation. Do it early. Do it regularly. It’s the smartest insurance against unexpected failure. 📌 If you’re in substation maintenance, protection testing, or asset management — don’t skip this test. It’s small, non-invasive, and saves transformers from silent failure. 💬 Have you used Tan Delta Testing in your utility or projects? 👇 Share your experience or drop your go-to testing tips in the comments. ♻️ Repost to share with your network if you find this helpful. 🔗 Follow Ashish Shorma Dipta for posts like this. #PowerTransformer #TanDeltaTest #ElectricalEngineering #TransformerMaintenance #SubstationTesting

🔹 Transformer Testing – Explanation & Procedure 1.Insulation Resistance (IR) Test Purpose: To check the insulation strength between windings to windings and winding & earth. Ensures no moisture or deterioration. Procedure: Use Megger (500V / 1000V / 2500V / 5000V as per rating). Disconnect all connections from transformer bushings. Apply DC voltage between: * HV ↔ LV * HV ↔ Earth * LV ↔ Earth Record insulation resistance values in MΩ. For better check, also calculate Polarization Index (PI = IR at 10 min / IR at 1 min) 2.Winding Resistance Test Purpose: To measure winding resistance of LV and HV windings. Detects loose connections, shorted turns, or high-resistance joints. Procedure: Use a DC resistance test kit (Micro-ohmmeter) Connect across each winding terminal (HV side & LV side). Pass DC current and measure resistance. Compare with design/previous values; should be balanced across phases. 3.Magnetic Balance Test Purpose: To detect inter-turn short circuits in three-phase transformers. Ensures magnetic circuit balance of windings. Procedure: Apply low voltage AC (around 230V single phase supply) between two phases of HV winding at a time. Measure voltages induced in the third phase. Normal condition → induced voltages follow a definite balanced pattern. Abnormal imbalance → indicates possible winding fault. 4.Vector Group Test Purpose: To confirm the vector group (phase displacement) of transformer windings. Ensures parallel operation compatibility. Procedure: Apply 3-phase supply to HV side. Measure phase-to-phase and phase-to-neutral voltages on HV & LV. Compare phase displacement between HV and LV voltages. Verify with nameplate vector group (e.g., Dyn11, YNd1, etc.). 5.Voltage Ratio Test Purpose: To verify that the ratio of primary to secondary voltages matches the design. Procedure: Apply rated voltage on HV side (or a reduced test voltage). Measure voltage on LV side. Calculate ratio: HV / LV. Compare with nameplate ratio (tolerance ±0.5%). 6.Turns Ratio (TTR) Test Purpose: To accurately check the number of turns ratio between HV and LV. More precise than simple voltage ratio test. PROCEDURE: Use TTR meter(special kit). Connect across HV and LV windings. Inject a low test voltage from TTR kit. Instrument directly displays turns ratio & phase angle error. Compare with rated ratio.

Transformers Tests: - 1 - Insulation Resistance Test Used to measure the insulation resistance of the transformer components. Apply HV DC then measure resistance. Indicate the condition of the insulation. 2 - Turns Ratio Test Used to measure the turns ratio of the transformer (Primary and Secondary Windings. Apply voltage on winding then measure the voltage induced in the other winding. Percentage between voltages is the turns ratio of the primary and secondary windings. Accurate test. East to perform. 3 - Winding Resistance Test Used to measure the resistance of the transformer windings (primary and secondary). Done using LV DC source + Multimeter. 4 - Polarity Test Conducted to verify the polarity of the transformer windings. Apply DC source to the primary then measure secondary voltage. Polarity of the windings determined based on the direction of the induced voltage in the secondary winding. Simple and quick. Prevent damage of the transformer during installation. 5 - Open Circuit Test Performed to determine: >No Load Losses. >Magnetizing Current. Keep the secondary open circuited then apply voltage on the primary winding, then measure the primary (current and voltage). Calculate (No-Load Losses & Magnetizing Current). Determine the equivalent circuit then calc Efficiency and Regulation. 6 - Short Circuit Test Performed to determine: >Full Load Current. >Transformer Impedance. Keep the secondary short circuited then apply voltage to the primary winding, then measure the primary (current and voltage). Calculate (Full-Load Current & Impedance). Determine Winding Resistance. Determine Leakage Inductance. 7 - Sweep Frequency Response Analysis (SFRA) Non-destructive test used to detect any changes in the transformer mechanical structure. It can detect Winding Deformation or Shorted-Turns. It makes comprehensive assessment of the transformer condition. 8 - Dissolved Gas Analysis Test (DGA) Used to detect the presence of combustible gases in the transformer oil. Analyze a sample of the transformer oil to detect any changes in the gas concentration. It can detect incipient faults before they become major problems which allows predictive maintenance 9 - Partial Discharge Test Used to detect any partial discharges occurring within the transformer insulation. Apply HV to the transformer, then measure any partial discharge in the insulation. Can detect insulation faults before they cause significant issues to the transformer. 10 - Dielectric Withstand Test Apply HV to the transformer to test the ability of the insulation to withstand any voltage stress. Detect insulation weakness and that enables us to ensure the safety and reliability of the transformer. 11 - Thermal Imaging Test Uses infrared imaging to detect hot spots or temp gradients. It can detect problems such as: >Loose Connections. >Overload Components. It provides a non-invasive assessment of the transformer condition.