Analyzing Single-Line-to-Ground Faults Using Phasors

𝗠𝗮𝗻𝘆 𝗲𝗻𝗴𝗶𝗻𝗲𝗲𝗿𝘀 𝗿𝘂𝗻 𝗮 𝗳𝗮𝘂𝗹𝘁 𝗶𝗻 𝗘𝗧𝗔𝗣, 𝘀𝗲𝗲 𝗮 𝗻𝘂𝗺𝗯𝗲𝗿, 𝗮𝗻𝗱 𝗺𝗼𝘃𝗲 𝗼𝗻. 𝗬𝗼𝘂 𝗰𝗮𝗿𝗲 𝗮𝗯𝗼𝘂𝘁 𝘄𝗵𝗮𝘁 𝘁𝗵𝗮𝘁 𝗻𝘂𝗺𝗯𝗲𝗿 𝗺𝗲𝗮𝗻𝘀 𝗼𝗻 𝗲𝗮𝗰𝗵 𝘀𝗶𝗱𝗲 𝗼𝗳 𝘁𝗵𝗲 𝘁𝗿𝗮𝗻𝘀𝗳𝗼𝗿𝗺𝗲𝗿. 𝗧𝗵𝗿𝗲𝗲-𝗽𝗵𝗮𝘀𝗲 𝗳𝗶𝗿𝘀𝘁. Here the rule is simple.  • Reflected HV current = LV fault current × (LV/HV ratio).  • Δ–Y, Y–Y, Y–Δ. It does not change the value.  • Positive sequence drives the result. 𝗦𝗶𝗻𝗴𝗹𝗲-𝗹𝗶𝗻𝗲-𝘁𝗼-𝗴𝗿𝗼𝘂𝗻𝗱 𝗶𝘀 𝘄𝗵𝗲𝗿𝗲 𝗳𝗲𝗮𝗿 𝗰𝗿𝗲𝗲𝗽𝘀 𝗶𝗻.  • In Δ–Y, zero sequence loops inside the delta.  • Your HV side does not “see” that earth fault since zero sequence will not cross the delta.  • It appears as a line-to-line fault across two phases.  • Your HV earth-fault relay stay silent while the LV burns due to SLG fault. 𝗧𝗵𝗮𝘁 𝗶𝘀 𝗮 𝘀𝗰𝗮𝗿𝘆 𝗴𝗮𝗽.  • You want clarity, not surprises during utility review.  • You want settings that stand when someone asks “why.”  • You want to stop over-protecting one side and leaving the other exposed.  • Do this in your next study.  • Model grounding honestly.  • Solid, resistance, reactance, NGR.  • Feed the right zero-sequence impedances.  • Create one fault at a time. Single bus. Then read both sides.  • If you fault every LV bus together, you will hide the reflection.  • Track what you are plotting.  • For SLG fault in LV Side, I0 at HV is zero in Δ–Y transformer.  • Switch to phase currents and you will catch the two-phase reflection.  • Watch the healthy-phase voltage.  • With C-factor at 1.1, it lifts toward line value. 𝗗𝗼 𝗻𝗼𝘁 𝗽𝗮𝗻𝗶𝗰.  • It is expected behaviour.  • Use load flow to set OLTC range and PF correction.  • Use short circuit to set short-time duties for cables, CTs, busbars, and breakers.  • Map these to relays.  • Then write it in your report in plain language. Want to learn the basics of etap check this out https://lnkd.in/gCmHu8QB #powerprojects #etap #electricalengineering

Charles Legeyt Fortescue’s work lives on- A helpful browser based tool for visualizing sequence components Link to the toolkit (https://lnkd.in/gSh26yXH) I know that some of you that have been reading my post know that I have made scripts for various things in Octave that demonstrated sequence components, DC offset, arc flash energy calculation etc. I know the problem with this is that not many people want to download Octave, figure out how to load a script and play around with the tool. Everyone only has so much time in a day. So, I ported it to HTML so no one would have to download anything if they wanted to play with the toolkit. Why do I think it is important to play with the toolkit? There are a lot of concepts that don't fully sink in until you have actually had a chance to play with the phasors for the phase and sequence components and recreate various situations like single-line-to-ground faults, phase-to-phase faults, and review things ABC and CBA phase rotation, and how sequence components sum to the phase components. In school, you do the matrix multiplication on a TI-89 to go back and forth from the phase and sequence domain but just doing calcs by themselves often doesn't give you a good grasp. A lot of this on the surface sounds trivial and the math is not really that complicated but it is difficult to get a good grasp of things if you don't have a good mental model. That is true with a lot of things in engineering. A good mental model is often more important than being able to grind through the math because so much now is done with software. Without a good mental model, how is an engineer going to be able to recognize when a model has problems like maybe someone fat-fingered a few numbers? An engineer is an engineer because he understands things well enough to know when they aren't right. What does the Sequence Network Toolkit include? Phasors for phase and sequence components Oscillography related to these rotating phasors ABC and CBA phase rotation options Buttons to apply single-line-to-ground (SLG) and phase-to-phase faults Sliders for adjusting the magnitude and angle of the phases Sliders for adjusting the magnitude and angle of the sequence components That said, it was a lot more work to do this in HTML than in the Matlab clone, Octave. It is still very doable and easy to make look nice. The animations run faster in HTML than in Octave, which I guess really shows how slow Octave is as a procedural language. The syntax is more clouded up but I suppose that is to be expected because html wasn't designed to just run math calculations. I was initially surprised actually that it was able to do as much as it did. Just give it a shot. It should work with any browser that has Canvas and Javascript, which I think is now the default with modern browsers. Just remember you can zoom in with ctrl - and + like a webpage. #utilities #renewables #energystorage #electricalengineering

𝗨𝗻𝗱𝗲𝗿𝘀𝘁𝗮𝗻𝗱𝗶𝗻𝗴 𝗙𝗮𝘂𝗹𝘁 𝗖𝘂𝗿𝗿𝗲𝗻𝘁𝘀: 𝗪𝗵𝘆 𝗦𝗟𝗚 𝗗𝗼𝗺𝗶𝗻𝗮𝘁𝗲𝘀 𝗮𝘁 𝗟𝗶𝗴𝗵𝘁 𝗟𝗼𝗮𝗱     Under no-load or light-load conditions, the generator or system voltage tends to be higher than nominal because there is very little current flowing, so the internal voltage drop across reactances is minimal. This affects fault currents differently for various fault types: 𝙒𝙝𝙮 𝙎𝙇𝙂 (𝙎𝙞𝙣𝙜𝙡𝙚 𝙇𝙞𝙣𝙚-𝙩𝙤-𝙂𝙧𝙤𝙪𝙣𝙙) 𝙛𝙖𝙪𝙡𝙩 𝙘𝙪𝙧𝙧𝙚𝙣𝙩 𝙞𝙨 𝙝𝙞𝙜𝙝𝙚𝙧 𝙩𝙝𝙖𝙣 𝙖 𝙩𝙝𝙧𝙚𝙚-𝙥𝙝𝙖𝙨𝙚 𝙛𝙖𝙪𝙡𝙩 𝙘𝙪𝙧𝙧𝙚𝙣𝙩: 1. 𝙕𝙚𝙧𝙤-𝙨𝙚𝙦𝙪𝙚𝙣𝙘𝙚 𝙥𝙖𝙩𝙝 𝙞𝙣𝙫𝙤𝙡𝙫𝙚𝙢𝙚𝙣𝙩: In an SLG fault, the fault current flows through the positive, negative, and zero-sequence networks. The zero-sequence impedance is usually much lower than the positive-sequence impedance, especially if the neutral is solidly grounded. This reduces the overall impedance seen by the fault, increasing current. 2. 𝙎𝙮𝙨𝙩𝙚𝙢 𝙫𝙤𝙡𝙩𝙖𝙜𝙚 𝙖𝙩 𝙛𝙖𝙪𝙡𝙩 𝙥𝙤𝙞𝙣𝙩: At no-load, the pre-fault voltage is close to the generator’s open-circuit voltage (often slightly above nominal). So, the fault starts with a higher voltage, which increases the initial fault current. 3. 𝙏𝙝𝙧𝙚𝙚-𝙥𝙝𝙖𝙨𝙚 𝙛𝙖𝙪𝙡𝙩 𝙞𝙢𝙥𝙚𝙙𝙖𝙣𝙘𝙚: A three-phase fault involves only the positive-sequence network, which has relatively higher impedance compared to the combined sequence network in SLG faults. So, its current is lower under the same conditions.   𝗘𝘅𝗮𝗺𝗽𝗹𝗲 𝗰𝗼𝗺𝗽𝗮𝗿𝗶𝗻𝗴 𝗦𝗟𝗚 𝗳𝗮𝘂𝗹𝘁 𝗮𝗻𝗱 𝘁𝗵𝗿𝗲𝗲-𝗽𝗵𝗮𝘀𝗲 𝗳𝗮𝘂𝗹𝘁 𝘂𝗻𝗱𝗲𝗿 𝗹𝗶𝗴𝗵𝘁-𝗹𝗼𝗮𝗱 𝗰𝗼𝗻𝗱𝗶𝘁𝗶𝗼𝗻𝘀: Assumptions • System voltage: 11 kV (line-to-line) • Generator reactance:  o Positive-sequence X1=0.2 p.u o Negative-sequence X2=0.2 p.u o Zero-sequence X0=0.05 p.u • 𝗕𝗮𝘀𝗲 𝗰𝘂𝗿𝗿𝗲𝗻𝘁:  Ibase = Sbase / (sqrt(3)*VLL) Assume Sbase=100 MVA, VLL=11 kV. Step 1: 𝗖𝗮𝗹𝗰𝘂𝗹𝗮𝘁𝗲 𝗕𝗮𝘀𝗲 𝗖𝘂𝗿𝗿𝗲𝗻𝘁 Ibase = 100×106 / 3×11×103 ≈ 5,250 A Step 2: 𝗧𝗵𝗿𝗲𝗲-𝗣𝗵𝗮𝘀𝗲 𝗙𝗮𝘂𝗹𝘁 𝗖𝘂𝗿𝗿𝗲𝗻𝘁 I3ϕ= E / X1 = 1.0 / 0.2 = 5.0 p.u 𝗖𝗼𝗻𝘃𝗲𝗿𝘁 𝘁𝗼 𝗮𝗺𝗽𝗲𝗿𝗲𝘀: I3ϕ= 5.0×5,250 ≈ 26,250 A Step 3: 𝗦𝗟𝗚 𝗙𝗮𝘂𝗹𝘁 𝗖𝘂𝗿𝗿𝗲𝗻𝘁 For 𝘚𝘓𝘎 𝘧𝘢𝘶𝘭𝘵: ISLG= 3*E / (X1+X2+X0) = (3*1.0) / (0.2+0.2+0.05) = 3 / 0.45 ≈ 6.67 p.u  Convert to amperes: ISLG = 6.67×5,250 ≈ 35,000A 𝗖𝗼𝗻𝗰𝗹𝘂𝘀𝗶𝗼𝗻: • Three-phase fault current: ~26.3 kA • SLG fault current: ~35.0 kA 𝗦𝗟𝗚 𝗳𝗮𝘂𝗹𝘁 𝗶𝘀 ~𝟯𝟯% 𝗵𝗶𝗴𝗵𝗲𝗿 𝘁𝗵𝗮𝗻 𝘁𝗵𝗿𝗲𝗲-𝗽𝗵𝗮𝘀𝗲 𝗳𝗮𝘂𝗹𝘁 𝗯𝗲𝗰𝗮𝘂𝘀𝗲 𝗼𝗳 𝘁𝗵𝗲 𝗹𝗼𝘄 𝘇𝗲𝗿𝗼-𝘀𝗲𝗾𝘂𝗲𝗻𝗰𝗲 𝗶𝗺𝗽𝗲𝗱𝗮𝗻𝗰𝗲. If you want to learn and enhance your skill enroll this link: https://lnkd.in/gnSmwUHS #shortcircuitanalysis #protectionsoptimized #gridstability