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Electrical Zindagi
Transformer
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Quick One-line Revision (30+ points) May You Like These Posts Join Us for Regular Updates Donate & Support Community Sponsored / Ads SEO KeywordsQuick Revision — Vital one-liners for AE/JE and similar exams (read fast, memorize easy tricks):
1. Transformer principle: electromagnetic induction — remember "coil + changing flux = induced EMF" (trick: tap your finger on the core to recall 'flux change' = induction).
2. Turns ratio Np/Ns = Vp/Vs — if turns double, voltage doubles; for exams: treat turns ratio as a direct voltage multiplier shortcut.
3. EMF equation: E = 4.44 × f × N × Î¦m (sinusoidal) — memorize 4.44 as the exam anchor for induced voltage calculations.
4. Ideal transformer assumption: zero winding resistance, zero leakage — useful for quick conceptual MCQs where losses are ignored.
5. Leakage flux causes voltage drop — exam trick: if voltage regulation asked, leakage reactance is the culprit for drop under load.
6. Copper loss = I²R — warm-up trick: double current → quadruple copper loss; use to compare loss changes with load variations.
7. Core loss = hysteresis + eddy current — remember "H + E = core losses" and to reduce eddy use thin laminations.
8. Use silicon steel laminations to reduce eddy currents — thin sheets reduce loop area for eddy currents and heating.
9. Turns ratio check (ratio test): measure open-circuit voltage at secondary to confirm manufacturing correctness.
10. Open-circuit test gives core loss & magnetizing current; short-circuit test gives series impedance & copper loss — classic exam pair.
11. Voltage regulation = (Vnl − Vfl)/Vfl × 100% — memorize formula and that regulation improves with lower leakage reactance and power factor.
12. Polarity test: ensure dot ends alignment — exam tip: wrong polarity = phase reversal in parallel operation questions.
13. Inrush current occurs when energizing at peak flux — safety note: always apply closing angle tricks to reduce magnetizing surge.
14. Auto-transformer conserves copper but provides no full isolation — quick exam distinction: better economy but less safety isolation.
15. Three-phase connections: Y-Δ, Δ-Y, Y-Y — vector group determines phase shift; remember Δ-Y gives +30° shift (use table memory).
16. Tap-changers (OLTC vs. OLTC vs off-load) — on-load tap-changers change taps under load; off-load require de-energize — trick: 'ON = live adjust'.
17. Buchholz relay detects internal faults by gas accumulation — common MCQ item: works only for oil-immersed transformers with conservator tanks.
18. DGA (Dissolved Gas Analysis) helps spot incipient faults in oil — exam common: rising hydrogen and acetylene hint arcing or severe faults.
19. ONAN cooling: Oil Natural Air Natural — memorize online acronym list for cooling methods (ONAN, ONAF, OFAF etc.).
20. Core type vs shell type: core has windings around limb; shell encloses windings — shell type is mechanically stronger and used for distribution tests.
21. Vector group notation (e.g., Dyn11) encodes winding connections & phase shift — exam trick: Dyn11 means delta prim, star sec with 330° shift (or −30°).
22. Impedance (per unit) limits short-circuit current — to calculate fault current quickly use I_fault = I_sc = Rated_V/LnZ_pu shortcut in many exam problems.
23. Efficiency peaks at load where copper loss = core loss — memorize "maximum efficiency when Pcu = Pcore" for quick answers.
24. Polarity dots indicate instantaneous polarity of induced voltage — use dot method for series/parallel tests in MCQs to avoid sign errors.
25. Insulation class (e.g., Class A, B, F, H) limits maximum operating temperature — common exam recall item for reliability design tasks.
26. Impulse testing checks lightning withstand — remember impulse for external overvoltage strength questions on insulation coordination.
27. Stray losses and proximity effects appear in windings — quick exam citation: stray losses rise with short-circuit currents and poor layout.
28. Magnetostriction causes humming noise — MCQ clue: vibration & audible noise → magnetostriction, tighten core clamping to reduce noise.
29. Neutral grounding of transformer reduces transient overvoltages — grounding lesson: choose earthing method per system fault-handling spec questions.
30. Breathers with silica gel prevent moisture ingress into oil — common maintenance MCQ: replace silica when blue→pink or dry indicator state changes.
31. Ratio test & polarity tests are simple field checks for commissioning — exam trick: polarity + ratio verify correct phasing and voltage scaling before operation.
32. Use FRA (Frequency Response Analysis) to detect winding movement after short-circuit damage — recent practical topic appearing in maintenance-style questions.
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