Transformer MCQ
Step-Up, Step-Down, Auto Transformer — working, losses, efficiency, cooling methods. Gulf substations mein transformer knowledge critical hai. 5 parts mein divide.
Transformer Kya Hota Hai?
Main Mohammad Arif hoon — 12+ saal se Gulf aur Mumbai ke sites pe electrical supervisor hoon. Netmagic Data Center se Sidra Hospital tak, har site pe transformers ka kaam dekha hai. Gulf substations mein transformer ki knowledge critical hai — kyunki 11kV/415V distribution ka backbone yahi hai.
Transformer ek static device hai jo electrical energy ko ek circuit se doosre circuit me transfer karta hai Mutual Induction ke principle pe, frequency change kiye bina. Voltage ko step-up (badhana) ya step-down (kam karna) kar sakta hai. Simple hai — lekin isme bahut kuch samajhna padta hai: losses, efficiency, cooling, testing.
Transformer Ke Types
Gulf sites pe 4 main types ke transformers milenge:
| Type | Primary Use | Rating Range | Gulf Application |
|---|---|---|---|
| Step-Up | Voltage increase | 10 MVA+ | Generation to transmission |
| Step-Down | Voltage decrease | 25kVA-2.5MVA | Distribution to homes/offices |
| Auto Transformer | Voltage regulation | Variable | Interconnection, testing |
| Isolation Transformer | Electrical isolation | 1kVA-5MVA | Hospitals, data centers |
Distribution vs Power Transformer
Distribution Transformer: 25kVA-2.5MVA, efficiency maximum at 50-75% load, voltage regulation primary concern. Gulf residential/commercial supply.
Power Transformer: 10MVA+, efficiency maximum at full load, used in substations for bulk power transfer.
Transformer Construction — Main Parts
Core
- CRGO Silicon Steel — low hysteresis loss
- Laminated — eddy current loss reduce
Windings
- Copper winding — high conductivity
- Primary & Secondary — turns ratio decides voltage
Oil & Cooling
- Mineral Oil — insulation + cooling
- Conservator — oil expansion space
Accessories
- Buchholz Relay — gas detection
- Tap Changer — voltage regulation
Transformer Losses — Kahan Power Waste Hoti Hai?
Iron (Core) Loss = Hysteresis loss + Eddy current loss → Constant, depends on voltage & frequency
Copper Loss (I²R) = I₁²R₁ + I₂²R₂ → Variable, depends on load current
Stray Loss = Leakage flux losses → Small percentage
Dielectric Loss = Insulation losses → Very small
Efficiency maximum kab hoti hai? Jab Copper Loss = Iron Loss. Distribution transformers typically 50-75% load pe design kiye jaate hain. Gulf sites pe efficiency 95-99% range mein hoti hai.
Transformer Testing — Site Pe Kaam Aayega
Routine Tests
- Insulation Resistance (Megger)
- Turns Ratio (TTR) test
- Winding Resistance test
Advanced Tests
- DGA (Dissolved Gas Analysis)
- SFRA (Sweep Frequency Response)
- Tan Delta (Power Factor) test
Cooling Methods — ONAN, ONAF, OFAF
| Code | Full Form | Cooling Type | Use |
|---|---|---|---|
| ONAN | Oil Natural Air Natural | Natural convection | Small distribution |
| ONAF | Oil Natural Air Forced | Fans for air | Medium transformers |
| OFAF | Oil Forced Air Forced | Pumps + fans | Large power transformers |
| ODAF | Oil Directed Air Forced | Directed oil flow | Very large transformers |
Gulf Interview Tips — Transformer Pe
- kVA rating calculation: 3-phase kVA = √3 × VL × IL / 1000 — ye formula yaad rakh.
- Vector group: Dyn11 (Delta primary, Star secondary with neutral, 30° lead) sabse common hai Gulf distribution me.
- Buchholz Relay: “Oil-immersed transformer me internal fault detect karta hai — gas ya oil flow se alarm/trip” — ye ek line bahut kaam aata hai.
- Differential protection: “Primary aur secondary current compare karta hai — difference internal fault hai” — real site experience wala jawab.
- Parallel operation: “Same voltage ratio, same vector group, similar %Z hona chahiye — warna circulating current hoga.”
Transformer Calculator Bhi Try Karo
kVA sizing, FLC, cable size, breaker selection — sab ek jagah. Nameplate values daalo, sab instantly milega.