MCQ Practice Test — Category 04
Transformer MCQ
Step-Up, Step-Down, Auto Transformer — working, losses, efficiency aur cooling methods. Gulf interview ke liye zaroor padho.
10 Questions (Page 1)
Medium-Hard Level
Hinglish Explanation
Attempted: 0/10
Correct: 0
Wrong: 0
Question 01Easy
Transformer kaise kaam karta hai?
ADC current se
BElectromagnetic induction se AC voltage step-up/down karta hai
CBattery se charge hota hai
DMechanical rotation se
✓ Sahi Jawab: B
Transformer mutual electromagnetic induction pe kaam karta hai. Primary winding me AC current se magnetic flux generate hota hai jo secondary winding me EMF induce karta hai. DC pe transformer kaam nahi karta. Frequency change nahi hoti — sirf voltage change hoti hai.
Question 02Easy
Turn ratio 10:1 aur primary voltage 11kV hai to secondary voltage kya hogi?
A110kV
B11kV
C1.1kV (1100V)
D110V
✓ Sahi Jawab: C — 1100V
V2 = V1 / Turn Ratio = 11000 / 10 = 1100V = 1.1kV. Formula: N1/N2 = V1/V2. Gulf me 11kV/415V transformer ka turn ratio approx 26.5:1 hota hai. Ye calculation Gulf interview me zaroor puchhi jaati hai.
Question 03Medium
Transformer me Buchholz relay kahan lagta hai aur kya karta hai?
AMain tank aur conservator ke beech — internal faults detect karta hai
BPrimary winding pe
CCooling fan pe
DSecondary bushing pe
✓ Sahi Jawab: A
Buchholz relay oil-filled transformers me main tank aur conservator ke beech pipe me lagta hai. Internal fault hone pe gas generate hoti hai — minor fault pe alarm, major fault pe trip. Gulf me power transformers pe ye mandatory hai.
Question 04Medium
Transformer ki efficiency maximum kab hoti hai?
AFull load pe hamesha
BJab copper loss = iron loss ho
CNo load pe
DOverload pe
✓ Sahi Jawab: B
Transformer efficiency maximum hoti hai jab copper loss = iron loss. Ye typically 50-75% load pe hota hai. Iron loss constant hai, copper loss load ke saath badhta hai. Gulf interview me ye classic question hai.
Question 05Medium
ONAN cooling method ka matlab kya hai?
AOil Natural Air Natural
BOil Normal Air Normal
COnly Natural Air Needed
DOil Needed Air Natural
✓ Sahi Jawab: A — Oil Natural Air Natural
ONAN = Oil Natural Air Natural — oil convection se naturally circulate hota hai. ONAF = Oil Natural Air Forced (fans). OFAF = Oil Forced Air Forced. Gulf me garmi ki wajah se ONAF ya OFAF zyada common hai — 50°C ambient pe natural cooling kaafi nahi hoti.
Question 06Medium
Transformer me Iron loss (core loss) kis cheez pe depend karta hai?
ALoad current pe
BWinding resistance pe
CApplied voltage aur frequency pe (constant)
DTemperature pe
✓ Sahi Jawab: C
Iron loss (Hysteresis + Eddy current loss) voltage aur frequency pe depend karta hai — load se independent hai, isliye constant loss kehte hain. Copper loss (I²R) load pe depend karta hai — variable loss. No-load test se iron loss measure karte hain.
Question 07Hard
Auto transformer aur 2-winding transformer me kya fark hai?
AAuto transformer zyada expensive hai
BKoi fark nahi
CAuto transformer me zyada insulation hai
DAuto me ek hi winding hai, electrical isolation nahi hoti
✓ Sahi Jawab: D
Auto transformer me ek hi winding hoti hai jisko tap se divide karte hain. Primary aur secondary electrically connected hain — galvanic isolation nahi. 2-winding me complete isolation hai. Star-Delta starting me auto transformer use hota hai. Safety ke liye hospital jaise sensitive locations pe 2-winding transformer use karte hain.
Question 08Hard
500kVA transformer ka full load secondary current kitna hoga? (11kV/415V)
A500A
B695A
C1200A
D26.2A
✓ Sahi Jawab: B — 695A
I = kVA / (√3 × V) = 500,000 / (1.732 × 415) = 500,000 / 719 = 695A. Ye Gulf me 500kVA distribution transformer ka standard secondary current hai. MCCB incomer typically 800A hoga. Primary current = 500,000 / (1.732 × 11,000) = 26.2A.
Question 09Medium
Transformer ka Vector Group Dyn11 me kya matlab hai?
APrimary Delta, Secondary Star with neutral, 30° phase shift
BPrimary Star, Secondary Delta
CDono Delta connection
DDono Star connection
✓ Sahi Jawab: A
Dyn11: D = Primary Delta, y = Secondary Star, n = neutral available, 11 = 330° (30° lag in clock notation). Gulf me 11kV/415V distribution transformers ka standard vector group Dyn11 hai. Neutral available hone se single phase loads chalaye ja sakte hain.
Question 10Hard
Transformer oil (insulating oil) ka kya kaam hai?
ASirf cooling ke liye
BSirf insulation ke liye
CCooling + Insulation + Arc quenching
DMotor ko lubricate karna
✓ Sahi Jawab: C
Transformer oil teen kaam karta hai: (1) Cooling — heat dissipate karta hai, (2) Insulation — windings ke beech dielectric strength, (3) Arc quenching — on-load tap changer me arc bujhaata hai. Oil BDV (Breakdown Voltage) test regularly karo — minimum 30kV honi chahiye. Gulf me heat ki wajah se oil degradation zyada hoti hai.
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