301. The main purpose of laminating the transformer core is to
A) Reduce eddy current loss
B) Reduce hysteresis loss
C) Reduce copper loss
D) Reduce mechanical vibrations
Answer: A
302. In transformer, the emf per turn is same for
A) Primary and secondary
B) Only primary
C) Only secondary
D) None
Answer: A
303. The insulation resistance of transformer winding can be measured by
A) Megger
B) Ammeter
C) Voltmeter
D) Multimeter
Answer: A
304. The material used for transformer core is
A) Silicon steel
B) Cast iron
C) Copper
D) Aluminum
Answer: A
305. In a transformer, if the supply frequency increases, the iron loss
A) Increases
B) Decreases
C) Remains same
D) Becomes zero
Answer: A
306. Transformer efficiency at unity power factor is
A) More than at lagging PF
B) Less than at lagging PF
C) Same
D) Always 100%
Answer: A
307. In transformer, the magnetizing component of no-load current is
A) Lagging by 90°
B) Leading by 90°
C) In phase
D) Opposite
Answer: A
308. The open circuit test is performed on
A) LV side at rated voltage
B) HV side at rated current
C) LV side at reduced voltage
D) HV side at short circuit
Answer: A
309. The short circuit test is performed to determine
A) Equivalent impedance
B) Iron loss
C) Regulation
D) All of these
Answer: D
310. If the primary of transformer is connected to DC supply
A) It will burn
B) It will work normally
C) Output voltage doubles
D) Copper loss reduces
Answer: A
311. A 100 kVA transformer has maximum efficiency at 75% load. Its iron loss = ?
A) (0.75)² × Copper loss
B) (3/4)² × Copper loss
C) 0.5625 × Copper loss
D) Iron loss = (0.75)² × Cu loss
Answer: D
312. The voltage regulation of transformer at unity power factor is
A) Minimum
B) Maximum
C) Negative
D) Zero
Answer: A
313. The losses occurring in transformer even when no load is connected are
A) Iron losses
B) Copper losses
C) Both
D) None
Answer: A
314. The leakage reactance of transformer depends on
A) Leakage flux
B) Winding arrangement
C) Core geometry
D) All of these
Answer: D
315. The efficiency of distribution transformer is maximum at
A) 50% load
B) Full load
C) 75% load
D) No-load
Answer: A
316. The open-delta connection is also known as
A) V–V connection
B) T–T connection
C) Y–Δ connection
D) Δ–Y connection
Answer: A
317. For the same kVA rating, auto-transformer size is
A) Smaller
B) Larger
C) Same
D) None
Answer: A
318. The advantage of delta connection on primary is
A) Third harmonics are circulated
B) Voltage per winding is reduced
C) Neutral not required
D) All of the above
Answer: D
319. The polarity of transformer is checked by
A) DC supply test
B) AC short-circuit test
C) Connection method
D) Using voltmeter method
Answer: D
320. The phase shift between primary and secondary in Dyn11 transformer is
A) 30° lead
B) 30° lag
C) 0°
D) 180°
Answer: A
321. Transformer efficiency is maximum when
A) Variable losses are equal to constant losses
B) Iron loss = copper loss
C) Both A and B
D) None
Answer: C
322. The temperature rise in transformer depends upon
A) Copper loss
B) Iron loss
C) Cooling method
D) All
Answer: D
323. The inrush current in transformer is
A) Magnetizing current
B) Very high at switching ON
C) Harmonic-rich
D) All of these
Answer: D
324. The voltage per turn is given by
A) 4.44 f Φm
B) Φ/N
C) N/Φ
D) E/N
Answer: D
325. The secondary voltage of a transformer decreases under load because of
A) Leakage impedance
B) Flux drop
C) Iron loss
D) Resistance
Answer: A
326. The transformer can be used as an isolation device because
A) Primary and secondary are magnetically coupled only
B) Electrically isolated
C) Frequency unchanged
D) All
Answer: D
327. In a transformer, the load current flows due to
A) Mutual induction
B) Electromagnetic coupling
C) Secondary induced emf
D) All
Answer: D
328. The harmonics in transformer emf can be reduced by
A) Using stepped core
B) Using distributed winding
C) Skewing core
D) Both A & B
Answer: D
329. Transformer insulation failure mainly occurs due to
A) Overheating
B) Moisture
C) Overvoltage
D) All of these
Answer: D
330. The per unit impedance of transformer is independent of
A) kVA rating
B) Voltage rating
C) Design
D) Material
Answer: A
331. Which of the following is not a type of transformer cooling?
A) ONAN
B) ONAF
C) OFWF
D) DCAF
Answer: D
332. The dielectric loss in transformer oil increases with
A) Moisture content
B) Voltage
C) Frequency
D) All
Answer: D
333. In three-phase transformer, tertiary winding is used for
A) Suppressing harmonics
B) Balancing unbalanced loads
C) Providing path for zero sequence current
D) All
Answer: D
334. In an auto-transformer, power transferred inductively is
A) Part of total power
B) Full power
C) Zero
D) None
Answer: A
335. The rating of instrument transformer is expressed in
A) VA
B) kVA
C) W
D) VAR
Answer: A
336. The rated secondary current of current transformer is
A) 5A or 1A
B) 10A
C) 100mA
D) 50A
Answer: A
337. The accuracy of CT decreases when
A) Burden increases
B) Power factor decreases
C) Both A and B
D) None
Answer: C
338. The PT (Potential Transformer) is used to
A) Step down voltage for metering
B) Step up current
C) Provide power to load
D) Act as isolation
Answer: A
339. The rated burden of CT or PT is expressed in
A) VA
B) kVA
C) W
D) VAR
Answer: A
340. The secondary of CT should be
A) Short-circuited when not in use
B) Open circuited
C) Connected to voltmeter
D) Grounded
Answer: A
341. In transformer, which loss is independent of load?
A) Iron loss
B) Copper loss
C) Eddy loss
D) Friction loss
Answer: A
342. Eddy current losses can be minimized by
A) Using laminated core
B) Using thicker plates
C) Increasing flux
D) Increasing frequency
Answer: A
343. The leakage reactance causes
A) Voltage drop
B) Poor regulation
C) Both A and B
D) None
Answer: C
344. The core type transformer has
A) Two limbs
B) One limb
C) Three limbs
D) No limbs
Answer: A
345. The shell type transformer has
A) Three limbs
B) Two limbs
C) One limb
D) None
Answer: A
346. The temperature rise limit for Class A insulation is
A) 55°C
B) 65°C
C) 75°C
D) 90°C
Answer: A
347. The efficiency of power transformer is
A) 98–99%
B) 80%
C) 70%
D) 60%
Answer: A
348. The transformer’s noise level increases mainly due to
A) Magnetostriction
B) Loose laminations
C) Cooling fans
D) All
Answer: D
349. The zero-sequence impedance of delta-connected transformer is
A) Infinite
B) Zero
C) High
D) Low
Answer: A
350. The tertiary winding of transformer is generally connected in
A) Delta
B) Star
C) Open delta
D) Zig-zag
Answer: A
No comments:
Post a Comment