Transformers MCQ Questions
- In the transformer the function of a conservator is to
(a) provide fresh air for cooling the transformer
(b) supply cooling oil to transformer in time of need
(c) protect the transformer from damage when oil expends due to heating
(d) none of the above
Ans: c - Natural oil cooling is used for transformers up to a rating of
(a) 3000 kVA
(b) 1000 kVA
(c) 500 kVA
(d) 250 kVA
Ans: a - Power transformers are designed to have maximum efficiency at
(a) nearly full load
(b) 70% full load
(c) 50% full load
(d) no load
Ans: a - The maximum efficiency of a distribution transformer is
(a) at no load
(b) at 50% full load
(c) at 80% full load
(d) at full load
Ans: b - Transformer breaths in when
(a) load on it increases
(b) load on it decreases
(c) load remains constant
(d) none of the above
Ans: b - No-load current of a transformer has
(a) has high magnitude and low power factor
(b) has high magnitude and high power factor
(c) has small magnitude and high power factor
(d) has small magnitude and low power factor
Ans: d
- Spacers are provided between adjacent coils
(a) to provide free passage to the cooling oil
(b) to insulate the coils from each other
(c) both (a) and (b)
(d) none of the above
Ans: a - Greater the secondary leakage flux
(a) less will be the secondary induced e.m.f.
(b) less will be the primary induced e.m.f.
(c) less will be the primary terminal voltage
(d) none of the above
Ans: a - The purpose of providing iron core in a step-up transformer is
(a) to provide coupling between primary and secondary
(b) to increase the magnitude of mutual flux
(c) to decrease the magnitude of mag-netizing current
(d) to provide all above features
Ans: c - The power transformer is a constant
(a) voltage device
(b) current device
(c) power device
(d) main flux device
Ans: d - Two transformers operating in parallel will share the load depending upon their
(a) leakage reactance
(b) per unit impedance
(c) efficiencies
(d) ratings
Ans: b - If R2 is the resistance of secondary winding of the transformer and K is the transformation ratio
then the equivalent secondary resistance referred to primary will be
(a) R2/VK
(b) R2IK2
(c) R22!K2
(d) R22/K
Ans: b - What will happen if the transformers working in parallel are not connected with regard to
polarity ?
(a) The power factor of the two trans-formers will be different from the power factor of common load
(b) Incorrect polarity will result in dead short circuit
(c) The transformers will not share load in proportion to their kVA ratings
(d) none of the above
Ans: b - If the percentage impedances of the two transformers working in parallel are different, then
(a) transformers will be overheated
(b) power factors of both the transformers will be same
(c) parallel operation will be not possible
(d) parallel operation will still be possible, but the power factors at which the two transformers
operate will be different from the power factor of the common load Ans: d
- In a transformer the tappings are generally provided on
(a) primary side
(b) secondary side
(c) low voltage side
(d) high voltage side
Ans: c - The use of higher flux density in the transformer design
(a) reduces weight per kVA
(6) reduces iron losses
(c) reduces copper losses
(d) increases part load efficiency
Ans: a - The chemical used in breather for transformer should have the quality of
(a) ionizing air
(b) absorbing moisture
(c) cleansing the transformer oil
(d) cooling the transformer oil.
Ans: b - The chemical used in breather is
(a) asbestos fiber
(b) silica sand
(c) sodium chloride
(d) silica gel
Ans: d - An ideal transformer has infinite values of primary and secondary inductances. The statement is
(a) true
(b) false
Ans: b - The transformer ratings are usually expressed in terms of
(a) volts
(b) amperes
(c) kW
(d) kVA
Ans: d - The noise resulting from vibrations of laminations set by magnetic forces, is termed as
(a) magnetostrication
(b) boo
(c) hum
(d) zoom
Ans: c - Hysteresis loss in a transformer varies as CBmax = maximum flux density)
(a) Bmax
(b) Bmax1-6
(C) Bmax1-83
(d) B max
Ans: b - Material used for construction of transformer core is usually
(a) wood
(b) copper
(c) aluminium
(d) silicon steel
Ans: d
- The thickness of laminations used in a transformer is usually
(a) 0.4 mm to 0.5 mm
(b) 4 mm to 5 mm
(c) 14 mm to 15 mm
(d) 25 mm to 40 mm
Ans: a - The function of conservator in a transformer is
(a) to project against’internal fault
(b) to reduce copper as well as core losses
(c) to cool the transformer oil
(d) to take care of the expansion and contraction of transformer oil due to variation of temperature of
sur-roundings
Ans: d