Electrical Engineering · Question Bank

Transformers

258 questions · page 8 of 13. Answer in your head first, then check the solution.

📘 EE Mock Board Exam
TypeAll 258Problem solving 148Objective 110
DifficultyAll 258Easy 171Medium 71Hard 16
#141📜 EE Pre-Board March 2017📘 PowerhouseEasy
Conservator of a transformer consists of
Aan air-tight metal drum fixed at the top of the tank
Bdrum placed at the bottom of the tank
Coverload protection
Dnone of these
#142📜 EE Pre-Board March 2017📘 PowerhouseEasy
A transformer has negligible resistance and a p.u. reactance of 0.1. What is its voltage regulation on full load with a leading p.f. angle of 30°?
A-10%
B10%
C5%
D-5%
#143📜 EE Pre-Board March 2017📘 PowerhouseEasy
A transformer breathes in when
Aload on it increases
Bload on it decreases
Cload remains constant
Dnone of these
#144📜 EE Pre-Board August 2017📘 PowerhouseEasy
The output current corresponding to maximum efficiency for a transformer having a core loss of 100 watts and an equivalent resistance referred to the secondary of 0.25 Ω is ________ amperes.
A10
B20
C25
D40
#145📜 EE Pre-Board August 2017📘 PowerhouseEasy
If the copper loss of a transformer at 7/8 of full load is 4,900 W, what is its full-load copper loss?
A4,288 W
B6,400 W
C5,600 W
D3,752 W
#146📜 EE Pre-Board August 2017📘 PowerhouseEasy
Ideal transformer assumptions do not include
Azero winding resistance
Binfinite core permeability
Cno leakage flux
Da finite magnetizing current
#147📜 EE Pre-Board August 2017📘 PowerhouseHard
Two transformers are connected in open delta and deliver a balanced three-phase load of 245 kW at 460 volts and a power factor of 0.707. Calculate the power delivered by the individual transformers.
A122.5 kW, 122.5 kW
B193.2 kW, 51.8 kW
C173.2 kW, 71.8 kW
D141.4 kW, 103.6 kW
#148📜 EE Pre-Board August 2017📘 PowerhouseMedium
A 20 kV/7.87 kV autotransformer has a secondary line current of 100 A. What is the current in the common winding?
A39.35 A
B60.65 A
C100 A
D139.35 A
#149📜 EE Pre-Board August 2017📘 PowerhouseMedium
Three 30:1 step-down transformers are connected Y–Δ for stepping down the 132,000 volt three-phase transmission voltage. Calculate the secondary line voltage.
A4,400 V
B7,621 V
C2,540 V
D1,467 V
#150📜 EE Pre-Board March 2018📘 PowerhouseEasy
Its primary purpose is to provide a ground source.
Azig-zag transformer
Bsectionalizer
Csurge arrester
Dtertiary transformer
#151📜 EE Pre-Board March 2018📘 PowerhouseMedium
A 20 KV/7.87 KV autotransformer has a secondary line current of 100 A. What is the current in the common winding?
A139.25 A
B100 A
C60.65 A
D39.35 A
#152📜 EE Pre-Board March 2018📘 PowerhouseEasy
Two single-phase, 25-kVA transformers are connected in an open-delta bank. Determine the maximum kW the bank can supply without overloading at 0.8 p.f. lagging.
A43.3
B34.64
C40
D50
#153📜 EE Pre-Board March 2018📘 PowerhouseEasy
Three 1:1 transformer units connected Δ/Y supply a 3-phase load from a 400 volt, 3-phase source. What is the line voltage on the load side?
A2,000v
B3,464v
C693v
D1,200v
#154📜 EE Pre-Board March 2018📘 PowerhouseEasy
The impedance of a 69 kV transformer is 14.28 Ω when referred to the primary. The transformer is a 10-MVA unit. What is the percent impedance of the transformer?
A4
B6.2
C3
D4.5
#155📜 EE Pre-Board August 2018📘 PowerhouseEasy
In transformers, the
Ahigh tension winding is used near the core
Bhigh tension winding is used away from the core
Clow tension winding is used near the core
Dlow tension winding is used away from the core
#156📜 EE Pre-Board August 2018📘 PowerhouseEasy
The overload kVA of each transformer of an open-delta bank is 11.56 kVA. If each transformer is rated 37.5 kVA, what is the kVA of the balanced 3Φ load?
A70
B80
C85
D90
#157📜 EE Pre-Board August 2018📘 PowerhouseEasy
A 7.5 MVA, 69/13.8 kV, 3-phase transformer has 8% impedance. What is the per unit impedance on a 10 MVA base?
A0.24
B0.106
C0.06
D0.096
#158📜 EE Pre-Board August 2018📘 PowerhouseEasy
Open circuit test on transformer is conducted to determine
Ahysteresis loss
Bcopper loss
Ccore loss
Deddy current loss
#159📜 EE Pre-Board August 2018📘 PowerhouseMedium
A transformer is rated 10kVA, 440/110V and 60 Hz when operated as conventional 2 winding transformer. This transformer is to be used as 550/440 V step-down autotransformer in a distribution system. What is the new kVA rating of the transformer in this manner?
A20
B10
C37.5
D50
#160📜 EE Pre-Board August 2018📘 PowerhouseEasy
What is the maximum flux in mWb of a transformer with 200 primary turns when connected to a 60 Hz, 200 V supply?
A10.35
B6.25
C50.5
D3.75

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