1) A transformer is
A. Steps up or down dc voltagesB. Changes ac to dc
C. Steps up or down ac voltages
D. Changes dc to ac
Answer: C
Explanation:
A transformer is an electrical device that uses the principle of electromagnetic induction to transfer energy from one electric circuit to another. It is designed to either increase or decrease AC voltage between the circuits while maintaining the frequency of the current.
2) The primary winding of a transformer has a 120 V ac supply. What is the value of secondary voltage if the turn ratio is 10?
A. 120 V
B. 12 V
C. 12000 V
D. 1200 V
Answer: D
Explanation:
Given,
N2/N1 = 10
V1 = 120
As we know,
V2/V1 = N2/N1
V2/120 = 10
V2 = 120*10
V2 = 1200 V
3) Power transformers are designed to have maximum efficiency at
A. No-load
B. 60 % load
C. 80 % load
D. Full load
Answer: D
4) If the supply frequency (f) of a transformer decreases, the effect of frequency on the transformer's secondary output voltage?
A. Remain the same
B. Decreases
C. Increases
D. All of these
Answer: A
5) During the open circuit test of a transformer
A. The secondary is supplied rated KVA.
B. Primary is supplied with no-load current.
C. Primary is supplied current at high voltage.
D. Primary is supplied rated voltage.
Answer: D
6) Lamination of the transformer core is made up of
A. Aluminum
B. Iron
C. Steel
D. Silicon steel
Answer: D
8) Transformer core are laminated in order to
A. Reduce copper loss
B. Minimize eddy current loss
C. Reduce eddy current and hysteresis loss
D. Reduce hysteresis loss
Answer: B
9) A transformer has a primary coil with 1600 loops and a secondary coil with 1200 loops. If the current in the primary coil is 6 Ampere, then what is the current in the secondary coil of a transformer.
A. 78 Ampere
B. 98 Ampere
C. 68 Ampere
D. 58 Ampere
Answer: B
Explanation:
Given,
Primary coil (Np) = 1600 loops
Secondary coil (Ns) = 1200 loops
The current in the primary coil (Ip) = 6 Ampere
Is =?
As we know,
Is/Ip = Np/Ns
The current in the secondary coil is
Is/6 = 1600/1200
Is/6 = 1.33
Is = 1.33 * 6
Is = 7.98 Ampere
10) The short circuit test in the transformer is performed on
A. High voltage side
B. light voltage side
C. Both
D. Either option a or b.
Answer: A
11) The secondary voltage is 440 Volt, and primary voltage is 220 Volt, then a comparison of the secondary coil and primary coil is
A. 4/1
B. 5/2
C. 2/1
D. 7/5
Answer: C
Explanation:
Given
Secondary voltage (Vs) = 440 Volt
Primary voltage (Vp) = 220 Volt
Then,
Ns/Np
As we know,
Vs/Vp = Ns/Np
440/220 = Ns/Np
44/22 = Ns/Np
2/1 = Ns/Np
12) Which test determines the efficiency of two identical transformers under load conditions?
A. Low voltage test
B. Full - load test
C. Back-to-Back (Sumpner's Test)
D. Open circuit test.
Answer: C
13) The transformer ratings are expressed in terms of
A. KW (Kilo-Watt)
B. Volts
C. KVAR (Kilo-Volt-Ampere-Reactive)
D. KVA (Kilo-Volt-Ampere)
Answer: D
14) A transformer has 6 windings in its primary core and 3 in its secondary coil. If the primary voltage is 440 V, find the secondary voltage.
A. 175 V
B. 185 V
C. 155 V
D. 165 V
Answer: D
Explanation: As we know, electric power is the same in both the coils of the transformer, so that the given relationship must be true
N1/N2 = V1/V2 = I2/I1
In the given question, we only need the number of turns (n) and voltage (V)
N1/N2 = V1/V2
Rearranging the above equation, we get,
V2 = V1N2/N1
Given,
V1 = 440, N1 = 6 Turns, N2 = 3 turns
V2 = V1N2/N1 = (440 V) (3 turns)/ (8 turns)
= 165 V
15) Oil is provided in an oil-filled transformer for
A. Lubrication
B. Cooling
C. Insulation
D. Both cooling and Insulation
Answer: D.
16) A Buchholz relay can be installed on
A. Oil cooled transformers
B. Autotransformers
C. Welding transformers
D. Air-cooled transformers
Answer: A
17) The noise of the transformer primarily due to
A. Mechanical vibration
B. Cooling fan
C. Magnetostriction in an iron core
D. All of the above
Answer: C
18) If a transformer is connected to a direct current supply, what happened?
A. Damage the transformer
B. No effect
C. Operate with low frequency
D. Operate with high frequency
Answer: A
19) Cruciform shape is used in the transformer core to
A. Reduce core reluctance
B. Reduce core loss
C. Reduce copper winding
D. All of the above
Answer: D
20) Which of the following does not change in an ordinary transformer?
A. Current
B. Frequency
C. Voltage
D. All of the above
Answer: B
21) The dielectric strength of transformer oil is expected to be
A. 3 kV
B. 33 kV
C. 330 kV
D. 100 kV
Answer: B
22) In the transformer, the function of a conservator is to
A. Protect the transformer form damage when oil expands due to heating.
B. It provides air for cooling the transformer.
C. It provided colling oil to transformer when transformer needed.
D. None of the above
Answer: A
23) The efficiency of a transformer is maximum when
A. Eddy current loss = iron loss
B. Hysteresis loss = copper loss.
C. Eddy current loss = hysteresis loss
D. Iron loss = Copper loss.
Answer: D
24) Which winding in a transformer has a greater number of turns
A. Constant voltage winding
B. Low voltage winding
C. Secondary winding
D. High voltage winding
Answer: D
25) In a transformer, tappings are usually provided.
A. High voltage side
B. Low voltage side
C. Primary side
D. Both option a and b
Answer: D
26) The highest voltage for transmitting electrical power in India is
A. 132 kV
B. 400 kV
C. 33 kV
D. 66 kV
Answer: B
27) The purpose of a breather in a transformer to
A. Filter the transformer oil
B. Provide cold air in the transformer
C. Absorb moisture of air during breathing
D. None of the above
Answer: C
28) The necessary condition for the parallel operation of two single-phase transformers is that they must have the same.
A. Turn Ratio
B. Polarity
C. KVA Rating
D. Both option a & b
Answer: D
29) The primary purpose of performing a short circuit test in a transformer is to measure its
A. Core loss
B. Iron loss
C. Insulation loss
D. Copper loss
Answer: D
30) The flashpoint of transformer oil must be greater than
A. 100 degree
B. 125 degree
C. 140 degree
D. 160 degree
Answer: C
- Delta connection and Star connection: In a Delta connection, each winding is connected to two other windings, forming a loop, and the line voltage equals the phase voltage. In a Star (or Wye) connection, one end of each winding is connected to a common point (the neutral), and the line voltage is √3 times the phase voltage. The insulation requirements depend on the voltage levels rather than the connection scheme.
- Important Points:
- Neutral connection: The neutral wire in a three-phase system, usually found in a Star connection, is intended to carry any unbalanced current. In most scenarios, it operates at a relatively low voltage, so the insulation requirements might not be as high as for the phase conductors. However, it is essential to follow the specific regulations and guidelines for the particular electrical system.
- Star connection: As mentioned above, the Star connection involves a neutral point. Each phase is insulated for the phase voltage.
- Delta connection: In the Delta connection, each winding end connects to another winding start, forming a closed loop. Each winding or phase must be insulated for the full line voltage.
- So, more insulation is typically required for the Delta connection because the full line voltage is across each winding. In a Star connection, each winding only has to withstand the phase voltage, which is the line voltage divided by √3. Hence, Delta connections require more insulation than Star connections.
2) The primary winding of a transformer has a 120 V ac supply. What is the value of secondary voltage if the turn ratio is 10?
A. 120 V
B. 12 V
C. 12000 V
D. 1200 V
Answer: D
Explanation:
Given,
N2/N1 = 10
V1 = 120
As we know,
V2/V1 = N2/N1
V2/120 = 10
V2 = 120*10
V2 = 1200 V
3) Power transformers are designed to have maximum efficiency at
A. No-load
B. 60 % load
C. 80 % load
D. Full load
Answer: D
4) If the supply frequency (f) of a transformer decreases, the effect of frequency on the transformer's secondary output voltage?
A. Remain the same
B. Decreases
C. Increases
D. All of these
Answer: A
5) During the open circuit test of a transformer
A. The secondary is supplied rated KVA.
B. Primary is supplied with no-load current.
C. Primary is supplied current at high voltage.
D. Primary is supplied rated voltage.
Answer: D
6) Lamination of the transformer core is made up of
A. Aluminum
B. Iron
C. Steel
D. Silicon steel
Answer: D
8) Transformer core are laminated in order to
A. Reduce copper loss
B. Minimize eddy current loss
C. Reduce eddy current and hysteresis loss
D. Reduce hysteresis loss
Answer: B
9) A transformer has a primary coil with 1600 loops and a secondary coil with 1200 loops. If the current in the primary coil is 6 Ampere, then what is the current in the secondary coil of a transformer.
A. 78 Ampere
B. 98 Ampere
C. 68 Ampere
D. 58 Ampere
Answer: B
Explanation:
Given,
Primary coil (Np) = 1600 loops
Secondary coil (Ns) = 1200 loops
The current in the primary coil (Ip) = 6 Ampere
Is =?
As we know,
Is/Ip = Np/Ns
The current in the secondary coil is
Is/6 = 1600/1200
Is/6 = 1.33
Is = 1.33 * 6
Is = 7.98 Ampere
10) The short circuit test in the transformer is performed on
A. High voltage side
B. light voltage side
C. Both
D. Either option a or b.
Answer: A
11) The secondary voltage is 440 Volt, and primary voltage is 220 Volt, then a comparison of the secondary coil and primary coil is
A. 4/1
B. 5/2
C. 2/1
D. 7/5
Answer: C
Explanation:
Given
Secondary voltage (Vs) = 440 Volt
Primary voltage (Vp) = 220 Volt
Then,
Ns/Np
As we know,
Vs/Vp = Ns/Np
440/220 = Ns/Np
44/22 = Ns/Np
2/1 = Ns/Np
12) Which test determines the efficiency of two identical transformers under load conditions?
A. Low voltage test
B. Full - load test
C. Back-to-Back (Sumpner's Test)
D. Open circuit test.
Answer: C
13) The transformer ratings are expressed in terms of
A. KW (Kilo-Watt)
B. Volts
C. KVAR (Kilo-Volt-Ampere-Reactive)
D. KVA (Kilo-Volt-Ampere)
Answer: D
14) A transformer has 6 windings in its primary core and 3 in its secondary coil. If the primary voltage is 440 V, find the secondary voltage.
A. 175 V
B. 185 V
C. 155 V
D. 165 V
Answer: D
Explanation: As we know, electric power is the same in both the coils of the transformer, so that the given relationship must be true
N1/N2 = V1/V2 = I2/I1
In the given question, we only need the number of turns (n) and voltage (V)
N1/N2 = V1/V2
Rearranging the above equation, we get,
V2 = V1N2/N1
Given,
V1 = 440, N1 = 6 Turns, N2 = 3 turns
V2 = V1N2/N1 = (440 V) (3 turns)/ (8 turns)
= 165 V
15) Oil is provided in an oil-filled transformer for
A. Lubrication
B. Cooling
C. Insulation
D. Both cooling and Insulation
Answer: D.
16) A Buchholz relay can be installed on
A. Oil cooled transformers
B. Autotransformers
C. Welding transformers
D. Air-cooled transformers
Answer: A
17) The noise of the transformer primarily due to
A. Mechanical vibration
B. Cooling fan
C. Magnetostriction in an iron core
D. All of the above
Answer: C
18) If a transformer is connected to a direct current supply, what happened?
A. Damage the transformer
B. No effect
C. Operate with low frequency
D. Operate with high frequency
Answer: A
19) Cruciform shape is used in the transformer core to
A. Reduce core reluctance
B. Reduce core loss
C. Reduce copper winding
D. All of the above
Answer: D
20) Which of the following does not change in an ordinary transformer?
A. Current
B. Frequency
C. Voltage
D. All of the above
Answer: B
21) The dielectric strength of transformer oil is expected to be
A. 3 kV
B. 33 kV
C. 330 kV
D. 100 kV
Answer: B
22) In the transformer, the function of a conservator is to
A. Protect the transformer form damage when oil expands due to heating.
B. It provides air for cooling the transformer.
C. It provided colling oil to transformer when transformer needed.
D. None of the above
Answer: A
23) The efficiency of a transformer is maximum when
A. Eddy current loss = iron loss
B. Hysteresis loss = copper loss.
C. Eddy current loss = hysteresis loss
D. Iron loss = Copper loss.
Answer: D
24) Which winding in a transformer has a greater number of turns
A. Constant voltage winding
B. Low voltage winding
C. Secondary winding
D. High voltage winding
Answer: D
25) In a transformer, tappings are usually provided.
A. High voltage side
B. Low voltage side
C. Primary side
D. Both option a and b
Answer: D
26) The highest voltage for transmitting electrical power in India is
A. 132 kV
B. 400 kV
C. 33 kV
D. 66 kV
Answer: B
27) The purpose of a breather in a transformer to
A. Filter the transformer oil
B. Provide cold air in the transformer
C. Absorb moisture of air during breathing
D. None of the above
Answer: C
28) The necessary condition for the parallel operation of two single-phase transformers is that they must have the same.
A. Turn Ratio
B. Polarity
C. KVA Rating
D. Both option a & b
Answer: D
29) The primary purpose of performing a short circuit test in a transformer is to measure its
A. Core loss
B. Iron loss
C. Insulation loss
D. Copper loss
Answer: D
30) The flashpoint of transformer oil must be greater than
A. 100 degree
B. 125 degree
C. 140 degree
D. 160 degree
Answer: C
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