### **Transformer Construction**
1. What is the primary function of a transformer?
a) Convert DC to AC
b) Change voltage levels
c) Generate power
d) Regulate current
**Answer: b)**
2. What is the most commonly used core material in transformers?
a) Aluminum
b) Copper
c) Silicon steel
d) Cast iron
**Answer: c)**
3. Why are transformer cores laminated?
a) To reduce eddy current losses
b) To reduce hysteresis losses
c) To improve cooling
d) To increase inductance
**Answer: a)**
---
### **Ideal and Practical Transformer**
4. In an ideal transformer, which losses are considered negligible?
a) Copper loss only
b) Iron loss only
c) Both copper and iron losses
d) Stray losses
**Answer: c)**
5. The efficiency of an ideal transformer is:
a) 50%
b) 90%
c) 100%
d) 75%
**Answer: c)**
---
### **Exact and Approximate Equivalent Circuits**
6. The equivalent circuit of a transformer is drawn to:
a) Calculate losses
b) Analyze transformer performance
c) Find exact power flow
d) Study winding resistance only
**Answer: b)**
7. In the approximate equivalent circuit of a transformer, which component is neglected?
a) Primary winding resistance
b) Secondary winding resistance
c) Magnetizing branch
d) Leakage reactance
**Answer: c)**
---
### **No Load and On Load Operation**
8. What is the power factor of a transformer on no load?
a) Unity
b) Lagging
c) Leading
d) Zero
**Answer: b)**
9. In a transformer, on-load operation causes:
a) No voltage drop
b) Voltage drop due to winding resistance and leakage reactance
c) Voltage rise
d) Constant voltage output
**Answer: b)**
---
### **Phasor Diagrams**
10. The phasor diagram of a transformer represents:
a) Energy losses
b) Voltage and current relationships
c) Efficiency variation
d) Core construction
**Answer: b)**
11. In a transformer under load, the angle between the primary voltage and magnetizing current is:
a) 0°
b) 90°
c) 180°
d) 45°
**Answer: b)**
---
### **Power and Energy Efficiency**
12. Transformer efficiency is maximum when:
a) Iron losses = copper losses
b) Load is half
c) Copper losses = hysteresis losses
d) Load is full
**Answer: a)**
13. A transformer’s efficiency at full load is typically:
a) 50%
b) 85%
c) 95%
d) 100%
**Answer: c)**
---
### **Voltage Regulation**
14. Voltage regulation of a transformer depends on:
a) Efficiency
b) Power factor of the load
c) Core material
d) Cooling system
**Answer: b)**
15. Voltage regulation of a transformer at unity power factor is:
a) Positive
b) Negative
c) Zero
d) Infinite
**Answer: c)**
---
### **Parallel Operation**
16. Parallel operation of transformers requires:
a) Same voltage ratio only
b) Same kVA rating
c) Same phase sequence and voltage ratio
d) Same cooling method
**Answer: c)**
17. Unequal load sharing during parallel operation of transformers occurs due to:
a) Different phase sequence
b) Different impedances
c) Voltage ratio mismatch
d) Core saturation
**Answer: b)**
---
### **Effect of Load on Power Factor**
18. At leading power factor, voltage regulation in a transformer is:
a) Negative
b) Positive
c) Zero
d) Infinite
**Answer: a)**
19. At lagging power factor, the voltage regulation of a transformer:
a) Decreases
b) Increases
c) Remains constant
d) Becomes zero
**Answer: b)**
---
### **Per Unit System**
20. Per unit system is used to:
a) Measure exact losses
b) Simplify calculations
c) Eliminate voltage regulation
d) Analyze core losses
**Answer: b)**
21. The base value of power in the per-unit system is usually:
a) Apparent power
b) Active power
c) Reactive power
d) Core loss
**Answer: a)**
---
### **Excitation Phenomenon in Transformers**
22. Magnetizing current in a transformer is:
a) Leading
b) Lagging
c) In phase with the applied voltage
d) Zero
**Answer: b)**
23. The phenomenon of over-fluxing in transformers occurs due to:
a) Overload
b) High excitation voltage
c) Core saturation
d) Low frequency
**Answer: b)**
---
### **Switching Transients**
24. Switching transients in a transformer are caused by:
a) Overheating
b) Rapid switching of load
c) Magnetic saturation
d) Excessive efficiency
**Answer: b)**
---
### **Auto Transformers**
25. An auto transformer has:
a) Two windings
b) A single winding
c) No windings
d) A separate core
**Answer: b)**
---
### **Variable Frequency Transformer**
26. A variable frequency transformer is used for:
a) AC to DC conversion
b) Varying power factor
c) Interconnecting grids of different frequencies
d) Energy storage
**Answer: c)**
---
### **Voltage and Current Transformers**
27. Voltage transformers are used for:
a) Measuring high currents
b) Measuring high voltages
c) Protection only
d) Energy conversion
**Answer: b)**
28. The secondary winding of a current transformer is always:
a) Open
b) Short-circuited
c) Connected in series
d) Connected in parallel
**Answer: b)**
---
### **Welding Transformers**
29. Welding transformers operate at:
a) High voltage and low current
b) High voltage and high current
c) Low voltage and high current
d) Low voltage and low current
**Answer: c)**
---
### **Pulse Transformer**
30. Pulse transformers are primarily used for:
a) High-frequency applications
b) Low-frequency applications
c) DC voltage regulation
d) Generating high voltages
**Answer: a)**
---
Let me know if you need more specific types of questions or explanations for any topic!
Here’s a list of potential **MCQs** based on the chapter "Three Phase Transformers":
---
### **Constructional Features of Three Phase Transformers**
1. A three-phase transformer is generally preferred over three single-phase transformers because:
a) It is more efficient and economical
b) It occupies more space
c) It has lower efficiency
d) It is easier to install
**Answer: a)**
2. The windings of a three-phase transformer are generally wound on:
a) Separate cores for each phase
b) A single three-legged core
c) Air-core structures
d) A laminated iron core
**Answer: b)**
3. Three-phase transformers typically have cores made of:
a) Aluminum
b) Laminated silicon steel
c) Cast iron
d) Brass
**Answer: b)**
---
### **Cooling Methodology**
4. The purpose of transformer oil is:
a) Insulation and cooling
b) Insulation only
c) Cooling only
d) Preventing corrosion
**Answer: a)**
5. The cooling method in large transformers is referred to as:
a) Air natural cooling (AN)
b) Oil natural air forced (ONAF)
c) Water cooling
d) Oil natural air natural (ONAN)
**Answer: d)**
6. Which cooling method is most suitable for large power transformers?
a) Air blast cooling
b) ONAN cooling
c) ONAF cooling
d) Dry cooling
**Answer: c)**
---
### **Standard and Special Transformer Connections**
7. In a delta-delta connection, the phase voltage is equal to:
a) Line voltage
b) Line voltage divided by √3
c) Line voltage multiplied by √3
d) Zero
**Answer: a)**
8. In a star-delta transformer connection, the secondary voltage is:
a) Equal to the primary voltage
b) 1/√3 of the primary voltage
c) √3 times the primary voltage
d) Independent of the primary voltage
**Answer: b)**
9. A Scott connection is used to:
a) Convert single-phase to three-phase power
b) Convert three-phase to single-phase power
c) Convert three-phase to two-phase power
d) Convert two-phase to three-phase power
**Answer: c)**
---
### **Phase Conversion**
10. A Scott transformer is used for:
a) 3-phase to 2-phase conversion
b) Single-phase to 3-phase conversion
c) Voltage regulation
d) Parallel operation
**Answer: a)**
11. What is the purpose of a zigzag transformer connection?
a) Phase conversion
b) Harmonic suppression
c) Voltage regulation
d) Load sharing
**Answer: b)**
---
### **Parallel Operation of Three-Phase Transformers**
12. Parallel operation of transformers requires:
a) Equal impedance, phase sequence, and voltage ratio
b) Equal frequency only
c) Identical cooling systems
d) Identical core materials
**Answer: a)**
13. Unequal load sharing during parallel operation of three-phase transformers is caused by:
a) Voltage mismatch
b) Frequency mismatch
c) Core saturation
d) Different transformer efficiencies
**Answer: a)**
---
### **Three-Winding Transformers and Equivalent Circuit**
14. The tertiary winding of a three-winding transformer is typically used for:
a) Voltage regulation
b) Reducing harmonics
c) Interconnecting systems
d) All of the above
**Answer: d)**
15. The equivalent circuit of a three-winding transformer is:
a) Similar to that of a single-phase transformer
b) A simplified version of three single-phase transformers
c) A complex circuit with multiple leakage reactances
d) A completely different model
**Answer: c)**
---
### **On Load Tap Changing of Transformers**
16. On-load tap changers (OLTC) are primarily used to:
a) Regulate load current
b) Regulate secondary voltage
c) Improve efficiency
d) Prevent harmonics
**Answer: b)**
17. On-load tap changers are placed:
a) On the primary winding
b) On the secondary winding
c) On the tertiary winding
d) Either primary or secondary winding
**Answer: d)**
18. The purpose of diverter switches in OLTC is to:
a) Reduce core losses
b) Bypass the load during tap changing
c) Minimize arcing during tap changing
d) Provide insulation
**Answer: c)**
---
### **Modern Trends in Transformers**
19. Which of the following is a modern advancement in transformers?
a) Oil-cooled transformers
b) Solid-state transformers
c) Air-core transformers
d) Core-less transformers
**Answer: b)**
20. The primary advantage of solid-state transformers is:
a) Lower cost
b) Compact size and efficiency
c) Simple construction
d) Easy cooling
**Answer: b)**
---
### **Type and Routine Tests**
21. Type tests of a transformer include:
a) Load test and impedance test
b) Short circuit and open circuit tests
c) Lightning impulse test and temperature rise test
d) Voltage ratio and polarity test
**Answer: c)**
22. Routine tests of a transformer include:
a) Efficiency test
b) Winding resistance and polarity test
c) Lightning impulse test
d) Temperature rise test
**Answer: b)**
23. Which test checks the ability of a transformer to withstand high voltage surges?
a) Open circuit test
b) Lightning impulse test
c) Short circuit test
d) Winding resistance test
**Answer: b)**
---
### **Standards**
24. Which standard is widely used for transformer testing?
a) IEEE C57
b) IEC 60076
c) NEMA MG1
d) ASTM D877
**Answer: b)**
25. The efficiency and performance of a transformer are specified according to:
a) ISO standards
b) IEC and IEEE standards
c) Local standards only
d) Manufacturer specifications
**Answer: b)**
---
Let me know if you need further assistance or more detailed questions!
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