Here are the top 50 interview questions and answers related to transformers for an electrical engineering viva:
Check now
1. What is a transformer?
Answer: A transformer is an electrical device used to change the voltage level in an alternating current (AC) circuit by using electromagnetic induction.
2. How does a transformer work?
Answer: A transformer works on the principle of electromagnetic induction, where an alternating current in the primary coil generates a magnetic field that induces a current in the secondary coil.
3. What are the main components of a transformer?
Answer: The main components of a transformer are the primary winding, secondary winding, core, and insulating materials.
4. What is the difference between a step-up and a step-down transformer?
Answer: A step-up transformer increases the voltage from primary to secondary winding, whereas a step-down transformer reduces the voltage from primary to secondary winding.
5. What is the principle behind transformer operation?
Answer: Transformers operate on the principle of electromagnetic induction. The alternating current in the primary winding generates a magnetic field, which induces a current in the secondary winding.
6. What is the role of the core in a transformer?
Answer: The core provides a path for the magnetic flux generated by the primary winding to link to the secondary winding, thereby increasing the efficiency of the transformer.
7. What are the types of transformer windings?
Answer: The two main types of transformer windings are primary and secondary windings. They can be wound in different configurations: concentric, layer winding, or spiral winding.
8. What is the difference between a core type and a shell type transformer?
Answer: In a core-type transformer, the windings surround the core, while in a shell-type transformer, the core surrounds the windings. Shell-type transformers have a better magnetic flux path.
9. What is the formula for the voltage ratio in a transformer?
Answer: The voltage ratio in a transformer is given by:
V1V2=N1N2\frac{V_1}{V_2} = \frac{N_1}{N_2}
Where V1V_1 and V2V_2 are the primary and secondary voltages, and N1N_1 and N2N_2 are the number of turns in the primary and secondary windings, respectively.
10. What is the efficiency of a transformer?
Answer: The efficiency of a transformer is the ratio of output power to input power, given by:
Efficiency=Output PowerInput Power×100\text{Efficiency} = \frac{\text{Output Power}}{\text{Input Power}} \times 100
It is typically high, above 95%.
11. What is a short-circuit test in transformers?
Answer: A short-circuit test is conducted to determine the equivalent impedance and losses in the transformer under full-load conditions by applying a reduced voltage to the primary and measuring the current.
12. What is an open-circuit test in transformers?
Answer: The open-circuit test is conducted on the transformer by applying rated voltage to the primary winding while the secondary winding is left open. This test helps determine core losses and magnetizing current.
13. What is the difference between primary and secondary voltage in a transformer?
Answer: The primary voltage is the input voltage supplied to the transformer, while the secondary voltage is the output voltage, which is either stepped up or stepped down depending on the winding ratio.
14. What is the turn’s ratio in a transformer?
Answer: The turn’s ratio is the ratio of the number of turns in the primary winding to the number of turns in the secondary winding. It determines the voltage transformation.
15. What is the significance of frequency in transformer operation?
Answer: The operating frequency of the input AC voltage affects the size and design of the transformer. Higher frequencies generally lead to smaller transformers, while lower frequencies require larger cores to handle the flux.
16. What is the role of insulating oil in transformers?
Answer: Insulating oil serves to insulate the windings and core, cooling the transformer by dissipating heat, and helps in preventing corona discharge and oxidation of the components.
17. What are the losses in a transformer?
Answer: The two main losses in a transformer are core losses (hysteresis and eddy current losses) and copper losses (I²R losses in the windings).
18. What is the purpose of a tap changer in transformers?
Answer: A tap changer is used to adjust the transformer’s output voltage by varying the number of turns in the primary winding, helping to maintain a constant secondary voltage under varying load conditions.
19. What is the no-load current in a transformer?
Answer: The no-load current is the current drawn by the transformer’s primary winding when no load is connected to the secondary side. It is responsible for magnetizing the core.
20. What is a transformer’s voltage regulation?
Answer: Voltage regulation refers to the change in secondary voltage as the load on the transformer varies from no-load to full-load conditions. A good transformer should have minimal voltage regulation.
21. What are the applications of transformers?
Answer: Transformers are used in power distribution, voltage conversion in electrical grids, electrical isolation, impedance matching, and in devices like welders, power supplies, and audio equipment.
22. What is a delta-wye transformer connection?
Answer: A delta-wye connection is a type of three-phase transformer winding where one side of the transformer is connected in a delta configuration and the other in a wye (star) configuration.
23. What is meant by the primary and secondary winding ratings?
Answer: The primary winding rating refers to the voltage and current values the primary winding is designed to handle, while the secondary winding rating refers to the corresponding voltage and current the secondary can deliver.
24. What is a transformer’s impedance?
Answer: Transformer impedance is the opposition to current flow in the windings, consisting of both resistive and inductive components, affecting both the voltage drop and current under load.
25. What is the primary cause of transformer overheating?
Answer: Overheating in transformers is typically caused by excessive load, poor cooling, insufficient oil circulation, or inadequate ventilation, leading to increased core and copper losses.
26. What is the importance of the transformer core material?
Answer: The core material, typically made of laminated silicon steel, reduces eddy current losses and provides high magnetic permeability, which enhances transformer efficiency.
27. What is a transformer fault?
Answer: A transformer fault is an abnormal condition, such as a short circuit, overload, or insulation failure, that affects its normal operation and can cause damage.
28. What is the working principle of a three-phase transformer?
Answer: A three-phase transformer operates on the same principle as a single-phase transformer, but it uses three separate sets of windings, providing three-phase voltage output.
29. What is the no-load loss in a transformer?
Answer: No-load loss refers to the core losses (hysteresis and eddy currents) in the transformer when it is energized but not supplying any load current.
30. What is the effect of harmonic distortion on a transformer?
Answer: Harmonics cause additional heating, increased losses, and premature aging of transformer insulation. Transformers are designed to minimize harmonic effects.
31. What is a transformer’s fault current?
Answer: Fault current refers to the current that flows through the transformer’s windings when a short circuit or ground fault occurs.
If you are looking for more details, kindly visit Tianya.
32. What is the difference between oil-cooled and air-cooled transformers?
Answer: Oil-cooled transformers use oil for insulation and cooling, whereas air-cooled transformers rely on air flow to dissipate heat. Oil-cooled transformers are more suitable for high-power applications.
33. What is a ferroresonant transformer?
Answer: A ferroresonant transformer is designed to operate with a core that exhibits nonlinear magnetic behavior, stabilizing voltage and limiting overvoltage conditions.
34. What is an autotransformer?
Answer: An autotransformer is a type of transformer in which the primary and secondary windings share part of the same winding, leading to reduced size and cost for voltage transformation.
35. What is the role of a Buchholz relay?
Answer: A Buchholz relay is used in oil-filled transformers to detect faults like gas buildup or oil movement, providing early warning signs of internal issues.
36. What is a voltage drop in a transformer?
Answer: Voltage drop is the decrease in voltage from the primary side to the secondary side, which increases with the load and depends on the transformer’s impedance.
37. What is the purpose of a transformer’s breather?
Answer: A breather allows the transformer to breathe and vent air as the oil level fluctuates, preventing moisture from entering the transformer and maintaining insulation integrity.
38. What is the significance of dielectric strength in transformer oil?
Answer: Dielectric strength refers to the ability of transformer oil to resist electrical breakdown. A higher dielectric strength ensures better insulation and reliability in the transformer.
39. What is a transformer’s rating?
Answer: The rating of a transformer is defined by its capacity to handle voltage, current, and power under specific conditions, such as full-load and continuous operation.
40. What are the causes of transformer humming noise?
Answer: Transformer humming noise is caused by magnetostriction, the vibration of the transformer core under magnetic flux, and mechanical vibrations from the windings.
41. What is the difference between star-delta and delta-star transformer connections?
Answer: In star-delta, the primary winding is connected in a star configuration, and the secondary in a delta configuration. In delta-star, the primary is delta, and the secondary is star. These configurations are used to balance phase and voltage levels.
42. What is the purpose of a transformer’s cooling system?
Answer: A transformer’s cooling system ensures that the temperature remains within safe limits, preventing overheating and ensuring efficient operation.
43. How can a transformer be protected from overload?
Answer: Transformers are protected from overload by using fuses, circuit breakers, and thermal overload relays that disconnect the transformer when it exceeds the safe load limit.
44. What is transformer earthing?
Answer: Transformer earthing refers to connecting the transformer’s neutral point or body to the ground to ensure safety by providing a low-resistance path for fault currents.
45. What is a laminated core in a transformer?
Answer: A laminated core reduces eddy current losses by providing thin sheets of magnetic material stacked together with insulation, improving the transformer’s efficiency.
46. What is the function of the transformer’s tank?
Answer: The tank houses the transformer’s core and windings, provides structural support, and is filled with oil for cooling and insulation purposes.
47. What is a step-down transformer used for?
Answer: A step-down transformer is used to reduce the voltage from a higher level to a lower level, commonly used in power distribution systems.
48. What is a transformer’s rated capacity?
Answer: The rated capacity is the maximum amount of power (in VA or kVA) that a transformer can handle without exceeding its temperature limits or causing damage.
49. What is the role of a transformer in a power grid?
Answer: Transformers in a power grid are used to step up or step down the voltage to ensure efficient transmission over long distances and to provide the appropriate voltage for different loads.
50. What is the function of an OLTC (On-Load Tap Changer)?
Answer: An OLTC adjusts the transformer’s voltage under load conditions by changing the tap on the primary winding, helping to maintain a stable output voltage as the load changes.
These questions cover a broad spectrum of transformer-related concepts, ensuring you're well-prepared for transformer-related interviews and viva questions.
Regards
Transformers are often an afterthought. They don’t experience failures that often – but when they do, the costs can be devastating.
The biggest impact for an unplanned failure is the cost for your facility to not have power. How long can your facility be without power? For some manufacturers, every hour could cost you tens of thousands of dollars in lost business if they’re not up and running.
Other facilities may have emergency measures in place, such as generators, but many of those cost thousands per hour just in fuel costs. Not to mention the cost of a rush job to get a new transformer installed.
Call Us Today
Here are questions you need to have the answers to if you’re curious about the health of your transformer. Often, answers to these questions will guide you towards repairing or replacing your transformer. If that is the case, ELSCO is here for you.
1. How Old Is My Transformer?
Age is the biggest contributor to unplanned failures. A quality transformer should last for a while, but if you neglected to invest in a well-built transformer, you could be in for some trouble. Over time, dirt collection and heavy usage breaks your unit’s insulation down. If your transformer is over 20 years old, it’s worth considering its condition so that you’re not surprised by an unplanned failure.
2. Has My Transformer Ever Been Damaged?
If you’ve already had an outage, this indicates that your transformer could have an issue, or was possibly damaged due to immediate power surge when the power coming back on. Additionally, some incidents could occur without your knowing, and could have weakened your transformer in the process.
3. How Clean Is My Transformer?
Dirt, dust, and residue can reduce the life, safety and performance of your transformer. Overtime, that buildup can degrade the insulation and cause your transformer to run hotter than it needs to. This can shorten its life. If your working conditions are unusually dirty or your transformer isn’t in a secure housing, you may want to consider your replacement options soon.
4. How Well Was My Transformer Installed?
A poor install could make your transformer noisy, reduce its performance and longevity. If your transformer has any of the following issues, you may want to take a closer look at the state of your transformer:
– Bus bars are not directly connected to your facilities power unit (compare to flexible braided shunts between bus bars) – The electrical hookups were not properly cleaned after varnishing – Your transformer’s base is sitting directly on concrete or steel, with no rubber feet
5. Have I Increased My Capacity Since Installing My Transformer?
Transformers are built to handle a certain amount of power. If your unit is currently at capacity and you wish to add more power to it, you could push the unit beyond its potential and cause an unplanned failure.
6. When Was The Last Time My Transformer Had Maintenance Done?
Regular check-ups help to ensure that your unit is free of anything inhibiting its longevity, safety and performance. Have you performed any recent tests on the unit to detect any abnormal behavior?
7. What Is My Transformer’s Power Factor?
It might be hard to check your purchase order, but there’s a chance it’s on record somewhere. Typically the power factor won’t be on a purchase order, but should be on a test report. Either one from the manufacturer or one from acceptance testing by a certified electrical testing company. The power factor test measures the dryness of the transformer’s insulation. Although 1% is the legal limit for transformers, most transformers are at or near that level, indicating a lower quality transformer – meaning it has a shorter life and less-efficient performance. ELSCO dry-type transformers are consistently at or below .1 because of their high-quality manufacturing. The lower your score, the greater the safety, longevity and performance.
8. What Is My Plan If My Transformer Fails?
What if your unit were to go down today, unexpectedly? How long could your facility go without power? How much would it cost you each day your power was off? Unplanned failures could really cost you – how much money would you lose every hour if your power went down? Generators are an emergency option, but they are very expensive. Simple preventative measures can ensure that you don’t end up with a surprise failure.
If you can’t answer some of these questions, it’s time to give your transformer a little attention. ELSCO would be happy to discuss your transformer’s health, and help you devise a plan to avoid failure and keep your operation up and running.
The company is the world’s best Electrical Transformer supplier. We are your one-stop shop for all needs. Our staff are highly-specialized and will help you find the product you need.
Comments
All Comments (0)