Here are the top 50 interview questions and answers related to transformers for an electrical engineering viva:
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Answer: A transformer is an electrical device used to change the voltage level in an alternating current (AC) circuit by using electromagnetic induction.
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.
Answer: The main components of a transformer are the primary winding, secondary winding, core, and insulating materials.
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.
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.
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.
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.
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.
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.
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%.
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.
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.
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.
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.
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.
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.
Answer: The two main losses in a transformer are core losses (hysteresis and eddy current losses) and copper losses (I²R losses in the windings).
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.
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.
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.
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.
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.
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.
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.
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.
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Answer: The core material, typically made of laminated silicon steel, reduces eddy current losses and provides high magnetic permeability, which enhances transformer efficiency.
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.
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.
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.
Answer: Harmonics cause additional heating, increased losses, and premature aging of transformer insulation. Transformers are designed to minimize harmonic effects.
Answer: Fault current refers to the current that flows through the transformer’s windings when a short circuit or ground fault occurs.
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.
Answer: A ferroresonant transformer is designed to operate with a core that exhibits nonlinear magnetic behavior, stabilizing voltage and limiting overvoltage conditions.
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.
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.
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.
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.
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.
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.
Answer: Transformer humming noise is caused by magnetostriction, the vibration of the transformer core under magnetic flux, and mechanical vibrations from the windings.
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.
Answer: A transformer’s cooling system ensures that the temperature remains within safe limits, preventing overheating and ensuring efficient operation.
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.
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.
Answer: A laminated core reduces eddy current losses by providing thin sheets of magnetic material stacked together with insulation, improving the transformer’s efficiency.
Answer: The tank houses the transformer’s core and windings, provides structural support, and is filled with oil for cooling and insulation purposes.
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.
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.
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.
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.
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So, are you looking for a transformer manufacturer in Gujarat? Well, this can turn out to be a daunting task for you as there are a number of companies that are now engaged in manufacturing transformers. Thus, you need to select a reliable transformer manufacturer that can offer you quality products at the best possible prices. Obviously, you would be in need of a stable amount of power that provides current without interruption. Or if it turns out to be the case in which you’ve installed a transformer that isn’t operating and the company isn’t ready at all to fix the issue on time? Obviously, this will affect your productivity in a way you can’t imagine.
So as to make the right decision of purchasing the right transformer, it is vital that you pay much attention to the below-listed points before making any deal with transformer manufacturers in India.
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