Which of the following is a loss in a transformer?
A Core loss
B Copper loss
C Dielectric loss
D All of the above
Core losses (due to hysteresis and eddy currents) and copper losses (due to the resistance of the windings) are common losses in transformers. Dielectric losses can also occur in the insulating materials as well.
What is the main advantage of using a dry-type transformer?
A Higher efficiency than oil-filled transformers
B Reduced risk of fire
C Better cooling
D Lower cost
Dry-type transformers do not use oil for cooling, eliminating the risk of oil leakage and fire. They are ideal for use in indoor environments, especially in commercial and residential areas where fire safety is a concern.
What is the primary cause of inrush current when a transformer is energized?
A The voltage drop across the windings
B The magnetic flux in the core
C The short-circuit current
D The power factor of the load
Inrush current occurs when a transformer is first energized. This surge of current is caused by the magnetization of the core material, which requires a high initial current until the core becomes fully magnetized.
What is the purpose of an isolation transformer?
A To step down voltage
B To provide electrical isolation between the primary and secondary circuits
C To increase the current
D To regulate the voltage
An isolation transformer is used to isolate the secondary side from the primary side, preventing the transmission of electrical noise, surges, or faults between circuits. This is important for sensitive equipment or safety-critical applications.
What is the main advantage of using a three-phase transformer over a single-phase transformer?
A Higher efficiency in power distribution
B Lower voltage regulation
C Simpler design
D Lower cost
Three-phase transformers are more efficient for power transmission and distribution, especially over long distances. They provide continuous power and are capable of handling higher loads compared to single-phase transformers.
Which of the following is a key characteristic of an autotransformer?
A It uses separate windings for primary and secondary circuits
B It shares a common winding for both primary and secondary circuits
C It provides electrical isolation
D It is used exclusively for high-power applications
An autotransformer shares part of its winding for both the primary and secondary circuits, making it more efficient and compact than a traditional transformer. It is often used for voltage regulation.
Which of the following tests is typically used to measure the efficiency of a transformer under load?
A Short-circuit test
B Load test
C Open-circuit test
D Impedance test
The load test measures a transformer’s efficiency under actual working conditions when it is supplying power to a load. This test helps to assess how well the transformer handles real-world operating scenarios.
What is meant by the term “magnetizing current” in a transformer?
A The current required to magnetize the core of the transformer
B The current flowing in the secondary winding
C The current required to supply the load
D The current flowing through the transformer’s protective circuit
Magnetizing current is the small current that flows in the primary winding of a transformer when no load is connected. It is required to establish the magnetic field in the transformer’s core.
What is the typical frequency of AC supply used in transformers?
A 25 Hz
B 50 Hz or 60 Hz
C 100 Hz
D 200 Hz
Most transformers are designed to operate with AC supply frequencies of 50 Hz or 60 Hz, depending on the region. These are the standard frequencies for electrical power transmission and distribution.
What is the main purpose of a tap changer in a transformer?
A To change the core material
B To adjust the transformer’s turns ratio under load
C To measure the insulation resistance
D To cool the transformer
A tap changer allows the transformer to adjust its voltage output by changing the turns ratio without disconnecting from the circuit. It helps regulate voltage during variations in load to maintain a stable supply.
What is the primary function of a transformer?
A To store energy
B To convert AC to DC
C To change voltage levels in an alternating current (AC) system
D To store electrical energy
The primary function of a transformer is to change voltage levels in an alternating current (AC) system. It can either step up (increase) or step down (decrease) the voltage depending on the turns ratio of the primary and secondary windings.
What type of transformer is most commonly used in power generation plants to increase the voltage for transmission?
A Step-up transformer
B Step-down transformer
C Distribution transformer
D Isolation transformer
Step-up transformers are commonly used in power plants to increase the voltage before it is transmitted over long distances. This helps to reduce energy losses during transmission.
What is the primary cause of energy losses in a transformer?
A Magnetic losses
B Copper losses and core losses
C Voltage regulation
D Cooling inefficiency
Energy losses in a transformer primarily occur due to copper losses (caused by the resistance of the windings) and core losses (caused by hysteresis and eddy currents in the core material).
Which of the following is a core material used in transformer construction?
A Copper
B Aluminium
C Silicon steel
D Iron oxide
Silicon steel is commonly used as the core material in transformers due to its high magnetic permeability and low hysteresis loss, which enhances transformer efficiency.
What is the purpose of a transformer’s cooling system?
A To store excess energy
B To keep the transformer at a safe operating temperature
C To prevent voltage regulation issues
D To reduce electrical losses
The cooling system of a transformer is essential for dissipating the heat generated during operation. If the transformer overheats, it can lead to insulation breakdown, reduced efficiency, and even failure. Cooling methods include oil cooling and air cooling.
What is a characteristic of a dry-type transformer?
A It uses oil for cooling
B It uses air for cooling and does not require oil
C It operates at lower voltages
D It is used only for high-voltage applications
Dry-type transformers use air as a cooling medium and do not use oil. They are typically used in applications where fire safety is a concern or in indoor settings.
What does the turns ratio in a transformer refer to?
A The ratio of the current in the primary and secondary windings
B The ratio of the number of turns in the primary winding to the number of turns in the secondary winding
C The ratio of the transformer’s efficiency
D The ratio of copper losses to core losses
The turns ratio in a transformer determines the relationship between the primary and secondary voltages. It is the ratio of the number of turns in the primary winding to the number of turns in the secondary winding.
What is the key difference between a single-phase and a three-phase transformer?
A The number of windings used
B The number of phases the transformer is designed to handle
C The size of the core
D The voltage rating
A single-phase transformer handles one phase of AC power, while a three-phase transformer handles three-phase AC power, which is typically used in industrial and large-scale power distribution systems.
What happens if a transformer is overloaded?
A The voltage decreases
B The transformer becomes more efficient
C The transformer may overheat and fail
D The current is reduced
When a transformer is overloaded, it draws more current than it is designed to handle. This can cause excessive heating, which may damage the insulation and lead to failure if the overload is not addressed.
What is the purpose of a tap changer in a transformer?
A To measure the load current
B To change the turns ratio for voltage regulation
C To maintain the core temperature
D To prevent transformer damage due to short circuits
A tap changer allows the voltage to be adjusted by changing the number of turns in the transformer winding, thus regulating the output voltage as the load varies. This helps maintain a stable output despite fluctuations in the load.
What is the typical efficiency range of modern transformers?
A 50-60%
B 70-80%
C 90-98%
D 100%
Modern transformers are highly efficient, with typical efficiencies ranging from 90% to 98%. The design and materials used, such as high-quality core materials and low-resistance windings, contribute to these high efficiency levels.
What type of transformer is most commonly used in residential power distribution?
A Step-up transformer
B Power transformer
C Distribution transformer
D Isolation transformer
Distribution transformers are used to step down the voltage from transmission levels to the lower voltages required for residential, commercial, and industrial use.
What is an earthing transformer used for?
A To isolate the primary and secondary circuits
B To provide a neutral point in a system
C To increase voltage
D To reduce harmonic distortion
An earthing transformer provides a neutral point in systems where one is not available, such as delta-connected systems. It helps in grounding the system, improving safety, and preventing voltage fluctuations.
What is meant by “voltage regulation” in a transformer?
A The ability to adjust the voltage in the transformer
B The ability to maintain a constant voltage despite changes in load
C The efficiency of the transformer
D The method of reducing energy losses
Voltage regulation refers to a transformer’s ability to maintain a stable output voltage as the load on the transformer changes. A good voltage regulator minimizes the fluctuations in output voltage, ensuring that connected equipment operates safely.
What does “inrush current” refer to in a transformer?
A The current that flows during normal operation
B The sudden surge of current when the transformer is energized
C The current used for cooling
D The current required to magnetize the core
Inrush current occurs when a transformer is first energized. It is a temporary surge of current that can be several times higher than the rated current and is caused by the magnetization of the core.
Which of the following is a loss in a transformer?
A Core loss
B Copper loss
C Dielectric loss
D All of the above
Transformers experience several types of losses: core loss (due to hysteresis and eddy currents in the core), copper loss (due to the resistance of the windings), and dielectric loss (in the insulation materials). These losses contribute to the inefficiency of the transformer.
What type of cooling method is used in large, high-power transformers?
A Air cooling
B Water cooling
C Oil cooling
D Liquid nitrogen cooling
Oil cooling is commonly used in large transformers because oil has excellent heat dissipation properties. It helps to remove heat generated by the transformer’s operation and also provides insulation between the windings.
What is a common method of testing a transformer’s insulation resistance?
A Load test
B Short-circuit test
C Megger test (insulation resistance test)
D Open-circuit test
The Megger test, or insulation resistance test, is used to measure the resistance of the transformer’s insulation. This test helps ensure that the insulation is in good condition and prevents electrical faults due to breakdowns.
What is the role of a transformer’s secondary winding?
A To generate magnetic flux
B To transfer power to the load
C To supply current to the primary winding
D To adjust the voltage
The secondary winding of a transformer receives induced voltage from the primary winding and supplies power to the connected load. The voltage and current in the secondary winding depend on the turns ratio and the load characteristics.
What is a parallel operation of transformers used for?
A To share the load between multiple transformers
B To increase the transformer’s efficiency
C To reduce harmonic distortion
D To convert AC to DC
Parallel operation of transformers involves connecting two or more transformers together to share the load. This helps increase capacity, improve efficiency, and ensure reliability in the power supply.
What does a step-down transformer do?
A Increases voltage
B Reduces voltage
C Increases current
D Reduces current
A step-down transformer reduces the voltage from a higher level to a lower level. It has more turns in the primary winding than in the secondary winding, which causes the voltage to decrease while maintaining the current capacity.
What is the main function of an autotransformer?
A To convert AC to DC
B To share a common winding between primary and secondary circuits
C To isolate circuits
D To provide electrical protection
An autotransformer uses a single winding that acts as both the primary and secondary. This makes it more efficient than a conventional transformer for voltage regulation because the voltage transformation happens using part of the same winding.
Which type of transformer is most commonly used for residential applications?
A Power transformer
B Distribution transformer
C Isolation transformer
D Autotransformer
Distribution transformers are used to step down the voltage from high transmission levels to lower levels suitable for residential and commercial use. They are found in power distribution systems.
What is the main characteristic of dry-type transformers?
A They use oil as a coolant
B They do not use liquid for cooling
C They are designed for high-voltage applications only
D They require external cooling
Dry-type transformers use air for cooling instead of oil. They are typically used in environments where safety is a concern, such as in indoor settings, and are more environmentally friendly compared to oil-filled transformers.
What is the primary use of an oil-filled transformer?
A To store electrical energy
B To provide insulation and cooling
C To step up voltage
D To step down voltage
Oil-filled transformers use oil both as an insulator and as a coolant. The oil prevents electrical arcing between windings and also helps to dissipate heat generated during operation, keeping it at a safe temperature.
What is inrush current in a transformer?
A The current that flows through the secondary winding under load
B The surge of current when the transformer is first energized
C The current required to maintain the magnetic field
D The current used to heat the core
Inrush current is a brief surge of high current that occurs when a transformer is first connected to the electrical supply. This surge can be many times higher than the normal operating current, and it is typically caused by the core magnetization process.
What is the purpose of a transformer’s core?
A To increase voltage
B To guide the magnetic flux
C To insulate the windings
D To store electrical energy
The core of a transformer serves as a path for the magnetic flux generated by the primary winding. The core enhances the efficiency of electromagnetic induction between the windings and reduces energy losses.
What type of transformer is used to isolate electrical circuits from each other?
A Step-up transformer
B Isolation transformer
C Distribution transformer
D Autotransformer
An isolation transformer is designed to electrically isolate the primary circuit from the secondary circuit. It provides safety by preventing direct electrical connection between circuits, protecting sensitive equipment from power spikes and faults.
What does the “magnetizing current” in a transformer refer to?
A The current required to power the load
B The current required to magnetize the core of the transformer
C The current flowing in the secondary winding
D The current caused by an overload
Magnetizing current is the small current drawn by the primary winding of a transformer when it is under no load. This current is required to establish the magnetic flux in the core, which is essential for the operation of the transformer.
Which test is used to measure the core loss in a transformer?
A Short-circuit test
B Open-circuit test
C Load test
D Impedance test
The open-circuit test is used to measure the core losses of a transformer. In this test, the secondary winding is open, and the primary winding is supplied with the rated voltage, measuring the losses due to the magnetic properties of the core.
What is the purpose of a transformer’s core?
A To increase voltage
B To guide the magnetic flux
C To insulate the windings
D To store electrical energy
The core of a transformer serves as a path for the magnetic flux generated by the primary winding. The core enhances the efficiency of electromagnetic induction between the windings and reduces energy losses.
What type of transformer is used to isolate electrical circuits from each other?
A Step-up transformer
B Isolation transformer
C Distribution transformer
D Autotransformer
An isolation transformer is designed to electrically isolate the primary circuit from the secondary circuit. It provides safety by preventing direct electrical connection between circuits, protecting sensitive equipment from power spikes and faults.
What does the “magnetizing current” in a transformer refer to?
A The current required to power the load
B The current required to magnetize the core of the transformer
C The current flowing in the secondary winding
D The current caused by an overload
Magnetizing current is the small current drawn by the primary winding of a transformer when it is under no load. This current is required to establish the magnetic flux in the core, which is essential for the operation of the transformer.
Which test is used to measure the core loss in a transformer?
A Short-circuit test
B Open-circuit test
C Load test
D Impedance test
The open-circuit test is used to measure the core losses of a transformer. In this test, the secondary winding is open, and the primary winding is supplied with the rated voltage, measuring the losses due to the magnetic properties of the core.
What is the purpose of a transformer’s core?
A To increase voltage
B To guide the magnetic flux
C To insulate the windings
D To store electrical energy
The core of a transformer serves as a path for the magnetic flux generated by the primary winding. The core enhances the efficiency of electromagnetic induction between the windings and reduces energy losses.
What type of transformer is used to isolate electrical circuits from each other?
A Step-up transformer
B Isolation transformer
C Distribution transformer
D Autotransformer
An isolation transformer is designed to electrically isolate the primary circuit from the secondary circuit. It provides safety by preventing direct electrical connection between circuits, protecting sensitive equipment from power spikes and faults.
What does the “magnetizing current” in a transformer refer to?
A The current required to power the load
B The current required to magnetize the core of the transformer
C The current flowing in the secondary winding
D The current caused by an overload
Magnetizing current is the small current drawn by the primary winding of a transformer when it is under no load. This current is required to establish the magnetic flux in the core, which is essential for the operation of the transformer.
Which test is used to measure the core loss in a transformer?
A Short-circuit test
B Open-circuit test
C Load test
D Impedance test
The open-circuit test is used to measure the core losses of a transformer. In this test, the secondary winding is open, and the primary winding is supplied with the rated voltage, measuring the losses due to the magnetic properties of the core.
What is the main advantage of using dry-type transformers?
A Higher voltage ratings
B Reduced fire risk
C Better cooling performance
D Higher efficiency
Dry-type transformers do not use oil or other flammable liquids, making them safer to use in fire-sensitive environments. They rely on air cooling, which reduces the risk of fire caused by leaks or accidents.
What is the most common method of cooling used in large transformers?
A Air cooling
B Oil cooling
C Liquid nitrogen cooling
D Water cooling
Oil cooling is the most common method used for large transformers. The oil serves both as an insulator and a coolant, removing heat generated by the transformer and preventing overheating.