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.