Which of the following is a primary function of a step-down transformer?
A To increase the voltage
B To decrease the voltage
C To reduce the current
D To regulate the frequency
A step-down transformer is used to reduce the voltage from the primary side to a lower level on the secondary side. The number of turns in the secondary winding is fewer than that in the primary winding, which reduces the voltage while maintaining the same frequency.
What does a transformer’s impedance mainly consist of?
A Resistance and capacitance
B Resistance and reactance
C Resistance and voltage
D Voltage and current
The impedance of a transformer is the total opposition to alternating current, which includes both resistance (the real part) and reactance (the imaginary part). Reactance is caused by inductance and capacitance within the transformer windings, while resistance is the opposition to current flow due to the material of the windings.
Which type of transformer is used to maintain voltage stability and prevent power loss in long-distance transmission?
A Step-up transformer
B Step-down transformer
C Isolation transformer
D Autotransformer
Step-up transformers are used in power transmission to increase the voltage and decrease the current, which reduces power losses during long-distance transmission. Higher voltage allows for the use of thinner conductors, reducing energy losses due to the resistance of the transmission line.
What is the primary purpose of the cooling system in oil-filled transformers?
A To increase the insulation resistance
B To prevent the transformer from overheating
C To enhance the transformer’s magnetic field
D To regulate the voltage
In oil-filled transformers, the oil serves as both an insulating material and a coolant. It absorbs the heat generated during the transformer’s operation and dissipates it into the surrounding environment. This prevents the transformer from overheating and ensures efficient operation.
Which of the following is the best insulating material for transformers?
A Wood
B Oil
C Air
D Water
Oil is commonly used as an insulating material in transformers because it has excellent dielectric properties and can efficiently dissipate heat. This makes it ideal for maintaining the electrical insulation and cooling of the transformer during operation.
What type of transformer is typically used to convert high-voltage AC to low-voltage AC for household appliances?
A Distribution transformer
B Isolation transformer
C Power transformer
D Autotransformer
A distribution transformer is commonly used to step down high voltage from power lines to the low voltage required for household appliances. These transformers are typically found in electrical substations and on utility poles.
Which test is used to evaluate the copper losses in a transformer?
A Open-circuit test
B Short-circuit test
C Load test
D Insulation test
The short-circuit test is performed to determine the copper losses in a transformer. During this test, the secondary winding is shorted, and the primary winding is supplied with a reduced voltage. The power loss measured during this test corresponds to the copper losses due to the resistance of the windings.
What is the purpose of an earthing transformer?
A To increase the voltage
B To provide a neutral point in an electrical system
C To step down the voltage
D To protect the transformer from overcurrent
An earthing transformer is used in systems that lack a neutral point, such as a delta-connected system. It creates a neutral point to safely ground the system, preventing dangerous floating voltages and ensuring safe operation.
Which type of transformer is commonly used for protection against electrical shocks in critical systems?
A Step-up transformer
B Isolation transformer
C Power transformer
D Autotransformer
Isolation transformers provide electrical isolation between the primary and secondary windings. They are commonly used in critical applications, such as medical equipment or sensitive electronics, to prevent electric shocks and ensure safety by isolating the connected equipment from the main power supply.
What is the typical frequency of operation for most transformers?
A 20 Hz
B 50 Hz or 60 Hz
C 100 Hz
D 200 Hz
Most transformers operate at a frequency of 50 Hz or 60 Hz, depending on the country or region. These are the standard frequencies for alternating current (AC) in most electrical power systems worldwide.
What is the main advantage of using a dry-type transformer over an oil-filled transformer?
A Higher efficiency
B Reduced risk of fire
C Smaller size
D Easier installation
Dry-type transformers use air for cooling and do not contain flammable oils, making them safer in environments where fire risk is a concern. While they may have slightly lower efficiency than oil-filled transformers, they are commonly used in residential, commercial, and industrial applications where safety is a priority.
What is the main function of transformer protection devices?
A To reduce energy losses
B To protect against overloading, short circuits, and faults
C To regulate voltage
D To increase transformer efficiency
Transformer protection devices, such as fuses, circuit breakers, and relays, are used to safeguard the transformer from damage due to overloading, short circuits, and other electrical faults. These devices disconnect the transformer from the circuit when dangerous conditions are detected, preventing further damage.
Which of the following losses occur in the core of a transformer?
A Copper loss
B Core loss (hysteresis and eddy current loss)
C Dielectric loss
D All of the above
Core losses in a transformer are mainly due to hysteresis (energy lost due to the magnetization and demagnetization of the core material) and eddy currents (currents induced within the core material). These losses occur regardless of the load and are typically reduced using laminated core designs.
What happens when the transformer experiences inrush current during startup?
A The voltage increases significantly
B The transformer experiences a brief surge of high current
C The transformer becomes inefficient
D The transformer becomes overloaded
Inrush current is the initial surge of current that occurs when a transformer is first energized. This surge can be several times higher than the normal operating current and can cause damage if not properly managed. Inrush current is typically limited using devices like inrush current limiters.
What is the purpose of load testing a transformer?
A To determine the transformer’s core losses
B To determine the efficiency and temperature rise under load conditions
C To measure the insulation strength
D To measure the impedance of the transformer
Load testing is conducted to evaluate a transformer’s performance under normal operating conditions when supplying power to a load. It checks parameters like voltage regulation, efficiency, and temperature rise. This test helps ensure that the transformer operates safely and efficiently under typical load conditions.
What is the role of harmonics in transformer operation?
A Harmonics improve the transformer’s efficiency
B Harmonics increase transformer losses and cause overheating
C Harmonics reduce voltage regulation
D Harmonics have no effect on transformer performance
Harmonics in the supply voltage can distort the waveform, increasing losses in the transformer and causing overheating. Harmonics are often generated by non-linear loads, such as variable-speed drives, and may require filtering to ensure transformer health and efficient operation.
Which of the following transformers is commonly used in industrial applications to isolate different circuits?
A Power transformer
B Isolation transformer
C Step-up transformer
D Autotransformer
Isolation transformers are used in industrial applications to isolate electrical circuits. They provide safety by preventing direct electrical connection between the primary and secondary circuits, thus reducing the risk of electric shock and providing protection from power surges.
What does the “no-load loss” of a transformer refer to?
A Losses due to the resistance of the windings when no load is connected
B Losses caused by core magnetization and eddy currents when no load is connected
C Losses that occur only during load operation
D Losses due to the heating of the oil in oil-filled transformers
No-load loss, also known as core loss, occurs when the transformer is energized but not supplying any load. These losses are mainly caused by the magnetization of the core material and the eddy currents induced within it. They are independent of the load and are present whenever the transformer is operating.
What is the role of insulation in transformers?
A To increase the efficiency of the transformer
B To provide safety by preventing electrical faults
C To store electrical energy
D To reduce the size of the transformer
Insulation in transformers is essential to prevent electrical faults such as short circuits between windings. It ensures that the windings are electrically separated from each other and from the core, preventing arcing and reducing the risk of electrical shock.
What is a common fault in transformers?
A Overvoltage
B Overheating
C Low current
D Short circuit
Overheating is a common fault in transformers, often caused by overloading, poor cooling, or excessive losses. Overheating can damage the insulation and windings, leading to transformer failure. Proper cooling and load management are essential to prevent overheating.