What is the main function of a step-down transformer?
A Increase voltage
B Decrease voltage
C Increase current
D Decrease current
A step-down transformer decreases the voltage from a higher level to a lower level, making it suitable for applications like household power supply, where high voltage from transmission lines needs to be reduced to safe levels for use.
What is the effect of inrush current when a transformer is energized?
A Overheating
B Increased impedance
C Increased efficiency
D Voltage increase
Inrush current is the initial surge of current when a transformer is first energized, often many times higher than the normal operating current. This can lead to overheating, causing potential damage to the transformer’s windings and insulation if not managed.
What does the magnetizing current of a transformer primarily create?
A Harmonics
B Heat
C Magnetic field
D Voltage
Magnetizing current is the small current in the primary winding of a transformer that creates the magnetic field necessary for induction. This magnetic field enables voltage to be induced in the secondary winding, allowing power transfer.
Which type of transformer is typically used in large power plants for high voltage transmission?
A Distribution transformer
B Autotransformer
C Step-down transformer
D Power transformer
Power transformers are used in large power plants to step up the voltage for efficient long-distance transmission. These transformers handle high-voltage levels to reduce current, minimizing energy losses during transmission.
What is the main role of the secondary winding in a transformer?
A Measure power
B Create magnetic flux
C Induce voltage
D Control current
The secondary winding in a transformer is responsible for inducing voltage from the magnetic field created by the primary winding. This voltage is used to supply power to the load connected to the transformer.
What causes transformer core losses?
A Voltage imbalance
B Magnetic hysteresis and eddy currents
C Resistance of windings
D Load fluctuation
Core losses in a transformer, also known as iron losses, are caused by magnetic hysteresis and eddy currents within the core material. These losses occur continuously, even under no-load conditions, and reduce transformer efficiency.
Which of the following methods is used to protect transformers from overload?
A Overcurrent relay
B Buchholz relay
C Differential relay
D Impedance relay
An overcurrent relay protects a transformer from overload conditions by detecting when the current exceeds a preset limit. It disconnects the transformer from the circuit to prevent damage to the windings and insulation from excessive current flow.
What type of transformer is used to connect two circuits with different voltages while maintaining electrical isolation?
A Step-up transformer
B Power transformer
C Step-down transformer
D Isolation transformer
An isolation transformer is used to electrically isolate two circuits with different voltage levels. It ensures that the circuits are not directly connected, providing safety from electrical faults and noise while maintaining voltage conversion.
What does the impedance in a transformer’s equivalent circuit represent?
A Magnetic flux
B Voltage drop
C Winding resistance and leakage reactance
D Core losses
In the transformer’s equivalent circuit, impedance represents the combined effect of the winding resistance (which causes copper losses) and the leakage reactance (which limits the flow of current between the windings). It impacts voltage regulation and efficiency.
Which of the following tests is performed to check the transformer’s voltage regulation?
A Insulation test
B Load test
C Short-circuit test
D Open-circuit test
A load test is performed to assess voltage regulation in a transformer. It involves applying a full-rated load and measuring the output voltage to determine the voltage drop under load conditions. A lower drop indicates better regulation.
What is the main advantage of using autotransformers over conventional transformers?
A Reduced size and cost
B Increased voltage capacity
C Higher efficiency
D Better insulation
Autotransformers use a single winding for both the primary and secondary sides, making them smaller and more cost-effective than conventional transformers. This configuration reduces the amount of copper needed, making them more affordable and efficient for certain applications.
What is the primary characteristic of a distribution transformer?
A Used for high power applications
B High voltage capacity
C Step-down voltage for local distribution
D Large size
Distribution transformers are used to step down high voltage from transmission lines to lower, usable voltages for local distribution. They are commonly found in neighborhoods and provide the final voltage adjustment before power reaches homes and businesses.
What is the significance of the no-load current in a transformer?
A Measures efficiency
B Induces voltage
C Causes short circuit
D Causes core losses
The no-load current in a transformer is responsible for establishing the magnetic flux in the core. This current also causes core losses, including hysteresis and eddy current losses, even when the transformer is not supplying any load.
What is the main use of a step-up transformer in power systems?
A Limit current
B Provide isolation
C Increase voltage
D Decrease voltage
Step-up transformers are used to increase voltage in power systems. This is essential for efficient long-distance power transmission, as higher voltage reduces the current and minimizes energy losses during transmission.
What is the effect of harmonics on transformer operation?
A Causes heating and losses
B Increases efficiency
C Improves voltage regulation
D Reduces load capacity
Harmonics can cause significant heating in transformers due to additional losses in the core and windings. These losses reduce the transformer’s efficiency, causing the system to operate less efficiently and potentially damaging the transformer over time.