What is the primary function of a transformer in an electrical system?
A Voltage conversion
B Current measurement
C Energy generation
D Power storage
A transformer is a static electrical device that transfers electrical energy between two or more circuits through electromagnetic induction. Its primary function is to convert voltage levels from one value to another, either stepping up or stepping down, without changing the frequency. Transformers are widely used in power distribution and transmission to ensure efficient electricity supply.
How does a transformer change voltage levels without physical contact between windings?
A Mechanical movement
B Chemical reaction
C Direct conduction
D Electromagnetic induction
A transformer operates based on the principle of electromagnetic induction, where alternating current (AC) in the primary winding creates a changing magnetic field in the core, inducing a voltage in the secondary winding. There is no direct electrical connection between the windings, only magnetic coupling, ensuring safe voltage conversion.
What are the two main types of transformer cores?
A Air and Water
B Shell and Core
C Iron and Copper
D Series and Parallel
Transformers primarily use two types of core constructions: core type (where windings surround the core) and shell type (where the core surrounds the windings). Both designs help in efficiently transferring magnetic flux and minimizing losses, depending on the application.
Which loss occurs due to the resistance of the transformer windings?
A Core loss
B Hysteresis loss
C Copper loss
D Eddy current loss
Copper loss (I²R loss) occurs due to the resistance of the primary and secondary windings of the transformer. It depends on the square of the current flowing through the windings and the resistance of the conductor. Reducing resistance by using high-quality copper helps minimize these losses.
What is the purpose of transformer oil in an oil-filled transformer?
A Increase resistance
B Provide cooling
C Improve voltage
D Reduce frequency
Transformer oil serves as an insulating medium and cooling agent in oil-filled transformers. It helps dissipate heat generated due to iron and copper losses and prevents electrical breakdown by improving insulation properties. Regular testing ensures the oil remains effective.
What happens to the frequency of AC power after passing through a transformer?
A Remains same
B Increases
C Converts to DC
D Decreases
A transformer only changes the voltage and current levels; it does not alter the frequency of the AC power. Since transformers operate based on electromagnetic induction, the frequency of the output power remains the same as the input.
What test is performed on a transformer to determine core losses?
A Load test
B Impulse test
C Open-circuit test
D Short-circuit test
An open-circuit test is performed by applying rated voltage to the primary winding while keeping the secondary winding open. This helps measure core losses (hysteresis and eddy current losses) and the no-load current, which are crucial for efficiency analysis.
Which type of transformer is used to step down high-voltage electricity for home use?
A Autotransformer
B Distribution transformer
C Step-up transformer
D Isolation transformer
Distribution transformers step down high-voltage electricity from transmission lines to lower voltages suitable for household and commercial use. They typically operate at low loads and provide efficient voltage regulation for local distribution networks.
What is the main function of an autotransformer?
A Harmonic filtering
B DC to AC conversion
C Power generation
D Voltage regulation
An autotransformer has a single winding with a shared core that allows variable voltage adjustment. It provides more efficient voltage regulation compared to conventional transformers by using a smaller core and less copper, making it cost-effective for certain applications.
What causes inrush current in a transformer during startup?
A Magnetic saturation
B High resistance
C Excessive load
D Sudden voltage drop
Inrush current occurs when a transformer is first energized, causing the core to saturate momentarily due to the sudden application of AC voltage. This results in a high initial current surge, which can be several times greater than the rated current, potentially damaging the transformer.
What does voltage regulation in a transformer indicate?
A Current rating
B Losses in the core
C Change in voltage under load
D Efficiency of winding
Voltage regulation refers to the difference between no-load and full-load secondary voltage, expressed as a percentage. A lower voltage regulation percentage indicates better transformer performance, as it means the voltage drop under load conditions is minimal.
Why is silicon steel commonly used in transformer cores?
A Improves voltage
B Reduces eddy current loss
C Lowers temperature
D Increases resistance
Silicon steel has high permeability and low hysteresis loss, which minimizes core losses, particularly eddy current losses. The addition of silicon reduces electrical conductivity, making the core more efficient by lowering energy wastage.
What is the primary function of an isolation transformer?
A Provide electrical isolation
B Convert AC to DC
C Step-up voltage
D Increase current
An isolation transformer electrically separates the primary and secondary circuits, preventing direct current flow between them. This enhances safety by reducing the risk of electric shock and minimizing electrical noise in sensitive equipment.
Which component in a transformer reduces humming noise?
A Cooling fan
B Insulation oil
C Copper windings
D Laminated core
The laminated core construction reduces magnetic vibrations and eddy current losses, helping to minimize the humming noise in a transformer. Proper core design and mounting techniques further reduce operational noise levels.
What type of transformer is used for long-distance power transmission?
A Isolation transformer
B Earthing transformer
C Step-up transformer
D Step-down transformer
Step-up transformers increase the voltage for efficient long-distance power transmission. Higher voltage reduces current flow, minimizing transmission losses due to resistance. At the receiving end, step-down transformers bring the voltage back to usable levels.