What is the main purpose of using a laminated core in transformers?
A Lower resistance
B Reduce losses
C Improve insulation
D Increase flux
Laminated cores are used in transformers to reduce eddy current losses. The thin layers of metal, separated by insulation, prevent large circulating currents in the core material, thereby minimizing energy loss and heat generation during operation.
What is the basic principle of operation of a transformer?
A Magnetic induction
B Chemical reaction
C Electrostatic induction
D Electromagnetic radiation
Transformers operate on the principle of magnetic induction. The alternating current in the primary winding creates a changing magnetic field, which induces voltage in the secondary winding, transferring electrical energy without physical connection.
What is the effect of increasing the number of turns in the secondary winding of a transformer?
A Decreased impedance
B Increased current
C Decreased voltage
D Increased voltage
According to the transformer equation, increasing the number of turns in the secondary winding will increase the secondary voltage. The voltage is directly proportional to the number of turns in the coil.
In which transformer configuration is the primary and secondary winding physically connected?
A Step-up transformer
B Autotransformer
C Step-down transformer
D Isolation transformer
In an autotransformer, the primary and secondary windings are electrically connected and share a common winding. This configuration allows efficient voltage adjustment with a smaller size and cost, but it lacks isolation between the two sides.
What material is commonly used for the core of a transformer?
A Iron
B Copper
C Silicon steel
D Aluminum
Silicon steel is commonly used for transformer cores due to its high magnetic permeability, which allows efficient transmission of magnetic flux. The addition of silicon reduces core losses and improves overall efficiency by reducing eddy currents.
What is the function of a transformer’s insulating oil?
A Improve cooling
B Increase efficiency
C Protect the core
D Increase voltage
Insulating oil in a transformer serves to both insulate the windings and dissipate heat. It provides cooling by absorbing the heat generated from the core and windings, preventing overheating and maintaining the transformer’s safe operation.
Which of these transformers is most often used in high voltage power transmission?
A Isolation transformer
B Step-down transformer
C Distribution transformer
D Power transformer
Power transformers are typically used in high-voltage power transmission systems to step up voltage for efficient long-distance transmission. They operate at high ratings and help minimize energy loss over long distances by reducing current flow.
What is the purpose of the primary winding in a transformer?
A Maintain voltage
B Generate heat
C Create magnetic flux
D Induce current
The primary winding of a transformer generates a magnetic flux when alternating current flows through it. This magnetic field induces voltage in the secondary winding, enabling the transformer to transfer electrical energy.
How is the efficiency of a transformer affected by core losses?
A Core losses improve voltage
B Core losses decrease efficiency
C Core losses increase efficiency
D Core losses do not affect efficiency
Core losses, consisting of hysteresis and eddy current losses, contribute to energy loss in transformers. These losses reduce the efficiency of the transformer by converting electrical energy into heat, making it crucial to minimize core losses through design.
What happens when a transformer is overloaded?
A It may overheat
B It reduces frequency
C It cools down
D It increases voltage
When a transformer is overloaded, it carries more current than its rated capacity. This causes the windings to overheat, potentially damaging the transformer. Prolonged overload can lead to insulation breakdown and eventual failure.
What is a key difference between dry-type and oil-filled transformers?
A Voltage rating
B Efficiency
C Cooling method
D Insulation material
The primary difference between dry-type and oil-filled transformers is the cooling method. Dry-type transformers use air for cooling, while oil-filled transformers use oil to both insulate and cool the windings. Oil-filled transformers are typically used for higher power applications.
Which type of transformer is used to protect against electrical surges?
A Protection transformer
B Autotransformer
C Step-up transformer
D Isolation transformer
An isolation transformer is used to protect against electrical surges by electrically isolating the secondary circuit from the primary one. This prevents the transmission of surges and noise between circuits, protecting sensitive equipment from power fluctuations.
What is the most common test used to measure the efficiency of a transformer?
A Impedance test
B Load test
C Open-circuit test
D Short-circuit test
A load test is commonly used to measure the efficiency of a transformer under real operating conditions. It involves running the transformer at rated load and measuring both input and output power to calculate efficiency based on losses.
What is the purpose of the secondary winding in a transformer?
A Transfer energy to load
B Control voltage
C Provide magnetic flux
D Generate heat
The secondary winding of a transformer is responsible for transferring the energy from the magnetic flux generated in the primary winding to the load. The induced voltage in the secondary is used to supply power to the connected circuit.
In a three-phase transformer, how are the windings typically arranged?
A In a circle
B In series
C In star or delta
D In parallel
In a three-phase transformer, the windings are typically arranged in either a star (wye) or delta configuration. The star configuration is used for higher voltage systems, while the delta configuration is used for higher current systems, providing flexible voltage conversion.