Electrical Machines Quizz 1

What is the primary function of a transformer?

• To convert direct current to alternating current.

• To increase the frequency of electrical signals.

• To store electrical energy for later use.

• To change the voltage level of alternating current.

Explain the difference between step-up and step-down transformers.

• Both step-up and step-down transformers increase voltage.

• Step-up transformers are used for AC only; step-down transformers are used for DC only.

• Step-up transformers increase voltage; step-down transformers decrease voltage.

• Step-up transformers decrease voltage; step-down transformers increase voltage.

What is the formula for calculating the turns ratio in a transformer?

• Turns Ratio = Ns / Np

• Turns Ratio = Np + Ns

• Turns Ratio = Np / Ns

• Turns Ratio = Np - Ns

Describe the star connection in a three-phase system.

• A star connection in a three-phase system connects each phase to a common neutral point, allowing for balanced loads and providing a return path for unbalanced currents.

• A star connection connects all phases directly to the power source without a neutral point.

• In a star connection, each phase is connected to the ground instead of a neutral point.

• A star connection is used only for single-phase systems, not three-phase systems.

How does a delta connection differ from a star connection?

• A delta connection uses a single wire for each phase, while a star connection uses multiple wires for each phase.

• A delta connection connects phases to a common neutral point, while a star connection connects phases in a closed loop.

• A delta connection connects phases in a closed loop, while a star connection connects phases to a common neutral point.

• A delta connection is used for low voltage applications, while a star connection is used for high voltage applications.

What is the line voltage in a star-connected system?

• V_L = V_Ph

• V_L = 2 * V_Ph

• V_L = V_Ph / √3

• V_L = √3 * V_Ph

What is the phase voltage in a delta-connected system?

• The phase voltage is half of the line voltage.

• The phase voltage is three times the line voltage.

• The phase voltage is independent of the line voltage.

• The phase voltage is equal to the line voltage.

Explain the concept of phase shift in a three-phase system.

• Phase shift is the voltage difference between the three phases.

• Phase shift refers to the frequency difference between the currents.

• Phase shift is the time delay between the three phases in a system.

• Phase shift in a three-phase system is the angular difference (120 degrees) between the three alternating currents.

What is the relationship between line and phase currents in a star connection?

• In a star connection, line current is twice the phase current (I_L = 2I_P).

• In a star connection, line current is half the phase current (I_L = 0.5I_P).

• In a star connection, line current is unrelated to phase current (I_L ≠ I_P).

• In a star connection, line current is equal to phase current (I_L = I_P).

What are the common types of transformers used in electrical systems?

• Capacitor bank

• Step-up transformer, Step-down transformer, Isolation transformer, Autotransformer

• Voltage regulator

• Inductor coil