Three Phase Systems In Power Applications MCQ Questions & Answers | Electrical Engineering

Three-phase induction motor is the most common type of AC motor used in industrial and commercial applications.

This is because it has a simple design, rugged construction, and requires low maintenance compared to other motor types.

It operates with a self-starting torque and provides high efficiency and reliability.

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Let's break down why the answer is a three-phase induction motor:

* Induction Motors: These are workhorse motors that rely on electromagnetic induction to operate.
* Three-Phase Power: The vast majority of industrial and commercial power distribution systems use three-phase power. This is because it provides more efficient and consistent power delivery.
* Why Three-Phase Induction Motors are Common:
* High Efficiency: They are generally more efficient than single-phase motors, especially in larger sizes.
* High Starting Torque: Many three-phase induction motors have good starting torque, meaning they can easily start under load.
* Reliability: They are robust and have a long lifespan.
* Simplicity: The design is relatively simple, leading to lower manufacturing costs.
* Wide Availability: Due to their widespread use, they are readily available in a wide range of sizes and power ratings.

* Why the other options are less common:
* Single-phase induction motor: These are used where three-phase power isn't available (like in homes) and typically have lower power ratings.
* Two-phase induction motor: These are rare and have largely been replaced by three-phase systems.
* Two-phase squirrel-cage motor: The motor is very uncommon nowadays.
In summary: Because three-phase power is the standard for industrial applications, and three-phase induction motors are efficient, reliable, and readily available, they are the most common type of AC motor.

Understanding Y-connected Generators:
Imagine a Y-connected generator as a three-legged star. Each leg represents a phase, and the voltage across each phase is called the phase voltage.

The line voltage, on the other hand, is the voltage measured between any two of the three legs (lines).

Calculating Line Voltage:
In a Y-connection, the line voltage is not simply equal to the phase voltage. Because the phases are 120 degrees apart, the relationship is based on the geometry of an equilateral triangle.

The formula to find the line voltage (V_L) from the phase voltage (V_ph) is: V_L = √3 * V_ph

Solving the Problem:
We are given that the phase voltage (V_ph) is 90 VRMS. Using the formula:
V_L = √3 * 90 V ≈ 156 V

Therefore, the magnitude of each line voltage is approximately 156 V.

The Correct Answer:
The correct option is C: 156 V