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

The correct answer is Option B: False

Here's why:

* The stator is the stationary (non-rotating) part of a generator or motor.
* The rotor is the rotating part. Think of it as the part that spins.
* So, the statement that the stator is the rotating assembly is incorrect.

For both single-phase and three-phase systems, the current can be calculated using Ohm's Law:

I = V / R

Where:

I is the current,

V is the voltage,

R is the effective load resistance.

Given that the effective load resistance (R) is 15 Ω and the system voltage is 120 V, we can calculate the current for each system:

Single-phase system:

I_single = 120 V / 15 Ω

I_single = 8 A

For a single-phase system, the current-carrying capacity is 8 A.

Three-phase system:

In a three-phase system, the line current is the same as the current through each phase. The voltage used in the calculation is the line-to-neutral voltage (120 V), so:

I_three = 120 V / 15 Ω

I_three = 8 A

The current-carrying capacity for the three-phase system is also 8 A.

Therefore, the correct answer is:

Option B: Single-phase 16 A; three-phase 8 A

An alternator is indeed an electromechanical AC generator. It operates on the principle of electromagnetic induction to convert mechanical energy into electrical energy in the form of alternating current (AC). While someone may say "False" for various reasons, the generally accepted understanding in the field of electrical engineering is that an alternator is a type of AC generator.

Okay, let's break down this problem step-by-step:

First, let's understand the basics of a two-phase system.
In a two-phase system, you have two AC voltages that are out of phase with each other.

Here's how to solve for the current flowing through the neutral line:

Step 1: Calculate the current in each phase.
We use Ohm's Law, which is Voltage (V) = Current (I) * Resistance (R).
Rearranging for current, we get I = V / R.
Since each coil generates 120V and is connected to a 90Ω resistor, the current in each phase is:
I = 120V / 90Ω = 1.33 A
So, each phase carries 1.33 Amperes.

Step 2: Understand the phase relationship and neutral current.
In a two-phase system, the two voltages are 90 degrees out of phase.
The neutral current is the vector sum of the currents in the two phases.
Because the phases are 90 degrees apart, we can use the Pythagorean theorem to find the magnitude of the neutral current.

Step 3: Apply the Pythagorean theorem.
The neutral current (In) is the square root of the sum of the squares of the individual phase currents:
In = √(I1² + I2²)
In = √((1.33 A)² + (1.33 A)²)
In = √(1.77 + 1.77)
In = √3.54
In ≈ 1.88 A

Therefore, the current flowing through the common neutral line is approximately 1.88 A.
The correct answer is Option B: 1.88 A.