Question

Voltage of three phase motor is generally kept at

• A. 110 V
• B. 220 V
• C. 415 V
• D. 660 V

Hint:

Remember the fundamental relation: \(V_{\text{line}} = \sqrt{3} \times V_{\text{phase}}\). Multiplying a single-phase voltage of \(240 \text{ V}\) by \(\sqrt{3}\) (\(\approx 1.732\)) immediately identifies the correct three-phase voltage level near \(415 \text{ V}\).

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
Three-phase AC power systems are standard for industrial and agricultural applications because they provide steady power transmission and are highly efficient for driving induction motors. The operating voltage levels are determined by standardized utility distribution practices.

Step 2: Detailed Explanation:
In standard low-voltage electrical distribution networks (such as in India and European countries conforming to IEC standards):

The standard single-phase voltage, measured between any phase line and the neutral wire, is approximately \(230 \text{ V}\) to \(240 \text{ V}\).

In a three-phase star (\(Y\)) connection, the relationship between the line-to-line voltage (\(V_L\)) and the phase-to-neutral voltage (\(V_{ph}\)) is given by: \[ V_L = \sqrt{3} \times V_{ph} \] Substituting \(V_{ph} \approx 240 \text{ V}\) into this formula yields: \[ V_L = \sqrt{3} \times 240 \approx 1.732 \times 240 \approx 415.68 \text{ V} \] Therefore, the standardized operating line voltage for three-phase industrial and agricultural motors is designated as \(415 \text{ V}\).
Let us evaluate why other options are not standard for general-purpose three-phase motors:
- \(110 \text{ V}\) is a common single-phase household voltage in North America.
- \(220 \text{ V}\) is a common domestic single-phase voltage or a phase-to-phase voltage in low-voltage systems in other regions.
- \(660 \text{ V}\) is reserved for heavy-duty industrial or mining applications to reduce transmission current and cable size, but is not the general standard for common three-phase motors.

Step 3: Final Answer:
The voltage of a three-phase motor is generally kept at \(415 \text{ V}\), which corresponds to Option (C).