Question

In India the system adopted for transmission of electric power is

• A. 3-phase, 3 wire
• B. 1-phase, 3 wire
• C. 1-phase, 1 wire
• D. 3-phase, 1 wire

Hint:

To remember this easily:
- Transmission (High Voltage) \(\rightarrow\) Balanced loads \(\rightarrow\) 3-phase, 3-wire (no neutral).
- Distribution (Low Voltage) \(\rightarrow\) Unbalanced loads \(\rightarrow\) 3-phase, 4-wire (with neutral).

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
Electrical power transmission systems are designed to transport bulk electrical energy over long distances from generating stations to regional substations. The primary design goal is minimizing conductor material requirements and line losses.

Step 2: Detailed Explanation:
Let us evaluate the different AC power configurations:

3-phase, 3-wire system: This system is standard for high-voltage transmission (such as \(132 \text{ kV}\), \(220 \text{ kV}\), \(400 \text{ kV}\), or \(765 \text{ kV}\)).
In a balanced three-phase system, the vector sum of the three phase currents is zero: \[ I_R + I_Y + I_B = 0 \] Since the currents sum to zero, a return neutral conductor is not required under normal operating conditions.
Using three conductors instead of four saves significant amounts of conductor material, reduces the weight on transmission towers, and lowers mechanical structural requirements.

3-phase, 4-wire system: This configuration includes a neutral wire and is used for low-voltage secondary distribution systems (e.g., \(415 \text{ V} / 230 \text{ V}\)). The neutral wire is necessary to return unbalanced currents from single-phase domestic and commercial loads.

Single-phase systems: These require larger conductor cross-sections to transmit the same amount of power as a three-phase system, resulting in higher losses and cost. They are not used for bulk transmission.
Therefore, bulk power transmission in India utilizes a 3-phase, 3-wire system.

Step 3: Final Answer:
The standard system adopted for the transmission of electric power is the 3-phase, 3-wire system, which corresponds to Option (A).