ACtE08 · Chapter 8Demo2 · Set 1🏛️ Past Licensure QuestionID: a1316ea4
Which three-phase transformer connection provides a neutral conductor for serving single-phase commercial and residential loads?
Which three-phase transformer connection provides a neutral conductor for serving single-phase commercial and residential loads?
Multiple Choice Options
- A
Delta (Δ)
- B
Open-delta (V-V)
- C✓ Correct Option
Star (Y) with grounded neutral
- D
Delta with center-tap
Detailed Technical Solution & Explanation
In alternating current (AC) power distribution:
•
A Star (Wye, Y) connection connects the common ends of the three phase windings together to form a common central node known as the Neutral point.
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When grounded, a three-phase 4-wire Wye system () provides two distinct voltage levels: a line-to-line voltage (, e.g., ) for large industrial three-phase motors, and a line-to-neutral voltage () for standard single-phase consumer loads.
•
A pure Delta () connection has no common neutral point, making it unsuitable for standard single-phase consumer distribution without special zigzag grounding transformers.
Option Analysis:
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Option A (Delta (Δ)): Incorrect; 3-wire system with no inherent neutral point.
•
Option B (Open-delta): Incorrect; two-transformer configuration providing three-phase power without a balanced neutral.
•
Option C (Star (Y) with grounded neutral): Correct; the central junction provides the neutral return path for single-phase circuits.
•
Option D (Delta with center-tap): Incorrect; while high-leg delta provides a split single-phase neutral on one winding, the universal standard for commercial 3-phase 4-wire power is Star (Wye).
Reference: Demo2 · Set 1NEC Licensure Syllabus