Which is true for star connection? | Electrical MCQ | Examoogle

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Which is true for star connection?

$I_L = \sqrt{3} I_p$

$V_L = \sqrt{3} V_p$

Both of these

All of these

Correct Answer

⚙️ TE • Technical Concept & PrincipleElectricalBasic Electrical

Option B

$V_L = \sqrt{3} V_p$

Quick Summary:

In a balanced star (Y) connected three-phase system, the line voltage ( $V_L$ ) is the potential difference between any two phases, which is $\sqrt{3}$ times the phase voltage ( $V_p$ ) across a single winding. This relationship arises due to the $120°$ phase displacement between the three phase voltages.

⚙️TETechnical SolutionConcept & Principle

💡 Explanation

🔢 Key Formulas

$V_L = \sqrt{3} V_p$ — Relation between line and phase voltage in star

$I_L = I_p$ — Relation between line and phase current in star

⚙️ Working Principle

In a star connection, the start terminals of three windings are joined to a common neutral point. The line voltage $V_L$ is the phasor difference between two phase voltages $V_p$ . By performing the phasor subtraction $\vec{V_L} = \vec{V_{ph1}} - \vec{V_{ph2}}$ , the resulting magnitude is $2 \cdot V_p \cdot \cos(30°) = 2 \cdot V_p \cdot \frac{\sqrt{3}}{2} = \sqrt{3}V_p$ .

📌 Key Points

▸
In star connection, neutral wire is physically available.
▸
Line current is equal to phase current ( $I_L = I_p$ ).
▸
Star connection is preferred for long-distance power transmission to reduce insulation costs.

✅ Advantages

▸
Provides two different voltages ( $V_p$ and $V_L$ ).
▸
Suitable for unbalanced loads if neutral is grounded.

❌ Disadvantages / Limitations

▸
Line voltage is lower than delta connection for same phase voltage.
▸
Not suitable for high-current applications where delta is preferred.

🛠️ Applications / Uses

▸
Distribution transformers
▸
Industrial motor starting (Star-Delta starters)

🔄 Comparison Table

Feature	Star Connection	Delta Connection
Voltage Relation	$V_L = \sqrt{3} V_p$	$V_L = V_p$
Current Relation	$I_L = I_p$	$I_L = \sqrt{3} I_p$

📄 Additional Information

▸
For delta connection, $V_L = V_p$ and $I_L = \sqrt{3} I_p$ .
▸
Option A is incorrect because $I_L = I_p$ in a star connection, not $\sqrt{3} I_p$ .

📊 Diagram / Illustration

✅

B is correct — In a star connection, the line voltage is exactly $\sqrt{3}$ times the phase voltage.

Core Concepts Used

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Three-phase systems Phasor analysis Wye connection properties

💡 EXAM TIP

Remember 'Star-Current-Same' ( $I_{L}$ = $I_{p}$ ) and 'Delta-Voltage-Same' ( $V_{L}$ = $V_{p}$ ) to quickly answer relation questions in exams.

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