Question

A three-phase transformer has 600 primary turns and 150 secondary turns. If the supply voltage is 1.5 kV determine the secondary line voltage on no-load when windings are connected in delta-star.

• A. 649.50 V
• B. 549.50 V
• C. 595.50 V
• D. 449.50 V

Hint:

In a delta-star transformer, primary line voltage equals phase voltage, while secondary line voltage is \(\sqrt{3}\) times the phase voltage.

Answer 1

The Correct Option is A

Step 1: Determine the turns ratio of the transformer.
\[ \text{Turns ratio} = \frac{N_1}{N_2} = \frac{600}{150} = 4 \]
Step 2: Identify the primary phase voltage.
Primary winding is connected in delta, therefore
\[ V_{\text{phase, primary}} = V_{\text{line, primary}} = 1.5 \text{ kV} \]
Step 3: Calculate the secondary phase voltage.
Using the turns ratio,
\[ V_{\text{phase, secondary}} = \frac{1500}{4} = 375 \text{ V} \]
Step 4: Convert secondary phase voltage to line voltage.
Secondary winding is connected in star, so
\[ V_{\text{line, secondary}} = \sqrt{3} \times V_{\text{phase, secondary}} \]
\[ V_{\text{line, secondary}} = \sqrt{3} \times 375 = 649.50 \text{ V} \]
Step 5: Conclusion.
The secondary line voltage on no-load is
\[ \boxed{649.50 \text{ V}} \]