IEC Transformers and Distribution Systems

Question 1

What is the turns ratio of a single-phase transformer with a 480V primary winding and a 120V secondary winding?

Accepted Answer

4:1

Answer

2:1

Answer

8:1

Answer

16:1

Question 2

A 25 kVA, single-phase, 480V/240V transformer is operating at full load. What is the approximate rated secondary current?

Accepted Answer

104A

Answer

52A

Answer

156A

Answer

208A

Question 3

Which three-phase transformer connection provides a neutral conductor on the secondary side?

Accepted Answer

Delta-Wye

Answer

Delta-Delta

Answer

Wye-Delta

Answer

Open Delta

Question 4

According to NEC 450.3(B), a 480V transformer with a rated primary current of 9A requires primary overcurrent protection not exceeding what value?

Accepted Answer

15A

Answer

9A

Answer

11.25A

Answer

25A

Question 5

What is the primary purpose of a K-rated transformer?

Accepted Answer

To handle harmonic currents from non-linear loads

Answer

To provide voltage regulation above 10%

Answer

To improve the system power factor

Answer

To reduce audible transformer noise

Question 6

A 75 kVA, three-phase, 480V/208Y/120V transformer is operating at full load. What is the approximate full-load secondary line current?

Accepted Answer

208A

Answer

104A

Answer

156A

Answer

360A

Question 7

What type of transformer is designed to make small voltage adjustments, typically within ±5–20% of the supply voltage?

Accepted Answer

Buck-boost transformer

Answer

Autotransformer

Answer

Isolation transformer

Answer

Potential transformer