Licensed Electrical Contractor Transformers and Transformer Calculations

Question 1

A transformer has 480 primary turns and 120 secondary turns. What is the turns ratio?

Accepted Answer

4:1

Answer

1:4

Answer

2:1

Answer

1:2

Question 2

A transformer has a primary voltage of 480V and a turns ratio of 4:1. What is the secondary voltage?

Accepted Answer

120V

Answer

240V

Answer

960V

Answer

1920V

Question 3

Which type of transformer provides electrical separation between its primary and secondary windings with no direct electrical connection?

Accepted Answer

Isolation transformer

Answer

Autotransformer

Answer

Buck-boost transformer

Answer

Step-up transformer

Question 4

What does the kVA rating on a transformer nameplate represent?

Accepted Answer

The transformer's apparent power capacity

Answer

The transformer's voltage output

Answer

The transformer's efficiency percentage

Answer

The transformer's impedance value

Question 5

In an ideal transformer, when voltage is stepped up from primary to secondary, what happens to the current?

Accepted Answer

Current decreases proportionally

Answer

Current increases proportionally

Answer

Current remains unchanged

Answer

Current doubles regardless of ratio

Question 6

What is the primary purpose of dielectric oil in a liquid-filled transformer?

Accepted Answer

To insulate windings and dissipate heat

Answer

To lubricate the core laminations

Answer

To prevent corrosion on the tank

Answer

To regulate output voltage

Question 7

Which NEC article governs the installation requirements for transformers, including guarding, clearances, and overcurrent protection?

Accepted Answer

Article 450

Answer

Article 240

Answer

Article 430

Answer

Article 480