Transformers and Distribution Systems Flashcards

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

Answer: 4:1

The turns ratio is calculated by dividing primary turns by secondary turns: 480 ÷ 120 = 4:1.

A step-down transformer has a 2:1 turns ratio and a primary voltage of 240V. What is the secondary voltage?

Answer: 120V

With a 2:1 turns ratio, the secondary voltage is half the primary: 240V ÷ 2 = 120V.

What operating principle allows a transformer to transfer electrical energy between two circuits?

Answer: Mutual electromagnetic induction

Transformers operate on mutual electromagnetic induction, where a changing magnetic field in the primary winding induces a voltage in the secondary winding.

Which transformer type has its secondary winding electrically isolated from the primary winding with no common connection?

Answer: Isolation transformer

An isolation transformer has separate primary and secondary windings with no electrical connection between them, providing complete electrical isolation.

If an ideal transformer draws 5A at 240V on the primary, what is the secondary current when the secondary voltage is 120V?

Answer: 10A

In an ideal transformer, primary VA equals secondary VA: 240V × 5A = 120V × I, solving gives I = 10A.

What core material is most commonly used in power transformers to reduce eddy current losses?

Answer: Silicon steel laminations

Silicon steel laminations are used in transformer cores because they provide high magnetic permeability and their thin, insulated layers reduce eddy current losses.

A transformer nameplate shows a KVA rating of 75 KVA. What does this rating represent?

Answer: The apparent power capacity in kilovolt-amperes the transformer can handle continuously

The KVA rating represents the transformer's apparent power capacity—the maximum load it can handle continuously without exceeding its temperature rating.