CEA Transformers and Distribution Systems 2

Question 1

What advantage does a delta-wye transformer secondary provide over a delta-delta secondary?

Accepted Answer

A neutral point allowing both single-phase and three-phase loads

Answer

The wye secondary's neutral point allows the system to supply both single-phase line-to-neutral loads and three-phase loads from the same transformer bank.

Question 2

What standard secondary voltage does a center-tapped single-phase distribution transformer supply for typical US residential service?

Accepted Answer

120/240V single-phase

Answer

The standard US residential distribution transformer provides 120/240V single-phase service via a center-tapped secondary, delivering both 120V and 240V.

Question 3

In a three-phase delta transformer connection, how does the line voltage compare to the phase (winding) voltage?

Accepted Answer

Line voltage equals phase voltage

Answer

In a delta connection, each winding is connected directly between two line conductors, so line voltage equals phase voltage.

Question 4

What is the primary purpose of voltage taps on a distribution transformer?

Accepted Answer

To adjust the turns ratio and compensate for supply voltage variations

Answer

Transformer taps provide multiple connection points on the primary winding, allowing the turns ratio to be adjusted to maintain proper secondary voltage despite supply variations.

Question 5

A 480V to 208Y/120V transformer is best described as which winding configuration?

Accepted Answer

Delta-wye

Answer

The 480V primary has no neutral and is connected in delta; the 208Y/120V secondary with a neutral is connected in wye, making it a delta-wye transformer.

(CEA) Certified Electrical Apprentice Practice Test

(CEA) Certified Electrical Apprentice Practice Test

CEA Transformers and Distribution Systems 2