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

Higher output voltage only

Answer

Smaller physical size for the same KVA rating

Answer

Complete elimination of harmonic currents

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

480V single-phase

Answer

208V single-phase

Answer

277V single-phase

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

Line voltage = phase voltage × 1.732

Answer

Line voltage = phase voltage ÷ 1.732

Answer

Line voltage = phase voltage × 2

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

To connect the transformer mechanically to its mounting pad

Answer

To measure the transformer's secondary output current

Answer

To provide the required grounding connection per the NEC

Question 5

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

Accepted Answer

Delta-wye

Answer

Delta-delta

Answer

Wye-wye

Answer

Wye-delta

Question 6

What does transformer polarity (indicated by dot notation on a nameplate) describe?

Accepted Answer

The instantaneous voltage relationship between primary and secondary terminals

Answer

The direction of magnetic flux through the core

Answer

The direction of current flow in the primary winding only

Answer

The phase angle displacement between primary and secondary voltages

Question 7

Which three-phase transformer connection is most commonly used for commercial and industrial power distribution in the United States?

Accepted Answer

Delta-wye

Answer

Delta-delta

Answer

Wye-wye

Answer

Open-delta