Deck 21: Three-Phase Transformers, Power Relaying, and Monitoring

Question 1

Most three-phase, dry-type distribution transformers are connected as a primary wye connection.

Answer 1

False

Question 2

Three-phase transformers should have a voltage ____________________ to show the angular phase displacement between the primary and the secondary and also the phase-sequence order.

Answer 2

vector diagram

Question 3

In three-phase transformers, the ____________________ or phase sequence between the primary and the secondary is critical.

Answer 3

phase rotation

Question 4

If the pattern is a delta-delta pattern, the displacement must be 60°.

Question 5

What is the only way to change the angular displacement?

Question 6

N is the ____________________ in the vector diagram.

Question 7

It is only necessary to connect the similarly marked high- and low-voltage terminals if the transformers have the same voltage ratio, the same percent impedance, and the same angular displacement.

Question 8

How are the three high-voltage and secondary leads marked?

Question 9

If the transformers are delta-wye or wye-delta, the angular displacement is ____________________°.

Question 10

What are the advantages of paralleling three-phase transformers?

Question 11

Terminal markings indicate all the relationships between primary and secondary.

Question 12

How does the American National Standards Institute (ANSI) define the angular displacement?

Question 13

All phase windings within the transformer normally have the same relative polarity.

Question 14

When paralleling three phase transformer units, only transformers with the same ____________________ should be connected.

Question 15

What is the disadvantage of paralleling three-phase transformers?