Deck 14: Transformer Connections for Three-Phase Circuits

Question 1

In a T connection, one transformer is generally referred to as the main transformer and the other is called the ____________________ transformer.

Answer 1

teaser

Question 2

How are primary windings connected?

Answer 2

The high-voltage primary windings are connected in a closed-delta arrangement. H₁ is assumed to be the beginning of each high-voltage winding and H₂ is assumed to be the end. The end (H₂) of each primary winding is connected to the beginning (H₁) of the next primary winding to form a series arrangement. One three-phase line wire is connected to each junction of two windings. In other words, the primary winding of each transformer is connected directly across the line voltage. Each of the three line voltages is 2400 V and the primary winding of each transformer is correctly rated at 2400 V. Once the high-voltage primary connections are made, the three-phase 2400-V input may be energized and tested for the correct phase rotation.

Question 3

Determining whether a problem with harmonics exists in a three-phase system is similar to determining the problem in a single-phase system.

Answer 3

True

Question 4

In general, the low-voltage winding leads are not marked.

Question 5

What is the purpose of a harmonic analyzer?

Question 6

A(n) ____________________ wire is added to eliminate unbalanced voltages.

Question 7

What procedure should be used to make the low-voltage connections?

Question 8

A(n) ____________________ connection is used when three single-phase transformers are used to step down as three-phase voltage of 2400 V to 240 V, three phase.

Question 9

The primary side of the delta-connected transformer may be connected so as to reverse the ____________________ of one of its legs.

Question 10

List three general procedures for dealing with harmonics.

Question 11

It is generally not practical to remove the equipment causing the harmonic distortion, so other methods must be employed.

Question 12

The most accurate method for determining whether there is a harmonics problem is to use a(n) ____________________.

Question 13

The wye-wye connection cannot be used in those applications where the load on the secondary side is balanced.

Question 14

When two or three single-phase transformers are used to transform voltages on a three-phase system, they are known as a transformer connection.

Question 15

List two advantages of a 277/480-V, three-phase, four-wire system.