Deck 18: Single-Phase Transformers Connected in Wye Systems

Question 1

What are 480-volt systems desired for in many modern installations?

Answer 1

In many modern installations, 480-volt systems are desired for large motor loads such as supermarkets, large retail stores, manufacturing facilities, and so on.

Question 2

How can three-phase capacity be calculated using the line voltages and line current?

Answer 2

Three-phase capacity can be calculated by using the line voltages and line current, as follows: 3-phase KVA = Line E x Line I x 1.73.

Question 3

When is a wye-wye connection unsatisfactory?

Answer 3

The wye-wye connection is unsatisfactory in situations where the secondary load becomes greatly unbalanced. An unbalanced load results in a serious unbalance in the three output voltages of the transformer bank.

Question 4

Where is the 120/208-volt wye system commonly used?

Question 5

A wye-wye connected transformer bank cannot be reconnected in an emergency situation by using only two single-phase transformers.

Question 6

In a three-phase, four-wire system, the voltage between the neutral and any one of the three line leads on the secondary side is 240 volts.

Question 7

Many ____________________ are designed for a 277-volt, single-phase line to ground, known as a grounded neutral conductor.

Question 8

Because the neutral wire is ____________________, it helps protect the three high-voltage primary windings from lightning surges.

Question 9

How can voltage unbalancing in the secondary of the transformer bank be nearly eliminated?

Question 10

Caution: ____________________ all circuits before making connections.

Question 11

The wye configuration is sometimes known as a(n) "____________________" connection.

Question 12

The total kilovolt-ampere capacity of a wye-wye connected bank is found by adding the individual kVA ratings of the transformer.

Question 13

Wye-connected transformer banks have only 58% of the line voltage applied to each of the three transformer windings.

Question 14

Because each of the line wires is connected in ____________________ with one of the transformer windings, the current in each winding is equal to its respective line current.

Question 15

When three single-phase coils are connected so that each coil is connected to the beginning of another coil, a simple wye system is formed.