3-1-11 Transformers—Three-Phase Voltages

Question 1

The two primary systems used by the electrical industry are three phases connected in wye or delta.

Answer 1

True

Question 2

According to this lesson, there are __?__ basic transformer connections that can be derived from the two, three-phase systems in use today.

Answer 2

6

Question 3

The simplest of the 3-phase systems is the __?__.

Answer 3

delta

Question 4

Each side of the triangle in a delta system represents the amount of voltage on the lines.

Answer 4

True

Question 5

The most commonly used 3-phase system is called the __?__.

Answer 5

star (wye)

Question 6

The voltage from the tip to the center of the wye in a wye connection is the __?__ voltage.

Answer 6

phase

Question 7

In the wye system, __?__ voltage(s) are available.

Answer 7

2

Question 8

Wye systems are also called __?__-wire systems.

Answer 8

4

Question 9

In a wye system, the line voltage is __?__ times the phase voltage.

Answer 9

1.73

Question 10

One of the earliest electrical systems is the __?__ delta.

Answer 10

2400 V

Question 11

By converting a 2,400-volt delta system to a 4,160-volt wye system, the circuit loading can be increased by __?__ with the same line current as before.

Answer 11

73%

Question 12

The square root of __?__ is needed to calculate delta currents and wye voltages.

Answer 12

3

Question 13

If the voltage phase to ground is 2,400, the phase to phase voltage is __?__. (round off)

Answer 13

4160

Question 14

Two lines that have the same rotation will always phase together.

Answer 14

False

Question 15

A third harmonic can be as much as __?__ larger than the phase voltage.

Answer 15

150%

Question 16

If the windings of a generator or transformer bank are connected together at one end, the connection is a __?__.

Answer 16

wye

Question 17

In a 3-phase system made up of three equal voltages, the phases are separated by a phase angle of __?__.

Answer 17

120%

Question 18

An electrical distribution scheme that employs only one source of voltage is single-phase.

Answer 18

True

Question 19

Polyphase systems can have up to __?__ individual voltages.

Answer 19

12

Question 20

One drawback of generating single-phase voltage is that the pulsing of the power output causes excessive physical stress on the __?__.

Answer 20

generator

Question 21

In a 3-phase system, the three voltages are of different magnitudes.

Answer 21

False

Question 22

If B phase is lagging A phase by 120°, C phase would lag A phase by __?__.

Answer 22

240°

Question 23

An equilateral triangle is equal to the square root of three multiplied by __?__.

Answer 23

one of the neutral voltages

Question 24

In 3-phase production, the output power __?__.

Answer 24

remains constant

Question 25

The horsepower rating of 3-phase motors is __?__ greater than a single-phase motor of the same physical size.

Answer 25

150%

Question 26

A 3-phase system needs wires that are 75% larger than a single-phase two-wire system.

Answer 26

False