Deck 14: Three-Phase Transformers

Question 1

A true three-phase transformer contains six separate transformers wound on a single core.

Answer 1

False

Question 2

The amount of magnetic flux produced by one object that influences another is called magnetic ____.

A) coupling
B) induction
C) current
D) balance

Answer 2

A

Question 3

When all three lines of a delta-wye connection are carrying the same amount of amperage, what is the neutral current value?

A) zero
B) two
C) four
D) six

Answer 3

A

Question 4

Which of the following would most likely be used to show the power distribution system of a large industrial plant?

A) schematic
B) one line diagram
C) cutaway drawing
D) orthographic projection diagram

Question 5

If the output voltage of a delta secondary is 240 volts, and one winding of the delta connection has been reversed, the voltmeter will indicate a voltage of ____.

A) 214
B) 300
C) 480
D) 577

Question 6

A three-phase load that has unequal current flow through the phases is said to be ____.

A) volatile
B) neutral
C) positive
D) unbalanced

Question 7

The disadvantage for three-phase transformers is that if a single transformer should fail, the entire transformer must be repaired or replaced.

Question 8

What is the output power of an open delta connection?

A) 26.8%
B) 86.6%
C) 100%
D) 125.5%

Question 9

A voltmeter is a low-impedance device.

Question 10

As a general rule, three-phase transformers will have one side connected as a ____.

A) neutral
B) wye
C) delta
D) ground

Question 11

Which of the following is a three-phase connection formed by connecting the start end of a phase winding to the finish end of another?

A) primary
B) wye
C) alpha
D) delta

Question 12

Which term is used for the voltage measured from the center tap of one transformer in a delta connection to the junction of the transformer(s) that are not center tapped?

A) center tap
B) high leg
C) grounder
D) coupling

Question 13

A tap in the center of a transformer winding that will provide one half of the rated voltage of the winding is called a ____ tap.

A) secondary
B) balance
C) center
D) primary

Question 14

Which of the following is a three-phase connection formed by connecting one end of each phase together to form a center point?

A) delta
B) alpha
C) wye
D) series

Question 15

Three-phase transformer connections are often used to supply single-phase loads, which tend to unbalance the system.

Question 16

Single-phase transformers connected in three-phase configurations are called three-phase transformer ____.

A) secondaries
B) primaries
C) banks
D) cores

Question 17

Which of the following is a three-phase transformer connection requiring only two transformers?

A) open wye
B) open delta
C) closed delta
D) closed wye

Question 18

If power is applied to the transformer bank before the delta connection is closed, the voltmeter should indicate ____ volts.

A) 0
B) 1.12
C) 2.36
D) 4

Question 19

Delta connections should be checked for proper polarity after applying power.

Question 20

Checking a delta connection for proper connection is called ____.

A) loading
B) cropping
C) mitigating
D) phasing