Question 1

A delta-connected set of windings has a phase current of 10 A. What is the line current?

Accepted Answer

A)   5.77 A
B)   10 A
C)   17.32 A
D)   30 A

Question 2

Line voltage and phase voltage are the same in the _____ connection.

Accepted Answer

A)   delta
B)   wye

Question 3

In calculating apparent power (VA)  in a three-phase circuit, the phase values of voltage and current are multiplied by _____.

Accepted Answer

A)   three
B)   four
C)   five
D)   six

Question 4

If a three-phase load is a pure reactive load, then the power calculated has units of _____.

Accepted Answer

A)   VA
B)   W
C)   VARs

Question 5

Three-phase voltages are _____ out of phase with each other.

Accepted Answer

A)   80°
B)   90°
C)   100°
D)   120°

Question 6

In a three-phase circuit, the true power (watts)  is found by _____.

Accepted Answer

A)   multiplying line voltage by line current
B)   multiplying apparent power by the power factor
C)   dividing power factor by the apparent power
D)   multiplying phase voltage by phase current

Question 7

In a three-phase connection, what is the voltage measured between the lines?

Accepted Answer

A)   line voltage
B)   phase voltage

Question 8

In three-phase power systems, the delivered power _____.

Accepted Answer

A)   falls to zero three times per cycle
B)   falls to zero once per cycle
C)   never falls to zero
D)   falls to zero at least three times per cycle

Question 9

The horsepower rating of three-phase motors and the kilovolt-ampere rating of three-phase transformers are about _____ greater than for single-phase motors or transformers with a similar frame size.

Accepted Answer

A)   75 percent
B)   100 percent
C)   150 percent
D)   200 percent

Question 10

Another name for the three-phase wye connection is the _______________ connection.

Accepted Answer

The answer of Another name for the three-phase wye connection...

Question 11

A wye-connected alternator that has phase voltages of 277 V is feeding two loads. The first load is wye-connected inductors that have 40 Ω of XL. The second load is delta-connected capacitors that have XC of 60 Ω . How much is the alternator phase current?

Accepted Answer

A)   6.93 A
B)   14.93 A
C)   24.62 A
D)   28 A

Question 12

When calculating the power of a pure resistive load, the voltage and current are in phase with each other and the power factor is _____.

Accepted Answer

A)   one
B)   two
C)   three
D)   four

Question 13

A three-phase connection in which three separate inductive loads have been connected together is a(n)  _____ connection.

Accepted Answer

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

Question 14

In a three-phase connection, what is the voltage measured across a single winding?

Accepted Answer

A)   line voltage
B)   phase voltage

Question 15

The three-phase connection in which one end of each of the windings are connected together is called a(n)  _____ connection.

Accepted Answer

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

Question 16

In a balanced three-phase system, the conductors need be only about _____ the size of conductors for a single-phase, two-wire system of the same kilovolt-ampere (kVA)  rating.

Accepted Answer

A)   25 percent
B)   30 percent
C)   50 percent
D)   75 percent

Question 17

A delta-connected three-phase alternator is driving a wye-connected resistive load. The alternator output voltage is 480 V. The load resistors are 12 Ω each. What is the phase current in the alternator?

Accepted Answer

A)   13.33 A
B)   23.09 A
C)   39.28 A
D)   40 A

Question 18

A delta connected set of windings has a phase voltage of 100 V. What is the line voltage?

Accepted Answer

A)   57.7 V
B)   100 V
C)   173.2 V
D)   300 V B

Question 19

In a wye-connected system, the line voltage is higher than the phase voltage by a factor of _____.

Accepted Answer

A)   square root of  two
B)   square root of three
C)   two
D)   three

Question 20

A delta connected set of windings has a phase voltage of 480 V. What is the line voltage?

Accepted Answer

A)   277.14 V
B)   480 V
C)   831.36 V
D)   1440 V B

Exam 27: Three-Phase Circuits

A delta-connected set of windings has a phase current of 10 A. What is the line current?

Correct AnswerverifiedShow Answer

Line voltage and phase voltage are the same in the _____ connection.

Correct AnswerverifiedShow Answer

In calculating apparent power (VA) in a three-phase circuit, the phase values of voltage and current are multiplied by _____.

Correct AnswerverifiedShow Answer

If a three-phase load is a pure reactive load, then the power calculated has units of _____.

Correct AnswerverifiedShow Answer

Three-phase voltages are _____ out of phase with each other.

Correct AnswerverifiedShow Answer

In a three-phase circuit, the true power (watts) is found by _____.

Correct AnswerverifiedShow Answer

In a three-phase connection, what is the voltage measured between the lines?

Correct AnswerverifiedShow Answer

In three-phase power systems, the delivered power _____.

Correct AnswerverifiedShow Answer

The horsepower rating of three-phase motors and the kilovolt-ampere rating of three-phase transformers are about _____ greater than for single-phase motors or transformers with a similar frame size.

Correct AnswerverifiedShow Answer

Another name for the three-phase wye connection is the _______________ connection.

Correct AnswerverifiedShow Answer

A wye-connected alternator that has phase voltages of 277 V is feeding two loads. The first load is wye-connected inductors that have 40 Ω of XL. The second load is delta-connected capacitors that have XC of 60 Ω . How much is the alternator phase current?

Correct AnswerverifiedShow Answer

When calculating the power of a pure resistive load, the voltage and current are in phase with each other and the power factor is _____.

Correct AnswerverifiedShow Answer

A three-phase connection in which three separate inductive loads have been connected together is a(n) _____ connection.

Correct AnswerverifiedShow Answer

In a three-phase connection, what is the voltage measured across a single winding?

Correct AnswerverifiedShow Answer

The three-phase connection in which one end of each of the windings are connected together is called a(n) _____ connection.

Correct AnswerverifiedB

In a balanced three-phase system, the conductors need be only about _____ the size of conductors for a single-phase, two-wire system of the same kilovolt-ampere (kVA) rating.

Correct AnswerverifiedShow Answer

A delta-connected three-phase alternator is driving a wye-connected resistive load. The alternator output voltage is 480 V. The load resistors are 12 Ω each. What is the phase current in the alternator?

Correct AnswerverifiedShow Answer

A delta connected set of windings has a phase voltage of 100 V. What is the line voltage?

Correct AnswerverifiedB

In a wye-connected system, the line voltage is higher than the phase voltage by a factor of _____.

Correct AnswerverifiedShow Answer

A delta connected set of windings has a phase voltage of 480 V. What is the line voltage?

Correct AnswerverifiedB

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A wye-connected alternator that has phase voltages of 277 V is feeding two loads. The first load is wye-connected inductors that have 40 Ω of X_L. The second load is delta-connected capacitors that have X_C of 60 Ω . How much is the alternator phase current?

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B