DEL 27

Question 1

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

Answer 1

line voltage

Question 2

The alternator must supply the _____ for each of the loads.

Answer 2

line current

Question 3

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

Answer 3

100 V

Question 4

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?

Answer 4

40 A

Question 5

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

Answer 5

VARs

Question 6

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

Answer 6

square root of three

Question 7

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

Answer 7

delta

Question 8

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

Answer 8

phase voltage

Question 9

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

Answer 9

multiplying apparent power by the power factor

Question 10

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

Answer 10

one

Question 11

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.

Answer 11

75 percent

Question 12

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

Answer 12

wye

Question 13

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

Answer 13

three

Question 14

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

Answer 14

delta

Question 15

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

Answer 15

120 degrees

Question 16

Line current and phase current are the same in the _____ configuration.

Answer 16

wye

Question 17

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

Answer 17

17.32 A

Question 18

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

Answer 18

never falls to zero

Question 19

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

Answer 19

480 V

Question 20

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.

Answer 20

150 percent

Question 21

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?

Answer 21

6.93 A