Deck 12: Three-Phase Circuits

Question 1

The voltage measured across a single winding is known as the ____ voltage.

A) wye
B) delta
C) phase
D) line

Answer 1

C

Question 2

Figure 12-17 A wye-connected three-phase alternator supplies power to a delta-connected resistive load. The alternator has a line voltage of 480 V. Each resistor of the delta load has 8 ohms of resistance. Find the values in the following questions:
IP(Load) = ____ A.

A) 60
B) 120
C) 240
D) 480

Answer 2

A

Question 3

A single-phase alternating voltage can be produced by rotating a magnetic field through the conductors of a stationary coil.

Answer 3

True

Question 4

If the phase values of voltage and current are known, the apparent power can be computed using the formula VA = ____.

A)
B)
C)
D)

Question 5

The line current of a delta connection is higher than the phase current by a factor of the square root of ____.

A) 2
B) 3
C) 5
D) 6

Question 6

The phase voltage of a delta connection is different than the line voltage.

Question 7

Figure 12-18 A delta-connected alternator is connected to a wye-connected resistive load. The alternator produces a line voltage of 240 V and the resistors have a value of 6 ohms each. Find the specified values:
IL(Load) = ____ A.

A) 23.1
B) 24.2
C) 25.3
D) 26.4

Question 8

Figure 12-17 A wye-connected three-phase alternator supplies power to a delta-connected resistive load. The alternator has a line voltage of 480 V. Each resistor of the delta load has 8 ohms of resistance. Find the values in the following questions:
EP(Load) = ____ V.

A) 120
B) 240
C) 360
D) 480

Question 9

Three-phase voltages are ____ degrees apart.

A) 30
B) 90
C) 120
D) 180

Question 10

Figure 12-17 A wye-connected three-phase alternator supplies power to a delta-connected resistive load. The alternator has a line voltage of 480 V. Each resistor of the delta load has 8 ohms of resistance. Find the values in the following questions:
P = ____ W.

A) 53,489.29
B) 64,847.09
C) 77,232.11
D) 86,394.93

Question 11

Figure 12-18 A delta-connected alternator is connected to a wye-connected resistive load. The alternator produces a line voltage of 240 V and the resistors have a value of 6 ohms each. Find the specified values:
EP(Load) = ____ V.

A) 133.77
B) 138.57
C) 142.47
D) 145.89

Question 12

In a wye-connected system, phase current and line current are the same.

Question 13

Figure 12-18 A delta-connected alternator is connected to a wye-connected resistive load. The alternator produces a line voltage of 240 V and the resistors have a value of 6 ohms each. Find the specified values:
IL(Alt) = ____ A.

A) 23.1
B) 24.2
C) 25.3
D) 26.4

Question 14

Figure 12-17 A wye-connected three-phase alternator supplies power to a delta-connected resistive load. The alternator has a line voltage of 480 V. Each resistor of the delta load has 8 ohms of resistance. Find the values in the following questions:
IL(Alt) = ____ A.

A) 78.22
B) 81.20
C) 103.92
D) 107.88

Question 15

Figure 12-18 A delta-connected alternator is connected to a wye-connected resistive load. The alternator produces a line voltage of 240 V and the resistors have a value of 6 ohms each. Find the specified values:
EP(Alt) = ____ V.

A) 60
B) 120
C) 240
D) 480

Question 16

Figure 12-17 A wye-connected three-phase alternator supplies power to a delta-connected resistive load. The alternator has a line voltage of 480 V. Each resistor of the delta load has 8 ohms of resistance. Find the values in the following questions:
EL(Load) = ____ V.

A) 120
B) 240
C) 360
D) 480

Question 17

The horsepower rating of three-phase motors and the KVA (kilo-volt-amp) rating of three-phase transformers is about ____% greater than for single-phase motors or transformers with a similar frame size.

A) 50
B) 100
C) 150
D) 200

Question 18

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

A) 2
B) 3
C) 5
D) 7

Question 19

If a load is pure resistive, the power factor has a value of unity, or 1.

Question 20

The phase voltage of a wye connection is less than the line voltage by a factor of the square root of 2.