Question 1

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

Accepted Answer

A) True 
 B)False  True

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:
-IL(Alt) = ____ A.

Accepted Answer

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

Question 3

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

Accepted Answer

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

Question 4

Three-phase voltages are ____ degrees apart.

Accepted Answer

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

Question 5

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.

Accepted Answer

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

Question 6

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.

Accepted Answer

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

Question 7

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

Accepted Answer

A) True 
 B)False

Question 8

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

Accepted Answer

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

Question 9

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.

Accepted Answer

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

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:
-IP(Load) = ____ A.

Accepted Answer

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

Question 11

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

Accepted Answer

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

Question 12

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.

Accepted Answer

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

Question 13

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

Accepted Answer

A) True 
 B)False

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:
-EP(Load) = ____ V.

Accepted Answer

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

Question 15

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.

Accepted Answer

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

Question 16

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.

Accepted Answer

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

Question 17

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

Accepted Answer

A) True 
 B)False

Question 18

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

Accepted Answer

A) True 
 B)False

Question 19

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

Accepted Answer

A)    
B)    
C)    
D)    
A)    
B)    
C)    
D)

Question 20

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.

Accepted Answer

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

Exam 12: Three-Phase Circuits

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

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.

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

Three-phase voltages are ____ degrees apart.

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.

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.

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

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

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.

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.

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

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.

The phase voltage of a wye connection is less than the line voltage by a factor of the square root of 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: -EP(Load) = ____ V.

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.

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

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

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

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.

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