Question 1

What electrical quantity cannot be changed by a transformer?

Accepted Answer

A)  Voltage 
B)  Current 
C)  Impedance 
D)  Frequency 
A)  Voltage 
B)  Current 
C)  Impedance 
D)  Frequency D

Question 2

A delta-connected three-phase load is connected to a 560 V line. The loads have an impedance of 14   per phase. What is the apparent power of this connection?

Accepted Answer

A)  22.39 kVA 
B)  116.39 kVA 
C)  38.8 kVA 
D)  67.2 kVA 
A)  22.39 kVA 
B)  116.39 kVA 
C)  38.8 kVA 
D)  67.2 kVA C

Question 3

A transformer has a turns ratio of 1:3. The primary voltage is 120 V. The secondary current is 1.2 A. What is the primary current?

Accepted Answer

A)  0.4 A 
B)  0.84 A 
C)  2.4 A 
D)  3.6 A 
A)  0.4 A 
B)  0.84 A 
C)  2.4 A 
D)  3.6 A D

Question 4

A transformer has a turns ratio of 1:3. The primary voltage is 120 V. What is the secondary voltage?

Accepted Answer

A)  40 V 
B)  84 V 
C)  240 V 
D)  360 V 
A)  40 V 
B)  84 V 
C)  240 V 
D)  360 V

Question 5

A transformer that has 480 V applied to its primary winding and produces 120 V at its secondary winding is called a(n) ____.

Accepted Answer

A)  autotransformer 
B)  isolation transformer 
C)  step-up transformer 
D)  step-down transformer 
A)  autotransformer 
B)  isolation transformer 
C)  step-up transformer 
D)  step-down transformer

Question 6

A transformer has a turns ratio of 2.5:1. The primary voltage is 208 V. What is the voltage of the secondary winding?

Accepted Answer

A)  520 V 
B)  360.26 V 
C)  83.2 V 
D)  120 V 
A)  520 V 
B)  360.26 V 
C)  83.2 V 
D)  120 V

Question 7

The 1:1 transformer is used to provide ____________________ between electrical circuits.

Accepted Answer

The answer of The 1:1 transformer is used to provide...

Question 8

Which of the following statements is true for a delta-connected three-phase system?

Accepted Answer

A)  Line current is higher than phase current by a factor of 1.732. 
B)  Phase current is higher than line current by a factor of 1.732. 
C)  Line current is less than phase current by a factor of 1.732. 
D)  Line current and phase current are equal. 
A)  Line current is higher than phase current by a factor of 1.732. 
B)  Phase current is higher than line current by a factor of 1.732. 
C)  Line current is less than phase current by a factor of 1.732. 
D)  Line current and phase current are equal.

Question 9

An autotransformer ____.

Accepted Answer

A)  has its primary and secondary windings electrically and mechanically separated from each other 
B)  uses the same winding for both the primary and secondary windings 
C)  produces a lower secondary voltage than the primary voltage 
D)  produces a higher secondary voltage than the primary voltage 
A)  has its primary and secondary windings electrically and mechanically separated from each other 
B)  uses the same winding for both the primary and secondary windings 
C)  produces a lower secondary voltage than the primary voltage 
D)  produces a higher secondary voltage than the primary voltage

Question 10

A three-phase wye-connected load is connected to a 480 V three-phase line. The line current is 36 A. If this load is purely resistive, what is the total amount of power being used in this circuit?

Accepted Answer

A)  51.84 kW 
B)  29.93 kW 
C)  7.48 kW 
D)  12.96 kW 
A)  51.84 kW 
B)  29.93 kW 
C)  7.48 kW 
D)  12.96 kW

Question 11

The windings of an alternator are delta connected. The alternator is producing a line-to-line voltage of 480 V. A connected load draws 25.98 A of line current. What is the value of the phase current?

Accepted Answer

A)  25.98 A 
B)  45 A 
C)  15 A 
D)  17.32 A 
A)  25.98 A 
B)  45 A 
C)  15 A 
D)  17.32 A

Question 12

Which of the following statements is true for a wye-connected three-phase system?

Accepted Answer

A)  Line current is higher than phase current by a factor of 1.732. 
B)  Phase current is higher than line current by a factor of 1.732. 
C)  Line current is less than phase current by a factor of 1.732. 
D)  Line current and phase current are equal. 
A)  Line current is higher than phase current by a factor of 1.732. 
B)  Phase current is higher than line current by a factor of 1.732. 
C)  Line current is less than phase current by a factor of 1.732. 
D)  Line current and phase current are equal.

Question 13

The windings of an alternator are delta connected. The alternator is producing a line-to-line voltage of 480 V. What is the value of the phase voltage?

Accepted Answer

A)  480 V 
B)  120 V 
C)  277 V 
D)  831 V 
A)  480 V 
B)  120 V 
C)  277 V 
D)  831 V

Question 14

For a wye-connected three-phase system the line voltage is higher than phase voltage by a factor of 1.732.

Accepted Answer

A) True 
 B)False

Question 15

A transformer has a turns ratio of 2.5:1. The primary voltage is 208 V. The secondary current is 18 A. What is the primary current?

Accepted Answer

A)  7.2 A 
B)  83.2 A 
C)  45 A 
D)  11.56 A 
A)  7.2 A 
B)  83.2 A 
C)  45 A 
D)  11.56 A

Exam 19: Transformers

What electrical quantity cannot be changed by a transformer?

A delta-connected three-phase load is connected to a 560 V line. The loads have an impedance of 14 per phase. What is the apparent power of this connection?

A transformer has a turns ratio of 1:3. The primary voltage is 120 V. The secondary current is 1.2 A. What is the primary current?

A transformer has a turns ratio of 1:3. The primary voltage is 120 V. What is the secondary voltage?

A transformer that has 480 V applied to its primary winding and produces 120 V at its secondary winding is called a(n) ____.

A transformer has a turns ratio of 2.5:1. The primary voltage is 208 V. What is the voltage of the secondary winding?

The 1:1 transformer is used to provide ____________________ between electrical circuits.

Which of the following statements is true for a delta-connected three-phase system?

An autotransformer ____.

A three-phase wye-connected load is connected to a 480 V three-phase line. The line current is 36 A. If this load is purely resistive, what is the total amount of power being used in this circuit?

The windings of an alternator are delta connected. The alternator is producing a line-to-line voltage of 480 V. A connected load draws 25.98 A of line current. What is the value of the phase current?

Which of the following statements is true for a wye-connected three-phase system?

The windings of an alternator are delta connected. The alternator is producing a line-to-line voltage of 480 V. What is the value of the phase voltage?

For a wye-connected three-phase system the line voltage is higher than phase voltage by a factor of 1.732.

A transformer has a turns ratio of 2.5:1. The primary voltage is 208 V. The secondary current is 18 A. What is the primary current?

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