Deck 19: Transformers

Question 1

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

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

Answer 1

D

Question 2

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

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

Answer 2

C

Question 3

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?

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

Answer 3

A

Question 4

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

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

Question 5

An autotransformer ____.

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 6

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?

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

Question 7

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

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 8

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

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

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?

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

Question 10

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

Question 11

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

Question 12

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

Question 13

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

Question 14

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?

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

Question 15

What electrical quantity cannot be changed by a transformer?

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