Question 1

A simple two-phase generator consists of two conductive loops, separated by 180°, rotating in a magnetic field.

Accepted Answer

A) True 
 B)False

Question 2

Power is measured in three-phase systems using:

Accepted Answer

A)  wattmeters 
B)  AC voltmeters 
C)  voltmeters 
D)  ammeters 
A)  wattmeters 
B)  AC voltmeters 
C)  voltmeters 
D)  ammeters

Question 3

Compare the total copper cross sections in terms of current-carrying capacity for a single-phase system and a three-phase 120 V system with an effective load of 50 Ω.

Accepted Answer

A)  Single-phase 7.2 A; three-phase 4.8 A 
B)  Single-phase 4.8 A; three-phase 2.4 A 
C)  Single-phase 9.6 A; three-phase 14.4 A 
D)  Single-phase 4.8 A; three-phase 0 A 
A)  Single-phase 7.2 A; three-phase 4.8 A 
B)  Single-phase 4.8 A; three-phase 2.4 A 
C)  Single-phase 9.6 A; three-phase 14.4 A 
D)  Single-phase 4.8 A; three-phase 0 A

Question 4

Which of the following are source/load configurations?

Accepted Answer

A)  Y-Y system 
B)  O-Y system 
C)  Y-O system 
D)  O-O system 
E)  all of the above 
A)  Y-Y system 
B)  O-Y system 
C)  Y-O system 
D)  O-O system 
E)  all of the above

Question 5

In a Y-Y source/load configuration, the:

Accepted Answer

A)  phase current, the line current, and the load current are 120° out of phase. 
B)  phase current, the line current, and the load current are all equal in each phase. 
C)  phase current and the line current are in phase, and both are 120° out of phase with the load current. 
D)  line current and the load current are in phase, and both are out of phase with the phase current. 
A)  phase current, the line current, and the load current are 120° out of phase. 
B)  phase current, the line current, and the load current are all equal in each phase. 
C)  phase current and the line current are in phase, and both are 120° out of phase with the load current. 
D)  line current and the load current are in phase, and both are out of phase with the phase current.

Question 6

The output of an ac generator has a maximum value of 240 V. At what angle is the instantaneous voltage equal to 85 V?

Accepted Answer

A)  69.3° 
B)  19.5° 
C)  90° 
D)  20.7° 
A)  69.3° 
B)  19.5° 
C)  90° 
D)  20.7°

Question 7

A balanced load is one in which all impedances are equal.

Accepted Answer

A) True 
 B)False

Question 8

The secondary of a power transformer feeding an electrical transmission line acts as a to the transmission line.

Accepted Answer

A)  load 
B)  source 
A)  load 
B)  source

Question 9

In a O-connected generator, the phase voltages are 208 V. What are the line voltages?

Accepted Answer

A)  360 V 
B)  120 V 
C)  132 V 
D)  208 V 
A)  360 V 
B)  120 V 
C)  132 V 
D)  208 V

Question 10

In general, the three-phase system is more economical for transmitting power at a fixed power loss than is the single-phase system.

Accepted Answer

A) True 
 B)False

Question 11

In a certain O-connected balanced load, the line voltages are 230 V and the impedances are 60 235° Ω. Determine the magnitude of the phase currents.

Accepted Answer

A)  4.15 A 
B)  2.78 A 
C)  3.83 A 
D)  1.63 A 
A)  4.15 A 
B)  2.78 A 
C)  3.83 A 
D)  1.63 A

Question 12

A single-phase sinusoidal voltage of 120 V is connected to a 70 Ω load. Current in the circuit is:

Accepted Answer

A)  174 mA 
B)  1.71 A 
C)  17.1 A 
D)  17.1 mA 
A)  174 mA 
B)  1.71 A 
C)  17.1 A 
D)  17.1 mA

Question 13

In a O-connected source feeding a Y-connected load:

Accepted Answer

A)  each phase voltage equals the difference between the corresponding load voltages. 
B)  each phase voltage equals the corresponding load voltage. 
C)  each phase voltage is 60° out of phase with the corresponding load voltage. 
D)  each phase voltage is one-third the corresponding load voltage. 
A)  each phase voltage equals the difference between the corresponding load voltages. 
B)  each phase voltage equals the corresponding load voltage. 
C)  each phase voltage is 60° out of phase with the corresponding load voltage. 
D)  each phase voltage is one-third the corresponding load voltage.

Question 14

Determine the instantaneous voltage of an ac generator, where the maximum voltage is 208 V, and the angle is 40 degrees.

Accepted Answer

A)  208 V 
B)  159.3 V 
C)  147 V 
D)  133.7 V 
A)  208 V 
B)  159.3 V 
C)  147 V 
D)  133.7 V

A simple two-phase generator consists of two conductive loops, separated by 180°, rotating in a magnetic field.

Power is measured in three-phase systems using:

Compare the total copper cross sections in terms of current-carrying capacity for a single-phase system and a three-phase 120 V system with an effective load of 50 Ω.

Which of the following are source/load configurations?

In a Y-Y source/load configuration, the:

The output of an ac generator has a maximum value of 240 V. At what angle is the instantaneous voltage equal to 85 V?

A balanced load is one in which all impedances are equal.

The secondary of a power transformer feeding an electrical transmission line acts as a to the transmission line.

In a O-connected generator, the phase voltages are 208 V. What are the line voltages?

In general, the three-phase system is more economical for transmitting power at a fixed power loss than is the single-phase system.

In a certain O-connected balanced load, the line voltages are 230 V and the impedances are 60 235° Ω. Determine the magnitude of the phase currents.

A single-phase sinusoidal voltage of 120 V is connected to a 70 Ω load. Current in the circuit is:

In a O-connected source feeding a Y-connected load:

Determine the instantaneous voltage of an ac generator, where the maximum voltage is 208 V, and the angle is 40 degrees.

Quantities and Units

Voltage, Current, and Resistance

Ohms Law

Energy and Power

Series Circuits

Parallel Circuits

Series-Parallel Circuits

Circuit Theorems and Conversions

Branch, Loop, and Node Analyses

Magnetism and Electromagnetism

Introduction to Alternating Current and Voltage

Capacitors

Inductors

Transformers

Rc Circuits

Rl Circuits

Rlc Circuits and Resonance

Passive Filters

Circuit Theorems in Ac Analysis

Time Response of Reactive Circuits

Filters

Exam 21: Three-Phase Systems in Power Applications

A simple two-phase generator consists of two conductive loops, separated by 180°, rotating in a magnetic field.

Power is measured in three-phase systems using:

Compare the total copper cross sections in terms of current-carrying capacity for a single-phase system and a three-phase 120 V system with an effective load of 50 Ω.

Which of the following are source/load configurations?

In a Y-Y source/load configuration, the:

The output of an ac generator has a maximum value of 240 V. At what angle is the instantaneous voltage equal to 85 V?

A balanced load is one in which all impedances are equal.

The secondary of a power transformer feeding an electrical transmission line acts as a to the transmission line.

In a O-connected generator, the phase voltages are 208 V. What are the line voltages?

In general, the three-phase system is more economical for transmitting power at a fixed power loss than is the single-phase system.

In a certain O-connected balanced load, the line voltages are 230 V and the impedances are 60 235° Ω. Determine the magnitude of the phase currents.

A single-phase sinusoidal voltage of 120 V is connected to a 70 Ω load. Current in the circuit is:

In a O-connected source feeding a Y-connected load:

Determine the instantaneous voltage of an ac generator, where the maximum voltage is 208 V, and the angle is 40 degrees.

Quantities and Units

Voltage, Current, and Resistance

Ohms Law

Energy and Power

Series Circuits

Parallel Circuits

Series-Parallel Circuits

Circuit Theorems and Conversions

Branch, Loop, and Node Analyses

Magnetism and Electromagnetism

Introduction to Alternating Current and Voltage

Capacitors

Inductors

Transformers

Rc Circuits

Rl Circuits

Rlc Circuits and Resonance

Passive Filters

Circuit Theorems in Ac Analysis

Time Response of Reactive Circuits

Filters