Question 1

In three-phase systems, the three __________ are identified in various ways, including using letters (A-B-C), numerals, (1-2-3), etc.

Accepted Answer

A)  phases 
B)  lines 
A)  phases 
B)  lines B

Question 2

For a balanced three-phase load, the total power is equal to

Accepted Answer

A)  the square-root of 3 multiplied by the power of any one phase. 
B)  three times the power of any one phase. 
A)  the square-root of 3 multiplied by the power of any one phase. 
B)  three times the power of any one phase. B

Question 3

The current flowing within each winding or load of a three-phase system is called a

Accepted Answer

A)  load current. 
B)  branch current. 
C)  phase current. 
D)  line current. 
A)  load current. 
B)  branch current. 
C)  phase current. 
D)  line current. C

Question 4

For a balanced delta-connected load the line current is __________ times the phase current.

Accepted Answer

A)  0.707 
B)  1 
C)  1.414 
D)  1.732 
A)  0.707 
B)  1 
C)  1.414 
D)  1.732

Question 5

The voltages generated by a three-phase generator are displaced from each other by __________ electrical degrees.

Accepted Answer

A)  30 
B)  60 
C)  90 
D)  120 
A)  30 
B)  60 
C)  90 
D)  120

Question 6

The voltage measured directly across any one of the three-phase windings or loads is called a

Accepted Answer

A)  phase voltage. 
B)  line voltage. 
A)  phase voltage. 
B)  line voltage.

Question 7

A three-phase connection, in which the end of one the windings is connected to the start of the next, is called a

Accepted Answer

A)  star' or 'wye' connection. 
B)  delta' or 'mesh' connection. 
A)  star' or 'wye' connection. 
B)  delta' or 'mesh' connection.

Question 8

The order in which of these generated voltages each reach their maximum values is termed their

Accepted Answer

A)  synchronization. 
B)  phase sequence. 
C)  phase displacement. 
D)  phase rotation. 
A)  synchronization. 
B)  phase sequence. 
C)  phase displacement. 
D)  phase rotation.

Question 9

For a balanced three-phase load, the total power is equal to

Accepted Answer

A)  3 x line voltage x line current 
B)  3 x line voltage x line current x power factor 
C)  3 x phase voltage x phase current 
D)  3 x phase voltage x phase current x power factor 
A)  3 x line voltage x line current 
B)  3 x line voltage x line current x power factor 
C)  3 x phase voltage x phase current 
D)  3 x phase voltage x phase current x power factor

Question 10

Using 'double-subscript notation', IA is read as meaning

Accepted Answer

A)  the current in line A'. 
B)  the current in phase A'. 
A)  the current in line A'. 
B)  the current in phase A'.

Question 11

Under the EU harmonisation rules, three-phase systems use the following identification colours:

Accepted Answer

A)  red-yellow-blue. 
B)  red-white-blue. 
C)  brown-black-grey. 
D)  brown-black-orange. 
A)  red-yellow-blue. 
B)  red-white-blue. 
C)  brown-black-grey. 
D)  brown-black-orange.

Question 12

When we refer to a '400-kV' transmission line, or an '11-kV distribution line', we are describing their

Accepted Answer

A)  phase voltages. 
B)  line voltages. 
A)  phase voltages. 
B)  line voltages.

Question 13

The common point of connection, described in the previous question, is called the windings'

Accepted Answer

A)  star point'. 
B)  neutral point', 
C)  either above. 
A)  star point'. 
B)  neutral point', 
C)  either above.

Question 14

For a balanced three-phase load, the total power is equal to

Accepted Answer

A)  root 3 x line voltage x line current 
B)  root 3 x line voltage x line current x power factor 
C)  root 3 x phase voltage x phase current 
D)  root 3 x phase voltage x phase current x power factor 
A)  root 3 x line voltage x line current 
B)  root 3 x line voltage x line current x power factor 
C)  root 3 x phase voltage x phase current 
D)  root 3 x phase voltage x phase current x power factor

Question 15

The voltage measured directly between any pair of the three energised conductors connecting a three-phase supply to its load is called a

Accepted Answer

A)  phase voltage. 
B)  line voltage. 
A)  phase voltage. 
B)  line voltage.

Question 16

For a star-connected supply, the line voltage is __________ times the phase voltage.

Accepted Answer

A)  0.707 
B)  1 
C)  1.414 
D)  1.732 
A)  0.707 
B)  1 
C)  1.414 
D)  1.732

Question 17

A three-phase connection, in which there is a common point of connection between all three windings, is called a

Accepted Answer

A)  star' or 'wye' connection. 
B)  delta' or 'mesh' connection. 
A)  star' or 'wye' connection. 
B)  delta' or 'mesh' connection.

Question 18

In the above example, if the load has a phase current of 15 A, then the phase current of the supply must be approximately

Accepted Answer

A)  8.67 A. 
B)  15 A. 
C)  26 A. 
A)  8.67 A. 
B)  15 A. 
C)  26 A.

Question 19

The current flowing in the neutral of a star-connected load is

Accepted Answer

A)  always zero. 
B)  the algebraic sum of the three line currents. 
C)  the phasor sum of the three line currents. 
D)  the difference between the three line currents. 
A)  always zero. 
B)  the algebraic sum of the three line currents. 
C)  the phasor sum of the three line currents. 
D)  the difference between the three line currents.

Question 20

When constructing a three-phase phasor diagrem, it is usual to construct the phasors in the following sequence:

Accepted Answer

A)  phase voltage, phase current, line voltage, line current. 
B)  line voltage, line current, phase voltage, phase current 
C)  phase voltage, line voltage, phase current, line current. 
D)  phase current, line current, phase voltage, line voltage. 
A)  phase voltage, phase current, line voltage, line current. 
B)  line voltage, line current, phase voltage, phase current 
C)  phase voltage, line voltage, phase current, line current. 
D)  phase current, line current, phase voltage, line voltage.

Exam 22: Balanced Three-Phase Ac Systems

In three-phase systems, the three __________ are identified in various ways, including using letters (A-B-C), numerals, (1-2-3), etc.

For a balanced three-phase load, the total power is equal to

The current flowing within each winding or load of a three-phase system is called a

For a balanced delta-connected load the line current is __________ times the phase current.

The voltages generated by a three-phase generator are displaced from each other by __________ electrical degrees.

The voltage measured directly across any one of the three-phase windings or loads is called a

A three-phase connection, in which the end of one the windings is connected to the start of the next, is called a

The order in which of these generated voltages each reach their maximum values is termed their

For a balanced three-phase load, the total power is equal to

Using 'double-subscript notation', IA is read as meaning

Under the EU harmonisation rules, three-phase systems use the following identification colours:

When we refer to a '400-kV' transmission line, or an '11-kV distribution line', we are describing their

The common point of connection, described in the previous question, is called the windings'

For a balanced three-phase load, the total power is equal to

The voltage measured directly between any pair of the three energised conductors connecting a three-phase supply to its load is called a

For a star-connected supply, the line voltage is __________ times the phase voltage.

A three-phase connection, in which there is a common point of connection between all three windings, is called a

In the above example, if the load has a phase current of 15 A, then the phase current of the supply must be approximately

The current flowing in the neutral of a star-connected load is

When constructing a three-phase phasor diagrem, it is usual to construct the phasors in the following sequence:

The Electron Theory of Electricity

Electric Current

Potential and Potential Difference

Resistance

Practical Conductors and Insulators

Effect of Temperature Change Upon Resistance

Ohms Law of Constant Proportionality

Series, Parallel and Series-Parallel Circuits

Cells and Batteries

Internal Resistance of Voltage Sources

Energy, Work, Heat and Power

Magnetism

Electromagnetism

Magnetic Circuits

Electromagnetic Induction

Capacitors and Capacitance

Introduction to Alternating Current

Series Alternating-Current Circuits

Power in Alternating-Current Circuits

Parallel Alternating-Current Circuits

Power Factor Improvement

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