Electrical Principles And Practice NCV Level 4 — Document
November 2019 — NCV Level 4 — Electrical Principles And Practice
NCV Level 4
2019
NCV Engineering
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Q1— Section header —
1.1An electrical network is a system of interconnected elements , including resistors, inductors, capacitors, voltage sources, current sources and switches. Name FOUR classifications of electrical networks.
1.2Refer to the circuit diagram in FIGURE 1 below and calculate the following:
1.2.1The total resistance of the circuit (7
1.2.2The current flowing through the R resistor (2\
1.2.3If resistor is disconnected from the circuit, determine the total resistance of the circuit. (2
1.2.4etermine the total current of the circuit as the result of disconnecting resistor R (2\
1.3The voltage applied to an AC circuit is presented by the equation v = 200 sin 628 t. Determine the following:
1.3.1The rms value of the voltage (2\
1.3.2The frequency of this voltage (2\
1.3.3The instan taneous value of the voltage, 2 ms after the commencement of a cycle (3\ (12041004\
1.4Explain the difference between the form factor and the peak factor of a sine wave. (2
1.5The apparent input power to a single phase motor is 7 kVA at a power factor of 0,6 lagging. Determine the reactive power. (3\
1.6What do you understand by the term maximum value of a sine wave [30]30
Q2— Section header —
2.1The generation of electricity is the conversion of other forms of energy into electrical current, one of type of resources that is mainly used to generate electricity is Hydro electric energy Describe how hydro
2.2State the SIX advantages of the three phase distribution system. (6
2.3Star and delta connections are the two types of connections in three phase circuits. Compare these TWO connections with respect to their voltages. (2\
2.4There are several components and materials used in overhead transmission lines. Explain the purpose of poles in overhead transmission lines. (1
2.5A three phase AC motor draws a current of 12 A when connected in delta to a 380 V supply at a power factor of 0,9. Calculate the input power of the motor in kW. (3\ [15]15
Q3— Section header —
3.1Lives can be saved if earthing is maintained and inspected regularly.
3.1.1Give THREE reasons why it is important to earth the domestic installations and the electrical appliances (3
3.1.2Name THREE types of earth electrodes that can be used in the field of earthing. (3\
3.2Describe how you would test the continuity of bonding in an electrical installation. (3\ (12041004\ Copyright reserved Please turn over
3.3What do you understand by term earth electrode (2\
3.4What do you call the current that flows to earth in an electrically undamaged circuit? (1\
3.5Explain what is meant by the following earthing systems:
3.5.1TN (2\
3.5.2TN (1 [15]15
Q4— Section header —
4.1Given a working step down transformer without information(details\ , how would you identify the primary and the secondary terminals? (3\
4.2A 300 kVA transformer operat es at a power factor of 0,85. Calculate the efficiency of a transformer at full load if the total losses amount to 1,9 kW. (5\
4.3Your foreman has requested you to connect THREE single phase transformers to produce ONE three
4.4The windings of a transformer are supported by a core. Distinguish between hollow core and shell core type transformer. (2\
4.5Complete the following table by writing only the answer next to the question number (4.5.1
4.5.4\n the ANSWER BOOK. TRANSFORMER CONNECTIONS APPLICATIONS Delta delta connection
4.5.1Star Star connection
4.5.2Delta star connection
4.5.3Star delta connection
4.5.420
Q5— Section header —
5.1Separately excited generators are used in automatic motor control systems.
5.1.1Make a neat fully labelled sketch of the characteristic curve of a separately excited generator. (4\
5.1.2Explain the characteristic curve you have drawn in
Q5— Section header —
5.2A three phase induction motor is the type of electric motor that is used most extensively. Explain the operation of a three
5.3A six pole induction motor is connected to a 60 Hz supply. If the rotor runs at 900 rev/min Calculate the following:
5.3.1The synchronous speed of the magnetic field (2\
5.3.2The slip at full load (2
5.4Explain how the direction of rotation of a compound wound DC motor can be reversed. (2\
5.5Induction motors need to be tested regularly to ensure they are working properly. Explain the purpose of the open circuit test on induction motor. (2\ [20] TOTAL:20
Topics Identified
1
Business Plan
Mark Allocation
Total100 marks
Sections30 + 15 + 15 + 20 + 20 = 100 marks
Paper information
TitleDocument
SubjectElectrical Principles And Practice
LevelNCV Level 4
Document typeQuestion paper
Year2019
MonthNovember
Pages9
Downloads2
Examination context
Decade2010s
Years ago7y
SeasonSpring (SH)
Start dayFriday
Exam periodNovember 2019
Days since exam2,536
About Electrical Principles And Practice examination preparation
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