Electrotechnics N6 — Document

August 2019 — N6 — Electrotechnics

N6 2019 Nated Engineering

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🎯 100 marks ⏱️ 3h 📄 5 pages 📝 39 items found 📚 1 topics

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This section provides a quick preview of questions from the document. It may not display every question or the complete wording of each one. For the full content, including diagrams, tables and other information, view the original PDF above.

Q1— Section header —

1.1A series motor is running on a 440 V circuit with a regulating resistance of R ohms connected in series for speed adjustment. The armature and field coils have a total resistance of 0,3 . On a certain

1.1.1ew speed (6\

1.1.2atio of the two values of the power output of the motor (2\

1.2State TWO main advantages and TWO disadv antages of the Swinburne method used to determine the efficiency of a DC machine. (4\

1.3State ONE condition under which a DC machine may work at maximum efficiency. (2\ [14]14

Q2— Section header —

2.1Name TWO devices used for improving or correcting power factor

2.2A voltage e = 250 sin ( and an inductance of 0,05 H. Calculate each of

2.2.1xpression for the current (4\

2.2.2r.m.s. value of the current (2\

2.2.3r.m.s. value of the voltage (2\

2.2.4otal power supplied (2\

2.2.5ower factor (2\ [14]14

Q3— Section header —

3.1quivalent secondary resistance as referred to the primary

3.2quivalent secondary reactance as referred to the primary (2\

3.3otal equivalent primary resistance and reactance (4\

3.4otal equivalent primary impedance

3.5otal copper loss, first using individual resistances of the TWO windings and secondly, using equivalent resistances as referred to each side (4\ [16]16

Q4— Section header —

4.1Explain with the aid of a neat diagram, how an open circuit test is carried out on a three phase star connected alternator.

4.2A three phase 11 kV star connected alternator has an armature resistance of 0,25 ohms per phase and a synchronous reactance of 3 ohms per p hase. Calculate the percentage regulation for a load of 2 000 kW at a power factor

Q5— Section header —

5.1Explain, with the aid of phasor diagrams, how the power factor of a synchronous motor workin g on a constant mechanical load depends on its excitation. (6\

5.2A 5 kVA 400 V three phase 50 Hz star connected synchronous motor is fully loaded and draws 3,5 kW at a leading power factor. The machine has a percentage impedance of (4 + j40\ %. Calculate the follo wing:

5.2.1ower factor (1\

5.2.2esistive and reactive volt drops (3\

5.2.3EMF to which the machine is excited (3\

5.2.4oad angle in electrical degrees (1\ [14]14

Q6— Section header —

6.1Explain plugging as used in motor control. (2\

6.2Name the TWO main parts of an AC motor. (2\

6.3The input of a six pole three phase 50 Hz induction motor is 45 kW at a speed of 950 r/min. The stator losses of the motor are 1 kW and the friction and windage losses are 1,5 kW. Calculate each of

6.3.1(3\

6.3.2otor copper loss (4\

6.3.3utput of the motor (2\

6.3.4ull load efficiency (1\ [14]14

Q7— Section header —

Topics Identified

Business Plan

Mark Allocation

Total100 marks

Sections14 + 14 + 16 + 14 + 14 + 14 + 14 = 100 marks

Paper information

TitleDocument

SubjectElectrotechnics

LevelN6

Document typeQuestion paper

Year2019

MonthAugust

Pages9

Downloads3

Examination context

Decade2010s

Years ago7y

SeasonWinter (SH)

Start dayThursday

Exam periodAugust 2019

Days since exam2,629

About Electrotechnics examination preparation

This TVET examination resource can be used as part of a structured revision programme. Past papers are most useful when learners attempt questions independently, work within a realistic time limit, and review their answers afterwards.

How to use this resource for revision

A TVET past examination paper is most useful when it is treated as an active revision exercise. Try the questions yourself before checking the corresponding memorandum. Where you make an error, identify the reason — was it a knowledge gap, a calculation mistake, an interpretation issue, or an examination technique problem?

For stronger examination practice, complete the paper without unnecessary interruptions and keep track of the questions that take the most time. Afterwards, review the memorandum and separate knowledge gaps from mistakes caused by interpretation, calculation, structure, or examination technique.

understanding question requirements

applying subject knowledge

working under time constraints

checking answers

identifying revision priorities

A practical revision approach

Start by completing the resource without looking at the memorandum. Review incorrect and incomplete answers afterwards and make a short revision list based on the areas that caused difficulty.

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