Electrotechnics N6 — Document

August 2021 — N6 — Electrotechnics

N6 2021 Nated Engineering

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🎯 100 marks ⏱️ 3h 📄 5 pages 📝 42 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 —

1.1Explain how the speed of a DC motor varies in relation to the following:

1.1.1The armature voltage

1.1.2

1.2of 25 A when running at 750 r/min. Assume the flux to be proportional to the current. Calculate the following:

1.2.1The speed when the motor takes a current of 40 A (6\

1.2.2The ratio of the two torques developed (3\ [13]13

Q2— Section header —

2.1Explain the concept complex wave. (2\

2.2An EMF represented by e = 140,44 Sin 314t + 80,72 Sin 1 570t is applied across a resistor of 10 in parallel with an inductor of 0,02 Calculate the following:

2.2.1The power absorbed by the circuit (3\

2.2.2The RMS value of the current supplied to the circuit (10\ [15]15

Q3— Section header —

3.1Define the voltage regulation of a transformer. (3\

3.2Name TWO effects of harmonic voltages in a transformer. (2\ 8080096 Copyright reserved

3.3The percentage impedance referr ing to the primary coil of a 250 kVA, 1 800/450 V single phase, 50 Hz transformer is (0,6 + j4,4\

3.3.1he turns ratio (2\

3.3.2he percentage resistance (3\

3.3.3The percentage reactance (2\

3.3.4The full load copper loss (2\

3.3.5The power factor at which maximum regulation occurs (2\

3.3.6The voltage to be applied to the primary to circulate full load current in the secondary circuit (2\ [18]18

Q4— Section header —

4.1Calculate the number of poles (3\

4.2Calculate the useful flux per pole (8\ [11]11

Q5— Section header —

5.1What is a synchronous capacitor (2\

5.2A three phase synchronous motor is connected in parallel with a load of 500 kW at a power factor of 0,75 lagging. The excitation of the motor is adjusted until the total power factor is 0,9 lagging. The input of the motor

5.2.1Calculate the kVA input to the motor. (7\

5.2.2Calculate the power factor of the motor. (1\ [10] 808009610

Q6— Section header —

6.1Define torque in synchronous watts (2\

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

6.3The power input to the rotor of a 440 V, 50 Hz, 6 pole induction motor is 100 kW. The rotor electromotive force is observed to make 120 cycles per minute. Calculate the following:

6.3.1The slip

6.3.2The rotor speed

6.3.3The mechanical power developed

6.3.4The rotor copper loss per phase

6.3.5The speed of the stator field with respect to the rotor (5 2\ (10\ [14] QUESTION 7: GENERATION AND SUPPLY OF AC14

7.1Define regulation of a transmission line (3\

7.2State THREE effects of a poor power factor. (3\

7.3Apply the method to calculate the sending end voltage, current and power factor of a 150 km transmission line. The line delivers a three phase load of 15 MW at a power factor of 0,8 lagging and a line voltage of 90 kV, 50 Hz.

Topics Identified

Business Plan

Mark Allocation

Total100 marks

Sections13 + 15 + 18 + 11 + 10 + 14 + 19 = 100 marks

Paper information

TitleDocument

SubjectElectrotechnics

LevelN6

Document typeQuestion paper

Year2021

MonthAugust

Pages10

Downloads3

Examination context

Decade2020s

Years ago5y

SeasonWinter (SH)

Start daySunday

Exam periodAugust 2021

Days since exam1,896

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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