Electrical Trade Theory N3 — Document
April 2020 — N3 — Electrical Trade Theory
N3
2020
Nated Engineering
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Q1— Section header —
1.1Name the indicated components of the oven thermostat in IGURE by writing only the answer next to the question number (1.1.1
1.1.6\ in the ANSWER BOOK. FIGURE 1 (6\
1.2Briefly explain the operation of the oven thermostat cir cuit shown in
Q1— Section header —
Q2— Section header —
2.1Which conductor in a single phase domestic installation should be disc onnected by the earth leakage relay when it is activated (2\
2.2Make a neat, label led sketch of a thermal magnetic ype circuit breaker. (4\
2.3Give TWO reasons why circuit brea kers installed in different sub circuits of a domestic installati on have different rating (4\ [10]10
Q3— Section header —
3.1Various options are given as possible answers to the following questions. Choose the answer and write only the letter (A C\ next to the question number (3.1
3.14\ in the ANSWE
3.1.1Cold cathode neon lamps are used for indicating lights o n these electrical appliances: Fridge , stove and washing machines Stove , fridge
3.1.2Function of a glow starter in a fluorescent lamp Limit the current of the lamp Start the lamp by opening the circuit
3.1.3urpose of a choke in a hot cathode lamp Supply ing high voltage surge req uired for starting Limit
3.1.4
3.2Study the cir cuit in FIGURE below and answer the questions. FIGURE 2
3.2.1Identify the lamp. (1\
3.2.2State the purpose of the choke in the circuit diagram. (2\
3.2.3Explain how the lamp in IGURE 2 is started (3\ [10] UESTION 4: ALTERNATING CURRENT THEORY10
Q5— Section header —
5.3Voltage drop across the capacitor (2\
5.410
Q6— Section header —
6.1A three phase delta connected motor draws a current of 10 A at full load from a 415 V supply. Calculate each of the following:
6.1.1Phase voltage across the w indings (1\
6.1.2Phase current drawn by the motor (3\
6.1.3Apparent power rating of the motor (2\
6.2Draw a neat and fully labelled diagram showing how a load is connected in delta (4\ [10]10
Q7— Section header —
7.1A 750 kVA star/d elta transformer with a turns ratio of 10:1 has a secondary line voltage of 2, 2 Calculate each of the following:
7.1.1Primary phase and line voltages (4\
7.1.2Primary line current (2\
7.1.3ower delivered at full load with agging power factor of 0, 8 (2\ State the purpose of instrument transformers used AC circuits. (2\ [10]10
Q8— Section header —
8.1Name any TWO types of field coil connections used in DC motors (2\
8.2State the function of ea ch of the following components as applicable DC motor starters:
8.2.1volt release coil
8.2.2eries resistor
8.2.3
8.3Briefly explain the operating principle mot (2\
8.4Indicate whether the following statements are TRUE or FALSE. Choose the answer and write only 'true' or 'false' next to the question number (8.4.1
8.4.3\ in the ANSWER BOOK.
8.4.1The effect of armature action can be minimised by increasing the field flux.
8.4.2The direction of rotation of dc motors may be changed by reversing the direction of the current through the field windings and the armature windings simultaneously
8.4.310
Q9— Section header —
9.1Choose a term from COLUMN B that matches a description in COLUMN A. Write only the letter (A \ next to the question number (9.1 5\ in the ANSWER BOOK. COLUMN COLUMN
9.1.5Started by DOL, star delta, or auto transformer Drives fans, electric drills and other small appliances Used for water pumps in washing machines Used on re frigerator compressors
Q10— Section header —
10.1Explain each of the following terms in semiconductor theory
10.1.1Junction
10.1.2
10.2Redraw the circuit given in F IGURE 4 in your ANSWER BOOK and show how three wattmeters are to be connected in order to measure the total power Note: No calculations are necessary. (6\ FIGURE 4
10.3How can the range of the following inst ruments be increased?
10.3.1oltmeter
10.3.210
Mark Allocation
Total100 marks
Sections10 + 10 + 10 + 10 + 10 + 10 + 10 + 10 + 10 + 10 = 100 marks
Paper information
TitleDocument
SubjectElectrical Trade Theory
LevelN3
Document typeQuestion paper
Year2020
MonthApril
Pages10
Downloads3
Examination context
Decade2020s
Years ago6y
SeasonAutumn (SH)
Start dayWednesday
Exam periodApril 2020
Days since exam2,383
About Electrical Trade Theory examination preparation
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