NATIONAL SENIOR CERTIFICATE GRADE 12

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1 NAONA ENO EFAE GADE 12 EEA EHNOOGY: OWE YEM EXEMA 2018 MAK: 200 ME: 3 hours his question paper consists of 11 pages and a 2-page formula sheet.

2 Electrical echnology: ower ystems 2 DBE/2018 NUON AND NFOMAON his question paper consists of X questions. Answer A the questions. 3. ketches and diagrams must be large, neat and fully labelled. 4. how A calculations and round off answers correctly to WO decimal places. 5. Number the answers correctly according to the numbering system used in this question paper. 6. You may use a non-programmable calculator. 7. how the units for A answers of calculations. 8. A formula sheet is provided at the end of this question paper. 9. Write neatly and legibly.

3 Electrical echnology: ower ystems 3 DBE/2018 QUEON 1: OUAONA HEAH AND AFEY (GENE) 1.1 Define the term workplace with reference to the Occupational Health and afety Act, 1993 (Act 85 of 1993) (2) 1.2 Name WO general duties for employees at the workplace. (2) 1.3 Explain why 'insufficient ventilation' is an unsafe condition in the workshop. (2) 1.4 tate WO functions of a health and safety representative. (2) 1.5 Explain quantitative risk analysis. (2) [10] QUEON 2: U (GENE) 2.1 Explain the phase relationship between current and voltage in the following A circuits: esistive circuit (2) ure capacitive circuit (2) ure inductive circuit (2) 2.2 FGUE 2.2 below shows an series circuit, which consists of a 12 Ω resistor, a 30 mh inductor and a 150 µf capacitor, all connected across a 120 /60 Hz supply. 12 Ω 30 mh 150 µf 120 / 60 Hz Given: 12 Ω 30 mh 150 µf s 120 /60 Hz f 50 Hz FGUE 2.2: EE U

4 Electrical echnology: ower ystems 4 DBE/2018 alculate the: nductive reactance (3) apacitive reactance (3) mpedance (3) otal current (3) ower factor (3) tate whether the phase angle is leading or lagging. (1) 2.3 efer to FGUE 2.3 and answer the questions that follow. Z (Ω) D X Xc F Frequency (Hz) FGUE 2.3 : FEQUENY EU MEDANE Describe how an increase in the frequency of the supply voltage will affect the: (a) nductive reactance (2) (b) apacitive reactance (2) Explain why the response of line is parallel to line F (2) Name the electrical quantity that is equal to at point D. (1)

5 Electrical echnology: ower ystems 5 DBE/ An parallel circuit consists of a 30 mh inductor, a 10 Ω resistor and a 120 µf capacitor connected across a 120 alternating supply. Given: 30 mh 120 µf 10 Ω 120 alculate the: esonant frequency (3) Q-factor (5) Bandwidth (3) [40]

6 Electrical echnology: ower ystems 6 DBE/2018 QUEON 3: HEE-HAE A GENEAON (EF) 3.1 Name HEE advantages of a three-phase A generation over a singlephase A generation. (3) 3.2 Draw a fully labelled waveform to represent the generation of a three-phase voltage system. (6) 3.3 Explain the following terms: Efficiency (2) ower factor (2) 3.4 efer to the losses occurring during the transmission of electrical power from the power station to the distributing point and answer the following questions: Name the main type of losses occurring in the transmission line. (1) Describe how these losses can be reduced. (2) 3.5 A 380 /50 Hz three-phase A delta-connected motor has an output power of 12,75 kw and operates at a lagging power factor of 0,77. he efficiency of the motor is 85%. Given: ŋ θ out % 0,77 lagging 12,75 kw alculate the: nput power (3) ine current (3) hase current (3) 3.6 tate the function of a kwh meter. (2) 3.7 A two-wattmeter method is used to measure the input power in a balanced three-phase load. f the wattmeter readings are 8 kw and 4 kw respectively, calculate the total input power. (3) [30]

7 Electrical echnology: ower ystems 7 DBE/2018 QUEON 4: HEE-HAE ANFOME (EF) 4.1 Name WO construction types of transformers. + (2) 4.2 tate HEE factors that may contribute to the excessive heating of transformers. (3) 4.3 Explain how the following losses occur in the transformers: Hysteresis losses (3) Eddy current losses in a transformer (3) 4.4 Describe how the phase current is induced in the secondary winding of the transformer. (4) 4.5 A 12 ka three-phase transformer is connected in delta-star and has a turns ratio of 5 : 1. he primary line voltage is 2,2 k. Given: 12 ka 5 : 1 2,3 k pf 0,9 lagging alculate the: rimary phase voltage (2) econdary line voltage (6) Active power if the transformer has a lagging power factor of 0,9 (3) 4.6 efer to QUEON 4.5 and answer the questions that follow Name WO applications of this type of transformer. (2) tate, with reason, whether the transformer is a step-down transformer or a step-up transformer. (2) [30]

8 Electrical echnology: ower ystems 8 DBE/2018 QUEON 5: HEE-HAE MOO AND AE (EF) 5.1 Define the term slip with reference to a three-phase A squirrel-cage induction motor. (2) 5.2 tate WO mechanical inspections that must be conducted after installation and before commissioning. (2) 5.3 Give WO reasons why the rotor of the squirrel-cage induction motor is skewed. (2) 5.4 Explain how the torque is developed in a squirrel-cage induction motor. (3) 5.5 tate WO applications of a squirrel-cage induction motor. (2) 5.6 efer to FGUE 5.6 below and answer the questions that follow. % of load-torque (a) ull-up torque (b) (c) % of speed FGUE 5.6: HAAE UE OF EED OQUE dentify the torque developed at the following points: (a) (1) (b) (1) Explain why the torque developed at (c) is zero (2)

9 Electrical echnology: ower ystems 9 DBE/ FGUE 5.7 below shows a control circuit. tudy the diagram and answer the questions that follow. O/ top button M1 N/O2 tart button M1 N/O1 M3 N/ N/ M2 N/ N/O M1 imer () M2 M3 N FGUE 5.7: ONO U dentify the control circuit diagram in FGUE 5.7. (1) Describe what will happen to the motor if the normally closed contact of the overload is permanently closed due to a fault. (2) Describe the function of the following components as used in the circuits: (a) top button (2) (b) M1 (N/O 1 ) (2) tate why the N/ contact of M3 is connected in series with a star contactor. (2) 5.8 A three-phase 15 kw induction motor is connected in delta to a 380 /50 Hz supply. he motor has a lagging power factor of 0,9. Given: f os Ø 15 kw 50 Hz 0,8 lagging 380 alculate the: ine current drawn from the supply (3) Apparent power of the motor (3) [30]

10 Electrical echnology: ower ystems 10 DBE/2018 QUEON 6: OGAMMABE OG ONOE (EF) 6.1 tate HEE safety precautions to be observed when connecting external cables to a. (3) 6.2 Name WO types of hardware components of the other than the central processing unit (U). (2) 6.3 tate HEE advantages of the over the hardwired system. (3) 6.4 tate why an interface is connected at the inputs of the U. (2) 6.5 Explain the programmed scan cycle under the following headings: nput scan (3) rocess scan (3) Output scan (2) 6.6 efer to analogue and digital input as used in the and answer the following questions: Explain the difference between an analogue input and a digital input (4) Give WO examples of the digital inputs. (2) tate HEE applications of the inductive proximity sensor as an analogue input. (3) 6.7 tate when a maker/flag function is used in the. (2) 6.8 efer to FGUE 6.8 on the next page and draw the ladder logic diagram that would execute the same function.

11 Electrical echnology: ower ystems 11 DBE/ efer to FGUE 6.8 below and draw the ladder logic diagram that would execute the same function. O/ top tart Forward M1 (N/O) tart everse M2 (N/O) M2 (N/) M1 (N/) M1 Forward M2 everse N FGUE 6.8: ONO U (10) 6.9 tate HEE basic applications of the variable speed drive (D). (3) 6.10 Name HEE methods in which the speed of the motor can be controlled with the exception of pulse width modulation. (3) 6.11 Describe how the pulse width modulation as a method of varying the speed of the motor achieves its function. (4) 6.12 Describe how the D controls the speed of motors under the following subcircuits: Diode bridge rectifier (2) Filtering circuit (3) nverting circuit (3) 6.13 Describe the concept of regenerative braking. (3) [60] OA: 200

12 Electrical echnology: ower ystems DBE/2018 FOMUA HEE HEE-HAE A GENEAON U X 2 f A and 3 H and H H Z 1 H F O 2π H X c 1 2 f DEA H and 3 H EE H H Z 2 H Z + ( X X ) 2 OWE ( ) app 3 Z Q ( ) 3 in θ os θ 3 osθ WO-WAMEE MEHOD + X and X 2 and ( ) 2 Z os θ Z os θ os θ 1 2 A HEE-HAE ANFOME 3 and H H X X Q Z Z AAE 1 + DEA 3 and H H and X X OWE Q ( ) app 3 ( ) 3 in θ os θ 2 osθ + ( ) 2 X X Q Z Z 1

13 Electrical echnology: ower ystems DBE/ ( ) app 3 ph ph p s N N p s osθ ph ph s p HEE-HAE MOO AND AE MOO EED 60 f n s p lip ns n n s r A 3 and H H DEA 3 and H H OWE Q ( ) app 3 ( ) 3 in θ os θ 3 osθ H Efficiency ( η) in losses in

GRAAD 12 NATIONAL SENIOR CERTIFICATE GRADE 12

GRAAD 12 NATIONAL SENIOR CERTIFICATE GRADE 12 GRAAD 12 NATONA SENOR ERTFATE GRADE 12 EETRA TEHNOOGY NOEMBER 2016 MARKS: 200 TME: 3 hours This question paper consists of 14 pages and a 2-page formula sheet. Electrical Technology 2 DBE/November 2016