Fault finding and protective devices, Study notes of Electrical and Electronics Engineering

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COMPILED QUESTIONS AND ANSWERS

FAULT FINDING

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PROTECTIVE DEVICES

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Contents

• HEAVY CURRENT
  • Basic philosophy
  • Symbols
    • Circuits
    • Instruments
    • Fault finding techniques
    • Typical Heavy Current Circuits
    • Electrical Insulating Material
    • Motor Protection
• LIGHT CURRENT
  • QUESTION
  • QUESTION
  • QUESTION
  • QUESTION

1.3. Name and explain the correct methods which could be applied with success when collecting facts. (6) 1.4. What has been achieved? (4) 1.5. What has been achieved is the stage where results are seen. There are then questions that can be asked. Write down and explain these questions. (9)

1.6. What is the best action to take? (3 x 2) (6)

2. Describe the basic philosophy concerning fault-finding. (4)
3. Why was the nine-point plan designed? (3)
4. With reference to the nine-point plan, explain what the problem with fault-finding is. (3)
5. State any EIGHT elements of the nine-point plan regarding fault finding. (8 × ½) (4)

Circuits

1. Make a sketch of an automatic star-delta motor starter for a three-phase induction motor. (8)

2. Draw a circuit diagram of a hand-operated autotransformer
3. Draw a simple inching circuit.

5. Draw a control circuit of a three-phase forward and reverse star/delta automatic starter. (10)

6. Draw a diagram of an automatic hand operated star delta. (10)

8. Draw a forward-reverse automatic star-delta control and main circuit for a three-phase motor.
9. Name THREE uses of an inching circuit. (3)

Instruments

1. Why does the moving-coil instrument need a low shunt resistance? (3)
2. Name TWO methods of damping in moving-coil instruments. (2)
3. Explain in your own words why ammeters are low- resistance instruments. (3)
4. Draw a Wheatstone-bridge circuit. (7)

11. Explain the operation of the voltage tester. (5)
12. Draw a neat, simple diagram of a moving-coil meter. (9)
13. States the disadvantages of a moving coil meter. (3)

14. Draw a Wheatstone bridge circuit and explain its operation. (8)
15. Make a sketch to show the construction of a voltage tester and describe its operation. (13)

Fault finding techniques

17. State SIX common problems that occur when misleading results are obtained while using testing equipment. (6)
18. Name TWO rules that a person should know if he/she wants to become more effective in fault-finding techniques
19. Fault finding is the detection of an abnormal condition within the system. State and describe THREE fault finding methods. (6)

20. List NINE maintenance-record systems. (9)
21. Downtime analysis provides valuable information, which can be classed as one or more forms of fault- finding aid. State THREE points of importance that can be found under the following: a. Downtime according to process or machine (3) b. Time for fault diagnosis and repair according to equipment (3)