JEP – 990

*JEP990*

II Semester M.E. (Power Electronics) Degree Examination, July 2014 (2K8 Scheme) PEL 24 : RELIABILITY ENGG. (Elective – I) Time : 3 Hours

Max. Marks : 100

Instruction : Answer any five full questions. 1. a) Define reliability, explain the three modes of failure using a suitable sketch.

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b) With usual notations, derive the expression for i) Failure rate Z(t) ii) Reliability R(t).

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2. a) Explain ‘r’ out of ‘n’ structure and the method for evaluating the reliability of the same.

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b) Five elements (a, b, c, d and e) of a system are connected as shown in the fig. Q. 2(b). Which also indicates the reliability of each element ? Calculate the system reliability.

Fig. Q. 2(b)

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P.T.O.

JEP – 990

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*JEP990*

3. a) What are the different failure mechanisms in accelerated life testing and explain. b) What is electrostatic discharge ? Explain, how it can be prevented with an suitable example. 4. a) Explain Monte-Carlo simulation in detail for power electronic system.

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b) A fuel pump with an MTTF of 3000 Hrs is to operate continuously on a 500 Hour mission. i) What is the mission reliability ? ii) If two such pumps are operated in a standby parallel configuration and there are no failures of the back-up pump. What is the system MTTF and the mission reliability ? iii) If the standby failure rate is 15% of the operational failure rate, what is the system MTTF and mission reliability ? 12 5. a) Define the following : i) Maintainability ii) Availability iii) Mean Time to Repair iv) Mean system downtime.

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b) Explain the terms, spares provisioning and power electronics system packaging as applicable to reliability engineering. 10 6. Explain Markov’s model analysis for power electronic system with a suitable example. 7. Write short notes on :

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(4×5=20)

a) Causes for the failures of a system b) Linear Hazard model c) Electrical overstress on equipments d) Tie-set method of estimating reliability of a system. –––––––––––––––––