Question 1

1.1 What is a variable speed drive (VSD), and how can it be used to reduce energy wastage in industrial applications? What systems can make use of VSDs? (Max. 100 words)

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1.2 The following questions apply to either brushed motors or induction motors. For each question, give the type of motor that correctly answers the question.

1.2.1 Which motor uses direct current?

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1. 1.2.2 Which motor does not have a commutator?

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2. 1.2.3 Which motor's stator contains permanent magnets?

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2. 1.2.4 Which motor has current supplied to its rotor?

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Question 2

The owner of a small factory has decided to replace two 40kW AC motors with new high-efficiency motors, costing R8,000 each. The motors run for 6,000 hours each year at three quarters of their load. The old motors each have an efficiency of 86%, while the new high-efficiency motors have a 90% efficiency.

2.1 What would the annual savings be as a result of installing the high-efficiency motors if electricity costs 132c/kWh? Be sure to show your calculations.

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2.2 What is the payback period for investing in these high-efficiency motors? Show your calculations.

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2.3 Why is motor replacement often better than motor repair? (Max. 50 words)

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Question 3

A stationery factory uses compressed air to inflate the packaging of its stationery sets before they are shipped. The factory's energy manager has noticed that the generation of compressed air accounts for 45% of energy use in the factory. The factory owner is very upset about this and has instructed the energy manager to make changes to the system so that this percentage decreases significantly.

3.1 Are there any alternatives to using compressed air? Briefly explain the options to the energy manager. (Max. 50 words)

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3.2 What would you recommend the energy manager to do to reduce energy costs in the compressed air system? Be sure to provide at least five recommendations. (Max. 200 words, bullet point format is allowed)

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Question 4

4.1 A centrifugal pump is used to pump water from one tank to another. The difference in height between these tanks is 140m. What is the theoretical minimum power required to pump 15,000kg of water from the bottom tank to the top tank in 6 hours? Assume that gravity = 10m/s². Show your calculations in your answer.

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4.2 In reality, there is friction in the piping, which means that an additional pressure equivalent to a height of 100 m is needed to pump the water from the bottom tank to the top tank. What is the minimum power required when accounting for friction? By what percentage has friction increased the minimum power required? Remember to show your calculations.

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Question 5

A certain fan system has a seasonal airflow requirement as shown inFigure 1. For four months of the year, the demand is almost double that of the other eight months.

Average air flow rates (monthly) 12 10 8 Flow rate (m3/s) 4 2 O Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec MonthDuration diagram 12 10 8 6 Flow rate (m3/s) 4 T O Nov Jan Feb Dec Jun May Sep Apr Jul Mar Oct Aug MonthDuration diagram (power) (approximated) 120 100 80 Fan output power (KW) 60 40 20 1 2 3 4 5 6 7 8 9 10 11 12 Month