UNIVERSITY OF CAPE TOWN

OFFICE OF ELECTRIC POWERED ENGINEERING

EEE3057S

Introduction to Electricity Systems (Modules A & B)

_________________________________________

FINAL EVALUATION: NOVEMBER 2012

TIME: a few HOURS

TOTAL MARKS: 100 (50 signifies for each module)

Recommendations:

This is a closed publication examination, study course notes, palm outs and sample solutions are not allowed. One A4 page formulation sheet is allowed every module. Make sure you submit the formula bed sheet with your response book. installment payments on your All numerical answers must be given to the ideal number of significant figures. several. All data needed to fix the problems get in this conventional paper. 4. Make sure you ensure that your problem paper has 7 webpages, excluding this cover page 5. Should you require further booklets, position the booklets of the identical Module with each other before submitting. 6. Component A involves questions intended for Power Consumer electronics (15 marks) and Electric powered Machines (35 marks) – 3 pages. 7. Component B contains questions intended for Part I (25 marks) and Component II (25 marks) – 4 web pages. Please answer Part-I and Part-II pertaining to Module W in independent booklets.

INTERNAL EXAMINERS: Prof E A Folly, Prof Meters A Khan, Dr P Barendse and Mrs T O Awodele EXTERNAL EXAMINER: Prof M Hippner and Dr R Holm

EEE3057S – Component A, EEE3031S

POWER CONSUMER ELECTRONICS [15 Marks]:

Question 1[6 marks]

A single-phase half-wave thyristor rectifier, which supplies a RL load, is definitely shown in the figure under. The peak input voltage can be 100V, the thyristor shooting angle is definitely and the extra conduction that occurs.

1 . 1 . Sketch the provision voltage as opposed to, the output volt quality vo as well as the current on the full routine (on the same axis).[3]

1 . 2 . Determine the output DC voltage.[3]

Issue 2[9 marks]

Consider the dc-dc ripping tools shown below (assume it really is operating in periodic steady point out and that).

2 .

2 . 1 . What is the voltage throughout the inductor,, as well as the derivative in the inductor current,, when the swap is sealed (in conditions of [2]

2 . 2 . What is the voltage over the inductor,, plus the derivative in the inductor current,, when the switch is open up (in terms of [2]

2 . three or more. Draw as well as for one period, assume the converter is continuous leasing mode.[2]

2 . 4. Make use of the expressions created in installment payments on your 2 and 2 . several to get an expression to spell out the relationship between and in terms of the duty pattern. Comment on this relationship. (Hint: the net region under VL over a complete period can be zero)[3]

POWER MACHINES [35 Marks]:

Question 3[10 marks]

A three-phase, 260V, 4-pole, Y-connected induction machine has 96 stator slot machines. The slots contain a double-layer winding with 4 becomes per coil, and a coil pitch of nineteen slots. Most coils in each period are linked in series. The speed of rotation in the airgap magnet field is definitely 1800 rpm.

3.

3. 1 . Calculate the pitch aspect for this machine.[2]

3. 2 . Calculate the distribution component.[2]

3. a few. How various turns every phase exist in this turning?[2]

3. 5. Calculate the flux every pole required to produce a range to series voltage of 260 V[3]

3. a few. Explain what is required to develop a revolving field in a several phase machine.[1]

Question four[15 marks]

A three-phase, 380V, 50Hz, 4-pole, Y-connected debut ? initiation ? inauguration ? introduction motor has got the following comparable circuit parameters:

R1

X1

R2'

X2'

Xm

zero. 12Ω

zero. 25Ω

0. 1Ω

zero. 25Ω

10Ω

Determine the following for this motor unit when it is linked to a 380V, 50Hz source and operating at a slip of 0. 05:

4. 1 . Draw the Thevenin equivalent circuit and determine the parameters.[3]

some. 2 . Use the Thevenin equal circuit to look for the rotor current.[2]

4. three or more. Calculate the airgap electricity.[1]

4. 5. Calculate the rotor copper losses.[1]

four. 5. Determine the designed mechanical power of the engine[1]

4. 6. Find the torque developed by the motor....

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