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日期：2022-07-16 02:22

School of Electrical Engineering

and Telecommunications

Term 2, 2022

ELEC 3105 - Electrical Energy

Assignment

INTRODUCTION

Assignments must be submitted as a single (either .doc, .docx or .pdf file) in a properly formatted document.

An appropriately prepared document (using Word, LaTeX etc) is strongly suggested. Handwritten assign-

ments in a digital device are also acceptable but will have to be legible. Scanned copies or photographs

of A4 pages of handwritten solutions will not be accepted or marked.

This assignment contributes 13% toward your final marks.

The last day of submitting the assignment is 11.59pm, Sunday, 17th July 2022 via the Turnitin Assignment

submission link in Moodle:

https://moodle.telt.unsw.edu.au/mod/turnitintooltwo/view.php?id=3916487.

Late submission will not be permitted under any circumstances. Submission via email attachment will also

not be considered.

Since this assignment counts towards your formal assessment for this subject, you are required to sign a

declaration and attach it as a cover sheet to the front of your submission. Without this signed declaration,

the assignment will not be considered for assessment. A fillable pdf file for signed declaration can be found

in Moodle.

Note that plagiarism (i.e. copying of assignment or pay someone to do your assignment) is an academic

offence. If suspected of plagiarism, you may be referred to disciplinary board and will be subjected to heavy

penalties.

Detailed information can be found in https://student.unsw.edu.au/plagiarism

LEARNING OUTCOMES AND GRADUATE ATTRIBUTES

This assignment covers the first three topics of ELEC3105; Energy generation, Three-phase systems and

Transformers.

The key learning outcomes of the activity are:

Develop the capacity to select, design and justify important power engineering devices for real-life

applications,

Be able to apply underlying theories and concepts in the design process.

The key graduate attributes linked to the activity are:

Analytical skills, critical thinking and creative problem solving.

Demonstration of the understanding of principles.

Effective use and communication of relevant information.

1

ASSIGNMENT TASKS [TOTAL OF 100 MARKS + 11 BONUS MARKS]

It’s January 2023.

The crypto-crash of mid-2022, followed by the crypto-crash of late 2022 and the great iceberg lettuce

shortage means that previously "profitable mining and donkey NFT businesses" have now pitched to also

cultivate leafy green vegetables in greenhouses heated by the stacks of graphics cards.

You have been assigned by your electrical engineering services company to investigate the power supply

issues at one such facility, known as "Sneed’s Fine Mine, Dine & Wine" (formerly Chuck’s).

Part 1 [30 marks]:

The three-phase supply to the facility includes a transformer with the following information in its nameplate.

TRANSFORMER

Primary Phases 3

Secondary Phases 3

Rated Power 6 MVA

Primary Voltage 33 kV

Secondary Voltage 11 kV

Frequency 50 Hz

Impedance (%) XTx%

Vector Symbol Dyn-1

Oil Specs IEC-60296

Type of Cooling ONAF

Further to the nameplate, you have also been provided with the testing report of the transformer where

following parameters have been provided:

Series Resistance: RTx%; Magnetizing Impedance: Xm %; No-load losses: PNoLoad kW.

1. [3 marks] Calculate the parameters of the equivalent transformer circuit in ?. Explain the steps in your

calculation.

2. [3 marks] Draw the equivalent per-phase circuit of the transformer in per-unit and in ? referred to the

secondary.

3. [6 marks] Calculate the efficiency of the transformer when it supplies 60% of its rated power at unity

power factor.

4. [15 marks] Plot the efficiency of the transformer (using MATLAB, python/Jupyter, Excel etc), as a

function of the total load through the transformer from 5% to 110%? rated power (in MVA) at unity power

factor (in steps of 5%). In the same graph, plot the efficiency of the transformer at 0.6 lagging power

factor and at 0.6 leading power factor for the same power range. Compare the three cases and comment

on the results.

5. [3 marks] What is the meaning of the vector symbol Dyn-1 in the transformer? Draw the winding

connections of the transformer clearly showing the phase and line voltages of the primary and secondary.

What is the turns ratio relation for this transformer? What other phase-shift angles between primary and

secondary can this connection provide?

Your code for the calculation of Question 4 should be included in the Appendix of the report and submitted

as a separate file in Moodle.

? A transformer can operate at powers above its rated power for short time intervals. We call this "overloading"

of a transformer and how long we can operate the transformer at this condition depends on the previous load

2

and the corresponding windings or oil temperature before overloading. Manufacturers will typically provide

instructions and information for the duration of overloading a transformer can handle.

Part 2 [37 marks]:

"Sneed’s Fine Mine, Dine & Wine" consists of three separate buildings which are all fed by the transformer

of part 1. The 33 kV supply substation connects to the primary of the transformer through a line with an

impedance of R1+ jX1 ? and the 11 kV secondary of the transformer feeds all the loads through a cable

with an impedance of R2+ jX2 ?.

The loads at the facility include:

1. Load 1: The mining graphics cards / heating elements: S1 MVA at a p f1 lagging power factor.

2. Load 2: Compressors and other electric machines: P2+ jQ2.

3. Load 3: Auxiliary loads of 500 kW at 0.85 lagging power factor.

1. [6 marks] Draw the equivalent circuit in per-unit. You can assume a simplified transformer equivalent

circuit. You may use per-unit impedances for the lines / transformers and per-unit power values for the

loads (AKA no need to calculate load impedance).

2. [9 marks] The rated voltage at the loads is 11 kV with a tolerance of ± 6%. Calculate the minimum and

maximum supply voltage from the 33 kV substation when all the loads are connected.

3. [6 marks] Draw the phasor diagrams for the minimum and maximum voltages from Question 2 (2 phasor

diagrams). Clearly define all voltages and currents based on the diagram of Question 1.

4. [9 marks] If the supply voltage is 33 kV, what is the voltage at the loads when :

1. All three loads are connected.

2. Loads 1 and 3 are connected.

3. Only Load 1 is connected.

For each case draw the corresponding phasor diagrams. Are the supply voltage limits of ±6% satisfied

at all conditions?

5. [7 marks] What is the value of the capacitors that need to be connected in each phase at the load side

to make the total power factor when all loads are connected equal to unity? What are the differences

between the possible connections of the capacitors?

Part 3 [33 marks]:

"Sneed’s Fine Mine, Dine & Wine" is part of "Umbrella Corporation", a global conglomerate with a substantial

carbon footprint. Local billionaire Mike Nikkon-Brookes has threatened with a hostile takeover unless 50% of

the energy consumed by each facility on a daily basis is generated by renewable energy resources (on a

nice sunny day at least).

1. [3 marks] Calculate the total energy consumption of your facility over one day and the amount of energy

that needs to be generated by renewables.

2. [6 marks] Explain why the five wind-turbines that your friend from high-school, Bruce, wants to sell you

for "mates rates", would not be sufficient, especially as "you can carry one of them in the back of his

ute".

3. [21 marks] Calculate the number of solar panels that you would require to satisfy the renewable energy

requirements of your facility. The PV panels will be connected to the grid through inverters which are

95% efficient, transformers which are 98% efficient and cables that have 1% losses.

3

You can use any of the solar panels described in the following datasheet.

1. Solar Panel 1: https://moodle.telt.unsw.edu.au/mod/resource/view.php?id=4779571

Assume that the power output of each solar panel is directly proportional to irradiance and that the solar

irradiance in the location where you plan to install your solar farm is given in the following table (e.g.

from 7:30 am to 8:30 am the irradiance averages 200 W/m2):

Table 1 Daily Solar Irradiance

Time Irradiance (W/m2)

8 am, 5 pm 200

9 am, 4 pm 400

10 am, 3 pm 600

11 am, 2 pm 800

12 pm, 1 pm 1000

Explain all steps in your calculations, appropriately.

4. [3 marks] Draw a single-line diagram of "Sneed’s Fine Mine, Dine & Wine" including all components in

the system from Part 1 to Part 3.

Bonus Questions:

1. [4 marks] How can overloading of a transformer be useful? Are there any potential drawbacks?

2. [4 marks] Calculate the voltage regulation (up and down) of the transformer for an operating condition

of your choice.

3. [3 marks] Is ELEC3105 memeable? Have a go, class of 2022! (3 marks because most of you chose 3

at the random number generator...)

Your parameters for the assignment can be found in the Moodle quiz question here:

https://moodle.telt.unsw.edu.au/mod/quiz/view.php?id=4779588

In the end, the "power supply issues" were just possums that ate the insulation of the cables and caused a