ELEC3575: Coursework 1
Electric Power Systems
School of Electronic and Electrical Engineering
Semester One 2025/2026
Coursework 1 Information (Summative Assessment of Unit 1):
· There are 3 pages to this Assignment (a total of 3 questions).
· You should attempt all 3 questions (with three parts each) after watching “Coursework 1 Instructions.mp4”.
· Each question has a recommended page limit. This is to help you determine how long your answer is allowed to be.
· You should use a minimum font size of 11 point.
· Your work must be typed and machine-readable, not handwritten. Images of hand-drawn diagrams or figures may be inserted into your answer.
· All symbols not specifically defined have their normally accepted meanings.
Submission instructions:
· You must submit this coursework as one single pdf or word document no later than the submission deadline of 2 pm, UK time, Thursday 6h of November 2025.
· Your work should be submitted using the Turnitin link within the “Assessment and Feedback” area of the module page in Minerva.
· You should receive an e-mail receipt from the Turnitin system to confirm that your work has been properly submitted.
· Contact the School if you encounter any difficulties submitting your assignment on Turnitin.
· Use the discussion board of the module if you have any questions about the assessment of Unit 1.
You need to answer Questions 1 and 2 based on the information, results and my measurements presented in “Coursework 1 Instructions.mp4”. Whenever necessary, provide evidence and measurement from the lab experiment and/or mathematical derivations to support your claims and statements. Question 3 is more fundamental and does not require any of the measurements taken in the lab experiment. In all questions, you should include units and label all vectors (if any).
Question 1 [30 marks]: Maximal length of the answer for this question is two page.
1-a) The Variac and inductor elements are not ideal (the former is not an ideal voltage source and has an internal impedance, and the latter has some internal resistance). Based on the discussions we had in the lab, and also over the course of ELEC3575, explain whether these two elements will become more non-ideal or closer to ideal (with respect to their intended use in our lab experiments) if we use them in another country with a 60 Hz nominal frequency? Assume these two elements are rated to work under both frequencies. [20 marks]
Hint: The suitability of these components depends on the specific experiment in which they are used. Please ensure your answer is based only on topics and concepts that have been discussed during the ELEC3575 module and lab sessions.
1-b) Detail your findings on the amplitude of the neutral current for the different configurations investigated in Tasks 1 and 2. Explain your observations in 1-b based on the properties of balanced three-phase currents. [10 marks]
Question 2 [40 marks]: Maximal length of the answer for this question is two pages.
2-a) Determine the active and reactive powers of ‘Phase a’ and those of the three-phase load, when using the RL impedance in Task 3. Calculate the value of the power factor. [10 marks]
2-b) Draw the single-phase equivalent circuit of the power system with an RL impedance per phase considered in Task 3. Based on the measurements and by using the single-phase equivalent circuit, construct a phasor diagram showing the voltages across the resistor, the inductor and the complete impedance as well as the load current and the power angle. Indicate the numerical values for all voltages and currents in the phasor diagram. [15 marks]
2-c) Detail how the power factor of the load changes after adding an additional resistor in series in each phase. Explain this change via a suitable mathematical argument (if necessary, see the screencasts and handout of Unit 1 for help). [15 marks]
Question 3 [30 marks]: Maximal length of the answer for this question is two pages.
In the next page, Figure 3.1 shows a balanced three-phase load under normal operating conditions, powered by an ideal three-phase voltage source. In this state, the load receives the maximum complex apparent power S, with each phase carrying the maximum allowable current |I|. Due to certain circumstances, however, the connection between the source and load in phase “c” has been opened, as shown in Figure 3.2.
Figure 3.1: Normal operation condition of the three-phase load.
Figure 3.2: Condition where the connection between load and source in phase “c” is opened.
3-a) In the condition illustrated in Figure 3.2, evaluate whether phases “a” and “b” of the source can continue to supply the load without risking overheating or causing damage to the components. [10 marks]
Hint: To answer this, you will need to parametrically calculate the current passing through each of the two remaining phases. Then you will have to reason whether these values are acceptable or not.
3-b) Determine the new complex apparent power delivered to the load of Figure 3.2 as a function of (i.e. the complex apparent power in the original balanced condition). [10 marks]
3-c) Based on our lecture discussions, what are the similarities and differences between the instantaneous power delivered to the load in the circuit shown in Figure 3.1 and that in Figure 3.2? [10 marks]