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UNIVERSITY COLLEGE LONDON
EXAMINATION FOR INTERNAL STUDENTS
MODULE CODE : MECH0071
MODULE NAME : Electrical Power Systems and Electrical
Propulsion
LEVEL : Postgraduate / Undergraduate
DATE: : 12/01/2024
TIME : 11:00
EXAM DURATION : 2 hours
Additional time for
Collation and Upload : 10 minutes answer collation and
20 minutes upload
This paper is suitable for candidates who attended classes for this module in the
following academic year(s):
Year
2023-24
Additional materials n/a
Special instructions n/a
Exam paper word count n/a
TURN OVER
1 MECH0071_2023/24
TURN OVER
Answer All Four Questions
Each question is equally weighted with marks as indicated.
There are 100 marks available on this paper.
Use separate sheets of paper for answers to each question.
Q1.
a) Sketch a plug-in petrol-electric parallel hybrid propulsion system for a road vehicle and hence explain its different
operating configurations. Hence explain two advantages of parallel-hybrid propulsion over series-hybrid propulsion.
[A maximum limit of 200 words in your answer].
[8 marks]
b) Consider your sketch in Q1a) and then replace the petrol-engine with a hydrogen PEM (Proton Exchange Membrane)
fuel cell in alternative arrangement. Explain using a new sketch how your configuration might now operate to provide
maximum efficiency and low operating cost in the new hybrid combination.
[A maximum limit of 200 words in your answer].
[8 marks]
c) “Battery Electric Vehicles are better for the environment.” Briefly discuss this statement in the context of mass
introduction of electric vehicles and their whole life cycle impact.
[A maximum limit of 200 words in your answer].
[9 marks]
Q2.
a) Explain the terms ‘Sub-transient reactance’, ‘Transient reactance’ and ‘Steady state reactance’ when referring to a
synchronous generator under three-phase faulted conditions.
[5 marks]
b) In a three-phase power system, a synchronous generator (G) is connected to a synchronous motor (M). Both
electrical machines are rated at 1250 kVA, 600 V, 50 Hz and have reactances given in Table 1. The single line diagram
of the system is given in Figure 1 where all symbols have their usual meanings.
Figure 1: Electrical Line Diagram on reactances for Q2 b).
Machine X1 (pu) X2 (pu) X0 (pu)
Generator 0.2 0.2 0.06
Motor 0.2 0.2 0.06
Table 1: Information on reactances for Q2(b)
Calculate the fault current at point F near the motor for:
(i) Single-phase to ground fault.
[10 marks]
(ii) Double-phase to ground fault.
[10 marks]
2 MECH0071_2023/24
CONTINUED
Q3.
a) Discuss the meaning of the following terms when considering harmonic distortion in electrical power systems:
i) RMS voltage. [2 marks]
ii) Distortion Factor. [2 marks]
iii) Total harmonic Distortion. [2 marks]
b) The marine propulsion network in Figure 2 contains a power electronic converter drawing square wave current at
120 A at fundamental frequency of 60 Hz. Determine the harmonic equivalent circuit for the 11th harmonic and hence
calculate the voltage at the point of common coupling (Busbar A). Use 10 MVA as base power.
[13 marks]
Figure 2: Electrical Line Diagram on reactances for Q3 b).
DATA for Figure 2:
G1 & G2: Synchronous Generator, 10 MVA, 0.8 PF_lag, 4.16 kV, X = 10%
T1: 4.16 kV / 1.1 kV, 18 MVA, X = 12%
T2: 4.16 kV / 440 V, 2 MVA, X = 11%
M1: 0 – 180 RPM Synchronous motor, 18 MVA, unity PF, Variable Voltage,
X = 10% at 180 RPM and X = 12% at 0 RPM
c) Briefly explain how a passive tuned harmonic filter could be used to remove the 11th harmonic hence explain one
advantage and one disadvantage of using this method over a passive damped harmonic filter.
[6 marks]
3 MECH0071_2023/24
Q4.
a) What is meant by a ‘slack bus’, ‘generator bus’ and ‘load bus’ in network analysis
[6 marks]
b) For the electrical network shown in Figure 3 determine the per unit voltage at Busbar 2 using the Gauss-Seidel
method of analysis when the admittances Y11 = Y22 = 1.6 < -80o pu and Y21 = Y12 = 1.9 < 100o pu. Figure 3: Electrical Network for Q4. [19 marks] Mark Guide: 5 marks for appropriate method of analysis 7 marks for accurate 1st iteration result 7 marks for subsequent iterations END OF PAPER