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ENGI4487-WE01/ENGI44I10-WE01

Smart Energy Networks 4

2022

Section A

Question 1

(a) Thévenin equivalent sequence  networks looking into the faulted bus of a power system are given  with  Z1 = j0.33, Z2 = j0.41, Z0 = j0.35  ,  and  E = 1∠0°  per  unit.  Compute  the  phase currents (Iabc), the fault current, and also the phase voltages (vabc) for the following faults at the faulted bus:

(i)  Line-to-line fault.

(ii) Balanced three-phase fault. [20%]

(b) Consider a three-bus power network for which the Y௨௦  matrix is shown below. In this network, two generators are connected using series impedances at buses 1 and 2 respectively. Find the bus voltages after a three-phase bolted fault on bus 3 of this system. Also find the sub-transient current in line 1-3. Neglect prefault currents.

[20%]

(c) A 50-Hz synchronous generator has a transient reactance of 0.2 per unit and an inertia constant of 4 MJ/MVA. The generator is connected to an infinite bus through a transformer and a double circuit transmission line, as shown in Figure Q1. Resistances are neglected and reactances are expressed on a common MVA base and are marked on the diagram. The generator is delivering a real power of 0.93 per unit to bus  1. Voltage magnitude at bus  1 is  1.05. The infinite bus voltage is Vbus = 1.0∠0° per unit.

(i)  Determine the swing equation.

(ii) Assume  that  a   permanent  three-phase   bolted  fault  occurs  on  one  of  the   parallel transmission lines at distance x from bus 1. The fault is cleared by operating the circuit breakers at the ends of that line and those circuit breakers then remain open. Determine the electric power P during the fault for three different cases where x=0, x=0.3L and x=L, where L is the length of the parallel lines. Draw the equal area curves for these cases, and explain how changes in x affect the stability of the system.

[60%]

Section B

Question 2

Write an essay to discuss important roles of demand side management (DSM) technologies in future  power systems for achieving the  Net-zero  goal.  Use  Durham  University’s  Engineering Department as an example to explain and discuss how DSM technologies can be used to improve economic and energy efficiency of the electric system. Graphs can be used for assisting your explanations and discussions.

Within the essay, you may need to consider the following points:

.    What future power systems will look like to achieve the Net-zero goal? [20%]

.    What are DSM technologies? And their effects and benefits in power systems? [20%]

.    How can DSM technologies benefit the Engineering Department? [20%]

.    What devices, consumers engagement, and/or education programmes will be needed in the Engineering Department? [20%]

.    Show your vision about what the Department will look like to achieve the Net-zero goal, and summarise main viewpoints. [20%]

Note: Make sure to provide evidence and/or discussions to support your viewpoints.