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Tampere University 11.12.2020
DEE-24026 Flectric Power Ouality

Pertti Pakonen Programmable calculator allowed 4 guestions/ a 6 p

By answering the guestions in this exam, you assure that you take the exam independently without
the help of other people. Potential misconducts will be treated as cheating in the exam.

1. How standards are related to power guality and the management of electromagnetic
compatibility in the context of power guality. Give examples of how the standards may be
applied in practice and what benefits may be achieved by applying them.

2. Whatis flicker and what causes it? Why flicker is harmful and how the intensity of flicker may
be evaluated? What characteristics of the source of flicker and the network affect the intensity
of flicker? Explain the aspects related to the management of flicker from the viewpoint of a
distribution system operator (DSO).

3. Explain from the distribution system operators (DSOs) point of view the main goals, needs
and functions related to power guality monitoring.

4. Consider a three phase short circuit occurring on one feeder of a radially operated 20 kV
distribution network supplied by a 110 kV network. The total resistance and reactance of the
supplying 110 kV network and the 110 /20 kV main transformer together, transformed to the
20 kV voltage level, are 1 ohm and 5 ohm, respectively. The feeder resistance is 0.34 ohm/km
and the reactance 0.38 ohm/km. The phase-to-phase voltages in the 20 kV network before the
fault are 21 kV.

a. draw the three phase and single phase eguivalent circuits of the fault case

b. explain why and how the voltages in the network change due to the fault

c. based on calculus, illustrate the dependence of the feeder short circuit current and the
substation 20 kV busbar phase-to-phase voltage during the fault on the fault location

d. explain shortly how the changes in voltage would be different and have to be
calculated differently if the fault was a two-phase short circuit