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Tampere University of Technology
Electrical Engineering

Flexible Transmission Systems DEE-24126 17.10. 2018

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The numbers in sguare brackets indicate the marks allotted to the part of the guestion against
which the mark is shown. These marks are for guidance only.

An electronic calculator may be used provided that it does not have a facility for either textual
storage or display, or for graphical display.
If a calculator is used, intermediate steps in the calculation should be indicated.

Ouestion 1:
A) State which are the characteristic harmonics of a six-pulse thyristor-controlled reactor
(TCR) and a twelve-pulse TCR. [2p]

B) A TCR connected to bus / through an interfacing transformer, draws reactive power, as
shown schematically in Figure 1. The nominal reactance of the TCR?'s linear inductor and
the transformer are j0.05 p.u. and j0.10 p.u., respectively. The nodal voltage magnitude is
to be keptat 1 p.u while drawing 0.6 p.u. of reactive power; determine the thyristor's firing
angle & rcr that would be reguired to achieve this. Carry out two Newton-Raphson
iterations. Choose arcr=120* as the initial starting condition. [4p]

 

 

 

A
V/=140 pu. Bus/
Orcr"0.6p.u. |
a rcr= JAL
jX7=j0.10 p.u. TR | Ya -Arep)+sinZarcr
JA] = j0.05 p.u.
X, =j0.05 p.u. jXy = j0.10 p.u.
Crcr x
Figure 1.

Ouestion 2:

A) Explain the working principles of the bipolar, sinusoidal PWM control operating
in the /inear region and in connection with a single-phase, full-bridge, two-level
inverter. [n particular, refer to the amplitude modulation index and to the freguency
modulation index, in your discussion. Use any eguations and figures that you may
find useful to enhance your explanation. [4p]

B) State the role that a Voltage Source Converter plays in a STATCOM application
aimed at reactive power and nodal voltage control. [2p]

103)
Tampere University of Technology
Electrical Engineering

Flexible Transmission Systems DEE-24126 17.10. 2018

Ouestion 3:
The schematic diagram of a conventional HVDC link is shown in Figure 3. It uses two 6-pulse
thyristor converters rated at 50 MW and 80 kV, to link a wind farm on an island to a load
supply point in the mainland. The island electrical subsystem is referred as System 1 and the
mainland subsystem is referred as System 2. The line-line voltage at the high-voltage side of
System 1*s converter transformer is 192 kV and the freguency is 50 Hz. Its source inductance
is 5 mH. The line-to-line voltage at the high-voltage side of System 2's converter transformer
is 270 kV and the freguency is 50 Hz. Its source inductance is 7 mH. The cable has a DC
resistance of 3.75 O. If the HVDC link is carrying constant current of 400 A and delivering 30
MW into the inverter station, find the firing advance angle of the inverter and the firing angle
of the rectifier. [6p]

 

: M [] /W = W W
<;=5 => <,
192v 0 YY vV/If to / o 270 kV
42 / y, Vaani Voi N 0 oisonz
n + &

"R ema/-i | /

Figure 3.

 

 

 

 

 

 

 

 

 

Ouestion 4:

A) Describe using your own words what an Optimal Power Flow (OPF) solution is. State
what are the main advantages of using a full OPF solution to determine the optimal
operation of a power grid compared to using the egual incrementa! costs method. [2p]

B) Determine the Economic Dispatch solution of the two-generator system shown in Figure
4. Carry out one iteration of the egual incremental costs method. [4p]

vZa V.20

 
   
 

Y1a=1-j10 puu

    

Yj a=1-j0 pu. Y25=2-j20 puu.

150

Pjospu
0, =2pu.

Figure 4

The generators cost functions and the power loss function are:

C=0.1 + 2P,+ 04P
C,=02 + 3P,,+ 0.6P,
A p,2 p 0
Tampere University of Technology
Electrical Engineering

Flexible Transmission Systems DEE-24126 17.10. 2018

Ouestion 5: — Describe in detail the main physical and operationa! characteristics of a STATCOM,
emphasizing those characteristics that can be accommodated within the Power Flow
application using the Newton-Raphson algorithm. Use as many diagrams and
eguations, which you may deemed necessary to carry out a comprehensive description.

[6p]