ELEKTROTEHNIŠKI VESTNIK 79(5): 242-247, 2012 
ENGLISH EDITION 
Development planning of the electric power network at the 
Ravne steelworks  
Matjaž Bobnar
1
, Igor Papič
1
, Jurij Bizjak
2
, Boštjan Blažič
1
   
1
University of Ljubljana, Faculty of electrical engineering, Tržaška 25, 1000 Ljubljana, Slovenia 
2
Petrol Energetika d. o. o., Koroška cesta 14, 2390 Ravne na Koroškem, Slovenia 
E-mail: matjaz.bobnar@fe.uni-lj.si 
 
Abstract.  In the paper, we present a process of development planning for the distribution power network at the Ravne 
steelworks for a ten-year period, precisely for 2011–2020. In the first part we describe a general approach to network planning, 
lay down the planning objectives and determine the methodology and technical and economic criteria according to which the 
network will be developed. Next, the current state of the Ravne power network (topology, equipment, power consumption) is 
described. Based on the measurement results, the state of the power quality is assessed with a particular emphasize laid on the 
flicker and harmonic distortion. We then make a simulation model of the steelworks power distribution network by using the 
DIgSILENT PowerFactory program. In the last part we propose a development plan for the Ravne steelworks based on the 
general planning criteria. We considered the current state of the power network (load, power quality), age of the equipment used, 
planned reconstruction and the predicted growth in electricity consumption.  
Keywords: flicker, power-supply quality, reactive-power compensation, distribution-network development. 
 
1 INTRODUCTION 
The main purpose of power network planning is to 
assure an adequate power quality and reliable power 
supply both for the current and future power consumers. 
The main goals pursued in such planning can be 
summarized in the following points: 
 determination of the necessary reinforcement 
and modernization of the network to assure 
adequate power quality and undisturbed power 
supply, accounting for the rising power 
demand and aging network elements, 
 enabling technically and economically optimal 
network development, to achieve an adequate 
cost-efficient level of the power supply, 
 determining the network elements performance 
specifications to assure optimal utilization, 
 determining an optimal work-completion 
schedule. 
When laying down a development plan, the main data 
required are in particular the data on the network current 
state including the network topology, data of the 
network elements, data about the network load and also 
load forecast about the expected network load for the 
period covered by the development plan. 
Of a particular importance for a good development plan 
are the methods to be used in analysing the operating 
states, reliability of the consumers’ supply, economic 
analysis and planning criteria providing the limits that 
should not be exceeded in order to assure the power-
supply quality, uninterrupted power supply and also 
optimal development of the network. 
As seen, the most important element of the power 
network is forecasting the power demand meeting. With 
this respect the most important data is that of the 
planned increase in the power demand meeting (e.g. 
production expansion, new users); where such data is 
not available, statistical forecasting methods are used. 
They include both statistical processing of the 
consumption data for a given power consumption area 
as well as consideration of the load-growth forecast in a 
particular industrial branch. Besides the basic objectives 
of the power network planning, in-depth analysis of the 
reactive power and flicker are also very important. 
Reactive-power compensation is a serious problem to be 
solved by large industrial consumers, mainly because of 
the potential resonances and consequently amplification 
of harmonics. Also to be accounted for is flicker which 
occurs as a consequence of operation at characteristics 
of arc furnaces. They negatively affect power 
consumers in a relatively large area. 
2 CRITERIA FOR POWER-SYSTEM 
DEVELOPMENT PLANNING 
As mentioned above, the goal of development planning 
of a power network is to enable continuous power 
supply and to assure an adequate level of power quality. 
Moreover, the network should be developed in an 
economically optimal way. The design criteria can be 
divided into the technical and economic criteria. The 
technical criteria are the power-supply reliability, 
voltage quality and admissible loading of the network 
elements [1]. 
 
Received November 15, 2012 
Accepted January 8, 2013 

DEVELOPMENT PLANNING OF THE ELECTRIC POWER NETWORK AT THE RAVNE STEELWORKS 243 
2.1 Power-supply reliability 
It is important that power supply is reliable as each 
power failure may result in considerable financial 
losses; in some cases it may also harmfully affect the 
load operation. 
Power supply interruptions are either planned or 
unplanned. For power consumers the number and 
duration of power supply interruptions is important. The 
parameters used as criteria for power supply reliability 
are: the number of long unplanned interruptions per 
year, the number of short unplanned interruptions per 
year and the total duration of unplanned interruptions 
per year. To determine the power-supply reliability of 
the planned network, we need to know: system 
topology, integrated switching elements, data about the 
protective-devices operation, data about reliability of 
individual elements (or failure frequency) given by 
statistically determined values (for transformers, lines, 
circuit breakers, etc.), share of the permanent and 
transient failures, time-to-failure elimination, time to 
provide emergency power supply and automatic 
reclosure time. 
The damage caused by power outages can be reduced 
by having the network correctly reconfigured. 
2.2 Voltage quality 
For the consumer devices to operate properly, the power 
quality or voltage quality is of the key importance. 
According to the currently applicable Slovenian 
legislation, the voltage quality must comply with the 
provisions of the EN 50160 standard [2]. According to 
the standard, the electromagnetic disturbances in the 
low-voltage (LV) and medium voltage (MV) network 
are identified at the consumption point, i.e. at the point 
of intersection between the consumer and the public 
power distribution network. 
2.3 Resonance phenomenon taking place in the 
network 
In planning a power network, a special attention should 
be paid to resonance states that might take place in the 
power system. Any of the electric circuits containing 
elements of an inductive and capacitive character has 
one or more resonance frequencies at which the system 
impedance can attain very high or very low levels, 
resulting in increased current and voltage harmonics. If 
a network impedance is, for example, near harmonic 
frequency ω
h
, a small load-current harmonic component 
will at this frequency already result in a high-harmonic 
voltage component. 
The resonance phenomenon is a serious problem when 
installing capacitors for reactive-power compensation. 
The resonance frequency of the system generally 
decreases with the increasing power of the compensator 
and with decreasing the resonance frequency of a tuned 
filter. While the resonance frequencies depend on the 
system inductance and capacitance, the impedance 
value at resonance depends on the resistive component 
of the system elements. 
Impedance frequency characteristics should be 
determined prior to installing any compensation 
capacitor into the power system. It should be taken into 
account that any change in the network topology or 
network elements (transformer replacement, short-
circuit power variations, etc.) affect the resonance 
frequency. We must also be fully aware that the loads 
are a source of harmonics causing high-harmonic 
distortion in the network. 
2.4 Network-element loading 
Concerning the network element loading, it is important 
that power lines and transformers are adequately loaded 
and that voltage drops do not exceed the set limit 
values. Overhead and cable lines can be loaded up to 
their thermal-capacity limit. Thermal current is 
determined on the basis of the maximum temperature at 
which the power line operates safely without damaging 
the conduction line and its insulation. 
As to line loading, important factors to be considered 
are its losses and voltage drops. To avoid the relatively 
large losses, a line may operate at its thermic limit only 
to provide emergency power supply. To avoid power 
losses under normal operating states, the load shall not 
exceed: 
 50 % of the thermal limit for overhead power 
lines, 
 75 % of the thermal limit for cables. 
In emergency states, the power lines can be loaded up to 
their thermal limit permitted by the voltage drops. 
Transformers can be permanently loaded with their 
rated power if their temperature does not exceed the 
upper limit over-temperature. It should be noted that the 
nominal data are given for a specific outdoor 
temperature, usually 20 ˚C. The transformer operational 
lifetime is determined by the lifetime of its insulation 
and depends mainly on the temperature. Permissible 
duration of the overload also depends on the transformer 
previous load. 
The permissible MV and LV line maximum voltage 
drop is typically 10 %, although a drop of maximally 
7.5 % is recommended. In accordance with the EN 
50160 standard, the lowest voltage in emergency 
operation should not be more than by 15 % lower than 
the nominal, and in normal operating states not more 
than by 10 % lower. 
2.5 Primary equipment operational lifetime 
For overhead lines and cable lines the expected lifetime 
is 40 years. For the HV/MV power transformers the 
predicted lifetime is 35 years and for the polyethylene 
insulated cable lines and MV/LV power transformers 30 
years. 
 

244 BOBNAR, PAPIČ, BIZJAK, BLAŽIČ 
3 DESCRIPTION OF THE NETWORK 
The loads at the Ravne steelworks are connected to the 
Central Transformer Substation (CTS) which is 
connected to the 110 kV transmission grid with two 
transmission lines, namely the HE Dravograd and the 
Ravne TS. The transmission power line running from 
the Ravne TS to substation at the town of Ravne is 
disconnected most of the time to avoid the too high 
flicker levels in Ravne. In CTS there are busbars of 
three voltage levels. The 110 kV busbar system can be 
separated in two busbar systems with each being 
powered from its 110 kV transmission line. The 20 kV 
busbars have two separate systems with one supplying 
an arc furnace and ladle furnaces and the other 
powering other consumers at a 20 kV voltage level. At 
the 5 kV level there are two busbar systems. In normal 
operational states, all loads are connected to the first 5 
kV system, while the second is not used. The 20 kV and 
5 kV busbars can be interconnected with two 20/5 kV 
power transformers, both of the nominal power of 2.5 
MVA. In normal operational states, they are 
disconnected. A simplified single-pole scheme is shown 
in Fig. 1 [1]. 
Figure 1: Simplified unipolar scheme of the Ravne power 
network. 
 
Most of the consumers are connected to their own 20 
kV or 5 kV busbars. The 20 kV substation of Valjarna I 
has two 20 kV busbars connected to the CTS. 
3.1 Power consumption 
Monitoring the power consumption at the point of the 
Ravne steelworks connection to the transmission system 
is made by energy meters recording power consumption 
on a 15-minute basis. Feeders are equipped with current 
meters SIMEAS recording the current values in second 
intervals. Fig. 2 shows the total annual power 
consumption in the area of the Ravne steelworks in the 
period 2006–2010. 
3.2 Reactive-power compensation 
Reactive-power compensation is very important for 
power system operation. At least two of its aspects 
should be addressed. The first is appropriate 
compensation meaning that compensators are 
adequately sized and flexible to enable the 
corresponding cosφ. The second aspect is proper 
configuration of the compensators (resonance frequency 
of the tuned filter) to prevent increasing of the harmonic 
components in the network. 
 
 
Figure 2: Total annual power consumption in the area of the 
power network of the Ravne steelworks in the period 2006–
2010. 
3.3 Results of the power-quality measurements 
Measurements of the power quality are used to illustrate 
the power-supply quality in Ravne power network, 
particularly with regard to flicker and harmonics as the 
most impacting voltage-quality parameters. Voltage-
quality measurements were performed at the 110 kV 
and at 20 kV busbars (system I). 
Flicker (P
lt
) exceeds the limit values of the EN 50160 
standard in which the maximum values, taking into 
account 95 % of the measurement time, range between 
2.4 and 2.8 (the maximum limit value is 1.0) [4]. Fig. 3 
shows the phase values of long-term flicker (P
lt
_L
1
, 
P
lt
_L
2
, P
lt
_L
3
). 
 
Figure 3: Development of long-term flicker, 110 kV busbars. 
 
Flicker is mainly the consequence of the electric arc-
furnace operation. A smaller proportion of flicker is 
contributed by other power consumers at the Ravne 
steelworks and also by some other consumers in the 
power transmission network. 
There are also some events due to which the threshold 
value is exceeded because of over-voltages between 
phase lines and grounding. However, this is due to 
slightly higher voltage levels at the 110 kV busbars at 
the time of our measurements. Other parameters of the 
Y
TR 
IV
System II 20 kV
110 kV
Ravne TS Dravograd HPP 
Y


TR 
UHP
Furnace 
UHP
Y
TR 
VII
20 kV
Y
System I

Y
TR I
5 kV
Y
G
Cogeneration
3 x 2,7 MVA
C K4
L K4
2,0 
MVAr
Y
TR 
V
Y
C K1
L K1
7,2 
MVAr
C K2
L K2
2,4 
MVAr


TR 
Pon
Ladle 
Furnace
Y
TR 
VI
Y
TR II
TR III
 
 
   
10 MVA
40/30/10 
MVA
20 MVA 20 MVA 40 MVA
36 MVA 8 MVA
2,5 MVA
2,5 MVA
44.4 46.4 46.3 44.3
48.9
162.9
168.8
118.9
149.5
0
50
100
150
200
2006 2007 2008 2009 2010
peak power (MW) energy (GWh)
Energy (GWh), Power (MW)
Total power consumption and peak power in the area of Ravne ZGK
Energy (GWh), Power (MW)

DEVELOPMENT PLANNING OF THE ELECTRIC POWER NETWORK AT THE RAVNE STEELWORKS 245 
voltage quality are within the limits defined by the EN 
50160 standard. 
The voltage asymmetry is low. Considering 95 % of the 
measurements time, it reaches the values of up to 0.3 % 
(the limit is 2 %). 
4 SIMULATION OF THE RAVNE NETWORK 
OPERATION 
Operation of the Ravne distribution network was 
analyzed using the DIgSILENT PowerFactory [5] 
software. Using the Ravne network simulation model, 
the load-flow was simulated. We observed the power 
flows in power lines and voltage drops appearing as a 
consequence of the line and transformer maximum 
loading. 
In our simulations we used the available power 
parameters of cables and transformers as well as data of 
the maximum power consumption of individual feeders. 
Knowing the cable and transformer power transmission 
capacities, we checked the network-cable load at the 
maximum load according to the cable current capacities. 
Being unlikely for all the loads to operate at the 
maximum power at the same time, our simulations were 
made also at reduced loads enabling us to determine the 
loading of the main power transformers in the Ravne 
network. 
The Ravne power distribution network is operated 
radially with all tie switches open in normal operating 
states. In the event of a failure, the tie switches can be 
closed, thus powering the loads from a different 
location. During our simulations we examined both the 
normal and as well as emergency operating states, the 
latter including reconfiguration of the network upon 
failure occurrence. 
4.1 Implementation of the third sector busbar 
With our simulations we also considered the option of a 
third busbar system at the 20 kV voltage level (System 
III) of the Central Substation. Our aim was to evaluate 
the levels of harmonics and flicker at System III. The 
source of flicker is mainly the arc furnace, while the 
sources of harmonics are, besides the arc furnace, also 
the converter drives connected to System I. We came to 
the conclusion that the Total Harmonic Distortion 
(THD) of System III is about three-times lower than the 
distortion of System I. The most distinct is the fifth 
harmonic. However, it should be noted that the 
harmonic distortion is highly dependent on the 
impedance of the system, which is also subject to the 
reactive-power compensation. Flicker levels of System I 
and System III are almost the same and vary only a little 
from the values at the 110 kV level. Some of the loads 
at the 20 kV level can cause a small increase in flicker, 
while directly connected motors, in principle, reduce 
flicker slightly. 
4.2 Analysis of the power consumption growth at 
the Ravne steelworks  
In assessing the future power consumption, we assumed 
that the power consumption will increase in the years to 
come and it is expected to return in 2012 to the values 
of 2008 (before the economic crisis). The growth in the 
power consumption after 2012 was estimated at 1.5 % 
annually. Similarly, we estimated that the peak power 
consumption will increase by 1.5 % per year, as shown 
in Fig. 4. In the near future (between 2013 and 2014), a 
new ESR III substation is foreseen to be constructed, 
which the existing electroslag remelting (ESR) furnaces 
and two additional ESR furnaces (each of 2.4 MVA) 
will be connected to. We therefore further increased the 
peak power consumption of the active power in 
forecasting for 2013 and 2014, in each year for 2.27 
MW (less than assessed in previous studies). For those 
years we also increased the power consumption for 2.3 
GWh annually, which corresponds to 1000 furnace 
operating hours per year. 
 
Figure 4: Total active-power consumption in the area of the 
Ravne network (current and foreseen). 
4.3 Simulations with increased load (2020) 
Using the simulation model of the Ravne steelworks 
network, we tested loading of the network elements 
with an increased load as a consequence of the 
production expansion in Ravne. We simulated the state 
predicted for 2020, where compared to 2010 we 
assumed a 1.5 % annual growth in power consumption 
and power for all the existing loads throughout the 
Ravne network, except for the UHP, VPP and ESR 
furnaces. We also considered that the power 
consumption will increase due to new loads (two ESR 
furnaces) and new topology, meaning a new TP ESR III 
and transition of the TP Kisikarna to the 20 kV level. 
Our simulations showed that there were no excessive 
values appearing in none of our scenarios. 
 
5 DEVELOPMENT PLANNING AT THE RAVNE 
NETWORK 
The development plan for the Ravne steelworks 
network foresaw network reinforcement and 
modernization to assure reliable and efficient network 
operation. 
163
169
119
150
158
169
172
174
177179 182
185
188190
0
50
100
150
200
2007 2009 2011 2013 2015 2017 2019
Energy (GWh)

246 BOBNAR, PAPIČ, BIZJAK, BLAŽIČ 
5.1 Cable feeders and main transformers 
Recommendations for the network reinforcement were 
given on the basis of the age and life expectancy of the 
primary network equipment and on the simulation 
results showing the feeder and transformer load. The 
simulation results showed that feeders and transformers 
were not overloaded under normal operating states. 
Under emergency operating states some of the 
connections were highly loaded (up to 100 % of the 
thermal current), but such operation was not permanent 
and is permissible for a limited amount of time. In our 
simulations we also took into account the maximum 
measured feeder loads. 
The main problem regarding the cable feeders was their 
age. Particularly problematic were the oil-insulated 
cables which are about 40 years old and require 
relatively expensive maintenance. 
The main problem regarding the transformers is 
especially the age of the stand-by transformers which 
are at the end of their operational life expectancy. Being 
stand-by transformers, i.e. not in permanent operation, 
their operational life is believed to be extended. 
5.2 Smart-grid concept 
One of the main directions imposed on power-system 
development leads towards the smart-grid concept. In 
smart distribution networks, generators and also loads 
play an active role and participate in network control. A 
higher network efficiency and flexibility can be 
achieved through further network automatisation, ICT 
network-linking-controllable elements and introduction 
of modern compensation devices. 
5.3 Reactive-power compensation 
Because of unpredictability of the compensator 
operation on the 0.4 kV voltage level (automatic 
switching based on the local power consumption) and 
the possibility of the occurrence of the resonance points 
over a wide frequency range, the main compensation at 
the MV level must improve impedance states at the 
harmonic frequencies characteristic for the power 
network at the Ravne steelworks. A possible solution is 
a 20 kV tuned-filter compensator with four levels of the 
nominal power of 3 MVAr. One level should be tuned 
to the frequency of 141 Hz, one to the frequency of 240 
Hz and two to the frequency of 335 Hz. 
Using such compensator, the resonance points from the 
load side of the 20 kV busbars in system I are located at 
frequencies where harmonics are not present (Fig. 5). 
Also, the compensators at the 0.4 kV voltage level do 
not substantially affect the resonance points. 
5.4 Flicker compensation  
The main power-quality problem within the Ravne 
steelworks and also in the Slovenian power transmission 
network is flicker. To solve the flicker problem, the 
possibility was considered of connecting an additional 
furnace of 70 MVA in the Ravne steelworks. Simulation 
results showed that the only solution allowing an 
adequate flicker minimisation is connecting the Ravne 
steelworks to the 220 kV voltage level and the 
connection of a static-var compensator (SVC) [6]. This 
way the flicker problem would be solved when the 
existing 36 MVA furnace and the new 70 MAV furnace 
are in operation. Independent operation of the 70 MVA 
furnace with no dynamic compensation is also 
acceptable, but it increases flicker in the power 
transmission system both in Slovenia and Austria. The 
simultaneous operation of the 36 MVA and the 70 
MVA furnace is not acceptable without dynamic 
compensation. Instead, a SVC should be used to 
maintain flicker within the set limits. The flicker level 
of the new furnace depends also on construction and 
operation of the furnace [5]. Results of our flicker 
simulations are given in Table 1. Results under I present 
the current status, under II connection of the 70 MVA 
furnace to the 220 kV system, under III connection of 
the 36 MVA furnace to the 220 kV system and under IV 
connection of the 36 MVA and 70 MVA furnaces and a 
SVC to the 220 kV system. 
 
Figure 5: Frequency characteristic of the network impedance at the 20 kV busbar system. 

DEVELOPMENT PLANNING OF THE ELECTRIC POWER NETWORK AT THE RAVNE STEELWORKS 247 
Table 1: Flicker values for the Ravne steelworks connected to 
the 220 kV voltage level. 
TS 
Voltage 
level 
(kV) 
I. Ravne                 
36 MVA 
II. Ravne        
70 MVA 
III. Ravne        
36 MVA 
IV. Ravne     
SVC+36+7
0 
Žel. Jesen. 110 7,17 7,04 7,16 6,94 
Moste 110 1,52 1,58 1,55 1,41 
Žel. Ravne 110 3,24 5,04 3,16 3,92 
Žel. Štore 110 1,24 1,20 1,14 1,23 
Okroglo 110 1,53 1,59 1,56 1,41 
Kleče 110 1,09 1,16 1,11 0,99 
Beričevo 110 0,86 0,94 0,88 0,77 
Lj. Center  110 0,91 0,98 0,93 0,82 
Slovenj 
Gradec 
110 1,85 0,56 0,49 0,55 
Podlog 110 0,93 0,85 0,76 0,85 
Pekre 110 0,74 0,44 0,37 0,40 
Hudo 110 0,50 0,53 0,47 0,48 
Divača 110 0,23 0,27 0,25 0,21 
Beričevo 220 0,60 0,74 0,65 0,56 
Podlog 220 0,45 0,76 0,59 0,59 
Kleče 220 0,59 0,71 0,64 0,54 
Beričevo 400 0,60 0,73 0,65 0,56 
Podlog 400 0,45 0,67 0,54 0,50 
Okroglo 400 0,71 0,83 0,75 0,64 
Obersielach 
(AT) 
400 0,27 0,58 0,42 0,45 
Obersielach 
(AT) 
220 0,25 0,80 0,55 0,62 
 
6 CONCLUSIONS 
The aim of the paper was to show the process of the 
power-distribution network planning for the case of the 
Ravne steelworks industrial network. The development 
plans was prepared for a ten-year period. An investment 
schedule was determined, too. 
At the beginning of the paper, some general guidelines 
for the distribution power network planning were given 
and planning objectives, methodology, technical and 
economic criteria were described.  
Operation of the Ravne steelworks network was 
analyzed by means of simulations. Using the network 
model, power flows and feeder and transformer loads 
were determined and voltage drops were analysed. 
Besides the normal operating states, emergency 
operating states were also evaluated. The power 
consumption growth and the peak-power growth for a 
ten-year period were also assessed. The issues of flicker 
and reactive-power compensation were addressed. In 
such compensation a particular attention should be paid 
to appropriate dimensioning of the filter-choke 
compensators to avoid increasing the harmonics in the 
network elements. To solve the flicker issue, we used 
several scenarios and came to the conclusion that the 
only comprehensive solution is connection of the Ravne 
steelworks to the 220 kV voltage level, which would 
also allow further expansion of production.  
In the last part of the paper, development plans for the 
Ravne network were proposed. The reason for the 
relatively considerable funds to be invested into the 
Ravne network is the age of some of the network 
elements which are already at the end of their expected 
operational life. 
 
REFERENCES 
[1] Papič Igor et. al.''Načrt razvoja elektroenergetskega omrežja na 
lokaciji ZGK Ravne'', Faculty of electrical engineering, 
University of Ljubljana, study, 2011.  
[2] SIST EN 50160:2000, ''Značilnosti napetosti v javnih razdelilnih 
omrežjih'', standard. 
[3] SIST EN 60868-0:2001,''Flickermeter, Part 0: Evaluation Of 
flicker severity'', standard. 
[4] Papič Igor et. al.'Analiza širjenja flikerja v prenosnem omrežju 
Slovenije'', Faculty of electrical engineering, University of 
Ljubljana, study, 2008. 
[5] DIgSILNET PowerFactory, Version 14.1, Tutorial, DIgSILENT 
GmbH Gomaringen, Germany, May 2011. 
[6] Papič Igor, Boštjan Blažič,''Priključitev jeklarne Ravne na 
napetostni nivo 220 kV'', Faculty of electrical engineering, 
University of Ljubljana, study, 2011.  
 
Matjaž Bobnar received his B.Sc. in electrical engineering 
from the University of Ljubljana, Slovenia in 2009. Since then 
he has been working as a researcher at the some faculty where 
he also studies towards his Ph.D. degree in the area of 
distributed power generation. His research work includes 
distributed power generation and active network operation.  
 
Igor Papič received his B.Sc., M.Sc. and Ph.D. degrees, all in 
electrical engineering, from the University of Ljubljana, 
Slovenia, in 1992, 1995 and 1998, respectively. From 1994 to 
1996 he was employed with the Siemens Power Transmission 
and Distribution Group in Erlangen, Germany. He is currently 
a professor at the Faculty of Electrical Engineering in 
Ljubljana. In 2001 he was a visiting professor at the 
University of Manitoba in Winnipeg, Canada. His research 
interests include power conditioners, FACTS devices, power 
quality and active distribution networks. 
 
Jurij Bizjak graduated in 1992 from the Faculty of Electrical 
Engineering of the University of Ljubljana. In 1992–2003 he 
was employed with Petrol Energetika l.l.c. Ravne. First he 
worked as a technical assistant in the area of power 
enginnering. Since then he has been occupying the post of 
Director. The scope of his work includes reliable operation of 
the electric power system (EPS), EPS development and power 
demand meeting of all in the region of Ravne and Štore. 
 
Boštjan Blažič received his B.Sc., M.Sc. and Ph.D. degrees, 
all in electrical engineering, from the University of Ljubljana, 
Slovenia, in 2000, 2003 and 2005, respectively. He is 
presently an assistant at the Faculty of Electrical Engineering, 
Ljubljana. His research interests encompass power quality, 
distributed generation, mathematical analysis and control of 
power converters.