Download overhead line and cable mapping of the greek electric - e

XVth International Symposium on High Voltage Engineering
University of Ljubljana, Elektroinštitut Milan Vidmar, Ljubljana, Slovenia, August 27-31, 2007
T2-348.pdf
OVERHEAD LINE AND CABLE MAPPING OF THE GREEK ELECTRIC
TRANSMISSION SYSTEM, FOR THE STUDY OF TRANSITIONAL OVERVOLTAGES,
USING EMTP-ATP
N. Lioutas , S. Lazarou* , G Marmidis , E. Pyrgioti , D. Agoris
High Voltage Laboratory, University of Patras
*Email: [email protected]
Abstract: The aim of this paper is an overall
description of the Greek Electric Transmission System,
which provides all the manufacturing and functional
elements that characterize its operation. Overhead line
and cable mapping is based on information that is
derived from official data and reliable sources. The
mapping procedure is presented and at the same time
some examples are shown providing some interesting
information about the transmission system. Finally, the
full map is illustrated and some suggestions are made at
the end of the paper for future use.
1 INTRODUCTION
The Greek electric transmission system is a part of
the interconnected electrical power system, which is
operated by the Public Power Corporation. It is mostly
composed of overhead transmission lines (there are only
a few underground lines) and its total length is
estimated to be 11.500 km. More specifically, it is
composed of single circuit lines of 66 kV and single and
double circuit lines of 150 and 400 kV.
1.1 Manufacturing characteristics
Overhead lines are constructed from Aluminium
Conductors with Steel Reinforcement (ACSR). In the
Greek transmission system 3 types of cables are found
depending on their cross sections. ACSR: 336 MCM ,
636 MCM and 954 MCM (according to American
stylization). The first one is used in the 66kV lines and
in the 150kV light lines, the second one in the 150kV
heavy lines and the third one in the 400kV lines.
Double circuit 400kV transmission lines are the back
bone of the transmission system since they transfer
electricity from the main generation centre of Greece,
which is in northern Greece (70% of the total electricity
is produced there) to the south where there is the highest
consumption. The underground cables are mostly used
to connect the islands to the national grid.
1.2 Functional characteristics
Each one of the three conductors in a three phase
line is characterized by electric resistance, inductive and
capacitance reactance. These parameters are taken from
standard tables provided by the manufacturers. For the
Greek transmission system all this data as well as the
values of reactive and apparent power of the lines, were
derived from official catalogues from the Public Power
Corporation of Greece and are presented on the
following tables.
Table 1. Electric characteristics of overhead line and cable of
the Greek transmission system [3].
Rated
Voltage
(kV)
(1)Type of
line
Cross
section
s of
lines
(mm2)
R
(Ω/k
m)
X
(Ω/km)
C
(nF/km)
L/66
1 x 170
0.183
0.400
9.0
150
L/150
1 x 170
0.183
0.446
8.2
150
H/150
1 x 322
0.097
0.422
8.7
150
2H/150
1 x 322
0.097
0.391
9.3
400
E’H’/400
2 x 484
0.031
0.337
10.5
400
2E’/H’/400
2 x 484
0.033
0.318
11.4
(1)
66
Table 2. Rated characteristics
transmission system [3]
Rated
voltage
(kV)
of
the
electric
(1)Type of
line
Cross
sections
of lines
(mm2)
Rated
Apparent
Power
(MVA)
Reactive
Power
(kVAr/km)
66
L/66
170
12
12
150
L/150
170
54
58
150
H/150
322
57
62
150
2H/150
322
2x62
2x66
400
E’H’/400
2 x 484
500
540
400
2E’H’/400
2 x 484
2x536
2x571
(1) L’: Light type of line, H’: Heavy type of line
E’H’: Extra heavy type of line, 2: Double circuit
line
During the procedure of mapping a very basic tool is
going to be used, that is the Electromagnetic Transients
program (ATP -EMTP) which is used for electrical
simulations and power analysis. The construction of the
network is presented in detail
1
2 ATP-EMTP
The Alternative Transients Program (ATP) is the
most widely used version of the Electromagnetic
Transients program ( EMTP ) in the world today --- by
far! In no small part, the acceptance of ATP is due to its
availability to nearly everyone in the world free of
royalty, and its compatibility with the computers of
most common interest. EMTP was developed in the
public domain at BPA (the Bonneville Power
Administration) prior to the commercial initiative in
1984 by DCG (the EMTP Development Coordination
Group, with which BPA has had no connection since the
expiration of the associated
2.1 Operation
The ATP program predicts variables of interest
within electric power networks as functions of time,
typically initiated by some disturbances. Basically, the
trapezoidal rule of integration is used to solve the
differential equations of system components in the time
domain. Non-zero initial conditions can be determined
either automatically by a steady-state phasor solution or
they can be entered by the user for simpler components
Symmetrical or unsymmetrical disturbances are
allowed, such as faults, lightning surges and several
kinds of switching operations including commutation
of valves. Frequency-domain harmonic anal ysis using
harmonic current injection method (HARMONIC
FREQUENCY SCAN) and calculation of the frequency
response of phasor networks using FREQUENCY
SCAN feature is also supported.
2.2 ATP tools
ATPdraw: ATPDraw is a graphical, mouse-driven
processor that creates *.atp files. The user can construct
the digital model of the circuit to be simulated using the
mouse and selecting predefined components from an
extensive palette, interactively. Once the circuit has
been constructed all the necessary input data can be
easily inserted in order for the user to proceed to the
simulation. ATP Control Center (ATPCC) is an easy
to use tool that can manage the different programs of
ATP-EMTP such as ATPDraw, PCPlot and every other
program that is related to ATP- EMTP runni ng on
Windows.PCPlot: Is a program that can design
waveforms and graphs. PCPlot receives as input data
the ATP_EMTP’s output files *.p14 and draws the
equivalent graphs PlotXY: It has the same functionality
as PCPlot but it can also support ASCII files.
GTPPLOT: The same as the previous two but ,in
addition, it can operate in Linux environment as well.
Programmer's File Editor (PFE): It is a text editor
that is running in windows. With this program the user
can control the input and output files of the EMTP. Its
evolution has been abandoned as it performs the same
actions as notepad.
3 MAPPING PROCEDURE OF THE
INTERCONNECTED
TRANSMISSION
NETWORK OF GREECE
During the process of construction of the Greek
transmission system it was firstly essential to gather all
those elements that characterise its operation. The
parameters of the transmission lines are distributed
along the length of the circuit and, therefore, i n order to
model the lines, models of distributed parameters,
composed of ohmic, inductive and capacity reactions,
were used. The models required as input the ohmic,
inductive and capacitive reactions of positive and zero
sequence as well as their lengths. Reactions come from
official catalogues from the Public Power Corporation
of Greece while their lengths where measured for each
line separately with the help of maps from the Ministry
of Development of Greece. More than 400 lines were
measured. The results are presented in tables depending
on the type of each line.
Table 3. Total electric characteristics that are used for fault
analysis [3]
Type of
line
R+
(Ω/km)
X+
(Ω/km)
C+
(nF/km)
Rο
(Ω/km)
Xο
(Ω/km)
Cο
(nF/km)
L/66
0.183
0.400
9.0
0.395
1.466
5.1
L/150
0.183
0.446
8.2
0.440
1.326
6.3
H/150
0.097
0.422
8.7
0.360
1.309
6.6
2H/150
0.097
0.391
9.3
0.497
2.349
4.1
H’H’
/400
0.031
0.337
10.5
0.295
1.035
7.7
2H’H’
/400
0.033
0.318
11.4
0.485
1.931
5.1
Figure 1. Example of data input in a distributed line model
As regards the rest of the network elements,
acceptances were made in order for it to be complete. It
2
must not be forgotten that the main aim of this paper is
not as much to produce precise simulation results as to
display the mapping procedure of the transmission
network. So the substations that are connected with the
lines are treated as three phase R,L loads. Every high
voltage substation has a rated apparent power of 50
MVA at 150kV and every extra high voltage substation
250MVA at 400kV. Both of them have a power factor
of 0.9. The substations at their input are star connected.
Hence we can easily calculate their resistance and their
inductive reactance which are found to be
For the 150kV substations: R=405 Ω and ΖL=196,15 Ω
For the 400kV substations: R=576 Ω και ΖL=278,97 Ω
After all elements have been defined the modeling
procedure started. The load values were in Ohms while
the values for the lines parameters were in Ω/ m for the
capacities..
The main concept of the modeling procedure was to
follow the geographical shape of the real transmission
system as it is outlined in the official Energy map of the
Hellenic Transmission System Operator (HTSO). The
modeling was developed gradually separating the
system in parts depending on their geographical
positions and then connecting the parts together. So for
our convenience the system was divided in eight parts.
It should also be mentioned that not all the islands are
included in the map as there are some special conditions
that regulate the energy transmission to them. An
example of this separation is shown in the figure.
that Peloponnesus has only 150kV single and double
circuit overhead transmission lines. This voltage is
generated by two thermal power stations (Megalopolis 1
and Megalopolis 2) that are located almost at the centre
of Peloponnesus. Power stations are represented by AC
sources that give an output of 150 kV at 50 Hz. To the
west this part is connected with the island of Zakinthos
through an underground cable, to the north with Central
Greece and to the north east with Athens. According to
the Hellenic Transmission System Operator there is a
new 400kV double circuit line that is going to be
manufactured which will connect Peloponnesus with the
main 400kV transmission system that already exists and
connect the northern with the southern Greece.
Fig.3: National Information Energy System Peloponnesus (Ministry of Development of Greece) [6]
Another geographical part that is worth mentioning
is the north-west of Greece. In that territory, as it has
already been mentioned, the 70 % of the total electricity
production is produced. Due to the large coal reserves
that have been found and the morphology of the ground,
there are a lot of thermal and hydro power plants. The
greater energy demand is in southern Greece and
especially in Athens where the heavy industry and the
majority of the population is gathered. So there is a
great need to transmit the energy to the south.
Figure 2. Part of the mapping process (Geographical
apartment of Peloponnesus)
This part of the grid represents the section shown at
the following map of the Ministry of Development of
Greece. The transmission lines are shown in green color
(150kV). From the observation of the image it is clear
Fig.4:Part of the mapping process ( (Geographical
apartment of Northwest of Greece)
3
Three 400 kV double circuit lines head to the central
and southern Greece and one more is planned to be
constructed in the near future, while another two
transmit the energy to the north-east of Greece. In
addition, two major lines that connect Greece with
Albania and FYROM within the scope of the electricity
exchange program have their origins in that area.
These two characteristic examples represent the
steps that were taken during the mapping process in
order to complete the whole transmission system. The
same procedure was followed for the other parts of the
network as well. When all parts were completed they
were connected producing in that way the final map
that is shown at figure 7.
Fig.5:National Information Energy System - Northwest
of Greece (Ministry of Development of Greece) [6]
Fig.6: Full Greek map [6]
At the early stages of the mapping process some
problems started to appear. While new lines were being
added and the size of the network was increasing, it was
not possible for the program to create the *.atp file
which is the output of the ATPdraw, meaning that the
program was unable to analyze the circuit. That was
caused because of the increasing number of the
parameters that the program had to calculate. The time
step of the simulation time (deltaT) had to be reduced in
order to provide more accurate results. So this is a factor
that someone should take under consideration while
using this program. Another difficulty that has come up,
was measuring the length of the lines as it required a
relative accuracy and their number was high. Mistakes
such as wrong values of the input parameters were
inevitable in such a big procedure but they were spotted
and corrected. Finally the system was ready as it is
presented at the figure below.
4
Fig.7: Full map of the Greek Electric Transmission System
4
CONCLUSIONS
After making the previous analysis it is now clear
that mapping is a time consuming proce dure that
requires the gathering of a big number of parameters as
well as plenty of measurements. At the end of this
process the readers ha ve at their disposal all the
manufacture and functional characteristics that can be
met at the Greek transmission system. The greater gain
though, is the network itself that has been designed with
the help of a powerful Electromagnetic transients
program the ATP-EMTP.
This network can constitute the basis for a future
study for different operating conditions such as
transitional overvoltages. It is very important to predict
the behaviour of the network under stable and fault
conditions so that we can plan measures of action.
Some small additions and modifications may be
required in order to give precise results. Moreover, it
could be very useful in the case of studying the effects
that could be caused from the integration to it of a large
wind farm or any kind of renewable generation. It is
obvious that some changes in this case are essential in
order to have reliable results. In conclusion, this design
could be used as the bedrock for the study of any
electrical additions that can affect the operation of the
transmission system and whose results, is essential to be
known.
5 REFERENCES
Books:
[1]
ATP – EMTP Rulebook, Canadian/American EMTP User
Group [2006]
[2] ATP – EMTP Theory Book, BPA, USA. [2006]
[3] System Planning Book, PPC, [2006]
Web sites:
[4] www.desmie.gr: Hellenic Transmission System Operator
[5]
[6]
[2006]
www.deh.gr: Public Power Coorporation [2006]
www.ypan.gr: Ministry of development [2006]
5