Mathematical Models and
Standards for Current Carrying
Capacity of Overhead Lines
Calculation
Nebojša Petrović, Serbian Transmission System and Market Operator
Ninel Čukalevski, Institute Mihailo Pupin
Sovjetka Krstonijević, Institute Mihailo Pupin
Serbia
DEMSEE 2009 – September 17-18, 2009 – Hotel Continental, Belgrade
DEMSEE 2009 – September 17-18, 2009 – Hotel Continental, Belgrade
Mathematical Models and Standards for Current Carrying Capacity of
Overhead Lines Calculation
CONTENT OF PAPER
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Continuous current carrying capacities and
short current carrying capacities are
determined according to temperatures of
conductors.
Continuous current carrying capacities are
determined limits of load transmission
overhead lines.
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DEMSEE 2009 – September 17-18, 2009 – Hotel Continental, Belgrade
Mathematical Models and Standards for Current Carrying Capacity of
3Overhead Lines Calculation
CONTENT OF PAPER
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The continuous and short-term current carrying
capacities of the overhead line, that are, also,
used for setting line overload protection, depend
on allowed conductor temperature.
Calculations continuous current carrying
capacities and short current carrying capacities
are very important for make decision in control
(dispatching) centre of transmission power
system.
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DEMSEE 2009 – September 17-18, 2009 – Hotel Continental, Belgrade
Mathematical Models and Standards for Current Carrying Capacity of
Overhead Lines Calculation
In this paper, the results of the continuous and short-term current
carrying capacities of the overhead line calculations employing four
mathematical models, according to :
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IEEE Std. 738-1993 Standard for Calculating the CurrentTemperature Relationship of Bare Overhead Conductors,
IEC 61597-1995 – Technical Report Type 3 - Overhead
electrical conductors – Calculation methods for stranded bare
conductors,
CIGRE Study Committee 22 – Working Group 12, Technical
Brochure 207 – Thermal Behaviour of Overhead Conductors,
Paris, august 2002,
IS 37 Overhead Lines with Nominal Voltages 400 kV, 220 kV
and 110 kV Continuous Current Carrying Capacities – Electric
Power Industry of Serbia 2003
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DEMSEE 2009 – September 17-18, 2009 – Hotel Continental, Belgrade
Mathematical Models and Standards for Current Carrying Capacity of
Overhead Lines Calculation
Why did this paper write ?
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The transmission overhead line conductor
temperatures calculation and/or measurement is
very important for a safety of people, vegetation,
buildings, equipment, economy, security and
reliability of transmission power system.
As an illustration, we can recall the black out on
August 2003, at USA and Canada and the one in
Italy, on September, of the same year.
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DEMSEE 2009 – September 17-18, 2009 – Hotel Continental, Belgrade
Mathematical Models and Standards for Current Carrying Capacity of
Overhead Lines Calculation
Why did this paper write ?
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At Italy is 28 September 2003 at 03:01 o’clock outage
OHL 400 kV between from Italy and Swiss because of
flashover on tree what is happened to cascade outages
other transmission overhead lines 400 kV and 220 kV
due to overload (activity protection from overload) and
complete disintegration electric power system in Italy
(Blackout in Italy).
Interim Report of the Investigation Committee on the 28 September 2003
Blackout in Italy, UCTE Report – 27 October 2003
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DEMSEE 2009 – September 17-18, 2009 – Hotel Continental, Belgrade
Mathematical Models and Standards for Current Carrying Capacity of
Overhead Lines Calculation
CALCULATIONS
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The Serbian Transmission System and Market Operator
are used, according to Internal standard, for ACSR
(aluminium conductors steel reinforced), AAC (aluminium
conductors) and AAAC (aluminium alloy conductors)
conductors, for the values of 60 degrees C and 80
degrees C for continuous and short current carrying
capacities conductor temperatures, respectively.
For copper conductors, these values are 50 degrees C
for continuous and 70 degrees C for short current
carrying capacities.
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DEMSEE 2009 – September 17-18, 2009 – Hotel Continental, Belgrade
Mathematical Models and Standards for Current Carrying Capacity of
Overhead Lines Calculation
CALCULATIONS
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Beside usual calculations for daily summer and winter
season conditions, there are also results of calculations
for supposed meteorological conditions for night summer
and winter season, between 19:00 p.m. and 07:00 a.m.
For summer night, adopted value for air temperature
parameter is 25 degrees C, and the same variable for
winter condition is 5 degrees C. The night conditions
values are based on the largest average values’
approximation for corresponding season, according to
the available literature.
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DEMSEE 2009 – September 17-18, 2009 – Hotel Continental, Belgrade
Mathematical Models and Standards for Current Carrying Capacity of
Overhead Lines Calculation
RESULT OF CALCULATIONS
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Differences between continuous current carrying
capacities daily and night period for ACSR
conductors, are from 45 % to 100 % for
summer season, and from 20 % to 30 % for
winter season.
Differences between continuous current carrying
capacities daily and night period for copper
conductors 95 mm2 are from 85 % to 200 % for
summer season, and from 5 % to 30 % for
winter season.
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DEMSEE 2009 – September 17-18, 2009 – Hotel Continental,
Belgrade
Mathematical Models and Standards for Current Carrying Capacity of
Overhead Lines Calculation
RESULTS OF CALCULATIONS
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For ACSR conductor 360/57 mm2, from whom the most of the 220 kV
overhead lines in transmission power system of Serbia are made, the
differences between continuous current carrying capacities for day and
night period, in percent, are:
from tables I and V is: (754 A/394 A - 1) · 100 % = 91,37 % – summer season;
from tables II and VI is: (823 A/485 A - 1) · 100 % = 69,69 % – summer season;
from tables III and VI is: (833 A/498 A - 1) · 100 % = 67,30 % – summer season;
from tables IV and VIII is: (833 A/498 A - 1) · 100 % = 54,54 % – summer season;
from tables IX and XI is: (833 A/498 A - 1) · 100 % = 25,67 % – winter season;
from tables X and XII is: (833 A/498 A - 1) · 100 % = 22,23 % – winter season.
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DEMSEE 2009 – September 17-18, 2009 – Hotel Continental,
Belgrade
Mathematical Models and Standards for Current Carrying Capacity of
Overhead Lines Calculation
CONCLUSIONS
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The efficient exploitation of transmission overhead lines,
as well as power system operation security and reliability,
are based on information of their continuous and shortterm current carrying capabilities.
These values are determined by allowed conductor
temperature and are different for different part of the day,
season of the year, due to different meteorological
conditions.
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DEMSEE 2009 – September 17-18, 2009 – Hotel Continental,
Belgrade
Mathematical Models and Standards for Current Carrying Capacity of
Overhead Lines Calculation
CONCLUSIONS
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The significant variability in time and place, emphasize the
need for real-time approach to overhead line conductor
continuous and short-term current carrying capacities. This
could be accomplished by implementing conductor
temperature calculations into existing control systems.
According to the results in this work, the use of IEEE and/or
CIGRE mathematical models for conductor temperature online calculations, can be recommended for practical use in
control centres.
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DEMSEE 2009 – September 17-18, 2009 – Hotel Continental,
Belgrade
Mathematical Models and Standards for Current Carrying Capacity of
Overhead Lines Calculation
RECOMMENDATIONS
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In 220 kV transmission network, in West Serbia, from Beograd, through
Bajina Basta and Pozega, to Nis, the transmission overhead lines overload
protection, during the summer months, is usually blocked. By establishing
continuous and short current carrying capacities for night conditions in
summer season, the operational security and reliability of 220 kV
transmission network in West Serbia, including Reversible Hydroelectric
Power Plant Bajina Basta in pumping regime, would increase, between
19:00 pm to 07:00 am.
Nowadays, digital devices for protection transmission overhead lines and
substation’s SCADA systems with GPS devices enable to set four various
values for continuous and short-term current carrying capacity according
to different part of the day and season of the year.
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