This document discusses transforming an existing 220 kV double circuit transmission line into a 400 kV single circuit line using twin conductors. It analyzes the technical feasibility and provides the procedures, including system study, analysis of tower strength, possible configurations, clearance requirements, and cost benefits compared to building a new transmission line. Upgrading the existing line requires less land acquisition and has lower costs than new construction while meeting the increasing electricity demand.

1. TRANSFORMING EXISTING 220 kV D/C LINE INTO
400 kV S/C LINE (TWIN CONDUCTORS)
CASE STUDY TOWARDS THE ENQUIRY FLOATED BY
RELIANCE INFRASTRUCTURE
SUPREME & CO. PVT. LTD.
P-200, BENARAS ROAD, HOWRAH -711108, WEST BENGAL, INDIA
Phone : +91-033-26516701 TO 05
Fax : +91-033-26516706
Email : sales@supreme.in & info@supreme.in
Website : www.supreme.in
1

2. WHY UPRATING / UPGRADING
IS REQUIRED ?
Existing and planned infrastructures have made it
extremely difficult to build new transmission line to
meet the electricity demand-supply gap.
It becomes highly pertinent to uprate or upgrade the
already existing line rather than constructing new
transmission line.2

3. PROCEDURE
System study
Analysis
Design and validation
Implementation
3

4. SYSTEM STUDY
 Study on existing power transmission system for
selecting the optimum solution.
 Conceptual study for optimal solution regarding
the upgrading of the existing 220 kV double
circuit transmission line corridor.
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5. ANALYSIS OF SYSTEM
Identify an optimum alternative to upgrade the
transmission line corridor.
Evaluate the performance of the power
transmission system.
Investigating the capability of existing towers and
foundations to withstand new mechanical
loadings.
Undertake financial analysis for most promising
alternative.
Estimate cost of various alternatives.5

6.  Possible configurations are indicated towards the preliminary
study conducted over the data available for existing towers [1].
POSSIBLE CONFIGURATIONS
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7. Technical
advantages
No new land
acquisition cost
Cost of erection is
minimized
Minimize
environmental
restriction
Reduces cost of
maintenance
Visually aesthetics
Foot print remains
the same*
* If the foundation has to be strengthened, there may be a mere increase in fo7

8. INCREASING POWER RATING
Power in a circuit is increased by:
 Uprating (increase in current flow).
 Upgrading (increase in voltage level).
 Both upgrading and uprating.
 Surge impedance loading.
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9. UPRATING
 Line modification that yields increase in current flow
limits is known as uprating [2].
 Conductors are normally operated below the thermal
rating of the line.
 Current flow is increased to operate the conductor
closer to its thermal limit.
 Reconductoring the line with HTLS conductor is one
of the solutions.
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10. HIGH PERFORMANCE
CONDUCTOR
 Carbon fibre core
 High operating temperature
 Ampacity twice as that of ACSR.
 Low sag.
 Higher Aluminium content.
 Resistance comparatively low.
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11. HIGH PERFORMANCE
CONDUCTOR FITTINGS
Supreme has developed and
conducted electrical tests on
conductor fittings, specifically
designed for HTLS conductors.
Since HTLS conductors
operate at higher
temperature, they require
special type of clamps and
fittings.
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12. LINE UPGRADING
Modifications that allow operation at higher voltage
level.
Results in higher increase in power flow, compared to
uprating.
Percentage voltage drop decreases.
Need to replace substation equipments.
Maintaining the electrical clearance increase as per
the voltage rating by reconfiguring insulator and12

13. FACTORS TO BE CONSIDERED FOR
LINE UPGRADING
Electrical Clearance.
RoW acquisition (may be required in exceptional
cases).
Civil and structural modifications (may be required).
Mitigation of Corona and Radio Interference Voltage
(RIV).
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14. CLEARANCES FOR 400 kV
AC Nominal Voltage 400 kV
Minimum clearance above ground
8.84 m
Minimum live metal clearance
2.6 m
Minimum phase to phase clearance
3.9 m
Angle of shield (maximum)
200
Minimum mid span clearance
9 m
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15. METHODS ADOPTED FOR
UPGRADING
Insulated Crossarms
Inter Phase Spacers
Intermediate Structures
Change of Conductor and Earthwire
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16. PRINCIPLE OF AN
INSULATOR
 Freedom of movement provided
to the conductor determines the
clearance required for the line
[3].
 Clearance should be provided
for both inward and outward
swing of the conductor.
 For a suspension insulator,
freedom of movement is very
high and hence more clearance
will be required.
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17. INSULATED CROSSARM
 Insulated crossarms are polymer
insulators that directly fixed to the
tower [4].
 This eliminates the use of metallic
crossarm.
 With the freedom of movement
restricted, the conductors swing
will be reduced significantly.
 This reduces the required live -
metal clearance level and thus
making the line compact.
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18. INTER PHASE SPACERS
 Inter Phase Spacers are used to
maintain phase to phase
clearance even under high wind
condition.
 This reduces short circuit
problems encountered in many
high voltage lines.
 Composite insulators which has
high strength to weight ratio are
mainly used as inter phase
spacer.18

19. INTERMEDIATE STRUCTURE
If an intermediate structure is
needed after final analysis, we
could opt the use of monopoles.
Monopoles will require lesser foot
print when compared with a lattice
tower.
Foot print can be restricted as per
the availability of space
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20. DISCONNECTION OF EXISTING LINK
DURING UPGRADING
Line shutdown is required for
making the erection works.
Temporary towers, supported by
guy wires without civil foundations,
can be installed in parallel with
existing line.
Line will be disconnected only at
the time of by-passing.
Power outage will only be in the20

21. Conductor type ACSR
Code name Moose
Diameter 31.77 mm
Area 597 sq mm
Weight 2.004 kg/m
UTS 16438 kgf
CONDUCTOR DETAILS
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22. CORONA INCEPTION VALUE
The voltage gradient necessary to produce corona at the
conductor surface is given by,
𝐸0 = 30 ∗ 𝑚 1 +
0.301
𝑟
where
r : radius of the conductor and
m : surface irregularity factor
For example, consider Moose conductor with radius 1.5885
cm and surface irregularity factor, m= 0.80
We get, E0 = 30.76 kV/cm.
Beyond or near this value, the conductor has corona effect.
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23. CALCULATION FOR CONDUCTOR
SURFACE GRADIENT:
The conductor surface gradient is calculated from the following
equation [5]:
E = (V/√3)*(b/(r*ln ((a/Re)*2h/ √(4h2+a2))))
where
E : conductor surface voltage gradient (kV/cm)
V : line voltage (kV)
b : factor for multiple conductors
r : radius of conductor (cm)
R : outside radius of bundle (cm)
Re : equivalent radius of bundle conductor (cm)
S : distance between component conductor centers (cm)
a : phase spacing (cm)
h : height of conductor above ground (cm)
n : number of component conductors in bundle
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24. FOR SINGLE CONDUCTOR FOR TWIN CONDUCTOR
Number of Conductors in Bundle: 1 Number of Conductors in Bundle: 2
Rated Voltage: 400 kV Rated Voltage: 400 kV
Phase Spacing: 390 cm Phase Spacing: 390 cm
Height of Conductor above Ground: 884 cm Height of Conductor above Ground: 884 cm
Voltage Gradient E = 26.5316 kV/cm Voltage Gradient E = 20.4383 kV/cm
Distance between Component Conductors:
Conductors: 45 cm
R =22.5000 cm
Re = 8.0246 cm
β = 0.5318
RESULTS OF CORONA CALCULATION
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25. SAG-TENSION CALCULATION
SPAN: 335 m; WIND ZONE: 3; TERRAIN CATEGORY: 1
LOADING CONDITION SAG (m) TENSION (kgf)
Initial Condition 7.664 2983.640
48° C Full Wind 5.805 3939.268
48° C 28% Wind 8.192 2791.232
48° C No Wind 8.613 2654.896
85° C Full Wind 6.585 3472.508
85° C 28% Wind 9.517 2402.742
85° C No Wind 10.039 2277.604
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26. RESULTS FROM TECHNICAL AND
FINANCIAL EVALUATION
Costs are substantially reduced when compared with
the costs of a new 400 kV OHL.
No land or right of way acquisition is necessary for
project implementation compared with the new line
solution.
Minimum environmental impact.
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27. REFERENCES
1. D. Marginean, E. Mateescu, H.S. Wechsler, G.
Florea, C. Matea, “Transforming Existing 220 kV
Double Circuit Line into 400 kV Single Circuit Line
in Romania”, IEEE- 2011.
2. Manual on Transmission Line, CBIP, 2014.
3. EPRI Transmission Line Reference Book—115-345
kV Compact Line Design, “The Blue Book”, 2008.
4. K. Papailiou, F. Schmuck, “Silicone Composite
Insulators: Materials, Design, Applications”,
Springer, 2012.
5. Cigre Green Book on Overhead Lines, 2014.
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28. THANK YOU
SUPREME & CO. PVT. LTD.
P-200, BENARAS ROAD, HOWRAH -711108, WEST BENGAL, INDIA
Phone : +91-033-26516701 TO 05
Fax : +91-033-26516706
Email : sales@supreme.in & info@supreme.in
Website : www.supreme.in
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