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

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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

PROCEDURESystem studyAnalysisDesign and validationImplementation

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SYSTEM STUDYStudy 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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ANALYSIS OF SYSTEMIdentify 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.

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Possible configurations are indicated towards the preliminary study conducted over the data available for existing towers [1].POSSIBLE CONFIGURATIONS

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Technical advantagesNo new land acquisition costCost of erection is minimizedMinimize environmental restrictionReduces cost of maintenanceVisually aestheticsFoot print remains the same** If the foundation has to be strengthened, there may be a mere increase in foot print. 7

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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UPRATINGLine 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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HIGH PERFORMANCE CONDUCTORCarbon fibre coreHigh operating temperatureAmpacity twice as that of ACSR.Low sag.Higher Aluminium content.Resistance comparatively low.

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HIGH PERFORMANCE CONDUCTOR FITTINGSSupreme 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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LINE UPGRADINGModifications 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 and conductor arrangement on existing structure.

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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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CLEARANCES FOR 400 kVAC Nominal Voltage400 kVMinimum clearance above ground8.84 mMinimum live metal clearance2.6 mMinimum phase to phase clearance3.9 mAngle of shield (maximum)200Minimum mid span clearance9 m

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METHODS ADOPTED FOR UPGRADINGInsulated CrossarmsInter Phase SpacersIntermediate StructuresChange of Conductor and Earthwire

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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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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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INTER PHASE SPACERSInter 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.

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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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DISCONNECTION OF EXISTING LINK DURING UPGRADINGLine 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 the range of few hours.

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Conductor type ACSRCode name MooseDiameter31.77 mmArea597 sq mmWeight2.004 kg/m UTS16438 kgf

CONDUCTOR DETAILS

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CORONA INCEPTION VALUE

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CALCULATION FOR CONDUCTOR SURFACE GRADIENT:

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FOR SINGLE CONDUCTORFOR TWIN CONDUCTORNumber of Conductors in Bundle: 1Number of Conductors in Bundle: 2Rated Voltage: 400 kVRated Voltage: 400 kVPhase Spacing: 390 cmPhase Spacing: 390 cmHeight of Conductor above Ground: 884 cmHeight of Conductor above Ground: 884 cmVoltage Gradient E = 26.5316 kV/cmVoltage Gradient E = 20.4383 kV/cmDistance between Component Conductors: 45 cmR =22.5000 cmRe = 8.0246 cm = 0.5318

RESULTS OF CORONA CALCULATION

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SAG-TENSION CALCULATIONSPAN: 335 m; WIND ZONE: 3; TERRAIN CATEGORY: 1LOADING CONDITIONSAG (m)TENSION (kgf)Initial Condition7.6642983.64048 C Full Wind5.8053939.26848 C 28% Wind8.1922791.23248 C No Wind8.6132654.89685 C Full Wind6.5853472.50885 C 28% Wind9.5172402.74285 C No Wind10.0392277.604

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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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REFERENCESD. 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.Manual on Transmission Line, CBIP, 2014.EPRI Transmission Line Reference Book115-345 kV Compact Line Design, The Blue Book, 2008.K. Papailiou, F. Schmuck, Silicone Composite Insulators: Materials, Design, Applications, Springer, 2012.Cigre Green Book on Overhead Lines, 2014.

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THANK YOUSUPREME & CO. PVT. LTD.P-200, BENARAS ROAD, HOWRAH -711108, WEST BENGAL, INDIAPhone : +91-033-26516701 TO 05Fax : +91-033-26516706 Email : sales@supreme.in & info@supreme.inWebsite : www.supreme.in

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