SUPER CONDUCTORS AS SURGE CURRENT PROTECTORS

Superconducting Power Cable Application in DC Electric Railway System

1 P.RAMESH 152622 NITW

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CONTENTINTRODUCTIONDC TRACTION SYSTEMANALYSIS MODEL USING HTS CONDUCTORANALYSIS OF DIFFERENT CHARACTERISTICS OF TRACTIONCONCLUSIONREFERENCES

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INTRODUCTIONPower cables using HT Super conductors have been developed recent times in many applications.Most of the Super conducting power cables projects are in AC supply in grid applications.Recently DC Super conducting power cables have attracted and now there are some projects running on DC Super conducting power cables.Here we are discussing about the prospective application of the Super conducting power cable in DC Electric railway system.3

Super conducting power cables

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5Super conducting power cables can transmits 5 to 10 times the electric current of traditional copper or alluminium cables with significantly improved efficiency.Super conducting power cables consists of the cable,which is comprised of 100s of strands of superconducting wire wrapped around a copper core ,and the cryogenic cooling system to maintain proper operating conditions.Comercially available Bi-2223 tapes are used to design the dc super conducting power cables for the application in electric railways.

6High power copper based cables endure a great deal of heat at high voltages.As electrical current increases,the copper heats and causes the wire to expand..The effect of heating,cooling,expanding and contracting causes fatigue known as thermal cycling and degrades the reliability of the insulation layer.But these HTS cables operated at liquid nitrogen temperatures(at 77 kelvins)& will not fatigue from changes in electrical current.

ELECTRIC TRACTIONDC TRACTION Operating voltages 600,750,1500,3000vDC Traction units use direct current drawn from either a conductor rail or an over head line. most suitable and used operating voltage level in dc traction system is 1500v and 3000v.DC series motors are used as regenerative traction motors7

Low voltage range in urban and sub urban areas uses 600v and 750v DC for third rail systems.A means of providing electric power to a railway train through a semi continuous rigid conductor placed along side or between the rails of a railway track and that additional rail is called conductor rail.For these expensive substations are required at frequent intervals and overhead wires or third rail must be relatively large and heavy.Another issue is how to respond to increasing number of passengers or speed up of trains while the existing substations are still used.8

Because of limited spacing for the substations,we look the feasibility of applying super conducting power cables to DC Electric Railway systems.DC Elecric railways have some problems such as relatively low voltage,regeneration cancellation and energy losses etc.Super conducting technology would be effective for novel design & efficient operation of next generation DC Electric Railway systems.Introduction of Super conducting power cable can also improves the regenative braking operation of electric traction.

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MODEL ANALYSIS10A Numerical analysis of a power feeding systems a model line is shown in fig.

11The total length of the line is 26.5kmsThere are 24 stations and 5 substations along the line are assumed.Cases of four and three substations were also analysed.Electric current flows from substations through the feeder to a train & returns through rail to the substation.A super conducting power cable is placed in parallel to the feeder & connected to all the substations as shown.The length of the super conducting cable is 22.2kms.

key parameters of the model line are summerised in table.12

The analysis model line with substations,trains and super conducting cables was built as a electric circuit as shown.

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The part having 2 trains between 2 adjacent substations.A Substation was modeled as a set of a no load voltage v0,resistance rs & a diode.The train is modeled as a current source It and a resistance rt.The current It is controlled to supply the reactance power under the voltage Vt.A resistance rlr includes both feeder resistance &rail resistance. 14

An equivalent resistance of current lead rc is also included in the circuit.MATLAB Simulink & SIMPOWER systems was used to analyse the model.Relative train operation characteristics considering different parameter variations are obtained and analysed.For with and without super conducting power cable cases were examined.15

The fig. shows a set of train operation curves assuemed in the analysis for a train operation interval of 5 minuts. 16TRAIN OPERATION:

Each curve indicates a trajectory of an operated train.Locations of 24 stations and 5 substations are also shownA periodic operation of trains with a period of 5 minuts was assuemed in the analysis for the evaluation of the system.In the analysis 2 track conditions were analysed,single track and double track conditions.The single track case included in the case where the route was a double track but their electric circuits were independent of each other.The analysis for 5 minutes is enough for evaluation of the system.

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Tracive Force and Power charestics:Tractive effort characteristics of a train have three regions as shown in fig.

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19The fig shows the curves of tractive and breaking forces of a train running from one station to an adjacent station with and without the train resistance taken in to account.

20At higher speeds the tractive force decreases a little and the braking force increases when the train resistance is taken in to account.In the present line conditions a coasting period operation period is short,So the train resistance is ignored during the coasting operation for simplification of the analysis model.Coasting period is the process of turn off of engine to save fuel at some particular speed,but the train continues to run due to the momentum attained.As power will be removed and the speed falls an account of friction & windage etc.

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Acceleration,Power and Speed curves21Fig.shows the acceleration and speed curves of the train.

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0 20 40 60 80 100 Time(s) 0 20 40 60 80 100 Time(s)0 20 40 60 80 100 Time(s)

23Table indicates the train operation conditions.

When the voltages of the breaking trains becomes higher and reach the upper limit of the train voltage VUL(=1800),then the regeneration cancellation occurs.Table 3 indicates the assumptions of cooling component characteristics.For a super conducting cable system the heat load along the cables of 1kw/km, the heat load cable terminals of 0.25kw/tonne.Coefficient of performance (cop)of the cooling system of 0.1 were assuemed.

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Analysis results

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28Influence of the number of substations

29Fig shows the influence of the number of substations on the maximum substation current.The open symbols indicates the conventional cases without super conducting cable.The solid simbols indicate the cases with superconducting cable. Although the energies are not much influenced by the number of substations. Even so it is still lower in the super conducting cable system with three substations than that of the conventional system with 5 substations both for single track and double track cases.The introduction of super conducting cables would make it possible to reduce the number of substations or to improve the redundancy of substations.

CONCLUSIONThe results showed that the introduction of super conducting power cables increased the regeneration rate and improved the energy saving.It could reduce the substation capacity,and/or improve the redundancy of the substations.Therefore, if the transportation capacity of a railway line needs to be increased,the introduction of super conducting cables could achieve it without changing the existing substations.30

References31

THANKS32