E. Cinieri', A. Fumi^, G.G. Buffarini^ & V. Morelli^ · 2014. 5. 14. · E. Cinieri', A. Fumi^, G.G. Buffarini^ & V. Morelli^ ^ Universita de L 'Aquila ^Ferrovie dello Stato - Divisione

Computer analysis of interaction between AC

and DC electric traction lines in Italy

E. Cinieri', A. Fumi^, G.G. Buffarini & V. Morelli^

^ Universita de L 'Aquila

Ferrovie dello Stato - Divisione Infrastruttura

Italferr S.p.A. Italy

Abstract

As it is known when AC and DC electric traction lines are located in proximity,(f.i. 2x25kV-50Hz and 3 kVdc systems) attention should be given to thecompatibility problems among the systems above. The mutual interactionbetween the two power supply systems due to the unbalances produced by thesingle-phase loads in the main supply system of the ac electric installation cancause the ac/dc converters to generate non-characteristic harmonics. Besides, asignificant problem is the one related to the possibility that in case of parallel 25kV - 50 Hz and 3 kV dc lines, e.m.f.s are induced in the track circuits of such anamplitude as to disturb the operation of the signalling system.In the paper preliminary evaluations are presented on:- the effects of the unbalances produced by the single phase traction loads, asobtained by simulation programs and compared with the measurements in thetest site of Castiglion del Lago, set up by Italian Railways.

- the voltages induced in the track circuits in normal operation and duringtransients calculated by multiconductor models.

1 Interference on track circuits

In Italy, the new high speed (HS) lines will be electrified using the 2x25 kV 50Hz system. Some sections of these lines run near to the existing lines using the 3kV d.c. system, that are equipped with two different types of track circuits (TC)operating at 50 Hz:a) station TC of maximum length 600-700 metres with single insulated rail,

serving the Interlocking Apparatus; for brevity, in the text these circuits willbe referred to as SRC (single rail track-circuits);

Computers in Railways VII, C.A. Brebbia J.Allan, R.J. Hill, G. Sciutto & S. Sone (Editors) © 2000 WIT Press, www.witpress.com, ISBN 1-85312-826-0

334 Computers in Railways VII

b) line TC, of maximum length 2000 metres, realised with double insulated rails,fed by coded currents, used for the automatic block and continuous cabsignalling. Continuity of the traction power return current is achieved byimpedance bonds installed at the extremities of each TC. For brevity, theseTC will be referred to as DRC (double rail track circuits).

In the case of SRC, due to the dissymmetry between the two tracks (one insulatedthe other not), on the reception relay the normal 50 Hz signal is subject tointerference at the same frequency. This interference, if its phase is near to that ofthe signal itself, could compromise the safety by causing a false free trackindication even if the track is engaged, for example, by an axle in the vicinity ofthe SRC supply.

In the case of a DRC, the interfering voltage that arises on reception is causedby the difference between the distances of the two tracks from the inducing line,and can trouble especially the operation regularity by causing an untimely code"absence". The entity of interference on DRC, despite their greater length, iseyidently much lower. This eases the situation, because corrective actions such aschanging the TC operating frequency (for example from 50 to 83.3 Hz), while inthe case of SRC would concern only the interested station equipment, for DRCwould also involve all cab apparatus.

As described in [4] an experimental site has been set up in Italy at Castigliondel Lago by Italian Railways: the two tracks of an existing line are supplied oneat 3kV d.c. and the other one at 25 kV a.c. in order to measure the interferencevalues. With reference to the results of the experiments above, by means ofmulticonductor computer models, parametric analyses have been performed forthe case of normal operation of the electric traction lines and of transientphenomena as the energization and the short circuits.

1.1 Interference in normal operation

Hereafter are described the preliminary results of the interference values innormal operation, obtained by the multiconductor program validated with themeasurements performed at the experimental site of Castiglione del Lago.

The use of this program allows to determine the best protection measures tobe applied.

The results showed a significant difference between the behaviour and theinterference values in the case of double track induced line and single trackinduced line.

The single track case can be approximately analysed by the application ofsimplified theoretical formulas, described in [1] and [2], in order to calculate theinterference values as it was done for the application to the experimental case.In the following are instead resumed the results obtained for the case of a doubletrack induced line with the hypothesis of 12 MW trains running in the inducingline, electrified by the 2x25 kV, being autotransformers stations 12 km spaced.

1.1.1 DRC caseThe maximum interference value results equal to 0.4 V and it is calculated infunction of the train position and of the track circuit location in the following


Computers in Railways VII ^or

hypothesis (reference case): track circuit length of 1500 m; distance between therailways lines equal to 50 m; earth resistivity equal to 100 ohm.m ; induced railsconductance equal to 0.1 S/km; conductance of the inducing line current returncircuit 1.5 S/km for each track.

With reference to case above, a parametrical analysis have been performed.• Influence of the distance: at 100m reduction of 33%; at 200 m reduction of

about 50%; at 300 m reduction of 66%.• Influence of the earth resistivity : The influence is modest, resulting a low

increase at the raise of the resistivity (5 % for 500 ohm.m).• Influence of the induced rail conductance: from 0.1 S/km to 0.5 S/km the

interference values raises of around 40%.• Influence of the conductance of the current return circuit. Due to the fact

that the new HS lines are equipped by grounding wires connected to the rails,the reference values is high yet and further increase do not have significantinfluence.

• Influence of the track circuit length: It is less than proportional, being theinterference voltage reduced to 57% for an half length of the TC and equal to40% for a third of the length of the TC.

Even if the combined effects of the different parameters should be investigated,the conclusion is that for the track circuits of a standard length of 1500 m in theworst conditions the interference voltage is maximum 0.6 V being 50 m thedistance between the two lines. This value becomes about 0.4 V for a distance of100 m, 0.3 V for a distance of 200 m and 0.2 V for a distance of 300 m.

On the base of this result, if for instance the limit of the immunity for thesignalling devices is 0.3 V, protection measures should be introduced when thedistance between the inducing line and the induced one is lower than 200 m.

1.1.2 SRC caseIn the case of the single rail track circuits, in the same reference conditions, for alength of the TC equal to 750 m, the simulation program gives a value of theinterference voltage equal to about 4 V for a distance of 50 m and about 3V for adistance of 100m. In order to reach the value of 0.3 V the distance should behigher than 1000m.

Even if the parametrical analysis is in progress, the preliminary result showthat for the SRC track circuit the protection measures are needed also for bigdistance between the lines.

As known, in the case of SRC a suitable solution could be the change of thesignalling devices frequency, without consequences on the cab signalling.

1.2 Interference during transients

Studies were carried out in order to determine the amplitude and the shape of thevoltages induced in the track signalling circuits of the existing 3.6 kV dc lines bythe transients phenomena that may occur in the 25kV-50Hz electric traction lines


^>o/r Computers in Railways VII

on the same route.By means of the ATP the two tracks of the electric traction line Castiglion del

Lago-Panicale used for the experimental tests on the compatibility of the new 25kV-50 Hz electric traction lines with the existing 3.6 kV dc ones wererepresented. One of the lines was supposed to be energized at 25 kV - 50 Hz withrespect to the track through a 10 MVA, 132/25 kV single-phase supplytransformer, connected to the 132 kV-50 Hz main line at Castiglion del Lago (seeFig.l). The parallel traction line Castiglion del Lago - Panicale (4.5 km long)energized at 3.6 kV dc, as in normal operation, was also represented. Thevoltages induced in the track circuits of this line following the energization of theline Castiglion del Lago - Panicale at no-load as well as those caused by shortcircuit phenomena along it were calculated in order to verify if these voltagescould be of such an amplitude and characteristics as to perturb the properoperation of the signalling relay system.

A parametric analysis was performed considering as variable parameters: theseparation between the lines; the ground resistivity; the leakage conductancebetween the rails and ground; in the cases of short circuits, the fault position.Cases with double-rail and single-rail circuits were considered. The electrictraction line was represented as distributed parameter line. A complete report onthe studies carried out will be presented in a paper under preparation. Only themain conclusions are here summarised.

At energization of the 25 kV-50 Hz line, a voltage is induced in the trackcircuit of the dc parallel line at the ends of the track sections. This voltage has amain component at high frequency (about 5 kHz in the case under consideration)superimposed to a voltage at 50 Hz. The first component decays to about zero in30-40 ms from the breaker closing time. The residual 50 Hz voltage induced isvery low. As the time duration of the first component is very small as comparedwith the operation time of the signalling relays and the amplitude of thecomponent at 50 Hz is very low, unable to cause operation of the relays underconsideration, it was concluded that no troubles may be caused to the signallingsystems of the existing 3.6 kV dc lines by the voltages induced by theenergization of the new 25kV-50Hz lines.

As far as the voltages induced by the short circuits phenomena in the 25 kVline is concerned the researches performed drew to the following conclusions.

The short circuits in the 25 kV-50 Hz line in the case of the experimentalinstallation under consideration, where the separation between the inducing lineand the induced one is only a few metres, induce a 50 Hz voltage in the trackcircuit of the dc line generally high, (7-10 V in the case under consideration). Theamplitude of this voltage reduces to 1.4-0.6 V if the separation between the twolines is increased to 50-100 m. The amplitude of the voltage under considerationis thus such as to cause improper operation of the signalling relays of the dc trackcircuits above. But, as these voltage last only for the time necessary for theinterruption of the fault current in the 50 Hz circuit (0.1-0.15s in general) noproblem generally will arise if a safe and prompt fault protection is provided inthe 25 kV single phase system and the signalling relays are suitably delayed.


Computers in Railways VII

2 Effects of the unbalances caused by 25 kV single phase on

3 kV dc supply system

The present section reports the results of the numerical and experimentalinvestigations carried out in order to assess the influence on the operation of theexisting 3 kV dc electric traction lines in Italy of the addition of the new planned25 kV - 50 Hz lines in case they were supplied, through single-phasetransformers, from the same power supply system.

It is known that the presence of a single-phase load in a three-phasesymmetrical system determines the build up of a negative sequence component inthe voltages. The unbalance may perturb the normal operation not only of thecomponents of the ac system (generators, asynchronous motors, etc.) but also ofthe dc systems above, if they are connected to the same supply network. As it isknown the main effect of the supply of six-pulse and twelve-pulse rectifierbridges as the ones presently in operation with the Italian Railways withunsymmetrical three-phase voltages is the generation of a 2^ order harmonic inthe dc voltage produced by the ac/dc converters that may perturb the operation ofthe apparatuses connected to them (the filters f.i.) or close to the dc traction lines(communication systems).

In the following the results are presented of the digital simulation of anexperimental installation set up in Italy in November 1999. On the basis of theresults obtained, a parametric analysis was performed in order to assess theinfluence of the various parameters. The results of the numerical simulations arecompared with the experimental recordings. A new method for compensation ofthe unbalances above is also presented.

2.1 Results of the parametric analysis

By use of the EMTP/ATP program the system in Fig. 1 was simulated. It showsthe 132 kV line Chiusi- Farneta supplying the ac/dc converter station of Farnetaand the 132/25 kV single-phase transformer supplying at 25 kV -50 Hz one trackof the line Castiglion del Lago-Panicale on the line Chiusi-Terontola where a25kV ac train was operated. The voltage and current at Castiglion del Lago aswell as the voltages and currents, 132 kV ac side and 3 kV dc side, at Farnetawere recorded. The current in one of the filtering capacitor unit was also recordedin order to determine the distortion effect.

The main data assumed in the digital simulation are summarised in thefollowing.Supply system at Chiusi: Psc =3400 MVA (maximum), Xo/X,= 2.5Primary constants of the 132 kV line Chiusi - Castiglion del Lago - Farneta:R,= 0.172 a/km, X,= 0.424 Q/km, C,= 8.50 muF/km.Ro= 0.320 Q/km, Xo= 1.040 Q/km, Co=5.60 muF/km.Single-phase transformer at Castiglion del Lago:Pn=10 MVA; K=132/25 kV; Vcc%=8%; Pcc%= 0.4%.AC/DC converter station of Farneta



The two transformers of the station, rated at Pn= 5750 kVA; K=132/2.710/2.710 kV, star/delta/delta connected, were represented with theirequivalent circuit obtained from the nameplate data.

CHIUSI

Pn=10MVAK=1 32/25 kVVcc%=8%Pcc%=0.4%

CASTIGLIONDEL LAGO

Tothe25kVacline

Fig. 1: Single line diagram of the experimental site represented.

Two 6-pulse rectifier bridges were represented at secondary side of eachtransformer together with the snubber and damping circuits. The filters equippingeach converter unit were represented with their resistance R, inductance L andcapacitance C: R=0.005 Q, L=6 mH, C= 360 jnF.

The load of the dc converters was supposed to be made of a traincharacterized by an internal inductance L=4 mH. The inductance of the linesupplying the train from the converter station was represented assuming a perunit length value 1 =1.4 mH/km.

In order to simulate cases with reduced short circuit capacity, in some casesthe length of the line supplying Castiglion del Lago was increased to 40 - 60 km.

The results of the calculations are summarized in Table 1. Fig. 2 a) and b)show the shape of the voltage and current generated at 3.6 kV side in Farneta incases n. 1 and n. 6 in Table 1. From the Table it can be noticed that:

If no single-phase load is present at Castiglion del Lago (case n.l) no negativesequence component of the voltage is present at Farneta (Vz=0). If the twoconverter units in Farneta are delivering the full load (2x5.4 MW) the firstharmonic component that is present at the dc busbar is the 6* as it could betheoretically foreseen. Its amplitude is 0.91% of the nominal voltage (V,, =3.6kV).


Computers in Railways VII 339

3540

3280

3020

2760

?500

A/WW

j

i

L

l/WWV

-[_ j

r ~i

ii _iiii

l/WVWWWW1111

h - - -Q_ -_- -i

iiii-i

— ! J

WWW

L_ 1

L

l/WWV

l_

ri

0.88 0.90 0.92 0.94 0.96(fileCHT.pl4;x-vart) v FAR+- FAR-° c: FAR+- FAR-°

0.98 1.00

Fig. 2a: Voltage, V, and current, I, at Farneta station in case n.l in Table 1.

3800

3540

3280

3020

25000/96

(file CHT.pl4; x-vart) c: FAR+- FAR^O v. FAR-*-- FAR-O0.98

Fig. 2b: Voltage, V, and current, I, at Farneta station in case n.6 in Table 1.

The next harmonic component is the 12* equal to about 0.12%. The componentsof the currents absorbed by the converter station from the supply line are alsoshown in the table.



Table 1: Parametric analysis of the influence of the AC / DC convertersubstations of the unbalances in the supply system.

Casen.

1

2

34

5

67

8

9

1011

PcdL[MW]

0.00

5.84

5.84

5.84

5.84

5.845.84

5.84

5.845.84

5.84

COS(p

-0.95

0.95

0.950.95

0.95

0.95

0.95

0.950.95

0.95

PF[%]

100

25

50100

200

100100

100

100100

100

v,[%]

0.00

0.420.42

0.42

0.42

0.831.15

0.42

0.420.42

1.15

Farneta - (3,6 kV cc)

VO[V]

336335803506

33563073

33333328

3356

33563356

3328

10 [A]

3016

7501501

3009

6003

298929853010

30103010

2984

V2nd%

0.00

0.750.59

0.56

0.631.101.55

1.071.67

2.70

7.73

V4th%

0.00

0.030.04

0.04

0.05

0.090.12

0.03

0.030.02

0.06

V6th %

0.91

0.780.88

0.92

1.08

0.91

0.91

0.88

0.870.860.84

VI 2th%

0.12

0.050.06

0.12

0.17

0.12

0.13

0.12

0.120.12

0.13

L(132kV)km

14.7

14.714.7

14.7

14.7

40

60

14.7

14.714.760

Ldc

km

1

111

1

11

5

1020

20

PO,L= Active power absorbed by the single-phase load at Castiglion del Lago (CdL):cos<P = Load power factor at CdLPF [%]= Power absorbed at Farneta, 3.6 kV dc side in percent of the rating of theconverter station (2x5,4 MW)V? [%]= Negative sequence component of the voltage at Farneta (132 kV side)V<) ,I<) = Voltage and current at Farneta (3.6 kV dc side)V2nd% ,Yuh% ,V&,h ,V,2,h% = Amplitude of the harmonic components of the voltage atFarneta, 3,6 kV dc sideL(132 kV)=lenght of the 132 kV line: L(dc)=distance between the substation and the load

If a single-phase load P=5.84 MW coscp=0.95 is present at Castiglion del Lago, anegative sequence component of the voltage appears at Farneta at the 132 kVside of the transformer and a 2™* order harmonic appears at the dc side, its valuebeing in between 0.56% and 0.75% according to the value of the load deliveredby the converter station. The 6* and the 12* harmonic components are notpractically affected by the single phase load at Castiglion del Lago (see cases n.and n. 4).

In the same load conditions as per case n. 4, if the line supplying Castigliondel Lago were 40 km long (case n. 6), and thus the short circuit capacity reducedin proportion, V% would have been higher, approximately double, and as aconsequence, also V^ would have increased to 1.1%. Case n. 7 is of courseworse from this point of view as the supply line length is increased to 60 km.

Cases n. 8, n.9 and n. 10 show that the position of the load in the 3.6 kV dcline affects the amplitude of the 2^ harmonic component. In case n. 10 V^ isincreased to 2.7%. A limit and critical case is case n. 11 where the length of the



132 kV line is supposed to be 60 km and the distance of the dc load from thesupply station 20 km. In this case V*"* reaches 7.73%.

The calculations above were repeated for the system obtained from the one inFig. 1 by representing also the ac/dc converter stations connected to Farneta bythe 3.6 kV dc traction lines (see Fig. 3). The length of the 132 lines supplyingSSE1 and Castiglion del Lago was increased to 40 km to simulate the mainsupply system configuration during the experimental tests performed on17/11/99. A dc train absorbing 2000A was supposed to be present in differentpositions in the line through SSE2 (Farneta) and SSE3. Table 2 reports the resultsof the calculations.

They confirm that also in this case the unbalance caused by single phase loadson the primary supply system causes the build up of 2^ harmonic components inthe dc voltage generated at 3.6 kV dc side of all the substations (SSE1 throughSSE4).

1 1 ' ' 16kmI

16km I I I I 16km , ,I I I

Vh=132kV!3ph=15kAHpb=10kA

32km

16km

K=13225kV\Ax?/rf=8%Rx?/<F0.4%

Totte25kVacline

Fig. 3: Single line diagram of the system represented in order to analyse theinfluence of the single-phase load in a complex system.

The amplitude of this component at SSE2 (Farneta) is in between 0.94% and2.24%. In case n. 5 in Table 2 the load supplied by SSE2 is 113 A and the 2^harmonic component V^ =1.34%. This value is close to the one recorded in theexperimental test referred to further ahead. In the other stations the amplitude ofthe 2^ harmonic component is also not negligible: V^ =0.38-3.13%.


Computers in Railways Vll

Table 2: Summary of the results of the analysis of the system in fig. 3.

Casen.

1

2

3

4

5

Casen.

1

2

3

4

5

Idc

1996.8

2003.7

2006.2

2007.8

1998.1

Idc

1996.8

2003.7

2006.2

2007.8

1998.1

D[km]

0

4

8

12

16

D[km]

0

4

8

12

16

SSE1

I<>[A]141.3

121.5

87.5

57.9

28.7

Vo[V]

3655.1

3649.2

3645.0

3661.2

3677.2

V2nd[%]

1.16

1.66

2.37

2.58

0.42

SSE3

I«[A]122.8

547.9

949.5

1348.8

1759.2

V,>[V]

3659.2

3611.7

3567.1

3536.8

3545.4

V2nd[%]0.75

1.26

2.22

1.94

1.36

SSE2

I<>[A]

1711.2

1299.1

909.9

520.5

113.9

Vo[V]

3549.9

3540.4

3560.0

3600.1

3648.4

V2nd[%]

0.94

1.43

2.24

2.09

1.35

SSE4

I<>[A]21.5

35.2

59.3

80.6

963

Vo[V]

3681.9

3657.0

3643.3

3633.8

3645.4

V2nd[%]

0.38

1.61

3.24

3.13

2.75

PcdL= 5.84 MW, coscp=0,95 = Single phase load at Castiglion del Lago (CdL)Vj [%] (Ll)=0.18%= Percentage value of the negative sequence component

of the voltage at SSE1 and at SSE3Vj [%] (L2)=0.83=% Percentage value of the negative sequence component

of the voltage at SSE2 and at SSE4Vo,Io = dc voltage and current at the substation busbars.Ijg= dc load currentV2,,d% = Amplitude of the 2nd harmonic component of the voltage at the 3.6 kV dc busbars.D= distance from SSE2 of a train in the section from SSE2 to SSE3

2.2 Experimental test results: Comparison with the digital computersimulation results

Fig. 4 presents the results of the analysis of the recordings relevant to anexperimental test at Castiglion del Lago performed on 17/11/99, identified asCP3. In the test, the ac train supplied by Castiglion del Lago was operated andthe rms value of the ac current absorbed in the time interval in between 13:03 and13:06, is plotted in Fig. 4 a). During the test the converter station of Farneta wassupplying a current variable in between 50 to 150 A The position of the load inthe dc line was not known. Fig. 4 b), c) and d) report the shape of the 2™*, 6* and12* harmonic component at Farneta as deduced from the analysis of the currentabsorbed by one filter capacitor unit. From the Figure it can be noticed that whilethe current absorbed by the 25 kV train at Castiglion del Lago varies in betweenLiL^lOO and 1 =225 A (close to the one assumed in case n. 5 in Tab. 2) the 2"<*



harmonic component of the voltage varies, approximately in proportion, inbetween 0.4% and about 1.8%. The values of the 2™* harmonic component at theinstant the 25 kV load current absorbed is maximum is somewhat 0.45 % higherthan in case n. 5 in Table 2.

This difference may be due to various reasons: differences in the assumedshort circuit capacity of the supply system with respect to the actual value,unsymmetries in the converter transformer windings, uncertainties in the loadconditions, etc. The 6* harmonic component amounts to about 1% as in thecalculations and is practically unaffected by the single phase load. The recordingsconfirm that the amplitude of the harmonic components higher than the 6* arevery low.

!25kV

VSbarra%300Hz

13.03.40 13.04.0017A11/99

13.04.20

Fig. 4: Test CP3, performed on 17/11/99 at Castiglion del Lago. a) rms value ofthe current absorbed by the ac train from the 132/25 kV transformer atCastiglion del Lago; b), c), d), 2"\ 6% 12* order harmonic componentsof the voltage at Farneta.



3 Conclusions

By means of a multiconductor program validated with the measurementsperformed at the experimental site of Castiglion del Lago, the calculation of thevoltages induced in the track circuits of a dc traction line in parallel with a 2x25kV electrified line designed for the new Italian HS system, assuming a maximumtrain power of 12 MW, in normal operation gave the following results:- induced voltage range on DRC (double rail track circuits): 0.2-0.6 V being theparallel distance from 300 to 50 m ;

- induced voltage on SRC (single rail track circuits) equal to 3-4 V for paralleldistance equal to 50-100 m reducing to 0.3 V only for distance higher than1000m.

In regard to the voltage induced during energization , the results showed that notroubles should be caused to the signalling systems of the existing 3.6 kV dclines because of the fact that the time duration of the first component is verysmall as compared with the operation time of the signalling relays and theamplitude of the component at 50 Hz is very low.

Also during the short circuits in the 25 kV system, even if the induced voltagein the d.c. track circuits can be high, no problem will be occur if a safe andprompt protection is provided in the a.c. system and the signalling relays aresuitably delayed.

As far as the effect of the unbalances caused in the supply system by theunsymmetrical loads made of the 2x25 kV traction lines, computer simulationsand field test results have confirmed that they can cause the build-up of a 2™*order harmonic component of non negligible value at the 3.6 kV dc busbar of asubstation supplied by the same primary system.

This fact shows the opportunity to follow the practise, foreseen in Italy, tosupply the new 25 kV traction lines by a dedicated HV system, as far as possibleindependent from the one supplying the ac/dc converter stations.

References

[1] E.Cinieri - G.Guidi Buffarini" Theoretical assessment of interference oftraction power at 25 kV 50 Hz on each track - Comparison with results ofsimulations" - AEI Workshop on Electromagnetic Compatibility inTransportation Systems, Florence, Nov. 26*, 1999.

[2] E.Cinieri, A.Fumi, G.Guidi Buffarini, V.Morelli "Compatibility problems ofac and dc electric traction lines" - Alternate Traction TechnologiesConference, Johannesburg , South-Africa, April 11-14, 2000

[3] J. C. Brown, J. Allan, B. Mellit - Calculation and measurement of railinternal impedances applicable to remote short circuit fault currents. IEEProceedings - B Vol. 139, N° 4, July 1992.

[4] F. Cipollone, E. Fedeli - Fenomeni di interferenza elettromagnetica tra unsistema di trazione 25 kV - 50 Hz e gli impianti esistenti nella tratta Chiusi —Terontola. Convegno AEI Workshop on Electromagnetic Compatibility inTransportation Systems, Florence, Nov. 26*, 1999.


Documents

E. Cinieri', A. Fumi^, G.G. Buffarini^ & V. Morelli^ · 2014. 5. 14. · E. Cinieri', A. Fumi^, G.G. Buffarini^ & V. Morelli^ ^ Universita de L 'Aquila ^Ferrovie dello Stato - Divisione