Comparison of Three Modes of AT-fed Traction Power Networks

doi:10.4236/epe.2013.54B196

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Energy and Power Engineering, 2013, 5, 1026-1031

doi:10.4236/epe.2013.54B196 Published Online July 2013 (http://www.scirp.org/journal/epe)

Comparison of Three Modes of AT-fed Traction Power

Networks

Qingan Ma, Qunzhan Li, Zehui Mi

Department of Electrical Engineering, Southwest Jiaotong University, Chengdu, China

Email: [email protected]

Received April, 2013

ABSTRACT

The features of three modes of AT-fed traction power networks (TPNs) have been briefly described in the existing lit-

erature, which is not adequate yet. In this paper, these three modes of TPNs are compared mainly on TPN capacity,

transformer capacity, rail potential and voltage level, etc., and conclusions are drawn.

Keywords: AT-fed Traction Power Network; Comparison; Capacity; Rail Potential; Voltage Level

1. Introduction

There are two existing modes of AT-fed traction power

networks (TPNs), i.e., Japanese-mode (J-mode) and

French-mode (F-mode), as shown in Figures 1(a) and

(b). Here, only single-line railway is shown for simplic-

ity, and T, R and F are abbreviated for trolley wire, rail

track and power feeder respectively. A Novel-mode

(N-mode) TPN was proposed by Ref [1] recently, as

shown in Figure 1(c). The features of the three modes of

TPNs have been briefly described in Ref [1], current dis-

tribution and equivalent impedance have been studied in

Ref [2, 3]. However, their features have not been totally

compared and should be studied further.

In this paper, these three modes of AT-fed TPNs are

compared on TPN capacity, transformer capacity, and

rail potential, voltage level, etc., and conclusions are

drawn at last.

2. TPN Capacity

2.1. Current Distribution Analysis

As all-parallel connection is always adopted in China,

terminal-parallel connection is not taken into considera-

tion in this paper.

Only the first AT-section is needed to be compared as

it is identical in other AT-sections of these three modes

of TPNs.

As current distributions are the same in J-mode and

F-mode TPNs except in transformer, only J-mode and

N-mode TPNs are compared here.

1) J-mode

Generalized method of symmetrical components can

be used to the first AT-section of J-mode TPN[4]. If AT

leakage impedance is neglected, it is easily to derive the

composite sequence network as shown in Figure 2(a).

The total current at any point is the sum of its sequence

components. So currents flowing in T and F in the fist

AT-section of the up TPN are

(a) J-mode

AT1 AT2

Transformer

n2n2

(b) F-mode

Figure 1. Three modes of AT-fed TPNs.

Q. A. MA ET AL. 1027

0123

TU L

IIII I









 

(1)

0123 4

IIII I



 

(2)

the sign “-” in Equ.(2) indicates that the current re-

verse the defined direction. Currents flowing in conduc-

tor T and F in the fist AT-section of the down TPN are

D 0123

IIIII



 

(3)

FD0 1 234

IIII I



 

(4)

2) N-mode

Using the method as before, the composite sequence

network for the N-mode TPN is shown in Figrue 2(b).

From Figrue 2(b), the following equations can be de-

rived

0123

TU L

IIII I



 





 

(5)

01 23

IIII I

 

(6)

D 0123

IIII I



 





 

(7)

FD0 1 23

IIII I

 

(8)





4zL



(a) J-mode TPN





(b) N-mode TPN

Figure 2. Composite sequence network of the first AT-sec-

tion of an double-line railway TPN.

It is easily induced from traction power system theory

that currents in TPN reach its maximum value at the ini-

tiating-terminal in the feeding section. The cross-section

area of every conductor doesn’t vary along the line for

convenience, and mainly depends on the current of its

initiating-terminal.

2.2. TPN Capacity

The RMS current at the initiating-terminal of every con-

ductor as the load passing through the first AT-section

can be defined as

 

ItdtItdt









(9)

where, Is(t) is the current flowing in the initiating-termi-

nal of the conductor, T1 is the time consumed by the load

to pass through the first AT-section, t* is per-unit time

taking T1 as base value.

Assuming that the velocity of the load is constant, t*

can be replaced by load location, thus the following equ-

ation is derived



Ixdx





 (10)

Here, x* is per-unit distance between substation and

the load choosing AT-section length D as base value.

RMS current can also be represented by its per-unit value

IIIIdx Idx









 







(11)

Here, ss

 is per-unit current flowing in the in-

itiating-terminal of the conductor.

It is assumed that the feeding section considered here

has three AT-sections and currents of all loads are equal

to I. Sometimes there may be 2 loads on the up and down

rail tracks of the first AT-section. As these 2 loads in the

first AT-section are different, it is assumed here that





 (12)

When there are 4 and 6 loads in the feeding section

respectively, and 2 of them are located in the first

AT-section, the RMS currents are calculated and shown

in Table 1. If the currents flowing in initiating-terminal

of conductor T and F are summed, it can be seen that the

summations are equal for these two modes of TPN, i.e.,

more load current is transferred from conductor T to

conductor F in the N-mode TPN, however the total cur-

rent flowing in TPN nearly does not change, as can be

seen in Table 2.

3. Transformer Capacity

As current distribution is the same in the transformer for

J-mode and F-mode, only J-mode and N-mode trans-

former capacities are compared here.

Q. A. MA ET AL.

1028

Table 1. RMS current of conductor T and F (pu).

J-mode N-mode

Load number T F T F

4 1.283 0.764 1.041 1.0

6 1.774 1.258 1.528 1.5

Table 2. Conductors summary current in TPN.

Load number J-mode N-mode

4 2.033 2.041

6 3.024 3.028

In the F-mode transformer, currents flowing in the two

segments of the secondary winding are unequal. How-

ever, the cross-section areas of these two sections of

winding are identical in manufacturing for convenience,

and they depend on the bigger one, that produced by the

up load is shown as below via generalized method of

symmetrical components











(13)

In the same manner, the current produced by the down

load is













(14)

Here,

—distance between substation and the down

load, the total current is derived by summing Equ.13 and







 









(15)

Taking into account Equ.12, Equ.15 becomes





(16)

If there are 4 loads in feeding section, the total current

flowing in the secondary winding of traction transformer





(17)

If there are 6 loads, the current is





(18)

As only positive sequence current flows in the second

winding of the J-mode transformer, the total current

flowing in the secondary winding is 2

 and 3

 for 4

or 6 loads, respectively. Let, the per-unit current

flowing in the secondary winding is derived and shown

in Table 3. Thus the capacity of the F-mode transformer

is bigger than that of the J-mode transformer.

I



4. Other Aspects

In this section, three modes of TPNs are compared on rail

potential, voltage level and earthling-current, etc., based

on its chain circuit model [5].

Here the load is represented by constant admittance of

0.02S. It is specified in Ref [6] that the resistance of the

earthling electrode in the traction substation should not

exceed 0.5Ω. In high soil resistivity area, the value

should not exceed 5Ω. Both 0.5Ω and 5Ω are applied in

the simulation for comparison.

TPN parameters are listed in Tables 4-7. Here, PW

(protection wire) and GW (grounding wire) are reduced

to conductor H. “U” and “D” is used for up and down

TPNS respectively.

4.1. Rail Potential

As current distribution is identical for J- mode and

F-mode of TPNs [5], it can be induced that rail potentials

are also the same. It is only needed to compare J-mode

and N-mode TPNs.

Table 3. Transformer capacity comparison.

Load number J-mode F-mode

4 2 2.5

6 3 3.5

Table 4. Admittances of current return circuit (S/km).

U R

U H

D R

HU 1.655 0 -0.646 0

RU 0 0.01 0 0

Table 5. Impedances of current return circuit (Ω/km).

U R

U H

D R

HU 0.163+0.584i0.050+0.372i 0.049+0.317i 0.049+0.317i

RU 0.050+0.372i0.117+0.801i 0.049+0.339i 0.049+0.339i

Table 6. Impedances of T and F (Ω/km).

U F

U T

D F

TU0.135+0.646i 0.052+0.381i 0.050+0.381i 0.050+0.340i

FU0.052+0.381i 0.190+0.777i 0.050+0.340i 0.050+0.317i

Table 7. Mutual impedances between T, F and H, R(Ω/km).

U F

U T

D F

HU0.048+0.374i 0.046+0.416i 0.049+0.338i 0.049+0.315i

RU0.048+0.375i 0.047+0.353i 0.049+0.358i 0.048+0.331i

Q. A. MA ET AL. 1029

Rail potential distributions are shown in Figure 3. It

can be seen that rail potential are nearly identical for both

modes of TPNs and the resistance of earthling electrode

have neglectable effect on rail potential.

4.2. Voltage Level

Voltage levels are shown in Figure 4 for J-mode and

N-mode of TPNs. As can be seen, the resistance of 0.5 Ω

or 5 Ω does not have obvious effect on voltage level.

Besides, the minimum appears about at 2/3 in the first

AT- section of J-mode AT-section; however, in the

N-mode TPN, it appears at the initiating-terminal, as can

be illustrated from the TPN’s equivalent impedance.

It can be seen from Figure 4 that, the minimum volt-

age is about 200 V lower in N-mode TPN than that in the

J-mode TPN. As the load is located in the first

AT-section, the minimum voltage hardly exceeds its

corresponding limit in engineering. Thus the voltage lev-

els are almost identical.

4.3. Earting-current and Electro-magnetic

Interference to Nearby Conductors

From the fact that the J-mode, F-mode TPNs have the

same equivalent circuit [5], it can be induced that both

modes of TPNs have the same earthling-current distribu-

tion. Thus only N-mode, J-mode TPNs are needed to be

compared.

Earthling-current distributions are shown in Figure

6(a) at several load locations in the first AT-section of

the J-mode TPN, and the maximum earthling-current on

the left- and right- side of the load is shown in Figure

6(b). The maximum earthling-current is nearly 60 A,

about 1/9

(a) Earthing resistance 0.5 Ω

(b) Earthing resistance 5Ω

Figure 3. Rail potential distribution.

of the load current. To evaluate the electro-magnetic in-

terference to other adjacent conductors, the relationship

between A·km index caused by the whole length of the

first AT-section and load location is calculated also and

given in Figure 7. A·km index reaches its maximum in

the middle of the AT-section, about 1.1 times the load

current.

(a) J-mode

(b) N-mode

Figure 4. Voltage level at the load location.

Figure 5. TPN impedance in relation with load location.

(a) Earthing-current distribution at several load locations

Q. A. MA ET AL.

1030

(b) Left- and right-side maximum earthing current

Figure 6. Earting current distribution in the first AT-sec-

tion of J-mode TPN with earthing resistance 0.5Ω.

Figure 7. A·km index of the first AT-section in J-mode

TPN.

(a) Earthing-current distribution at several load locations

(b) Left- and right-side maximum earthing current

Figure 8. Earting-current distribution in the first AT-sec-

tion of N-mode TPN with earthing resistance 0.5Ω.

For the first AT-section of the N-mode TPN, the

curves are shown in Figure 8. As the distance between

the load and adjacent ATP(AT post) exceeds 5km,

earthing-current reaches its maximum of about 90 A,

A·km index

Figure 9. A·km index of the first AT-section in N-mode

TPN.

nearly 1/6 of the load current. As can be seen from Fi-

grue 9, A·km index is nearly linear with the load loca-

tion, and the maximum is about 1330 A·km, about 2.4

times the load current.

It is found that earthling resistance has neglectable ef-

fect on the earthling current and electro-magnetic inter-

ference.

4.4. Fault Location

As substation AT is omitted in the N-mode TPN, the

fault location method—AT neutral current ratios, which

is widely utilized in engineering, does not work any more.

As the mutual impedance between T and R is nearly

equal to that between F and R, and the mutual effect of T

and F to R cancel each other out, the positive current has

neglectable effect to R. Thus earthling current and elec-

tro-magnetic interference mainly depend on the zero se-

quence current.

5. Conclusions

Three modes of AT-fed TPN are compared, mainly on

transformer capacity, TPN capacity, rail potential, etc. It

can be concluded that these three modes of TPN are

nearly identical on rail potential, TPN capacity, and vol-

tage level. In N-mode TPN, AT or transformer tapping is

not necessary in the substation, earthling-current is big-

ger than that of other modes of TPN, and the “AT neutral

current ratios” fault location method become invalid.

F-mode TPN needs transformer tapping and bigger

transformer capacity, however substation AT is omitted.

J-mode TPN doesn’t necessitate transformer tapping,

however substation AT is needed in instead.

REFERENCES

[1] Q. Z. Li, “On Some Technical Key Problems in the De-

velopment of Traction Power Supply System for

High-speed Railway in China,” Journal of the China

Railway Society, Vol. 32, No. 4, 2010, pp. 119-124

Q. A. MA ET AL.

1031

[2] A. W. Li, “Optimal at Power Supply and Transformer

Wiring Type,” master’s Thesis, Southwest Jiaotong Uni-

versity, Chengdu, 2010

[3] G. Li and G. S Lin, “Short Circuit Impedance Analysis

for Novel AT Power Traction Network,” Asia-Pacific

Power and Energy Engineering Conference of IEEE

Power & Energy Society (PES), Shanghai, 26-28 March

2012, pp. 1-5

[4] F. H. Wang, “A Generalized Method of Symmetrical

Components and Its Applications,” Journal of Southwest

Jiaotong University, Vol. 4, No.1, 1981, pp. 1-12.

doi:10.1007/s11771-997-0018-z

[5] M. L. Wu, “Study on Electrical Parameters and Mathe-

matical Model of Traction Power Supply Systems,” Ph.D.

Thesis, Beijing Jiaotong University, Beijing, 2006

[6] TB10009-2005, Design Code of Railway Electric Trac-

tion Feeding.