new approach of designing and exploatation of electrical traction substations

1. Connection of electric traction substations on the principle of input-output

2. Electric traction substation connected to the nearby electric power plant

Connection of electric traction on the principle of input-output with twotransmission feeders equipped with three-poles switches, three-phasebusbar disconnectors and a three-pole disconnectors with earthingblades

Electric traction substation connected to the nearby electric power plant

There are two transformers, two transmission feeders, the two bus feeders(high voltage and low voltage), two transformer feeders.Each transformer has its own voltage regulator. Each feeder is fitted in same way.

The number of redundant paths, redundant equipment and devices is a basicfeature of this concept and schemes shown at figures 1 and 2. A variety of sparedelivery paths (which would be used in the case of virtually unimaginablecoincidences failures of the left feeder, right switch and transformer left) andlots of devices make electric traction substations very complicated.

The solution of this problem is illustrated by applying auxiliary bus

Saving three measuring transformers of 110 kV (decrease the total cost,including installation, footages and required space).The result: more reliable and simpler substation

Based on long time researching and studies, as well as broad international survey conducted by the Committee A 50 Office for Research and testing (Office de Recherrches et d'Essais), International Union of Railways, in singlephasesubstations, surge arresters are not applied anymore.

This method of protection when the electric traction substation was built near already protected buses of a power plant is assessed as dangerous for operational reliability and plant staff and removed from the substations in developed countries

The result: transfersally feeders are not necessary on the 110 kV side .

Scheme of electric traction substations connected via a three-phase transmission line

Transformers that are shown in the picture are without voltage regulators, which are weak spots subjected to failures.Result: increased plant reliability.

The next step of substation simplification is transformer feeder 110 kV and 25kV feeder lacks and giving to circuit breaker in 110 kV feeder functions ofprotection of transformer , as it shown in the previous figure.

In this case energy measurement is in 25 kV because there are required currentand voltage transformers for the protection.So it is necessary to add kWh meters for measuring losses.

-using drawable circuit breakers in 25 kV feeders instead circuit breakers and disconnectors which are elements of wrong manipulations;- the application of switch-disconnectors instead circuit breakers in 25 kV transformer feeders;-aplication of combined instrument transformers (CT and VT in one element) in all feeders;

Bypassing neutral section in separating substations with neutral section and designing electeric traction substations with single transformer - parallel connection of electric traction substations

Thyristor voltage adjustor is required to make identical voltages in catenary in this case.

Distance between electric traction substations increase from40 - 50 km to 80 - 90 km.

Peak power reduction wherein speed of trains do not decrease.

There are necessity for selectivity and accuracy of catenary distant relays withpower direction relay in separating substations, because two substations deliverpower to electric vehicle and ground fault.

Selectivity of catenary distant relays is acquired with time grading inthree zone toward sources.

Equivalent circuit of electric traction system 25 kV; 50 Hz for parallelconnected electric traction substations

Short circuit current:

𝑰𝑲𝑺 = 𝑼

𝟐 ∙ 𝒁𝑴 + 𝒁𝑻 + 𝒁𝒆𝒌𝒗′ ∙ 𝒍

𝑨

𝒁𝑴 - impedance of electric network operator for two pole short circuit on 𝟏𝟏𝟎 𝒌𝑽 busbars in electric traction substation reduced on catenary voltage,

𝒁𝑻 - impedance of single phase transformer of electric traction substations,

𝒁𝒆𝒌𝒗′ - equivalent impedance per unit of length of catenary

𝒁𝑴 = 𝒋 ∙𝟏,𝟎𝟓∙𝑼 𝟐

𝑺𝒌𝜴

U–voltage of catenary 𝑽 ,

𝑺𝒌 – two phase fault power on electric traction substation busbar 𝑽𝑨

𝒁𝑻 = 𝒋 ∙𝒖𝒌(%)

𝟏𝟎𝟎

𝑼𝟐

𝑺𝑻𝜴 ,

where: 𝒖𝒌(%) – relative short circuit voltage % ,

𝑺𝑻 – nominal power of transformer 𝑽𝑨

𝒁𝒆𝒌𝒗′ = 𝒁𝒗

′ − 𝜺𝒁𝒎′ +

𝟏−𝒆−𝒌∙𝒍

𝒌∙𝒍𝟏 − 𝜺 𝟐𝒁Š𝑰

′ 𝜴

𝒌𝒎

Carson-Pollaczek formulaes:

𝒁𝒆𝒌𝒗′ = 𝒁𝒗

′ − 𝜺𝒁𝒎′ +

𝟏 − 𝒆−𝒌∙𝒍

𝒌 ∙ 𝒍𝟏 − 𝜺 𝟐𝒁Š𝑰

′ 𝜴

𝒌𝒎

𝒁𝑽′ – impedance per unit of length of catenary

𝜴

𝒌𝒎,

𝒁Š𝑰′ –impedance per unit of length of returning current circuit

𝜴

𝒌𝒎,

𝒍 – distance to electrica traction substation 𝒌𝒎 ,

𝒁𝒎′ – mutual impedance per unit of length catenary- returning current circuit

𝜴

𝒌𝒎,

𝜺 =𝒁𝒎′

𝒁Š𝑰′ ,

where: 𝒌 = 𝒁Š𝑰′ ∙ 𝒈 𝒌𝒎−𝟏 - propagation coefficient of gauge

𝒈- admittance per unit of length of gauge𝑺

𝒌𝒎

Impedance per unit of length of returning current circuit with two rails: 𝒁Š𝑰′ =

𝟎, 𝟓 𝒓Š𝒂 + 𝒋 𝒙′ + 𝒙′′ +𝝎𝑴𝟏,𝟐′ 𝜴

𝒌𝒎,

where: 𝒓Š𝒂 –resistance of rails𝜴

𝒌𝒎,

𝒙′- interior reactance per unit of length of rail otpor 𝜴

𝒌𝒎,

𝒙′′- external rail reactance per unit of length 𝜴

𝒌𝒎,

𝝎 = 𝟐𝝅𝒇 𝒔−𝟏 - circle frequency Internal reactance pwr unit of length of S-49 rail: 𝒙′ = 𝟎, 𝟕𝟓 ∙ 𝒓Š𝒂External rail reactance per unit of length:

𝒋𝒙′′ = 𝟎, 𝟎𝟒𝟗𝟑 − 𝒋𝟎, 𝟏𝟒𝟒𝟔 𝟏, 𝟓𝟑 + 𝒍𝒐𝒈 𝑹Š𝟐 ∙ 𝜸

𝜴

𝒌𝒎

𝑹Š - radius of equivalent conductor: 𝑹Š =𝑷

𝟐𝝅𝒄𝒎 ,

where P is rail perimeter 𝒄𝒎 .

Mutual rails impedance per unit of length: 𝒋𝝎𝑴𝟏,𝟐′ = 𝟎, 𝟎𝟒𝟗𝟑 − 𝒋𝟎, 𝟏𝟒𝟒𝟔 𝟏, 𝟓𝟑 +

Dependance of catenary impedance

per unit of length on distance

for S-49 and UIC 60 rails

Dependance of catenary impedance arguments on distance for S-49 and UIC 60 rails

Short circuit current of a single truck

Overall short circuit current on place of fault is addition of currents from two electrical traction substations.

Dependance of impedance on distance measured by distant relay

Short circuit impedance measured by impedance relays in separating substations (R-X diagram)

CONCLUSION

The existing designs of electric traction substations in exploitation proved to beexpensive, overcomplicated and unnecessary. Consequences are too large costs ofconstruction and maintenance, overcomplicated facilities, lack of diagramsclearness and problems during maintenance.In this paper, we proposed new ways of substations designing and changes indesigns of exploited substations when the reconstruction is needed. It reducescosts, economizes controlling, makes maintenance simplified and improvesclearness of electrical traction substations. Availability and safety of substationsremains high. Parallel connected traction substations could reduce peak powercosts and measurements of energy consumption are simpler. This paper provideselectrical calculations for protective relay adjustments in traction systems.Calculations of impedances and short circuit currents are performed using theWolfram Mathematica program.