new approach of designing and exploatation of electrical traction substations
TRANSCRIPT
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:
๐ฐ๐ฒ๐บ = ๐ผ
๐ โ ๐๐ด + ๐๐ป + ๐๐๐๐โฒ โ ๐
๐จ
๐๐ด - impedance of electric network operator for two pole short circuit on ๐๐๐ ๐๐ฝ busbars in electric traction substation reduced on catenary voltage,
๐๐ป - impedance of single phase transformer of electric traction substations,
๐๐๐๐โฒ - equivalent impedance per unit of length of catenary
๐๐ด = ๐ โ๐,๐๐โ๐ผ ๐
๐บ๐๐ด
Uโvoltage of catenary ๐ฝ ,
๐บ๐ โ two phase fault power on electric traction substation busbar ๐ฝ๐จ
๐๐ป = ๐ โ๐๐(%)
๐๐๐
๐ผ๐
๐บ๐ป๐ด ,
where: ๐๐(%) โ relative short circuit voltage % ,
๐บ๐ป โ nominal power of transformer ๐ฝ๐จ
๐๐๐๐โฒ = ๐๐
โฒ โ ๐บ๐๐โฒ +
๐โ๐โ๐โ๐
๐โ๐๐ โ ๐บ ๐๐ล ๐ฐ
โฒ ๐ด
๐๐
Carson-Pollaczek formulaes:
๐๐๐๐โฒ = ๐๐
โฒ โ ๐บ๐๐โฒ +
๐ โ ๐โ๐โ๐
๐ โ ๐๐ โ ๐บ ๐๐ล ๐ฐ
โฒ ๐ด
๐๐
๐๐ฝโฒ โ impedance per unit of length of catenary
๐ด
๐๐,
๐ล ๐ฐโฒ โimpedance per unit of length of returning current circuit
๐ด
๐๐,
๐ โ distance to electrica traction substation ๐๐ ,
๐๐โฒ โ mutual impedance per unit of length catenary- returning current circuit
๐ด
๐๐,
๐บ =๐๐โฒ
๐ล ๐ฐโฒ ,
where: ๐ = ๐ล ๐ฐโฒ โ ๐ ๐๐โ๐ - propagation coefficient of gauge
๐- admittance per unit of length of gauge๐บ
๐๐
Impedance per unit of length of returning current circuit with two rails: ๐ล ๐ฐโฒ =
๐, ๐ ๐ล ๐ + ๐ ๐โฒ + ๐โฒโฒ +๐๐ด๐,๐โฒ ๐ด
๐๐,
where: ๐ล ๐ โresistance of rails๐ด
๐๐,
๐โฒ- interior reactance per unit of length of rail otpor ๐ด
๐๐,
๐โฒโฒ- external rail reactance per unit of length ๐ด
๐๐,
๐ = ๐๐ ๐ ๐โ๐ - circle frequency Internal reactance pwr unit of length of S-49 rail: ๐โฒ = ๐, ๐๐ โ ๐ล ๐External rail reactance per unit of length:
๐๐โฒโฒ = ๐, ๐๐๐๐ โ ๐๐, ๐๐๐๐ ๐, ๐๐ + ๐๐๐ ๐นล ๐ โ ๐ธ
๐ด
๐๐
๐นล - radius of equivalent conductor: ๐นล =๐ท
๐๐ ๐๐ ,
where P is rail perimeter ๐๐ .
Mutual rails impedance per unit of length: ๐๐๐ด๐,๐โฒ = ๐, ๐๐๐๐ โ ๐๐, ๐๐๐๐ ๐, ๐๐ +
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.