electrical urban mass transport - rev final - ii part

Electrical urban mass transport: metro-transit systems

Semester 1 - Power systems for sustainable transportation

Lecturer: Maria Carmen Falvo

International Master In Sustainable Transportations and Electrical Power Systems

Universidad de Oviedo

Outline

An introduction on electrical urban mass transport

Metro-transit systems: main features

Power systems for metro-transit: Supplying architecture, traction line and electrical sub-stations

Metro-trains

Energy saving issues in metro-transit transport

Design&sizing basics and some tips on simulation software

Metro-transit system in Rome: an example of real application

2

Design&sizing basics and some tips on simulation software for metro-transit transport

For the design and sizing of metro-transit systems, different models are necessary: to simulate the electro-mechanical behavior of metro-trains for

the evaluation of the metro-trains power consumption and for defining the timetable of the line;

to simulate the electrical behavior of the supplying traction system to carry out all the variables necessary to evaluate the energy state of the traction system.

The objective of design and sizing is to define as minimum: Number, location and size of the groups in ESS;

Configuration of the traction line and section of each conductor.

3


With this task it is necessary: to have some standards as references for the voltage level

and main components size (ESS, traction line); to respect the typical limits reported in the technical

standards on the main electrical variables (voltage, current and power) and special requirements by the owner of the line;

to know the electrical load of the power systems (trains consumption).

4


Standards as references for the voltage level and main components size:

Rated voltage: 0.75, 1.5 kV;

Rated power of transformers in ESS: 3,6 or 5,4 MW;

Section of the traction line:

100-150 mm2 for the contact wires;

120-150 mm2 for the carrying cables;

100-150 mm2 for the feeder.

5


Limits reported in the technical standards on the main electrical variables: CENELEC EN 50163, 2004 “Railway applications. Supply voltages

of traction systems” on the maximum and minimum voltage at pantograph: 500-900 V for 750 Vdc, 1.000-1.800 for 1.500 Vdc.

the current and power limits on the traction line and on the machines in ESS, as a function of the size.

To these limits it is possible to add specific requirements in operation by the owner of the metro-system that can deal with the operation in fault conditions.

6


The first step is to know the electric loads to supply.

The main electric load of a traction power systems are the metro-trains that are variable load in time and space.

In function of the phase of the motion (traction/braking/coasting/stop) the value of the power required/produced at the pantograph changes.

In order to know this time and space variable load profile an electro-mechanical simulator is needed.

The electro-mechanical simulator starts from input data on train (mass, tractive/braking effort in function of speed) and on line (length, layout, slopes, curves).

7


It includes a model, able to give in output position, speed and acceleration of the train at each simulation time step.

The model is based on the balance of forces equation:

F = R + M (dv/dt) = (r1 + r2 + r3 + r4) × M

r1 = resistance on a flat and straight path (rolling and aerodynamic)

r2 = resistance associated to the slopes

r3 = resistance associated to the curves

r4 = equivalent resistance to acceleration (inertia)

All the components are referred to the unit of mass [daN/kg]. 8


The component r1 is the resistance on a flat and straight path and includes: Rolling friction component that is small and depending on the contact

between the wheels and rail;

Aerodynamic component that is a function of the square of the train speed and depends on the type of layout of the line and the shape of the train.

9 0 1 2 3 4 5 6 7 8 9

10

0 20 40 60 80 100 120 140 160 Speed [km/h]

r 1 [d

aN/t]


r2 and r3 are the resistance components associated to the slope and to the curves. The component associated to the curve is linked to the curve radius (R)

with the formula: r2 = a / (R - b). a and b are two coefficients given in function of the type of wheels and rail.

The component associated to the slope is directly link to the slope value in %0 (i) with the formula: r3 = R3 / M = (P/M) i = g i, where i = tgα

10

R (m) a b

>350 650 55

350-250 650 65

250-150 650 30 α

P

P cos α

P sen α


The tractive effort depends on the type of drive on board. In any case it is a function of the speed with a specific curve.

Generally for low speed the tractive effort is maximum, then it becomes inversely proportional to speed (constant power).

The traction curve gives the relation between the tractive force and the speed.

In case of braking the value of the electric effort depends on the specific drives: it is a component of the total braking effort.

11 Speed [km/h] F Tr

attiv

e ef

fort

[kN

]

v 0

F m = f P a

v MAX

0255075

100125150175200225250275300325350

0 10 20 30 40 50 60 70 80

Brak

ing

Effo

rt [k

N]

Speed [km/h]

Electrical Braking EffortPneumatic Braking EffortTotal Braking Effort


The intersection of the total resistance curve and tractive effort one gives the real speed of the train for each time step.

From the speed it is possible to know the acceleration and the position of the train in the time.

12

t [s]

a [m

/s2 ]

, v [m

/s],

s[m

] s = s(t)

v = v(t) a= a (t)

s a

t a

v [km/h]

F, R

[daN

]

F = f(v)R = r(v)

vregime

W =

w(v

)


The simulator takes in also the model for the evaluation of the power required and regenerated by the train during its motoring and braking phases, calculated at each simulation time step.

In fact the mechanical power required/given by the electrical motors P is given as the product of the tractive effort F and the speed v:

Pm = F × v

Knowing the efficiency of the electrical motor, it is possible to have the electrical power required/generated by the train in its traction and braking phases.

13


14


The electro-mechanical simulator is generally able to give as output also the timetable of the line for a given traffic scenario, drawing the position-time curve for each train present on the track in the simulated hour.

With this aim it is necessary to set in input: the trains departure time on the two ways, specific trains sequence, trains stop time period in each station, trains shift time on the two ways.

15

0,00

10,00

20,00

30,00

40,00

50,00

60,00

70,00

80,00

90,00

25200 25560 25920 26280 26640 27

Progressiva (km)

Putignano Grotte Castellana

Laureto (48 397)

Locorotondo

Alberobello

Noci (52+860)

Martina Franca


An electric simulator receives as input the data from the electro-mechanic tool, with the aim of carrying out all the variables necessary to evaluate the energy state of the traction system.

In addition the data for electrical infrastructure’s definition are required.

16


Input by electro-mechanical simulator: power profile and position of each train for each time step.

Input on the power systems configuration: Rated voltage of the system (standard);

Number and position on the line of ESSs (design choice);

Number and size of the groups in ESS (design/standard choice);

Number and section of conductors of the traction line (design/standard choice);

Equivalent resistance (per km) of the ESS groups (calculation);

Equivalent resistance (per km) of the traction line and rail (calculation).

17 eq

line Sr ρ

=p

rrail 21

=

RbinP L1 RbinP

L2 R binP

L3

R SSE1

R SSE2

R SSE3

R SSE4

RbinD L1 RbinD

L2 R binD

L3

VSSE VSSE VSSE

VSSE

P binDTr2

P binDTr3

P binDTr1

P binPTr2

P binPTr3

P binPTr1


Matching the consumption data of each train, the traffic scenario information and the electrical topology of the supplying power system, the tool performs a DC power flow calculation for each time step.

Since trains’ consumption is considered independent from voltage at pantograph, the equations are non-linear. An iterative method is required to solve the power flow problem: the Newton-Raphson algorithm is chosen for this task. 19


The output of the electric simulator are: The voltage in the nodes;

The current on the branches.

In their function it is possible to verify the respect of the limits in terms of: Maximum and minimum voltage (standard);

Maximum current on the traction line (thermal limit);

Maximum power on the ESS groups (temporary overload);

and the possible specific requirements given by the owner of the metro-transit system (usually regarding its operation in fault conditions).

20


The same models and software used for design and sizing can be applied for energy analysis on a given system.

In this case the output is used not for checking the right size and design of the power system, but for evaluating its energy performance.

In addition to the conventional electrical magnitudes (voltage, current and power), energy parameters are usually introduced.

A real case is shown to better explain: line A of Rome metro-transit.

21

Outline

An introduction on electrical urban mass transport

Metro-transit systems: main features

Power systems for metro-transit: Supplying architecture, traction line and electrical sub-stations

Metro-trains

Energy saving issues in metro-transit transport

Design&sizing basics and some tips on simulation software


22


The metro-transit system of Rome city includes just two lines. Only in the last years, an expansion project of 1962 has being in progress.

The past The present The future

23


The network opened in 1955, making it the oldest metro-transit system in Italy.

There are currently two metro-lines: Line A (orange) and Line B (blue).

The current network is 41.5 km long, has an “X” shape with the lines intersecting at Termini Station, the main train station in Rome.

Line B splits at the Bologna station in two branches.

24


Line Terminals Opened Last ext. Length [km]

n. of stations

N. of pass. in 1 year

[million]

Travel time [minutes]

Line A Battistini ↔ Anagnina 1980 2000 18.4 27 164.2 41

Line B Laurentina ↔

Rebibbia / Conca d'Oro

1955 2012 23.1 25 109.5 34/32

Total 41.5 km 52 - -

26

• Line A connects the north-west of the city with the south-east. It has 27 stations, with terminals at Battistini and Anagnina. Despite its name, Line A was the second metro-line in Rome.

• Line B connects the north-east of the city with the south-west. It has 25 stations with terminals at Rebibbia, Conca d'Oro and Laurentina. A new 3,9 km long branch (B1) with 4 new stations was opened connecting Piazza Bologna with Conca d'Oro on 13 June 2012.


Future expansion is scheduled for the metro-transit in Rome including 2 new lines: Line C, currently under construction;

Line D, whose start of the construction has been currently indefinitely postponed.

27


Line C will run from Grottarossa, north of the Vatican city, to Pantano.

Line C will intersect with Line A at Ottaviano and at San Giovanni, and with Line B at Colosseo.

It will also intersect with the planned Line D at Piazza Venezia, creating a second metro hub in Rome.

The route is about 25.5 km long and has 30 stations. 17.6 km are underground and the rest is in open air.

Maximum transport capacity: 24.000 passengers / h for 1 way 28


Progress on Line C has been slow and repeatedly delayed.

Rome is one of the oldest cities in the world and the construction of the metro system has encountered considerable obstacles owing to the frequent archaeological discoveries.

29


Train fleet for Line C will include 30 vehicles with train cars for: a total length of 107 m, maximum capacity of 1.200 passengers per train, maximum speed of 80 km/h, commercial speed 35 km/h.

The trains will be totally automatic, and will use the Ansaldo-Breda Driverless metro-trains also featured on Copenhagen metro-transit.

Estimated cost of the work: about 3 billions of Euros. 30


Line D would link the north eastern areas of Rome with EUR in the south west.

Line D would be 22 km long and will feature 22 stations.

It would intersect Line A at Spagna, Line B and Roma-Lido railway at EUR Magliana, Line B1 at Jonio, Line C at Venezia.

31


Power systems for the actual metro-transit in Rome includes:

6 main supplying feeders by the local electricity utility (ACEA) at 20 kV: 2 dedicated for Line A (Valcannuta and Cinecittà), 3 for Line B (S. Basilio, Laurentina) and B1 (Conca D’Oro) and 1 as backup entrance (Villa Borghese) for the others by Smistamento Termini bus.

16 ESSs (6 for Line A, 8 for Line B and 2 for B1), with a line rated voltage of 1.500 V DC.

32

LINEA B1


For Line A the power system is composed by 6 ESSs.

Each ESS includes conversion groups, whose voltage output is 1.5 kV DC for the traction line supplying, and equipped with AC/DC full diode bridge converters with a nominal power ratings of 3.6 MW.

By 2002 an expansion project of the metro-line had scheduled the change of the trains’ fleet, with a progressive introduction of new vehicles with superior energy consumption.

33

Traction Line

2*100 mm2 contact wires 2*120

mm2 carrying cables +2*150 mm2

feeder from ESS1 to ESS4 +1*120

mm2 feeders from ESS4 to ESS6


The new vehicles are MA300 trains, made by CAF Espania and including Bombardier Drives.

MA300 allows braking energy saving, but it has a higher energy consumption, due to the superior nominal power ratings of drives and to the presence of onboard conditioning plants.

34

Trains Main Figures

Rated Power [MW] 4,415

Weight in no-load (no passenger) and full-load (max n. of passengers) condition [kg] 181.600/233.000

Auxiliary Service Power [MW] 0,4

Constant Deceleration [m/s2] -1,1

Minimum Voltage for a Constant Power [kV] 1,05

Maximum Line Voltage for the recovery of the braking power [kV] 1,7

0255075

100125150175200225250275300325350

0 10 20 30 40 50 60 70 80

Brak

ing

Effo

rt [k

N]

Speed [km/h]

Electrical Braking EffortPneumatic Braking EffortTotal Braking Effort


A parallel upgrading action has been performed on the power

systems and Met.Ro. (Rome metro-transit company) involved the

Power System Research Group at Sapienza.

In this framework, some simulations have been carried out for the

assessment of the impact of the braking energy recovering on the

power consumptions.

The group proposed some energy performance indexes for getting an

assessment of energy saving that could be reached thanks to this

recovering.

35

Energy performance indexes are based on specific parameters:

EESS

W REC the supplied energy by ESS in case of recovering of the trains braking energy;

EESSW/O REC the supplied energy by ESS without

the recovering of the trains braking energy; ETR REC.ED the effective recovered braking energy; ETR REC.BLE the potential recoverable braking

energy; ETR REQ the requested energy by the trains.

36

EESSEESS

ETR REC.ED

ETR REC.BLE

ETR REQ

Eloss_ESS



Energy saving percentage (ES%), defined as:

EESS

W REC is the supplied energy by ESS in case of recovering of the trains braking energy;

EESSW/O REC is the supplied energy by ESS without the recovering of the

trains braking energy.

ES% values give an assessment of the impact of the braking energy recovering in terms of energy saving.

37


Effective recovered braking energy percentage (ER’%) in respect of the recoverable braking energy, defined as:

ETR REC.ED is the effective recovered braking energy;

ETR REC.BLE is the potential recoverable braking energy.

ER’% values give an assessment of the capacity of the line to receive the braking energy by the train.

38


Effective recovered braking energy percentage (ER’’%) in respect of the total required energy by the trains, defined as:

ETR REC.ED is the effective recovered braking energy;

ETR REQ is the requested energy by the trains.

ER”% values give an assessment of the contribute of the recovered braking energy at the traction load.

39


A specialized tool to evaluate the energy performance indexes has been developed. The tool is able to calculate and draw the parameters of interest for the energy saving’ assessments, such as: for each train, the recoverable and recovered braking power

and the pantograph voltage; for the global system, the total required power by the

trains, the total supplied power by the ESSs, the total potential recoverable and effective recovered braking power.

40


41

The simulations have been carried out for the system energy performance evaluation, considering MA300 trains running.

A constant stop time period in station, equal to 20 s, has been chosen as medium value.

Simulations are then performed referring to different values of trains’ time interval. The results are here reported for 3 Traffic Scenarios (TSs).

Trains Time Interval

[s]

Traffic Scenario 1 (peak hour) 180

Traffic Scenario 2 300

Traffic Scenario 3 (off-peak hour) 600


For each TS, global system energy values are calculated: in a base case (no recovering on the line): total supplied energy by all the

ESS; in case of recovery of the braking energy on the line: total potential

recoverable energy by all the trains, total effective recovered energy by all the trains, total required energy by all the trains, total supplied energy by all the ESS (HV side).

For each TS, single train energy values are calculated: the potential recoverable energy, the effective recovered energy, the required energy.

These values are the basis for the calculation of the indexes proposed for the energy performance analysis.

42


43

Global System Energy Values for 1h of simulation

In case of recovery of the braking energy on the line, without

reversible ESS and storage system on board Total Supplied

Energy by all the ESS in the base

case [MWh]

Total Potential Recoverable Energy by all

the trains [MWh]

Total Effective Recovered

Energy by all the trains

[MWh]

Total Required Energy by all

the trains [MWh]

Total Supplied

Energy by all the ESS (HV side) [MWh]

Traffic Scenario 1 10,33 9,47 29,05 22,46 34,45 Traffic Scenario 2 6,60 5,93 17,72 13,12 20,53 Traffic Scenario 3 3,31 2,54 9,51 7,61 10,80


Making a comparison between system energy values for different TS, it is possible to point out that for an increasing of the trains time interval: the total required energy by the trains decreases;

the total energy supplied by the ESS decreases;

the total potential recoverable braking energy decreases;

the total effective recovered braking energy decreases.

44


An energy saving from 29 to 35 % is possible thanks to recovering of the braking energy.

Not the whole recoverable energy is recovered, but a good percentage (76-91 %).

The recovered energy is a consistent percentage of the total load (27-32 %).

45

Energy Performance Indexes for the Whole System

ES% ER'% ER"%

Traffic Scenario 1 34,80% 91,67% 32,60%




For a total trains interval variation from 120” to 600”: ES% decreases from 38% to 30%;

ER’% decreases from 98% to 77%;

ER”% decreases from 35% to 27%.

In other words, when the trains number on the line is smaller, the braking energy potential available is smaller, the capacity of the line to receive this energy is reduced, and the energy saving is reduced.

46


The difference between the potential recoverable and the effective recovered braking energy changes for each trains time interval with a non-linear function, and it is included in a range from 0.2 to 1.2 MWh.

This differential energy is usually dissipated in heat by means of on-board rheostats.

In alternative it could be recovered using storage stationary systems.

47

0,00

2,00

4,00

6,00

8,00

10,00

12,00

14,00

16,00

18,00

120" 150" 180" 240" 300" 360" 600"

Total potential recoverable braking energy

Total effective recovered braking energy

Difference between total potential recoverable braking energy and total effective recovered braking energy

Trains frequency [s]

[]


To know the daily value, it is possible to consider a real diagram of trains’ frequency in 24 hours service that includes: 6 hours without service and 18 hours with service;

4 hours of service with a trains interval at 150”;

4 hours of service with a trains interval at 360”;

10 hours of service with a trains interval at 240”.

The daily value of energy dissipated in heat becomes 14.5 MWh.

A stationary system of storage would manage large quantity of energy that could be stored in batteries located along the traction line in each ESS.

48


Another comparison has been made between potential recoverable and effective recovered braking power of a train in specific TS (600’’ train interval).

Their difference is the power dissipated in heat by means of on-board rheostat and it is about 2 MW.

It is possible to find an effective recoverable braking energy of 251 kWh and a potential recovered braking energy of 205 kWh for the single train that means 50 kWh could be recovered using storage systems on board, in 1 hour of service. 49

1

1,5

2

2,5

3

3,5

4

4,5

5

5,5

0 60 120 180 240 300 360 420 480 540 600

[MW

]

[s]

Recovered Braking PowerRecoverable Braking PowerPantograph Voltage


Referring to a TS with 150” trains interval : an equal effective recoverable braking energy of 251 kWh is found

a potential recovered braking energy 249 kWh for a single train,

only 2 kWh could be recovered using storage systems in 1 hour of service.

These results point out that, if the storage system is located onboard the train, the value of energy that it has really to manage in 1 hour is very variable in function of the traffic condition.

50


In any case for a single train there are large powers (about 1 MW) and small energies (1-10 kWh), that means the most appropriate system to install onboard for storage are ultra-capacitors and not batteries.

Anyway the introduction of storage systems onboard train is a solution that would require an upgrading of the vehicle drive’s design and so it could not be operated by a metro-transit utility in brief time.

51


The example of application shows that: the indexes give an assessment on the effective energy saving

achievable thanks to the regeneration of the train braking energy;

their evaluations provide a procedure to assess the impact of different technical solutions for improving energy saving, such as storage devices at the electrical sub-stations and on board the vehicles;

the procedure based on the indexes proposed provides also a method to compare different metro-transit lines.

52

Related Project

The indexes have been used also to compare the energy performance of two real metro-lines in Italy (Rome) and in Spain (Madrid) in collaboration with the Instituto de Investigacion Tecnologica of the University of Comillas – ICAI in Madrid.

The results are presented in a paper on an International Journal: M.C. Falvo, D. Sbordone, A. Fernández-Cardador, A. P. Cucala, R. R. Pecharromán, A.J. López-López, “Energy savings in metro-transit systems: A comparison between operational Italian and Spanish lines”, Proceedings of the Institution of Mechanical Engineers, Part F: Journal of Rail and Rapid Transit.

53

Related projects

Zem2All (Zero Emissions Mobility To All) project, promoted by the Enel Group through Endesa and part of the Malaga Smart City project.

Electric vehicles on road can be charged for free at Malaga train station through a charging station in the underground car park, harnessing energy generated during the braking of trains.

The charging station can also draw energy from a PV system installed at the station which are equipped with a storage system.

http://www.enel.com/en-GB/media/news/enels-electric-mobility/p/090027d981fe4205



Related projects

Southeastern Pennsylvania Transportation Authority (SEPTA) is now taking innovative steps on Philadelphia Metro-transit systems, combining regenerative braking with electricity storage.

It installed a 1.5 MWh bank of lithium ion batteries at the Letterly substation in Philadelphia.

Other cities in US are starting to follow the same project.

http://www.scientificamerican.com/article/braking-trains-coupling-with-energy-storage-for-big-electricity-savings/ 55

http://www.scientificamerican.com/article/braking-trains-coupling-with-energy-storage-for-big-electricity-savings/




Related projects

Research Project, in collaboration and funded by Met.Ro. (Rome Metro-Transit System Operator), "Study on the power plants for the supplying of the trains on the metro-line A in Rome”.

Research Project, funded by the University of Rome Sapienza, "Study for the energy savings in an urban mass transport system in the presence of innovative devices for energy storage."

Research Project, funded by University of Rome Sapienza, "A smart grid for a smart transport. Design of an energy-efficient and environmentally sustainable integrated mobility system. New models for energy and power systems analysis project”.

Italian Research Project, funded by and in collaboration with ENEA (National Agency for Energy and Environment), call "Instruments and technologies for energy efficiency in the services sector", funded in Program Agreement MSE-ENEA on Electric System Research («Ricerca di Sistema»).

56

Electrical urban mass transport: metro-transit systems

Semester 1 - Power systems for sustainable transportation

Lecturer: Maria Carmen Falvo

International Master In Sustainable Transportations and Electrical Power Systems

Universidad de Oviedo

58

Sapienza Software - Electro-mechanical Simulator

59

Sapienza Software - Electro-mechanical Simulator: input on the train and traffic scenario

60

Sapienza Software - Electro-mechanical Simulator: input on the train and traffic scenario

61

Sapienza Software - Electro-mechanical Simulator: input on track

62

Software Sapienza: input on track

63

Sapienza Software - Electro-mechanical Simulator: output

64

Sapienza Software - Electro-mechanical Simulator: output

0,00

10,00

20,00

30,00

40,00

50,00

60,00

70,00

80,00

90,00

25200 25560 25920 26280 26640 27

km)

65

Sapienza Software - Electrical Simulator

66

Sapienza Software - Electrical Simulator: some output

2000

2200

2400

2600

2800

3000

3200

V [V

]

Time [min]

Voltage at the pantograph for different values of the tracion line section

Seq = 550 mm^2Seq = 600 mm^2Seq = 650 mm^2Seq = 750 mm^2

67


0

2000

4000

6000

8000

10000

12000

14000

16000

18000

P [k

W]

Time [min]

Power Required at ESSs

SSE5SSE6SSE7SSE8

68


-1000-500

0500

100015002000250030003500

I [A

]

Time [min]

Current on the branches supplied by ESS6

Binario 2 NordBinario 1 NordBinario 2 SudBinario 1 Sud

69


0

5

10

15

20

25

30

0 15 30 45 60 75 90 105120135150165180195210225240255270285300315330345360375390405420435450465480495510525540555570585600615630645660675690705720

[MW]

[s]

POTENZA RECUPERABILE POTENZA RECUPERATA

70


0

10

20

30

40

50

60

0 15 30 45 60 75 90 105120135150165180195210225240255270285300315330345360375390405420435450465480495510525540555570585600615630645660675690705720

[MW]

[s]

CONFRONTO TRA POTENZA RECUPERATA E POTENZA ASSORBITA DAI TRENI

POTENZA ASSORBITA DAI TRENI POTENZA RECUPERATA

71


1

1,5

2

2,5

3

3,5

4

4,5

5

0 60 120 180 240 300 360 420 480 540 600

[kW

]

[s]

Recovered Braking PowerRecoverable Braking PowerPantograph Voltage

electrical urban mass transport - rev final - ii part

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