interaction between dc light rail and 25kv ac heavy rail

Dr Stephen Goh, Jeff Russell INTERACTION BETWEEN DC LIGHT RAIL AND 25KV AC HEAVY RAIL Aurecon Australasia Pty Ltd

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24 – 26 November, Melbourne

INTERACTION BETWEEN DC LIGHT RAIL AND 25KV AC HEAVY RAIL

Dr Stephen Goh, Technical Director: Traction Power Systems, Aurecon

BSc(Hons), MSc, PhD, CEng, FIET, CPEng, RPEQ, FIEAust

Jeffrey Russell, Associate, Energy Services, Aurecon BE (Electrical)

Summary

Light rail is currently having a renaissance in cities around the world including Australian cities. To create an integrated transport system, the 750V DC light rail infrastructure is often constructed in close proximity to an existing 25kV AC heavy rail line. This integration invariably creates electrical interface issues such as Earthing and Bonding, Electromagnetic Compatibility (EMC), Signalling and Telecommunication (S&T) interface issues, which need to be resolved. The paper assesses the interface issues of light rail and heavy rail train services, to ensure the safety

of people and railway properties, as well as the reliability of the railways. European Standards EN

50122 Parts 1-3, EN50121 parts 1-3 and the new or emerging Harmonised Australian Railway

Standards are discussed and recommended to demonstrate EMC compatibility. The paper examines

recent Case Studies undertaken in Europe, and reveals how the European methodologies can be

adapted to provide innovative solutions for the Australian rail industry.

1. INTRODUCTION

Light rail is currently having a renaissance in cities around the world including Australian cities. For the purpose of creating an integrated transport system, the 750V DC light rail infrastructure is often constructed in close proximity to an existing 25kV AC heavy rail line. The outcome is that the light rail trains and heavy rail trains will be calling or terminating at interchange stations for the convenience and benefit of the passengers. This integration invariably creates electrical interface issues such as Earthing and Bonding, Electromagnetic Compatibility (EMC), Signalling and Telecommunication (S&T) interface issues, which will need to be resolved prior to the opening and running of both the light rail and the heavy rail services. These electrical interface issues arising from railway mutual conductive, inductive and capacitive electrical interactions for both normal operation and short term fault scenarios are not unique to Australian cities. They are numerous examples around the world, especially in European cities, where these issues are successfully resolved,

although some solutions are better than others. However, all the various solutions share a common goal, that is, their main aim is to ensure that the AC and DC railways can co-exist and do not interfere with each other or the outside world i.e. More than just ‘meeting the standards’. The interface issues of light rail and heavy rail

train services operating in close proximity, as

well as the station interfaces issues are

discussed and demonstrated how to mitigate

the electrical hazards to ensure the safety of

people and railway properties, as well as the

reliability of the railways. The application and

compliance of the European Standards such

as EN 50122 Parts 1-3, EN50121 parts 1-3

and the new or emerging Harmonised

Australian Railway Standards are discussed.

Recent Case Studies undertaken in Europe

are discussed and solutions revealed how the

European methodologies can be adapted to

provide innovative solutions for the Australian

rail industry.


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2. SYMBOLS AND ABBREVIATIONS A – Ampere AC – Alternating current AS/NZS - Australia/New Zealand standard ASA – Assets standard authority DLR – Dockland light railway (UK) E&B – Earthing and bonding EHV – Extra high voltage EMC - Electromagnetic Compatibility EMI - Electromagnetic interference EN – EuroNorm (European Standard) EPR – Earth Potential (Voltage) Rise GCLR – Gold coast light rail HV – High voltage kA – Kilo Ampere LUL – London underground Limited (UK) Min - minute MV – Medium voltage MW – Mega Watts NR – Network Rail (UK) RISSB - Rail Industry Safety and Standards Board S&T - Signalling and Telecommunication TCSSC - Train Control Systems Standing Tphpd – Trains per hour per direction Committee UK – United Kingdom V – Volt

3. ELECTRICAL MECHANISMS BETWEEN AC AND DC RAILWAYS

The three electrical mechanisms of interference between the AC and DC railways running in parallel are as follow: 3.1 Conductive coupling EMIs from AC and DC railways propagate between the two railway systems via earth and can lead to unacceptably high Earth Potential Rise (EPR). 3.2 Inductive coupling Electro-magnetic fields generated by AC railway (50Hz and harmonics) and DC railway (harmonics) can potentially interfered with each other via the inductive (mutual) coupling mechanism. This can result in unacceptably high Induced voltages (V) on both systems. 3.3 Capacitive coupling This is less important at lower frequencies and are often ignored.

4. KEY FACTORS AFFECTING AC AND DC SYSTEMS

4.1 Scenario 1: The Offender: AC Railway Type of AC Traction Power System & Feeding Arrangement:

25kV AC Rail Return System or

25kV AC Booster Transformer System or

25-0-25kV (2x25kV) AC Autotransformer System

High capacity passenger service:

24 trains per hour per direction (normal service) – 2.5 min headway

30 tphpd (perturbed) – 2 min headway High Current in overhead conductor or High Fault Level:

High power trains (5.5 MW) – 220A per train

Fault level of 6kA or 12kA The Victim: DC Railway 4.2 Scenario 2: The Offender: DC Railway Type of DC Traction Power System & Feeding Arrangement:

750V DC Floating Negative System or

750V DC Earthed Negative System

High capacity passenger service:

6 minute headway (normal service) – 10 tphpd

3 minute headway (special events) – 20 tphpd

High Current in overhead conductor or High Fault Level:

Low power trams (1MW) – 1300A per train

Fault level of 35kA between contact wire and rail(s)

The Victim: AC Railway


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5. ISSUES AND CONSEQUENCES What is at stake?

Issue Consequences

Earthing and Bonding

Inadequate E&B can lead to lack of high integrity traction and fault currents return paths

Touch Voltage

Risk of electric shock

Signalling System

If not immunised can lead to system malfunction / equipment damage

Telecom System

If not immunised can lead to system malfunction / equipment damage

6. APPLICABLE STANDARDS 6.1 Relevant European & International

Standards

EN 50122 part 3 – Mutual Interaction of AC &

DC Traction systems (Railway Application)

Demarcation of the mutual interaction zone

Touch voltage limits for the combined AC and DC systems, including workshops

Technical requirements in the mutual interaction zone

Excludes radio frequencies Plus many more standards to complete the

picture.

6.2 Relevant European & International Standards:

EN 50122 part 1 – Protective provision relating to electrical safety and earthing

EN 50122 part 2 – Provisions against the effects of stray currents caused by DC traction systems

EN 50121 parts 1 to 3 – Electromagnetic Compatibility (EMC)

International Telecommunication Union - Earthing and Bonding

IEEE 80 2000 – IEEE Guide for safety in AC substation grounding

6.3 Relevant Australian Standards:

AS 3000:2007 – Wiring Rules

AS 2067:2008 – Substation and high voltage installations exceeding 1kV AC

AS/NZS 60479.2:2002 – Effects of current on human beings and livestock

AS/NZS 61000.3.2:2007 – EMC Limits for harmonic current emissions

AS/NZS 61000.4.3:2006 – EMC – Testing and measurement techniques – Radiated, radio-frequency, electromagnetic field immunity test

AS/NZS 61000.4.30:2012 – EMC – Testing and measurement techniques – Power quality measurement methods

AS/NZS 61000.3.6:2001 – EMC Assessment of the emission limits for the3 connection of the unbalanced installations to MV, HV and EHV power systems

AS/NZS 1768:2007 – Lightning protection

ENA EG-0 – Power System Earthing Guide

ENA EG-1 – Substation Earthing Guide

Earth Potential Rise_ESAA_CODE_ERP-1984

6.4 Published Australian Standards by Rail Industry Safety and Standards Board (RISSB) and Train Control Systems Standing Committee (TCSSC):

• AS7663 – Signal Cables • AS7664 – Railway Signalling Cable

Routes, Cable Pits & Foundations • AS7666 – TPC Interoperability • AS7702 – Rail Equipment Type

Approval •

6.5 Australian Standards in Production by RISSB/TCSSC:

• AS7660 – Communications • AS7706 – Interfaces with points • AS7715 – Train Detection • AS7721 – Signals • AS7722 - EMC


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6.6 Proposed Australian Standards by RISSB/TCSSC:

• AS7707 – Automatic Train Control • AS7708 – Earthing & Surge Protection • AS7709 – Interlockings • AS7710 – Relays • AS7711 – Signal Engineering Process • AS7712 – Telecommunications • AS7714 – Train Describer

6.7 Relevant ASA (RailCorp) Standards:

• EP 12 10 00 10 SP - System Substation Earthing

• Guideline on earthing & bonding of railway stations

• T HR EL 12002 GU Electrolysis from Stray DC Current

• EP 12 20 00 01 SP Bonding of OHW Structures to Rail

• EP 12 10 00 13 SP 1500V Traction System Earthing, etc

7. ELECTRICAL HAZARDS IN THE MUTUAL INTERACTION ZONE

Treats of AC/DC Interface Area in a “Risk Zone” are as follow: 7.1 Earthing & Bonding An E&B design process is required to mitigate the risk of damage to people and properties. A good E&B schemes should provide:

• A low impedance path for normal traction current

• A low impedance path for fault current leading to rapid tripping of circuit breaker

• Protection to equipment (or properties) from excessive fault current

• Protection to people from excessive touch voltages which can lead to electric shock

7.2 Touch Voltages DC System: (EN 50122-1) 120V normal, 60V (Workshop) , Fault - A curve from 870V (0.02s) to 120V (>300s) AC System: (EN 50122-1) 60V normal, 25V (Workshop) , Fault - A curve from 865V (0.02s) to 60V (>300s) Combined System: EN 50122-3: As below:

7.3 DC Stray current DC stray current can lead to corrosion of:

• rail supporting structures • pipelines • cable sheaths

Measures can be taken: • Installing rails inside insulated boots -

to impede the flow of DC stray current (e.g. GCLR)

• Install DC stray current collection mats (and return it to DC Substations, e.g. DLR)

Beware of stray current hazards in the Risk Zone - Refer to Figures 1a & 1b. 7.4 Signalling System The hazard of fallen conductor or insulation flashover can result in high fault current in signalling system via

• Conduction - transfer of earth potential rise to signalling earthing system

• Induction - harmonic frequencies may affect signalling track circuits


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In the UK, the Network Rail ’50,000’ series of standards / guides have been adopted as National Technical Rules (NTRs)

• NR RT/E/EC 50018 – Methodology for the Demonstration of Interaction with Neighbouring Railways

• Series of Compatibility Standards with various signalling Track Circuits

7.5 Communications System Conductive and inductive interference on Communication systems shall not exceed Permissible Limits:

• 60 V under normal operation • 430V under fault condition

7.6 EMC – Electromagnetic Compatibility EMC includes all the above plus compatibility with other sensitive equipment:

• Rolling stock • Hospitals • Engineering companies • Schools / Universities • Others (e.g. service stations etc)

EMC can be modelled using the following tools:

• EMTP / ATP, PSCAD, MATLAB SimPower, Orcad (PSpice), CDEGS etc.

Site Testing & Measurements

• To demonstrate EMC compliance with all types of systems and equipment

• Recorded data use to refine and

validate computer models • Possible joint utilisation of corridor with

existing heavy rail - parallel running of 25kV AC system & 750V DC Tram system.

• Option to establish a third platform (for

passengers interchange) at existing 25kV ac rail Helensvale station

8. CASE STUDIES

8.1 Case 1: Gold Coast Light Rail Project,

QLD, Australia (see Figures 1a & 1b) [1]

Potential Parallel Running in Phase 2

Extension

• Phase 1 - A$1.67 billion Project, 13km, connecting 16 light rail stations from Broadbeach to Gold Coast University Hospital.

• Opened on 20 July 2014 and commenced operating by KDR Gold Coast Pty Ltd as 'G:link'

• Possible joint utilisation of corridor with existing heavy rail - parallel running up to 2km of 25kV AC system & 750V DC Tram system.

• Option to establish a third platform (for passengers interchange) at existing 25kV ac rail Helensvale station

8.2 Case 2: Crossrail Central Section, London, United Kingdom (see Figures 2a & 2b) Parallel running of Crossrail 2x25kV AC autotransformer line and London Underground Limited (LUL) 630V DC lines. Issues:

• DC current from LUL system can potentially cause Electrolysis on Crossrail infrastructure.

• AC harmonics from Crossrail system can potentially interfere with LUL signalling track circuits.

Mitigations/Solutions: • Use of autotransformers along the

Crossrail route to draw stray 50Hz and AC harmonics back to the 2x25kV system.

• Solutions for two earthing systems: (i) keep 2m separation, (ii) use of insulating barriers if less than 2m apart, (iii) bond them together

8.3 Case 3: Port of Rotterdam New Freight Line- Havenspoorlijn, Netherland (see Figures 3a, 3b & 3c) [2] AC freight line running part parallel to existing above ground 750V DC subway line. The proximity area is indicated in red in Figure 3b. If no additional measures are taken, the area where the 50Hz track circuits (which must be modified) are installed will be a much wider, due to 50 Hz current conducted towards the outer regions of the subway track and leaks away slowly to earth. A method is needed in order to ‘peel off’ the currents in the DC subway track more quickly, in order to limit the affected area.

http://www.goldcoast.qld.gov.au/thegoldcoast/g-link-light-rail-22700.html


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Issues: • 50Hz track circuits on DC line at risk of

mal-operation (WSF) from adjacent 50Hz current leaking from freight line.

• DC stray current victims, metro civil structure and pipe lines for petrochemical industry in the area, making earthing the DC line directly not an option.

Mitigations/Solutions:

• 50Hz track circuits on DC Subway have to be modified or replaced.

• By earthing subway tracks with capacitors at several DC Substation locations before and after the parallel proximity area, an unacceptable increase in DC stray currents is prevented outside the proximity area with 5km.

8.4 Case 4: Parallel Running 15kV AC and 750V DC Lines, Berlin, Germany [3] This case study concerns the parallel running 15kV AC and 750V DC railways, planning and design approach which led to the implementation of the EMC measures to resolve EMC issues on the North-South-Railway-Link (NSRL) in the centre of Berlin. Issues: • Parallel running of 15 kV AC and 750 V

DC railway lines very close to office buildings, banks and shopping centres with sensitive information technology and computer systems.

• EMC issues needing an effective solutions.

Mitigations/Solutions:

• Novel planning and design approach to achieve electromagnetic compatibility (EMC) and to tackle risks associated with power system borne electromagnetic interference (EMI).

• Monitoring EMI over 18 months of train operation.

• No incidence concerning EMI issues - concluded that the originally specified level of EMC has been achieved.

8.5 Case 5: Parallel Running 25kV AC and 1500V DC Lines, France Issues: • Parallel running of 25 kV AC and 1500 V

DC lines causing mutual interference.

Mitigations/Solutions: • Adopting TVM430 signalling system • All tunnel sections are I500V DC in Paris,

but the SNCF lines are electrified at 25kV AC and thus needing dual voltage EMUs. 9. CONCLUSIONS/

RECOMMENDATIONS Parallel running of AC and DC railways can potentially cause interface issues and are not unique to Australian cities. Case studies undertaken in Europe have been discussed and the solutions revealed how the European methodologies can be adapted to provide innovative solutions for the Australian rail industry. It is concluded that early planning and developing EMC solutions through computer modelling is essential and is key to achieving successful solutions to the interface issues. It is recommended that the application and

compliance of the European Standards such

as EN 50122 Parts 1-3, EN50121 parts 1-3

and the new or emerging Harmonised

Australian Railway Standards be adopted, to

ensure International Best Practice is achieved.

10. REFERENCES

[1] Russell J, Goh S, Managing mutual electrical interaction between a proposed light rail system adjacent to an existing 25kV heavy rail system, ARA Light Rail Conference 5-6 March 2015, InterContinental Hotel, 117 Macquarie Street, Sydney NSW 2000

[2] Koopal R, Evertz, EP, 50Hz track circuits parallel to a 25kV 50Hz railway line, Arcadis Nederland BV, Amersfoort, Netherland


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[3] Kuypers K, Tschiedel H, Planning and developing EMC along parallel running AC and DC railways in the centre of Berlin, Electromagnetic Compatibility and 19th International Zurich Symposium on Electromagnetic Compatibility, 2008. APEMC 2008. Asia-Pacific Symposium, 19- 23 May 2008

http://ieeexplore.ieee.org/search/searchresult.jsp?searchWithin=%22Authors%22:.QT.Tschiedel,%20H..QT.&newsearch=true


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APPENDIX 1: FIVE CASE STUDIES – ISSUES AND SOLUTIONS

Case Study 1: Gold Coast Light Rail Project, QLD, Australia

Figure 1a: Parallel Running for 2km of 25kV AC and 750V DC Trains

Figure 1a: Beware of Stray Current Hazards in the Risk Zone (Case study 1)

Figure 1b: Gold Coast Light Rail Train

Gold Coast Light Rail 2km Risk Zone situated outside Helensvalle Station

2x25kV AC Autotransformer

Heavy Rail System

Gold Coast Light Rail 2km Risk Zone situated

outside Helensvalle Station

750V DC Light

Rail System


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Case Study 2: Crossrail Central Section, London, UK:

Figure 2a: Crossrail Central Section

Bond St.Paddington TCR Farringdon Liverpool St. Whitechapel

Metropolitan LineCircle Line

H & C LineCrossrail

District Line

Central Line

125 Hz DEV TC

FS2500 JTC

(Main Line / Metro Type)

125 Hz DEV TC

Legend

Section adjacent to CRL

Section NOT adjacent to CRL

Station

Figure 2b: 2x25kV AC Crossrail line running parallel to LUL 630V DC lines

(AC & DC railways running in parallel – to bond or not to bond, that is the question?)


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Case Study 3: Port of Rotterdam New Freight Line- Havenspoorlijn, Netherland

Figure 3a: Proximity of AC/DC Area

Figure 3b: Parallel Running of 25kV AC Freight Line and

750V DC Subway Line

A single capacitive earthing location on both sides of the af fected area does not

provide sufficient reduction of DC stray current, therefore the capacitive earthing has to be

repeated at substations further away from the proximity area. The distance between the

chosen locations is essential because the impedance of the earth return will provide

the extra impedance needed to reduce the current in each mesh. Simulations w a s

u s e d to find the optimum configuration for the capacitive earthing.

track and 3th rail

Proximity area

Zgroun d Zgroun d

Zgroun d

Zgroun d

Zgroun d

Figure 3c: Mesh currents around proximity area


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Case 4: Parallel Running 15kV AC and 750V DC Railways Centre of Berlin, Germany

Figure 4: Parallel running 15kV AC and 750V DC railways

North-South-Railway-Link (NSRL) in the centre of Berlin


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Case 5: Parallel Running of 25kV AC and 1500V DC Railways, France

Figure 5a: French Railway Networks Converging on Paris

o 25 kV AC electrified lines blue

o 1500 V DC in brown

o Non-electrified lines in Green

Figure 5b: Railway Lines around Paris (As of April 2002)


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interaction between dc light rail and 25kv ac heavy rail

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