EN 50238-1:2003

STANDARDŽelezniške naprave – Združljivost voznih sredstev in sistemov za detekcijo vlakaRailway applications - Compatibility between rolling stock and train detection systems©
Standard je založil in izdal Slovenski inštitut za standardizacijo. Razmnoževanje ali kopiranje celote ali delov tega dokumenta ni dovoljenoReferenčna številkaSIST EN 50238:2003(en)ICS29.280; 45.060.10

EUROPEAN STANDARD
EN 50238 NORME EUROPÉENNE EUROPÄISCHE NORM
February 2003 CENELEC European Committee for Electrotechnical Standardization Comité Européen de Normalisation Electrotechnique Europäisches Komitee für Elektrotechnische Normung
Central Secretariat: rue de Stassart 35, B - 1050 Brussels
© 2003 CENELEC - All rights of exploitation in any form and by any means reserved worldwide for CENELEC members.
Ref. No. EN 50238:2003 E
ICS 29.180; 45.060.10
English version
Railway applications –
Compatibility between rolling stock
and train detection systems
Applications ferroviaires –
Compatibilité entre matériel roulant
et systèmes de détection de train
Bahnanwendungen –
Kompatibilität zwischen Fahrzeugen
und Gleisfreimeldesystemen
This European Standard was approved by CENELEC on 2002-12-01. CENELEC members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this European Standard the status of a national standard without any alteration.
Up-to-date lists and bibliographical references concerning such national standards may be obtained on application to the Central Secretariat or to any CENELEC member.
This European Standard exists in three official versions (English, French, German). A version in any other language made by translation under the responsibility of a CENELEC member into its own language and notified to the Central Secretariat has the same status as the official versions.
CENELEC members are the national electrotechnical committees of Austria, Belgium, Czech Republic, Denmark, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Luxembourg, Malta, Netherlands, Norway, Portugal, Slovakia, Spain, Sweden, Switzerland and United Kingdom.

EN 50238:2003 – 2 –
Foreword This European Standard was prepared by SC 9XA, Communication, signalling and processing systems, of Technical Committee CENELEC TC 9X, Electrical and electronic applications for railways.
The text of the draft was submitted to the formal vote and was approved by CENELEC as EN 50238 on 2002-12-01.
This European Standard was prepared under a mandate given to CENELEC by the European Commisssion and the European Free Trade Association and supports the essential requirements of Directive 96/48/EC.
The following dates were fixed:
- latest date by which the EN has to be implemented
at national level by publication of an identical
national standard or by endorsement (dop) 2003-12-01
- latest date by which the national standards conflicting
with the EN have to be withdrawn (dow) 2005-12-01
This European Standard is intended to be read in conjunction with the EN 50121 series.
Annexes designated “informative” are given for information only. In this standard annexes A, B, C and D are informative.
_____________
– 3 – EN 50238:2003 Contents
Page Introduction.5 1 Scope.5 2 Normative references.7 3 Definitions.7 4 Acceptance process.8 4.1 Overview.8 4.2 Responsibilities.9 4.3 Acceptance process.9 4.4 Compatibility case.11 4.5 Quality management.11 4.6 Route identification.11 4.7 Characterisation.11 4.8 Tests .12 4.9 Compatibility analysis.12 4.10 Certificate of acceptance.13 5 Characterisation of train detection systems.13 5.1 Objective of procedure.13 5.2 Physical compatibility.13 5.3 Electromagnetic compatibility.14 5.4 Factor of safety.17 5.5 Track circuit susceptibility.17 5.6 Wheel detector susceptibility.17 5.7 Train detection system gabarit.18 5.8 Interference signal generated by rolling stock and substations.18 5.9 Test report .19 6 Characterisation of rolling stock.20 6.1 Objectives of procedure.20 6.2 Description of rolling stock and factors affecting its characteristics.20 6.3 Configuration (design status).20 6.4 Test plan.20 6.5 Test report.22 6.6 Archive of test results.22 7 Characterisation of traction power supply systems.22 7.1 Objective.22 7.2 D.C. traction power supplies.23 7.3 A.C. traction power supplies.23

EN 50238:2003 – 4 –
Annex A (informative)
Guidelines for the determination of
susceptibility of train detection systems .24 Annex B (informative)
Guidelines for the measurement of rolling stock characteristics.32 Annex C (informative)
Factors affecting rolling stock characteristics.34 Annex D (informative)
D.C. traction power supplies.35 Figure 1 – Sources of electromagnetic interference.4 Figure 2 – The parties concerned in the acceptance process.8 Figure 3 – The acceptance process.9 Figure 4 – Relationship between gabarit and permissible interference.11 Figure A.1 – Interference mechanism with rails intact.23 Figure A.2 – Interference mechanism with self-revealing broken rail.23 Figure A.3 – Interference mechanism with unrevealed broken rail.24 Figure A.4 – Double rail track circuit.25 Figure A.5 – Double rail track circuit with broken rail.25 Figure A.6 – Interference mechanism due to voltage between axles – Case 1.26 Figure A.7 – Interference mechanism due to voltage between axles – Case 2.26 Figure A.8 – Effect of inter-vehicle current.27 Figure A.9 – Equivalent circuit for previous figure.27 Figure A.10 – Example of radiated interference.28 Figure A.11 – Sensitive zone of wheel detector.29 Figure B.1 – Example of system for measurement of interference currents.31 Figure D.1 – Rolling stock with DC supply.35 Figure D.2 – Circulation of interference current generated by rolling stock.35 Figure D.3 – Circulation of interference current generated by the substation.35

– 5 – EN 50238:2003 Introduction This European Standard defines a process to obtain the assurance that specific rolling stock operating on a specific route does not interfere with train detection systems installed on this route.
Compatibility problems between train detection systems and rolling stock are a significant obstacle to cross-acceptance of rolling stock in Europe. Unfortunately it is not possible to establish general rules for the maximum levels of interference allowed, valid for every country. This is due to the great diversity of rolling stock, power supply and return current systems, and train detection systems installed in Europe. This diversity leads to consideration of the problem of compatibility of rolling stock and train detection systems for specific routes to avoid unnecessarily restrictive specifications.
Compatibility is determined by both physical and electromagnetic considerations. With regard to EMC, the need is not for general values for maximum levels of interference permitted, but for convenient methods by which to specify the level of interference allowed for operation on specific routes.
Interference may be caused by − rail currents, − electromagnetic fields, − differential voltage between axles,
as shown in Figure 1:
Rail currenttransfer functionsElectromagnetic fieldtransfer functionsTrack circuitOthersWheeldetectorFeederstation
Figure 5 – Sources of electromagnetic interference
In practice, the susceptibility of the system is determined by − the sensitivity of individual components of the system, − the application of the components, i.e. the configuration of the system.
Therefore the problems concerning track circuits and axle counters or wheel detection systems will be looked at separately.

EN 50238:2003 – 6 –
For determining the susceptibility of signalling systems, laboratory/simulation testing methods as well as methods to conduct tests on the “real railway” are proposed. Modelling enables worst-case conditions to be simulated. In addition, particular test sites are used because, from experience, they are known to provide the test evidence required. Then, taking account of the experience of the railways, it is possible to establish a general method for determining the susceptibility of train detection systems, described in this European Standard.
Before measuring the interference level on rolling stock, a sufficient knowledge of the electric circuit diagram of the power equipment is required, e.g. switching frequencies of on-board static converters, type of regulation used for power converters, resonant frequency of each filter, operating limits under high and low supply voltages, downgraded modes of operation etc.

– 7 – EN 50238:2003 1 Scope The scope of this European Standard is to describe a procedure for mutual acceptance of rolling stock to run over specific routes. It describes the methods of measurement of interference currents, the methods of measurement of the susceptibility of train detection systems, the characterisation of traction power supplies and the procedure for acceptance. The result of the acceptance procedure is a structured justification document referred to as a “compatibility case”, which documents the evidence that the conditions for compatibility have been satisfied.
This European Standard is not generally applicable to those combinations of rolling stock, traction power supply and train detection system which were accepted as compatible prior to the issue of this European Standard. However, as far as is reasonably practicable, this European Standard may be applied to modifications of rolling stock, traction power supply or train detection systems which may affect compatibility.
The scope of the compatibility case is restricted to the demonstration of compatibility of rolling stock with a train detection system’s characterisation (e.g. gabarit). Radio based signalling systems are not within the scope of this European Standard.
2 Normative references This European Standard incorporates by dated or undated references, provisions from other publications. These normative references are cited at the appropriate places in the text and the publications are listed below. For dated references, subsequent amendments to or revisions of any of these publications apply to this European Standard only when incorporated in it by amendment or revision. For undated references the latest edition of the publication referred to applies (including amendments).
EN 50121
Series Railway applications – Electromagnetic compatibility EN 50126 Railway applications – The specification and demonstration of Reliability, Availability, Maintainability and Safety (RAMS) EN 50163 Railway applications – Supply voltages of traction systems EN/ISO 9001 Quality management systems – Requirements EN ISO/IEC 17025 General requirements for the competence of testing and calibration laboratories ORE B108/1 Unification of air-conditioning and electrical equipment in coaches UIC 737-3 The application of thyristors in railway technology: Measures for the prevention of functional disturbances in signalling installations UIC 550 Power supply installations for passenger stock
3 Definitions For the purposes of this European Standard, the following definitions apply:
3.1
accepting body the body responsible for the evaluation of the compatibility case and the issue of a certificate of acceptance

EN 50238:2003 – 8 –
3.2
compatibility case a suite of documents which records the evidence demonstrating the degree of compatibility between rolling stock, traction power supplies and train detection systems for a specific route or specific railway network
3.3
certificate of acceptance written autorisation from the accepting body that the compatibility case is acceptable to allow the new or modified systems to enter service (This may be qualified)
3.4
degraded modes modes of operation in the presence of faults which have been anticipated in the design of the rolling stock. Degraded modes will normally allow the rolling stock to complete its journey
3.5
gabarit the maximum permissible levels of interference signal, with respect to frequencies and duration, to which a train detection system may be exposed
3.6
railway infrastructure authority the body responsible for the safety of the track and signalling systems
3.7
right side failure a failure of a signalling system which results in a more restrictive condition for the movement of traffic than is appropriate
3.8
rolling stock operator the body responsible for the operation and maintenance of the rolling stock
3.9
wheel detector a sensor which detects the passage of a wheel. It may be used as part of an axle counter system or as a treadle
3.10
wrong side failure a failure of a signalling system which results in a less restrictive condition for the movement of traffic than is appropriate
4 Acceptance process 4.1 Overview The parties concerned in the acceptance process are shown in Figure 2:

– 9 – EN 50238:2003 AcceptanceRailwayinfrastructureauthority No. 1AcceptingbodyIndustry(Signalling)Industry(Rolling stock)LaboratoryLaboratoryRolling stockoperatorAcceptancecertificateCompatibilitycaseRailwayinfrastructureauthority No. 2
Figure 6 – The parties concerned in the acceptance process
4.2 Responsibilities The responsibility for demonstrating compatibility between rolling stock, train detection and traction power supply systems, and for maintaining it over the full life cycle of the equipment, is shared between those parties responsible for the particular railway infrastructure and the particular rolling stock. Specific responsibilities for a given compatibility case, including the party taking the lead role, shall be explicit. The documentation, in the form of a compatibility case, shall be submitted to an accepting body, and shall be reviewed when any modification is carried out.
4.2.1 Railway infrastructure authority For a defined route (the application of interest), the railway infrastructure authority
should characterise all train detection systems and the traction power supply system.
4.2.2 Rolling stock operator The rolling stock operator should characterise the interference which may be generated and propagated by the rolling stock.
4.2.3 Accepting body The accepting body shall review submitted documents and as a result issue a certificate of acceptance.
As part of this process, the accepting body should ensure that the compatibility case is reviewed by experts who are qualified to assess and evaluate it.
4.3 Acceptance process The acceptance process is summarised in Figure 3:

EN 50238:2003 – 10 –
Modifyrollingstock ?Theoretical analysisNoAdditionalinformationand/ormeasurementsNoYesBegin compatibility caseDescription of rollingstockTest planTesting and testreportNoYesAcceptance withtemporary restrictions ?NoYesModify traindetectionsystem ?Economic and technical comparisonof available solutions : selection ofoptimum solutionModifypowersupplysystem ?Description of powersupply systemCan a compatibilitycase be made ?Submission toaccepting bodyYesNoAcceptance withpermanent restrictions ?NocertificateYesmandatory actionoptional actionTemporaryacceptanceNoUnrestrictedacceptance ?More informationneeded ?YesNoFull acceptanceRestrictedacceptanceYesMore informationneeded ?YesNoTest plan approvedby accepting body ?Characterisation oftrain detectionsystem gabaritMore informationneeded ?
Figure 7 – The acceptance process

– 11 – EN 50238:2003 4.4 Compatibility case A compatibility case shall be prepared, including but not limited to, the following: − scope of compatibility case; − route identification; − characterisation of train detection systems; − characterisation of traction power supply system; − characterisation of rolling stock; − assumptions made; − test report; − evidence of quality management; − related compatibility cases; − assessment of compatibility.
The compatibility case shall be submitted to an accepting body for approval.
4.5 Quality management Quality management systems shall be in place. The importance of configuration management should be noted.
The configuration state of the relevant infrastructure and rolling stock (including maintenance processes and schedules) shall be recorded and referenced within the compatibility case. Any subsequent changes to these configurations shall lead to an examination of the continued validity of the compatibility case.
The organisation conducting the tests shall be able to demonstrate its competence to make measurements in a traction environment. It should preferably be certified to EN ISO/IEC 17025, but in any case shall have a documented quality system in accordance with a recognised standard.
In order to maintain objectivity (e.g. in the event that tests are being conducted by a manufacturer on equipment of his own supply) the organisation conducting tests should be subject to an audit by the accepting body.
4.6 Route identification In order to accept a particular rolling stock in respect of a particular route or network, the different types and applications of train detection systems and traction power supply systems on the route and on adjacent routes which may be affected shall be identified. In addition to the intended operational route(s), alternative route(s) which may be required in the event of disruption to traffic shall also be considered.
4.7 Characterisation The characteristics of the identified systems shall be obtained in accordance with the following clauses: − train detection systems 5; − rolling stock 6; − power supply system 7.

EN 50238:2003 – 12 –
4.8 Tests A test plan shall be prepared in accordance with 6.4.
Tests shall be conducted in accordance with the test plan and a test report produced in accordance with Clause 6.
4.9 Compatibility analysis In general terms, it shall be demonstrated that the rolling stock characteristics for generated and propagated interference comply with the train detection system gabarit, under defined operating conditions, including degraded modes. Their relationship is shown in Figure 4. The information flow may be in either direction depending on which system is to be changed.
EquipmentsensitivityTransferfunctionFactor ofsafetyPermissibleinterferenceper on-boardsourceSummationrulesTotalinterferencefrom on-boardsourcesPermissibleinterferenceSummationrulesTotalinterferenceGabaritcompareTRAIN DETECTION SYSTEMSUBSTATIONROLLING STOCKROLLING STOCKAND SUBSTATION
Figure 8 – Relationship between gabarit and permissible interference
Additionally, the physical characteristics of the rolling stock shall be demonstrated to be compatible with the train detection systems.
The compatibility analysis is mandatory and shall explain the technical principles which assure compatibility, including (or giving reference to) all supporting evidence e.g., calculations, test plans and results etc.
The method of analysis of fault modes shall be agreed between the parties listed in 4.2. If the parties consider it to be necessary, for complex systems, reference may be made to the clauses in EN 50126 entitled “risk” and “risk analysis”.

– 13 – EN 50238:2003
NOTE In accordance with the new organisation defined by EC Directive 91/440, it could be necessary to define a new “infrastructure gabarit” including both the train detection system gabarit and the substation characteristics.
4.10 Certificate of acceptance The accepting body shall review the compatibility case and issue a certificate of acceptance.
It is recognised that characterisation of interference generated and propagated by rolling stock can be a time consuming process, which may require a significant amount of testing during service operations in order to refine the characteristics. Therefore, provided that the risks to all parties can be demonstrated to be acceptable, temporary acceptance may be given prior to full acceptance. This also allows for the identification of contributory factors which had been overlooked in the preparation of the compatibility case.
Any temporary acceptance shall be time limited and be provided for a specific agreed purpose, whilst additional measures to identify interference and mitigate against possible hazards should be implemented.
In the event that the assessment identifies either a non-compliance with the existing gabarit, or a worsening of the existing gabarit (e.g. higher susceptibility), such that rolling stock with existing route acceptance becomes non-compliant, then the relevant Railway Infrastructure Authorities and rolling stock operators shall jointly determine the modifications to infrastructure and/or rolling stock to be made and initiate acceptance processes where applicable. If modifications are not possible or are not carried out, permanent restrictions shall be applied.
5 Characterisation of train detection systems 5.1 Objective of procedure To ensure the correct operation of train detection systems, their physical and electromagnetic properties shall be checked against those of the rolling stock and the traction power supply system.
5.2 Physical compatibility 5.2.1 Track circuits Physical compatibility, including but not limited to the following aspects, shall be considered: − minimum track circuit length; − minimum train length; − maximum speed of trains; − response time of track circuits; − shunt values of track circuits; − shunt impedance of trains, and reliability of shunting in all service conditions; − axle loads of vehicles; − axle spacing; − body overhang; − track characteristics; − substations earthing arrangements.

EN 50238:2003 – 14 –
5.2.2 Wheel detectors The reliable detection of wheels may be influenced by factors including but not limited to the following: − wheel geometry; − speed of trains; − wheel material; − equipment which may be mistaken for a wheel, e.g. track brakes or metal assemblies which are mounted close to the rail head.
5.2.2.1 Wheel dimensions and material Axle counters and treadles are generally specified to detect reliably wheel types used on main line vehicles. Other vehicle types may require special settings of the wheel detectors.
5.2.2.2 Interfering equipment Equipment mounted within the immediate vicinity of the rail may interfere with the reliability of wheel detection either by fouling mechanically or due to their electromagnetic properties (see Annex A).
This aspect of compatibility shall be assessed by testing.
5.3 Electromagnetic compatibility This subclause describes the measurement of the gabarit of the train detection system. It defines the general approach to be adopted, but since every installation is different in detail, it cannot describe the whole process exactly. The compatibility case shall cover all credible configurations and parameters – some examples of configuration and models are given in Annex A.
The required measurements are as follows.
5.3.1 The sensitivity of the train detection system equipment (see 5.3.3.1 for track circuits; 5.3.4.1 for wheel detectors). 5.3.2 The “transfer function” relating the interference signal at the train detection system equipment to the interference generated by the rolling stock (see 5.3.3.2 for track circuits; 5.3.4.2 for wheel detectors). Let the transfer function be denoted by F.
Let the interference signal at the train detection system equipment be denoted by ITDS.
Let the interference signal generated by the rolling stock be denoted by IRS.
The interference signal is then:
ITDS = F . IRS
Hence
IRS = ITDS / F
The maximum permissible interference signal at the train detection system equipment ITDSmax is determined by the sensitivity of the train detection system equipment. Let the total permissible interference generated by rolling stock be denoted by IRStot. Then:
IRStot = ITDSmax / F
Where multiple sources may contribute to the total interference signal, the permissible interference per source shall take this into account (see 5.8).

– 15 – EN 50238:2003 Note that the permissible interference signal will have two values determined by the following criteria: − the signal which may cause the train detection system to show clear when it is in fact occupied (a wrong side failure, i.e. a matter of safety); − the signal which may cause the train detection system to show occupied when it is in fact clear (a right side failure, i.e. a matter of reliability). The effect on interlocking logic shall however be considered.
5.3.3 Track circuits 5.3.3.1 Sensitivity and susceptibility of equipment alone The sensitivity of the track circuit equipment itself shall be determined. In general the susceptibility of the receiver will be more significant than that of the transmitter and will be the determining factor in the permissible level of interference; however the susceptibility of the transmitter shall also be checked.
Where the sensitivity of the track circuit is adjustable, it shall be measured for all the relevant settings and in particular for the worst case settings.
The susceptibility shall be determined as follows.
5.3.3.1.1 The parameters (amplitudes, frequencies and durations) of the voltage(s), current(s) or electro-magnetic fields which may cause the receiver to be energised, in the absence of a signal from the transmitter, such that a “track circuit unoccupied” indication is given. NOTE Some types of track circuit receiver which are designed to operate with an amplitude modulated signal may also be energised by a combination of unmodulated frequencies, and some types of track circuit receiver which are designed to operate with a frequency modulated signal may also be energised by one or more amplitude modulated frequencies.
5.3.3.1.2 The parameters (amplitudes, frequencies and durations) of the additional voltages, currents or electro-magnetic fields which may de-energise the receiver, or may influence the output signal of the transmitter, such that a “track circuit occupied” indication is given. The above information shall be obtained from the suppliers of the track circuit equipment. If it is not available (for example in the case of an obsolete design) it shall be obtained by laboratory measurements.
5.3.3.2 Transfer function of track circuit as installed The transfer function of the installed track circuit with regard to interference current shall be determined as follows.
5.3.3.2.1 Determine the electrical equivalent circuit of the track circuit and the traction power supply system in so far as the latter may affect the track circuit. In doing this all relevant conductors shall be considered, including catenaries or conductor rails, cross-bonded running rails, return conductors, impedance bonds, booster transformers, earthed structures, earth paths, etc. Normally the “worst case” transfer function will correspond to the maximum length track circuit. 5.3.3.2.2 Set up the equivalent circuit using a real test site or a hardware or software model. If a model is used it shall be verified by means of comparative site tests. 5.3.3.2.3 Measure the voltage or current at the track circuit equipment terminals resulting from a current generated by the rolling stock. The transfer function is then the ratio of the voltage at the track circuit equipment terminals to the interference current. NOTE 1 The value of the transfer function will depend on the position of the train with respect to the track circuit. The worst case value shall be determined.
NOTE 2 If the train has two or more on-board sources, or is composed of electric multiple unit stock, or utilises the rails for the return current path for auxiliary power supplies (see UIC 550), it may have to be represented by more than one current source.
5.3.3.2.4 Repeat the above tests with fault conditions applied, for example broken rails, broken cross-bonds and broken return conductors, examples of which are shown in Annex A (see 4.9). The “worst case” transfer function is the ratio of the highest value of interference voltage at the track circuit equipment terminals observed under fault conditions to the interference current(s).

EN 50238:2003 – 16 –
The transfer function of the installed track circuit with regard to electromagnetic fields shall be determined in a similar manner to that for interference currents, except that practical site tests will probably be more appropriate than computer modelling for the generation of useful results. An example is given in Annex A.
5.3.4 Wheel detectors The wheel detector circuits used in axle counting systems are usually galvanically decoupled from currents flowing in the rails.
Axle counters may be affected by electromagnetic interference coupled via the wheel detectors and the sensitivity of the axle counter is thus largely determined by the susceptibility to electromagnetic interference of the wheel detector used. Depending on the configuration, the axle counter may also be affected by interference on the transmission path between the trackside and an evaluation unit in an interlocking room.
The return current (d.c. or a.c.) in the rail can interfere with permanent-magnetic or inductively operating wheel detectors − directly, through its effect on the sensors, − indirectly through its effect on the permeability of the rail.
Direct coupled interference is expected to be most severe at the operating frequency of inductive sensors. Harmonics of rail current shall be considered.
Electromagnetic interference fields from equipment on the rolling stock can also affect the wheel detectors. Major sources of interference include: − transformers and converters, especially when fitted under the vehicle close to the rails. Harmonic content of interference shall be considered; − magnetic track brakes and eddy-current track brakes, which are mounted on the vehicle directly over the rail. The interference may be dependent on the train speed and the operational position of the brake; − transmitter antennas mounted on the vehicle, especially when mounted in the proximity of the rails; − catenary switching operations and the rupture or corrosion of contact wires causing transient currents in the rails which can interfere with the wheel detectors or the transmission path.
In addition to axle counter applications, wheel detectors are also used for switching functions, e.g. for switching on and off level-crossing protection systems. In these applications the effect of transient interference may be different to that of axle counters and shall be considered separately, but the characterisation of the wheel detector itself is common to both applications.
5.3.4.1 Sensitivity of equipment alone The sensitivity of the wheel detector equipment (wheel detector including signal evaluation electronic device) shall be determined as follows.
5.3.4.1.1 The parameters (including area of sensitivity, amplitudes, frequencies and durations) of the electro-magnetic fields and rail currents which will maintain the wheel detector in such a condition that passing wheels are not detected. 5.3.4.1.2 The parameters (including area of sensitivity, amplitudes, frequencies and durations) of the electro-magnetic fields and rail currents, which will cause the “wheel present” state of the wheel detector when no wheel is present. 5.3.4.2 Susceptibility of wheel detectors as installed The permissible value of interference signal, both transient and continuous, caused by currents in the rail or by other sources of interference will depend on the value of the internal signal exceeding the switching point of the electronic evaluation device of the wheel detector.

– 17 – EN 50238:2003 The transfer function of an installed wheel detector with regard to interference current and interference electromagnetic field depends on the physical principle and the geometric arrangement of the wheel detector and the signal evaluation device. Many different parameters (frequency and amplitude of interfering current; frequency, amplitude and direction of interfering electro-magnetic field) determine the transfer function. The inherent complexity and non-linearity of the transfer function make it unsuitable for use in this context.
Due to the inherent difficulties of designing a sufficiently complete electrical equivalent circuit for a type of wheel detector, field testing, or alternatively laboratory tests injecting interference currents into the rail and applying external electromagnetic fields shall be used for measuring the susceptibility of wheel detectors.
5.4 Factor of safety To allow for uncertainties in the accuracy of measurements and simulations, the susceptibility of the train detection system as determined above shall be increased by a factor of safety. The uncertainties shall be estimated and the factor of safety shall be sufficient to allow for them (see A.10).
Interference due to DC substation ripple may need to be taken into account in the factor of safety.
5.5 Track circuit susceptibility 5.5.1 Permissible interference signal for right side failure The permissible value of interference signal in the case of right side failure of the track circuit is determined without faults in the traction return system, since track circuits are not expected to work reliably in the presence of such faults.
Let the transfer function in this case be denoted by Fnorm.
Let the interference signal which causes the track circuit to show occupied while clear be denoted by ITDSocc.
Then the total permissible value of interference IRStot, occ for this case is given by:
IRStot, occ = ITDSocc / Fnorm
for all combinations of amplitude, frequency and duration of the interference signal.
5.5.2 Permissible interference signal for wrong side failure For wrong side failures the worst case fault in the traction return system, resulting in the “maximum” transfer function Fmax, shall be assumed.
Let the interference signal which causes the track circuit to show clear while occupied be denoted by ITDSclear.
Then the total permissible value of interference IRStot, clear for this case is given by:
IRStot, clear = ITDSclear / Fmax
for all combinations of amplitude, frequency and duration of the interference signal.
5.6 Wheel detector susceptibility Due to the principle of discrete detection of wheels passing a wheel detector, transient and continuous interference may be considered as equivalent.
The susceptibility of wheel detectors shall be determined under laboratory conditions as follows:

EN 50238:2003 – 18 –
5.6.1 Set up a wheel detector arrangement as in the field with worst case geometrical conditions (e.g. worn wheels, small wheel diameter, worn rail profiles). 5.6.2 Inject a defined interference current into the rail with the wheel detector mounted, or apply a defined interfering electromagnetic field, representing the rolling stock (traction current and harmonics), and measure the resulting change of internal signal (current, voltage or frequency), which is responsible for the switching function of the wheel detector. The frequency of harmonics shall include the operating frequency of the wheel detector.
The value of external interference signal causing an unwanted reaction of the wheel detector, both with and without a wheel passing, shall be measured.
For axle counters, it shall be shown that the reliability of counting will be maintained in spite of the expected interference. A differentiation between right side and wrong side counting failures due to interference is not required.
5.7 Train detection system gabarit The train detection system gabarit is the maximum permissible value of interference signal determined above, reduced by the factor of safety (see A.10).
5.8 Interference signal generated by rolling stock and substations The interference signal generated by rolling stock and substations is a function of the following: − the interference signal generated by each source; − the number of sources; − the rules adopted for the summation of interference signals from different sources.
5.8.1 Interference signal generated by each source: track circuits Track circuits are affected by the following sources of interference current: − the current drawn by the rolling stock − with the rolling stock considered as passive impedances, and − with the traction power supply interference voltages superimposed on the supply voltage. These currents are limited by setting a minimum impedance value for the rolling stock and by limiting the interference level generated by the substation. Under some circumstances the impedance of the rolling stock may interact with the impedance of the power supply to generate additional interference which is not attributable to either source alone; − the current generated by the rolling stock powered with a “pure” voltage (d.c. or undistorted sine wave a.c.). This current includes: − the interference current generated by the traction equipment; − the interference current generated by on-board converters for auxiliary power supplies (note that the return current from these may flow through the rails beneath the train); − unwanted coupling from the transmitter(s) of other track circuit(s).
5.8.2 Interference signal generated by each source: wheel detectors The major sources have been defined in 5.3.4. The effect of multiple source interference shall be considered in the particular case.

– 19 – EN 50238:2003 5.9 Test report The tests and the context in which they were performed shall be presented in a report, the main text and appendices of which should include the following.
5.9.1 Introduction A general presentation of the systems under test.
5.9.2 Test organisation A statement of who performed the tests and the contact address.
5.9.3 Configuration A definition of the design status of the train detection system, including the status of hardware and software listed in the documentation of the factors affecting the train detection system’s characteristics.
5.9.4 Reference documents This includes the test plan, the description of the train detection system and the document listing the factors affecting its characteristics.
5.9.5 Application of test plan With specific reference to compromises or amendments to the test plan which were found to be necessary, including − test conditions - technical characteristics of the test site, − instrumentation - a block diagram of the equipment used, the location of the measuring instruments, the interconnections between them, their accuracy, response characteristics, sensitivity, signal scalings, etc., − test procedure - calibration, verification of environmental noise, operational conditions of the system under investigation during tests.
5.9.6 Test results These include − the sensitivity of the train detection system alone, − the transfer function of the train detection system as installed, − the electrical equivalent circuit of the train detection system and traction power supply system, − description of model (if used), − verification of model (if used), − results of tests; “normal” and “maximum” transfer functions, − list of possible fault conditions considered, − gabarit of train detection system, − summation rules (for use by rolling stock operator).
5.9.7 Comments An evaluation of the results, their validity (e.g. why the site was chosen) and comparison with expected results.

EN 50238:2003 – 20 –
5.9.8 Archive of test results Measurements often entail the collection of large quantities of recordings. It is not always practical for these to be reproduced and circulated with a report, but provision s
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