10_class ii based power supplies [compatibility mode]

7/25/2019 10_Class II Based Power Supplies [Compatibility Mode]

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Date 18.08.10 Tahir Ayub Railway LV Systems 2

Signalling Power SystemsUtility Intakes

Signalling Supply Point

(SSP), Principal SupplyPoint (PSP)

Signalling PowerDistribution System

Interface to finalSignalling Loads


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Signalling Distribution System

Utility PSP FSP LOC Asset


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IT System Operation

PSP/SSP

Line side Equipment

650/110 Tx

Signaling

Load

Power

EnclosurePSP 400/650 TX

Earthing System (RA)

325V 325V

Ce Ce Ce Ce Ce Ce

650V


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IT Individual First Fault (ECP)

Line side Equipment

650/110 Tx

Signaling

Load

Power

Enclosure

Ce Ce Ce Ce Ce Ce

650V

IF

IF

IFIFIFIFIF

IF IFIF

IF IF IF

RF


PSP 400/650 TX

Elevated Voltage between exposed conductive part and earth

dependant on cable length and impedance of Ra. Very unlikelyto exceed 60V.


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IT Individual First Fault (Cable)

Line side Equipment

650/110 Tx

Signaling

Load

Power

Enclosure

Ce Ce Ce Ce Ce Ce

650V

IF

IF

IFIF

IF IFIF

IF IF IF

RF


PSP 400/650 TX

Residual risk of Direct Contact on exposed cables.

The risk is consistent with installations with

unarmoured cablesIF Very Small


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IT Individual Second Fault

PSP 400/650

TX

IF

IF

IF

IF

RF

RF

Residual risk of Direct Contact on exposed cables.

The risk is consistent with installations with

unarmoured cables

IF IF IF


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IT Individual Second Fault (ECP)

PSP 400/650

TX

IF

IF

IF

IF

RF

RF

Elevated Voltage between Exposed Conductive

Part and Earth likely to be very small (


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IT IndividualSecond Fault (SameECP)

PSP 400/650

TX

IF

IF

IF

IF

RF

RF

Elevated Voltage between exposed conductive

parts and earth likely to be > 60V

IF

IF IF IF

Vt

Vt Touch Voltage

IF Fault Current

IFIF

System protection not rated to disconnect on L-L or2 L-E fault


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IT Individual Line to Line Fault

PSP 400/650

TX

IF

IF

IF

IF

RFIF

IF IF IF

Vt Touch Voltage

IF Fault Current

IFIF

Protection must operate before thermal damage


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IT Collective System

650/110 Tx

Signaling

Load

Power

Enclosure

Earthing System Typically

10 Ohms (SSI8503)

RF

Line side Equipment X

650/110 Tx

Signaling

Load

Power

Enclosure

Earthing System Typically

10 Ohms (SSI8503)

Other LOC or REB

Installations

Circuit Protective Conductor (CPC)

Collective earth

CPC

Line side Equipment 1

PSP Earthing System

PSP 400/650 TX


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IT Collective First Fault (Cable)

PSP 400/650

TX

IF

IF

IF

IF

RF

Elevated Voltage between Exposed Conductive Part and Earth likely to be very

small (


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IT Collective Second Fault

PSP 400/650

TX

IF

IF

IF

IF

RF


lethal (>60V) and is dependant on voltage divider produced by current passing

through the CPC and Local earth. This could reach half system voltage

depending on all location cases. Vt dependant on local earth impedance and

cable distribution length

IF

IF IF

Vt Vt

Vt Touch Voltage

IF Fault Current

CPC

VtVt

RF

Protection must operate

to manage lethal touch

voltages

IF


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IT CollectiveSecond Fault(CPC Optimisation)

PSP 400/650

TX

IF

IF

IF

IF

RF


lethal (>60V) and is dependant on voltage divider produced by current passing

through the CPC and Local earth. This could reach half system voltage

depending on all location cases. Vt dependant on local earth impedance and

cable distribution length. If Local earth is not maintained then the elevated

voltage could be lethal at the ECP.

IF

IF IF

Vt Vt

Vt Touch Voltage

IF Fault Current

CPC

VtVt

RF

Protection must operate

to manage lethal touch

voltages

IF

Local Earth Impedance

utilised to optimise CPC


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IT Collective Line to Line Fault

PSP 400/650

TX

IF

IF

IF

IF

IF

IF IF

Vt Touch Voltage

IF Fault Current

CPC

RF

Protection must operate before thermal damage


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Class II Engineering Strategy

Engineering Strategy

Reduced CAPEX costs without reducing safety Improvement in Personnel Safety

Reduction in System Risk

Compliant to Standards

Reduced Maintenance Burden

Greater Tolerability to DC Corrosion

Simplified Earthing and Bonding in AC Electrified Areas

Ability to integrate into Legacy Systems


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Class II Proposal

Reduce the probability of insulation failure in the LOCs and REBs to

a negligible level so that power supply equipment enclosures neednot be earthed for protection, so earthing or bonding to a CPC is not

necessary.

Utilising Class II Equipment as a protective measure against electric

shock

Utilising a 2-core cable Distribution Strategy in place of a 3-core

Strategy

Realise the opportunity of complying with the requirements of BS7671

Realise the opportunity of reducing costs associated with signalling

power supplies


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Class II Strategy

No Circuit Protective Conductor (CPC)


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Class II Strategy

Double Insulation or Reinforced Insulation


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Class II ScopeThe Class II Based Design Solution is to be implemented into:

New Build Signalling Power Distribution Systems

Existing Signalling Power Distribution Systems

[3-core Armoured cable - CPC based system]

Legacy Signalling Power Distribution Systems

[2-core Unarmoured cable system]


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Design Strategy

Location Case/REB Equipment

Class II Switchgear Housings

Class II Signalling Transformers

Encased Cabling between Class II Switchgear and Class II Signalling

Transformer

Cable Consumables (Glands, Joints, Terminations etc)

Distribution Equipment

2 Core Enhanced Unarmoured Cable

OR

2 Core Armoured Solid Bonded Cable


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Solid Bonded Armoured Cable Solution

EPR

PSP 400/650 TX


Class II

650/110 TX

Signaling

Load

Class II

Power

Enclosure

IMLine side Equipment 1

Class II

650/110 TX

Signaling

Load

Class II

Power

Enclosure

Earthing System (RA) Earthing System (RA)

BS 5467

Armoured Cable

MET MET

Gapped


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Enhanced Unarmoured Cable Solution

EPR

PSP 400/650 TX


Class II

650/110 TX

Signaling

Load

Class II

Power

Enclosure

IMLine side Equipment 1

Class II

650/110 TX

Signaling

Load

Class II

Power

Enclosure

Earthing System (RA) Earthing System (RA)

MET MET

Enhanced Un-

armoured Cable


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Risk Assessment Results Risk of electrocution inside the LOC will, in practical terms, be removed by the

introduction of Class II equipment.

Power cable options ranked in order of safety are as follows:

1.Armoured, solid bonded (=1st)

2.Enhanced unarmoured (=1st)

3.Armoured, resistance bonded

4.Armoured, direct bonded

Other performance factors considered:

Reliability, Availability, Maintainability,

Logistics and Whole-Life Costs.

Conclusion

The Enhanced Unarmoured Cable option presents the highest overall level of Safety.


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Maintenance Comparisons with

Legacy and Existing Systems

Maintenance

factor

Solid Bonded Armoured Cable

(Class II)

Enhanced Unarmoured Cable

(Class II)

1st inspectionReduced dependency on LOC electrode

conditionNo dependency on LOC electrode condition

Periodicinspection

Reduced dependency on LOC electrode

conditionArmour continuity/loop impedance test required

No dependency on LOC electrode condition

Mid life

degradation

Reduced dependency on LOC electrode

condition

Armour/gland corrosion

No dependency on LOC electrode condition

Cable troughs and ducts maintained in good order

Impact of

possession

restriction

No impact No impact


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PRAMS Conclusion

Cableoptions

ranked in

descending

order of

preference

PRAMS ranking of cable options

0 = lower, 1 = higher

Performance Reliability/Availability Maintainability

Safety

Personnel System

Enh

UnArm1 1 1 1 1

Arm solid 0 0 0 0 0


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Cable Impact & Crush TestsImpact Tests Crush Tests


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Cable Damage Tests

Impact Tests Armoured Cables maximum 6 impacts to failure

Enhanced Unarmoured Cables 26 impacts, no failure

Crushing tests Armoured Cables maximum 1.2 tonnes to failure

Enhanced Unarmoured Cables, minimum 2.2 tonnes to failure

The tests showed that the Enhanced Unarmoured Cable design has

greater resistance to impact and crushing faults than a standard Armoured

cable.


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Safety Case

The update of the Safety Case from Stage 1 was undertaken to incorporate the

results of the FMECA and PRAMS analysis

The report presents evidence that the project has reached a stage where the

identified design options, may be selected for detailed design.

Conclusions

There is no identified safety reason to prevent the design development

stage of Class II Equipment using Enhanced Unarmoured Cable

proceeding.

It is important to recognise that Armoured Solid Bonded Cables remain aviable alternative both in terms of risk and standards compliance however,

FMECA analysis identified the highest failure mode criticality is associated

with the use of Armoured Cable.


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New Standards

NR/L2/ELP/27408 ProductSpecification for Signalling

Power Distribution Cables

NR/L2/ELP/27409 ProductSpecification for FunctionalSupply Points (FSP)

NR/L2/SIG/30007 [Issue: 2]Product Specification for PowerTransformers for Signalling

Systems

NR/L2/ELP/27410 Specificationfor Class II Based SignallingPower Distribution Systems


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Date 08.11.12 32

System TransformationPSP Installation

Signalling

Earthing

System

OvercurrentDevice

Enhanced Unarmoured

Cable

InsulationMonitor

Class IIFSP

SwitchgearAssembly

ConduitSystem

ClassIIHybrid

FSPIsolating

Transformer

PSP

Earthing

System

Enhanced Unarmoured

Cable

Signalling

Earthing

System

Enhanced Unarmoured

Cable

IsolatingTX

Signalling Load Signalling Load


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Date 08.11.12 33

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10_class ii based power supplies [compatibility mode]

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