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BRINCKERHOFFPARSONS

BRINCKERPARSONS

EMC Seminar17 November 2007

EMC Seminar17 November 2007

Harmonic Distortion Assessment

of a DC Railway Traction Power System

Harmonic Distortion Assessment

of a DC Railway Traction Power System

IEEE Hong Kong SectionEMC Chapter

IEEE Hong Kong SectionEMC Chapter

BRINCKERHOFFPARSONS

ContentContent

Introduction

Objective

Modelling of the System

Methodology

Summary of Findings

Conclusion

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IntroductionIntroduction

Harmonics generated by multiple-pulse rectifiers arewell known EMI disturbance to trackside equipment in adc traction railway environment.

The magnitude and frequency of harmonic currents canvary with many factors that may cause an impact on thefunctions of safety critical electronic equipment such asthe signaling system.

This paper describes a case study in which a model of dctraction power supply and traction current return circuit

has been used for assessing the effect of dc harmonics onthe signaling system in a quantitative manner.

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ObjectiveObjective

The objective of this exercise is to verify that the dcharmonics generated by the 1500 V dc traction powersupply will not cause any troubles to the normaloperation of signaling equipment. Mitigation measureswill be proposed if any risk of disturbance is identified.

Source of EMI is the transformer-rectifier unit intraction substations generating harmonics under normaland abnormal conditions

Victims susceptible to the EMI include audio frequencycoded track circuits and radiating cable loops andbeacons installed on the track.

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Modelling of the SystemModelling of the System

The System includes the 24-pulse Rectifiers in TractionSubstations (TSS), Electric Multiple Unit Trains (EMU),Overhead Line System (OHL) and Rails with tractionreturn bonding cables.

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MethodologyMethodology

Step 1: Determine Harmonic Voltage SpectraHarmonic voltages based on 12-pulse transformer rectifierunits were investigated taking into consideration a numberof equipment failure and imperfections scenarios

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MethodologyMethodology

Step 1: Determine Harmonic Voltage Spectra

FFT

FFT

Diode Arm broken

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MethodologyMethodology

Step 2: Estimate Harmonic Currents Flowing Throughan EMU and the Aggregate Effect of Several EMU

Simplified Model of

TSS and Single EMU

VH1 Z

EMU1

IH1

VH Z

EMU1

ZOHLx

ZRAILx

ZEMUx

IH1

IHx

Circuit for Weighting

Factor Estimation

One-sided ApproximationCurrent Divider Approximation

Multiplier on Single Train

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MethodologyMethodology

Step 2: Estimate Harmonic Currents Flowing Throughan EMU and the Aggregate Effect of Several EMU

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MethodologyMethodology

Step 3: Harmonic Current Flowing in Return Rails

S Bond between EMU and TBB TBB between EMU and S Bond

TBB

I3

I4

Axle "S" Bond

D1

D2

TBB

I1

I2

Axle "S" Bond

D2

D1

Unbalanced Current flowing through

the Track Circuit as a function of

train position

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Step 3: Harmonic Current Flowing in Return RailsThe immunity levels of various trackside signaling equipmentare defined as the maximum permissible in-band harmoniccurrents flowing in the rails

MethodologyMethodology

Check for In-band EMI levels to

determine severity of disturbance

f1 f2fH

S

f1 f2fH f1 f2

IHZT

FHZ

V

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MethodologyMethodology

d.c. Harmonic - Train LC Filter Parameter Variation

103

104

105

0

500

1000

1500

(VARYING INDUCTANCEL1AND FIXEDCAPACITANCEC1)

Frequency(Hz)

Tra

inImpedance(Ohm)

FTG-S

CVCM

CT BeaconRC 2L1

L1

0.5L1

0.1L1

0.01L1

Train Impedance Against Frequencywith Varying Inductance

(1 kHz 200 kHz)

Train Impedance Against Frequencywith Varying Inductance

(1 kHz 20 kHz)

103

104

0

50

100

150(VARYINGINDUCTANCE L1 ANDFIXEDCAPACITANCE C1)

Frequency (Hz)

Tra

inImpedance(Ohm)

FTG-S

CVCM

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MethodologyMethodology

d.c. Harmonic - Train LC Filter Parameter Variation

Range of C1: variation between 0.01 C1 to 10 C1

Train Impedance Against Frequencywith Varying Capacitance

(1 kHz 200 kHz)

103

104

105

0

200

400

600

800

1000

1200(VARYINGCAPACITANCE C1AND FIXEDINDUCTANCE L1)

Frequency (Hz)

Tra

inImpedance(Ohm)

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Summary of FindingsSummary of Findings

Track circuits were identified as the most vulnerabletype of signaling equipment under influence of harmoniccurrents.

The estimated harmonic currents within the 3dBbandwidth of the signaling equipment were comparedwith the corresponding maximum permissible currentlimits.

It is possible that the harmonic currents at two of theTrack Circuit operating frequencies will likely exceed thepermissible limits.

Other harmonics generated by the traction power supplyequipment in the interested frequency ranges are withinlimits with a quite generous safety margin.

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ConclusionConclusion

Different in-feed supply conditions, power supplyequipment failure and imperfections scenarios have beenassessed in this exercise.

Generally speaking, the estimated amount of harmonicsso generated will not exceed the limits as specified by thesignaling contractor except in a few specific conditions.

Based on the HDA findings, the EMC design and testspecifications for rolling stock and signaling system canbe developed and assessed.

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Thank YouThank You