‘Blue Book’ on Inductive Coordination Task Force Progress Report

Marvin J. Frazier Corr Comp

1415 S. Sunset Dr. Schaumburg, IL 60193

Voice & fax: 630-893-2322

Eilis M. Logan Union Pacific Railroad

1416 Dodge Street Omaha, NE 68179

402-271-2373 fax: 402-271-3298

Brian S. Cramer ComEd/Exelon

1319 S. First Ave. Maywood, IL 60153

708-410-5579 fax: 708-410-5225

ABSTRACT Electric power companies and railroads have found that the characteristics of these

systems, as well as their physical relationship, can introduce compatibility problems that

may require cooperative studies and corrective action. A task force of AREMA Committee

38 has been working on a revision to “Principles and Practices for Inductive Coordination

of Electric Supply and Railroad Communication/Signal Systems”, commonly referred to as

the ‘Blue Book’. The last prior revision was in September 1977. The current revision is

not yet completed.

The Blue Book is being revised to provide clearer objectives for induced voltages, to

include induced current objectives for human safety, and to incorporate induced voltage

objectives for equipment protection. The goal of the document is to provide a framework

for improved cooperation between the electric power and railroad industries to achieve

compatibility. The purpose of this paper is to review the status of the update and to review

some of the key issues being addressed by the task force.

INTRODUCTION

There is a need on the part of both railroad and power engineers for a set of induced

voltage and current objectives on railroad communication/signal circuits. The same

objectives should apply to induced voltages and currents whether the power system is on or

off the railroad right-of-way. They should apply to all railroad communications and signal

circuits, such as open wire or cable systems and to track circuits. These objectives should

serve as a guide to all concerned as to what is reasonable in securing acceptable inductive

coordination goals.

It is reasonable to expect a power system to cause some induced voltage and current. If

such interference is below the susceptibility of the communication/signal systems, then

those systems should continue to operate correctly. Two dominant considerations that

influence the tolerance of coupled voltage and current are:

(1) personnel safety, and

(2) signal equipment compatibility.

These considerations may not result in the same level of acceptable coupled voltage or

current. The maximum level of induction must ensure both personnel safety and operating

communication/signal-system compatibility.

Two broad operating conditions of the power system must be considered. These are the

steady state and the fault conditions. A railroad system must be able to function normally

for steady-state operation of the power system. The voltage and current induced onto the

railroad system can vary over a substantial range, depending on the power-system

conductor spacing, phase arrangement, the load, and other operating conditions.

The power system fault condition generally is of short duration, ranging from

approximately 30 to 250 milliseconds for transmission systems. The induced voltage

and currents for a single-phase to earth fault are typically much higher than for other fault

conditions or the steady state, because of significantly higher unbalanced currents in the

power system. For the faulted power condition, the principal concern is for the

survivability of both personnel and railroad communications/signal equipment. These

factors are summarized in Table 1. The updated ‘Blue Book’ will address both steady

state and fault conditions, but this summary paper will be limited to steady state issues.

PERSONNEL SAFETY

Current-Based Considerations

Quantitative data concerning personnel safety thresholds are generally based on

measurement of the current that results in a particular physiological response. Some of

the important physiological response data are based on animal studies and must be

extrapolated to the human form. The physiological response to a given current

stimulation may be dependent on the size and weight of the subject as well as the current-

conduction duration and path through the body. Relating the available current-based

information to a voltage-based objective is complicated by the need to consider the

impedance of both the electrified object and of the current flow path through the body.

Several different physiological responses to the flow of current through the body are

identified in literature. These responses can be useful for identifying ranges of body

current that are acceptable for different conditions. The responses are generally

dependent on the duration of the current. Different levels of current are acceptable for

steady state and faulted conditions of the power system.

Physiological response to body current is often segregated into the following:

• Threshold of perception, 0.5 (1),(2)

• Startle Reaction, 2.2 to 3.2 mA (3)

• Inability to let go, at 99.5%, 6 mA women, 9 mA men (4)

• Ventricular Fibrillation, >one second, 40-50 mA (1)

A reasonable personnel-safety objective for power-system coupling to railroad-system

conductors, based on the above physiological responses, is to:

• Minimize the chance for body current higher than the let-go threshold for steady

state conditions.

• Minimize the chance for lethal body current for fault-conditions (ventricular

fibrillation).

Selection of more than one objective may be warranted if different levels of personnel

awareness and precaution are incorporated. For example, informed maintenance

personnel, using special procedures may tolerate higher levels of available current than

maintenance personnel who expect a 'non-energized' circuit with no special precautions,

or if the general public has ready access to the conductor.

Voltage-Based Objective Considerations

The current-based thresholds reviewed above reflect the present state of knowledge and

are the most effective indicators, since the physiological response appears to be current or

current density dependent. Transforming to corresponding voltage-based thresholds adds

an additional level of complexity, uncertainty, and variability that can be contributed by:

• Body Impedance

• Conductor Circuit Impedance

• Coupling Mechanism

These factors suggest that care is necessary in interpreting a voltage-based guideline or

objective. The following provides a brief review of the above factors.

Body Impedance

Body impedance can depend on several factors including:

• path through the body

• conductor/skin contact area

• pressure of the conductor/skin contact

• wetness of the skin

• voltage applied

The impedance to current flow through the human body can vary over a wide range, with

a dominant factor being associated with the interface between the conductor and the skin.

The contact area and skin moisture conditions for common field maintenance situations

in which railroad-system conductors can be energized by power line system coupling can

not be readily determined. However, the IEC (1) results of Figure 1 should provide a

conservative range of total body impedance for use in identifying railroad safety

objectives for lower voltage, large contact-area exposures. It is seen that the body

impedance increases for contact to lower voltage sources. Induced rail voltage will

transfer to a locomotive or rail car on the energized segment of track, resulting in a

voltage between grab bars and the earth near the track. Safe contact voltage, for either

the rails or the rolling stock, may be relatively low due to the larger contact area.

Various sources (UL)(5), IEC (6) have identified body impedance for evaluating leakage

current or touch current over a broad range of frequencies. At 60 Hz the resistance is in

the range of 1500 to 2000 ohms to simulate the resistance for a person grasping a handle

or other grippable conductor.

Conductor Circuit Impedance

The impedance of the energized conductor circuit can have a significant effect on the

current that will flow through a person who contacts the conductor. The equivalent

source impedance of railroad-signal conductors energized by 60-Hz power coupling can

range from less than one ohm for rails to thousands of ohms for signal pole-line

conductors. Thus, measuring or calculating the voltage of the conductor for normal

conditions does not provide a good indication of the shock current that can flow through

a person who touches the conductor. The current that flows through a person contacting

an energized conductor depends not only on the voltage but also on the resistance of the

person and the impedance of the conductor circuit.

Coupling Mechanism

The conductor voltage and the current that can be drawn from the conductor will be

influenced by the coupling mechanism (inductive coupling, capacitive coupling or earth

conduction) between the power system and a signal-system conductor. Capacitive

coupling is typically only important for high-impedance circuits like pole-line signal

circuits, while inductive coupling is generally more important for low-impedance circuits

such as rails.

Existing Guidelines

Steady-State

This Blue Book in its earlier editions (last revised 1977) has given 60 V ac rms as the

acceptable level for steady state interference under normal conditions. The 60 V ac rms

value appears to have been based on telecommunication inductive coordination standards

such as promulgated by the CCITT (7). The current ITU-CCITT standard (8) also

recommends a 60 volt guideline for telecommunications. However, other current

Standards, such as IEEE Std. 776 (9) and the Canadian Standards Association (CSA) (10)

recommend an induced longitudinal voltage of 50 volts rms for personal contact with

telecommunications conductors. The anticipated energized conductor for the telephone

industry is a small-diameter conductor, namely conductors in a cable or open-wire line.

OSHA (11) also recommends a 50 volt limit for live parts of electrical equipment that are

not screened or only accessible to qualified persons.

The CSA (10) also recommends 50 volts for longitudinally induced voltages in railway

signaling and communications circuits, under normal power line conditions. For track

circuits, they include the special note: “For adjacent track sections of equal length

separated by a pair of insulated joints, the ac voltage developed across each insulated rail

joint is twice the maximum voltage of each rail with respect to remote earth. To limit the

voltage across insulated rail joints to 50 V, the maximum rail-to-remote earth voltage

should not exceed 25V.”

However, some personnel safety guidelines limit the steady state touch voltage to less

than 50 volts. A recent pipeline industry standard by NACE (12) has set this level at 15

Volts. The Foreword states,

“Some controversy has arisen in the latest issue of this standard regarding the shock

hazard stated in Section 5, Paragraph 5.2.1.1 and elsewhere in this standard. The reason

for a more conservative value in this revision of the standard is that early work by George

Bodier at Columbia University and by other investigators has shown that the average

hand-to-hand or hand-to-foot resistance for an adult male human body can range between

600 ohms and 10,000 ohms.(1) A reasonable safe value for the purpose of estimating

body currents is 1,500 ohms hand-to-hand or hand-to-foot. In other work by K.S. Gelges

and C.F. Dalziel on muscular contraction, the inability to release contact would occur in

the range of 6 to 20 milliamperes for adult males.(2) Ten milliamperes hand-to-hand or

hand-to-foot is generally established as the absolute maximum safe let-go current.

Conservative design would use an even lower value. Fifteen volts AC impressed across a

1,500-ohm load would yield a current flow of 10 milliamperes, thus the criterion within

this standard is set at 15 volts. Prudent design would suggest an even lower value under

certain circumstances.

(1) George Bodier, Bulletin de la Societe Francaise Des Electriciens,

October 1947.

(2) C.F. Dalziel, “The Effects of Electrical Shock on Man,”

Transactions on Medical Electronics, PGME-5, Institute of Radio

Engineers, 1956.”

Similarly, the CSA (13) also identifies a 15 volt value for pipeline induced voltage

personnel safety. As explanation, they note:

“The value of 15 V has been selected as a practical mitigation level that falls within

generally accepted guidelines for exposure of the general public to continuous 60 Hz rms

voltage. Some industries may accept different voltage levels where trained personnel or

other technical factors are involved.”

The ‘Blue Book’ Task Force has no information concerning any fatalities below 50 V ac

rms.

SIGNAL EQUIPMENT COMPATIBILITY CONSIDERATIONS

Overview

The question of railroad communication and signal equipment interference and damage is

at least as complex as the human safety issue. The variety of railroad system types,

manufacturers, and susceptibilities makes it difficult to produce a guideline for acceptable

induction. It is just this confusion that makes it important to set target levels so that

railroad and utility engineers, and manufacturers of equipment have common design

targets. The acceptable induced-voltage for any given application will be driven by the

existing or available signal equipment, and requires agreement of all parties. In all cases

the lower value for acceptable interference, equipment susceptibility, or human safety, will

be the required level. A goal for future compatibility is to have the equipment

susceptibility and personnel safety induced voltage criteria be the same. That is, if the

voltage induced onto the railroad conductors meets personnel safety guidelines, the signal

equipment connected to those same conductors should also be compatible with the induced

voltage.

The personnel safety issues are generally associated with voltage that appears from

conductor to earth (longitudinal mode voltage). However, equipment interference is

generally the result of coupled voltage that appears between the conductors,for example

rail-to-rail for a track circuit (also called metallic or differential-mode voltage).

The rail-to-rail induced 60 Hz voltage tolerance for several types of track signal systems

are specifically identified in AREMA Manual Parts (14). Table 2 summarizes the target

interference-tolerance voltages for several types of track signal equipment. It is seen that

these voltages are considerably less than the personnel safety voltages that were

discussed in the previous sections. Because the two conductors of a track signal circuit

are generally exposed to nominally the same exciting field of the power system, the two

conductors typically have nominally the same longitudinal induced voltage. Therefore

for normal conditions, the inherent balance of the rail system normally results in rail-to-

rail voltages that are less than the values of Table 2.

Interference susceptibility testing of track signal systems for realistic conditions is not

straightforward. Susceptibility has been noted to depend on the operating conditions and

the signal devices must operate as a system to produce reliable susceptibility results. To

satisfy those needs, the AAR and EPRI jointly commissioned the development of a Track

Simulator for Interference Testing (15). The Track Simulator, was designed for testing

signal units as a system by approximating key track-circuit electrical parameters such as:

• input impedance of the track at the signal system location,

• signal attenuation and distortion,

• rail impedance skin effect,

• ballast-resistance variation over a realistic range,

• track-storage effects.

The simulator consists of two variable-length signal blocks, with interference testing

using a low-distortion 60-Hz sinusoid or a 60-Hz harmonically rich waveform. Testing

for important static conditions, with or without superimposed interference such as:

• unoccupied circuit,

• occupied circuit,

• broken rail,

• shorted insulator,

• one grounded track lead.

The AAR/EPRI research also developed testing procedures and performed demonstration

tests on Low Frequency Electronic Track Circuits for comparison to field test results.

Recently, the Blue-Book Task Force prepared Track Simulator initial testing procedures

for highway grade crossing equipment for 60-Hz and harmonic interference (16).

Track Unbalancing Mechanisms

An important element of inductive coordination is to identify if existing railroad signal

equipment is compatible with the rail-to-rail voltage resulting from normal rail-system

unbalance, when personnel-safety guidelines are met. The conductor-to-conductor

voltage, for example between two rails, is typically in the range of a few percent of the

induced rail-to-ground voltage for nominally balanced track conditions, but can be

considerably higher for some unbalancing conditions. Important unbalancing conditions

should be evaluated in a compatibility investigation and for mitigation design.

Unbalancing conditions may include a shorted insulated joint, an earthed lead-in

conductor (with or without a train within the affected track region), or a locomotive

within the stagger region at an insulated-joint location.

Many in the railroad industry consider a single degraded insulating joint to be a normal

operating condition. That is because when no significant induced voltage is present,

many signal systems will function properly with a single degraded joint. Of course, the

signal systems also function properly when a single joint is shorted by a train-shunt

within the stagger region.

However, in the presence of significant induced rail-ground voltage, shorted or degraded-

resistance joint can result in non-negligible rail-to-rail voltage that may influence or

interfere with the normal operation of the signal system.

Figure 4 illustrates the measured insulated-joint resistances for an approximately 13-mile

segment of track, using a commercial IJ resistance test instrument. The average IJ

resistance is 40.4 ohms. While the resistance varies over approximately a 3:1 range, it is

seen that the unbalance of joint-pairs is relatively small. Thus for this measurement set,

the small existing unbalance may not result in interfering conditions, depending on the

induced rail-ground voltage and the types of signal equipment.

Figure 5 quantifies how the degradation of joint resistance affects the voltage that appears

rail-to-rail for a calculated example with all 100-ohm joints except for the one degraded

joint. The figure shows the calculated percentage of induced rail-to-ground voltage, with

all good joints, that is converted to rail-rail voltage by the degraded resistance of a single

joint. The figure shows that a degraded joint resistance of approximately 15 ohms results

in 20% of the normal rail-to-ground voltage appearing rail-to-rail. If the induced rail-to-

ground voltage satisfies a 25 volt personnel safety condition, conversion of 20% or more

to rail-to-rail voltage is 5-volts or more. For this condition, some equipment that meets

the 5-volt susceptibility guidelines of Table 2 may experience interference.

The rail-to-rail voltage caused by a degraded insulated joint can be made worse by the

presence of a train in the block, as is illustrated in Figure 6 and Figure 7. Figure 6

illustrates a segment of track with insulating joint locations A, B, and C. One shorted

insulator exists at location B, which is also the site of highway grade-crossing equipment

connected on both sides of the insulating joint. The voltage induced rail-to-rail on the

west and east sides of the (B) joints are designated as VBw and VBe. Successive sketches

in Figure 6 show the location of a train proceeding from west to east at Times 1 through

5.

Figure 7 shows sketches of power-line induced 60-Hz voltage envelopes VBw and VBe

that were recorded on a strip chart as a train moved through the two-block region of

Figure 6. A low-pass filter was used to reject the grade-crossing detector signals from the

strip chart input. Times 1 through 5 are also shown in Figure 7, along with a description

of the event at each time that relates to a change in the recorded envelope. The

waveforms illustrate that a train that bridges the pair of insulating joints adjacent to a

shorted IJ location can increase the rail-to-rail interference voltage relative to when the

train is not present. Therefore, to assess the effect of a shorted insulating joint on track

signal systems the influence of the occupied condition should be considered.

The above examples illustrate that a common corridor that is designed to satisfy a

personnel safety criterion of 25 volts rail-to-ground, may not be compatible with

commonly used signal equipment for track unbalance conditions that may occur.

Compatibility assurance necessitates knowledge of the range of unbalance conditions that

will occur, and the susceptibility thresholds of the equipment for those conditions.

Without that knowledge, the compatibility of the signal system and the power system can

not be assured, except on a trial and error basis.

The capabilities and characteristics of railroad signaling equipment, including induced-

voltage tolerance are rapidly evolving. The equipment manufacturer is in a unique position

to assess the compatibility of equipment that is applicable for a specific signaling function

with an expected induced voltage environment. Therefore, the resources and knowledge of

the manufacturer should be used to the full extent possible in helping to ensure the

compatibility of available equipment for an anticipated induced-voltage environment.

Railroad signal equipment can be susceptible to interference from rail-to-rail ac induction.

Grade crossing train detection equipment is susceptible to a greater degree than most other

railroad systems. It is imperative for future successful rail operations that utilities,

equipment suppliers and railroads address this issue in development of equipment, design

of power systems, and design of railroad signal systems. Cooperative efforts needed are:

• Utilities must make reduction of rail induced voltage a top priority in design of power

systems and mitigation.

• Equipment suppliers must make reduction of operational susceptibility a top priority in

design of new equipment and application of systems.

• Railroads must do their best to maintain balanced rail impedances, and where possible

to adapt signal systems to maintain reliable operation.

EXCITATION OF TRACK SYSTEM BY POWER SYSTEM

Thus far, we have discussed the effects of induced voltage onto the railroad system in

terms of personnel safety and interference to signal equipment without regard to the

details of the power system. The most prevalent cause of rail-system induced voltage is

the current that flows in the power-system conductors. The current in the power-system

conductors couples voltage onto the railroad system by magnetic-field induction, similar

to a simple single-turn transformer. Two important power-system parameters that

influence the induced rail-system voltage are:

• the spacing between the power conductors.

• the unbalance of the current in the three power phase conductors,

The unbalance of the power line currents is influenced by the spacing of the power

conductors to each other and to the earth and the loading of the line. Recent

measurement on many power lines characterized the unbalance of several voltage classes,

for many lines of each voltage, using phase current values recorded by the SCADA

systems (17). Figure 8 shows a plot of the average unbalance data as a deviation, δ, from

the mean circuit current magnitude, expressed as a percentage. The line shown in the

figure provides the trend of the data and permits extrapolation to line voltages not

measured.

Although the results of Figure 8 may not be representative of all power systems, it is

representative of one major system, and similar data is not known to be available for

other systems. Therefore, those data have been used to assess the voltage induced on a

representative 1.5-mile long track block as a function of phase-conductor spacing.

Figure 9 shows the average phase current for a vertical power line that will result in 25

volts rail-ground for a 1.5 mile block circuit versus the phase-to-phase separation. For

each voltage class analyzed, the unbalance of Figure 8 was assumed and was converted to

an equivalent residual current, by multiplying by √3. As a worst-case, the induced

voltage caused by the balanced current and residual current were assumed to add directly

in phase. Other representative conditions shown in the figure were assumed for the

calculations. The effect of separation between the power circuit and the track is also

shown as separate curves in the figure. The figure also shows the spacing for common

voltage-class power lines.

For block-lengths in the 1.5-mile length range, Figure 9 can be used to estimate the line

currents which may cause 25 volts or more rail-ground and thus require more detailed

investigation to assure personnel safety. As noted above, evaluation of signal equipment

compatibility may require lower values of power line current, more detailed evaluation of

track unbalance conditions, and the development of mitigation measures.

CONCLUSIONS

Table 3 summarizes the values most likely to be recommended to the full AREMA

Committee 38 by the Blue-Book Task Force. However, since full Committee review has

not been made, the levels are subject to change.

A common corridor that is designed to satisfy a rail-to-ground personnel-safety criterion

may not be compatible with commonly used signal equipment for track unbalance

conditions that may occur. It is imperative for future successful rail operations that

utilities, equipment suppliers, and railroads address this issue in development of

equipment, design of power systems, and design of railroad signal systems.

REFERENCES

1. IEC 479-1, Effects of current on human beings and livestock - Part 1: General Aspects, 1994,

International Electrotechnical Commission, Geneva, Switzerland.

2. Cabanes J., Physiological Effects of Electric Currents on Living Organisms,in Electrical Shock

Safety Criteria, Proceedings of the First International Symposium on Electrical Shock Safety

Criteria, Edited by Bridges,J.E., et al, Pergamon Press, 1985, ISBN 0-08-25399-7.

3. Electrical Stimulation and Electropathology, Reilly, J.P. Editor, Cambridge University Press,

1992, ISBN 0-521-41791-0,in Ch. 7.

4. Dalziel, C.F., Reevaluation of Lethal Electric Currents. IEEE Transactions Inductrial

Applications IGA-4(5), 1968, 467-476.

5. In Reference (3), in Ch. 11 by Skuggevig, W. of UL

6. IEC 990 Methods of measurement of touch-current and protective conductor current, 1990

7. Directives Concerning the Protection of Telecommunication Lines Against Harmful Effects

from Electricity Lines, International Telegraph and Telephone Consultative Committee

(CCITT), published by the International Telecommunication Union, 1963, Chapter IV

8. ITU, Directives concerning the protection of telecommunication lines against harmful effects

from electric power and electrified railway lines, Volume VI, Danger and Disturbance, Geneva

1989, ISBN 92-61-04041-3.

9. IEEE Std 776-1992, IEEE Recommended Practice for Inductive Coordination of Electric

Supply and Communications Lines, IEEE, Inc., 345 East 47th Street, New York, NY 10017-

2394.

10. Electrical Coordination, Canadian Electrical Code, Part III, Canadian Standards Association

(CSA), C22.3 No. 3-98, August 1998.

11. OSHA Title 29, Volume 5, CFR Ch. XVII (7-1-98 Edition) Sec. 1910.303, Page 826-831, U.S.

Government Printing Office.

12. NACE (National Association of Corrosion Engineers) Standard RP0177-95, Mitigation of

Alternating Current and Lightning Effects on Metallic Structures and Corrosion Control

Systems

13. Principles and Practices of Electrical Coordination Between Pipelines and Electric Supply

Lines, CAN/CSA-C.22.3, No. 6-M91, Canadian Standards Association, 178 Rexdale Blvd,

Etobicoke, Ontario, Canada M9W 1R3

14. AREMA Communication & Signal Manual Parts, 2000.

15. Mutual Design: Overhead Transmission Lines and Railroad Facilities - Susceptibility Program

Phase II, Vol's 1, 2, and 3, Final Report, M. Frazier Principal Investigator, RP 1902-7, Electric

Power Research Institute, June 1994.

16. Cramer, B.S. for Working Group F2, “Selecting Highway-Rail Grade Crossing Train Detection

Electronics in an AC Power Interference Environment”. Proceedings of the 1998 AREMA

C&S Annual Technical Conference, September 14-16, St. Louis, MO

17. Cramer, B.S., “Phase Imbalance on ComEd’s Transmission and Distribution Systems”,

Proceedings Of The American Power Conference, April 1995

Table 1. Summary of Compatibility Considerations.

Principal Considerations Power Condition Personnel Safety Equipment Compatibility

Steady State Let Go* Non-Degraded Operation Faulted Survivability Survivability *Startle reaction may be more appropriate in certain circumstances.

Table 2. AREMA Guidelines for Interference Tolerance of Selected Signal Equipment.

C&S Manual Part Equipment Type Interference Tolerance 3.1.20 Motion Sensitive Systems to Control

Highway Grade Crossings 5 V rms 60 Hz

3.1.26 Constant Warning Time Systems to Control Highway Grade Crossings

5 V rms 60 Hz

8.2.1 Audio Frequency Track Circuits 10 V rms, 60-180 Hz

Table 3. Voltage and Current Limits Being Considered for Personnel Safety.

Condition Current (milliamperes) Voltage (volts)

Rails & Attachments 10[2] 25[2] Steady State

Other Signal Conductors 10[1] 50[3]

Fault All Conductors IEEE Std-80 methods

[1] For well-isolated signal conductors that are subjected to electrostatic induction the conductor to earth current through a low impedance, (2000 ohms) is the most appropriate indicator. For those conditions do not rely on measure of the conductor voltage. [2] Generally caused by magnetic -field induction. The voltage is to ground, and is consistent with a 2500-ohm body resistance between the conductor and ground. Those conditions are consistent with the10 milliamperes body current (through the resistor) shown in the current column. This will result in a maximum of 50 volts across an IJ. [3] Generally caused by magnetic -field induction. The voltage is the accessible voltage, which can be to ground or to another conductor. The voltage is consistent with higher contact resistance to smaller conductors.

Figure 1. Values of total body impedance hand-hand or hand-foot for ac 50/60 Hz.

100

1,000

10,000

10 100 1,000

Touch Voltage (Volts rms)

To

tal B

od

y Im

ped

ance

(o

hm

s)

95%

50%

5%

Large area contact:8000mm2 (12.4 in2),Dry skin.

Percentage population with resistance not exceeding value of curve.

(Trend lines through data values presented in IEC 479-1)

Figure 2. IEEE Std-80 Fault Touch-Potential Model.

V

Ib1000 ohm

6” Soil ρ (ohm·m)

( )ρ+=

5.11000V

Ib

Figure 3. IEEE Std 80-1986 Guideline for 99.5% Safe Touch Potential.

100

1,000

10,000

0.01 0.1 1

Shock Duration (seconds)

Saf

e T

ou

ch P

ote

nti

al (

volt

s)

Soil Resistivity (ohm-m)

1000

500

100

70 kg (155 lb) person

Figure 4. In-Situ Measured Resistance of Rail Insulated Joints.

450 455 460 465 470

Milepost

0

10

20

30

40

50

60

70

80

90

100

110

120

130

140

150IJ

Res

ista

nce

(oh

ms)

N Rail IJ RS Rail IJ R

Figure 5. Conversion of Rail-Ground Voltage to Rail-Rail Voltage vs. Resistance of Single Degraded IJ.

1

10

100

1 10 100

Degraded IJ Resistance (ohms)

Per

cent

Vol

tage

Con

vers

ion

At Adjacent IJ Location

At Degraded IJ Location

Analysis Assumptions: 1.5 mile Blocks; Soil resistivity = 100ohm-m,Ballast = 100 ohms; Good IJ R's = 100 ohms;Rail-connected signal-equipment impedance=j10 ohms

Vw Ve

BA C

Shorted IJ

Train

Time 5

Time 4

Time 3

Time 2

Time 1

Train

Train

Train

Train

Direction of Motion

InsulatedJoint

.

.

Figure 6. Geometry of Moving Train and Degraded Rail Insulator.

Vw

Ve

Time1 2 3 4 5

Fro

nt C

ross

es IJ

A

Fro

nt C

ross

es IJ

B

End

Cro

sses

IJ B

Fro

nt C

ross

es IJ

C

End

Cro

sses

IJ C

.

. Figure 7. Induced 60 Hz Rail-to-Rail Voltage Measured at Degraded IJ Site.

Figure 8. Measured Phase Current Deviation from the Circuit Mean.

1

10

100

1 10 100 1000

Line-to-Line Voltage (kV)

Ave

rag

e D

evia

tio

n, %

of

Mea

n C

ircu

it C

urr

ent

Mag

nit

ud

e

Average Measured PhaseCurrent Deviation from theMean for Each Voltage Class,Cramer (17)

Trendline: Average Deviation, d (%) = 23.04V-0.3653

d = {|Ia-avg| + |Ib-avg| + |Ic-avg|}/3V in kilovolts, line-to-line.

Figure 9. Maximum Average Line Current for 25V Induced Rail Voltage, Vertical Circuit with Unbalance.

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

0 5 10 15 20 25 30 35

Phase Separation (ft)

Ave

rag

e P

has

e C

urr

ent

Mag

nit

ud

e (k

A)

800 ft

500 ft

300 ft

200 ft

150 ft

100 ft

50 ft

Po

wer

-to

-Tra

ck D

ista

nce

(ft

)

500 kV230 kV 345 kV138 kV115 kV34 kV

1.5-mile Track BlocksEarth Resistivity = 1000 ohm-mBallast Resistivity = 100 ohm-kftAlumoweld OHSW,Unbalance of Figure 8.

TABLE CAPTIONS Table 1. Summary of Compatibility Considerations. Table 2. AREMA Guidelines for Interference Tolerance of Selected Signal Equipment. Table 3. Voltage and Current Limits Being Considered for Personnel Safety. FIGURE CAPTIONS Figure 1. Values of total body impedance hand-hand or hand-foot for ac 50/60 Hz. Figure 2. IEEE Std-80 Fault Touch-Potential Model. Figure 3. IEEE Std 80-1986 Guideline for 99.5% Safe Touch Potential. Figure 4. In-Situ Measured Resistance of Rail Insulated Joints. Figure 5. Conversion of Rail-Ground Voltage to Rail-Rail Voltage vs. Resistance of Single Degraded IJ.

Figure 6. Geometry of Moving Train and Degraded Rail Insulator.

Figure 7. Induced 60 Hz Rail-to-Rail Voltage Measured at Degraded IJ Site.

Figure 8. Measured Phase Current Deviation from the Circuit Mean. Figure 9. Maximum Average Line Current for 25V Induced Rail Voltage, Vertical Circuit with Unbalance.