Risk regarding safety
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Risk regarding safety. Phil Day Protection Specialist, Telstra Corp, Australia. Introduction. This presentation will introduce: Missing risk components Risk mechanisms The magnitudes of voltages and currents relevant to electric shock; Discussion on 62305-2 Future work.

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Risk regarding safety

Risk regarding safety

Phil Day

Protection Specialist, Telstra Corp, Australia


Introduction

Introduction

  • This presentation will introduce:

    • Missing risk components

    • Risk mechanisms

    • The magnitudes of voltages and currents relevant to electric shock;

    • Discussion on 62305-2

    • Future work


Risk regarding safety

Lightning as source of damages

Close to the tlc line

Direct to the tlc line

Direct to the structure

Close to the structure

RU Injury to people

RV Physical damage

RW Equipment failure

RA Injury to people

RB Physical damage

RC Equipment failure

RMEquipment failure

RZEquipment failure

R1: Risk of loss of human life = RA+RB+RU+RV+(RC+RW+RM+RZ)

R2: Risk of loss of service = RB+RC+RV+RW+RM+RZ

R3: Risk of loss of cultural heritage = RB+RV

R4: Risk of loss of economic value = RB+RC+RV+RW+RM+RZ


Missing risk components

Missing Risk components

  • RA is the risk of electric shock component due to a strike to the structure

    • Does not calculate inside structure

      • Note in 620305

    • Remote telecommunication earth is a particular risk and not calculated

    • Following figures show mechanisms


Missing risk components1

Missing Risk components

  • RU is the risk of eclectic shock component due to a strike to the services

    • Remote telecommunication earth is a particular risk and not calculated

    • Following figures show mechanisms


Risk mechanisms

Risk mechanisms

R

A1

Figure 3 - Direct strike to structure (touch potential with respect to the ground outside the structure)


Risk mechanisms cont

Risk mechanisms (cont)

Figure 4 - Direct strike to structure (touch potential with respect to the floor of the structure)


Risk mechanisms cont1

Risk mechanisms (cont)

Figure 5 - Direct strike to structure (touch potential; earthed object to a telecommunication line which is connected to a remote earth)


Risk mechanisms cont2

Risk mechanisms (cont)

Figure 6 - Direct strike to structure (touch potential; floor to a telecommunication line which is connected to a remote earth)


Risk mechanisms cont3

Risk mechanisms (cont)

R

B1

Figure 7 - Direct strike to structure (flashover to internal wiring or plumbing)


Risk mechanisms cont4

Risk mechanisms (cont)

Figure 8 - Direct strike to structure (flashover to telecommunication line due to EPR)


Risk mechanisms cont5

Risk mechanisms (cont)

Figure 9 - Direct strike to structure (Damage to telecommunication equipment)

(No SPDs)


Risk mechanisms cont6

Risk mechanisms (cont)

Figure 10 - Direct strike to overhead power line (touch potential with respect to the floor of the structure)


Risk mechanisms cont7

Risk mechanisms (cont)

Figure 11 - Direct strike to a power line (touch potential earthed object to the telecommunication line which is connected to a remote earth)


Risk mechanisms cont8

Risk mechanisms (cont)

Figure 12 - Direct strike to a power line (touch potential floor to the telecommunication line which is connected to a remote earth)


Risk mechanisms cont9

Risk mechanisms (cont)

Figure 13 - Direct strike to telecommunication line (touch potential with respect to the floor of the structure)


Risk mechanisms cont10

Risk mechanisms (cont)

Figure 14 - Direct strike to telecommunication line (touch potential with respect to earthed object)


Risk mechanisms cont11

Risk mechanisms (cont)

Figure 15 - Direct strike to power line (flashover to telecommunication line due to EPR)


Risk mechanisms cont12

Risk mechanisms (cont)

Figure 16 - Direct strike to telecommunication line (flashover to structure)


Risk mechanisms cont13

Risk mechanisms (cont)

Figure 17 - Direct strike to power line/cable (Damage to telecommunication equipment)


Risk mechanisms cont14

Risk mechanisms (cont)

Figure 18 - Direct strike to telecommunication line/cable (Damage to telecommunication equipment)


Magnitudes

Magnitudes

Figure 1 - Resistance to ground at strike point


Magnitudes cont

Magnitudes (cont)

Figure 2 - EPR at strike point versus current


Magnitudes cont1

Cable type

Limiting voltage

Magnitudes (cont)

Cellular (blown) CPFUT MB

b/d voltage to screen 5 - 10 kV

Solid PEIFLI MBHJ

b/d voltage to screen up to 75 kV

Unshielded PE cable

b/d voltage to ground up to 150 kV

Table 1 – Limiting voltage of different cable types

Cable limits the voltage

(MB = PE sheathed with Moisture Barrier screen; HJ = nylon jacket; PEIFLI = solid PE insulated conductors, grease filled lead-in cable; CPFUT = cellular insulated unit twin conductors;)


Magnitudes cont2

Type of soil or floor

Contact resistance (kΩ)*

ra and ru

Magnitudes (cont)

Agricultural, Concrete

≤ 1

10-2

Marble, Ceramic

1-10

10-3

Gravel, Moquette, Carpets

10-100

10-4

Asphalt, Linoleum, Wood

≥ 100

10-5

(*) Values measured between a 400 cm² electrode compressed with a force of 500 N and a point of infinity.

Table 2 – Values of ra

Low voltages only?


Discussion on 62305 2

Discussion on 62305-2

  • As described by Roberto the Risk of loss = NX * PX * LX

    • Nx for services uses Lc for the line length. Need to validate values for Lc

      • Maybe different for direct strikes versus induction

      • What determines the value of Lc

      • Need consistency for single section versus multiple sections


Discussion on 62305 2 cont

Discussion on 62305-2 (cont)

  • Px is the probability of damage. This includes:

    • Whether SPDs are installed

    • Shielding factors

    • Screen resistance

      • Some rationale has been provided by Roberto

    • IEC have assumed both an LPS and coordinated SPDs (software)

      • My approach is add one at a time. The most common protection is an MSPD and possibly a GDT on the telecommunication line


Discussion on 62305 2 cont1

Discussion on 62305-2 (cont)

  • Lx is the consequence of loss. The factors include:

    • np, nt and tI have difficulty considering these as loss. They relate more to probability

    • In particular ra, ru, rp, rf and hz relate directly to probability of injury or damage

    • There is no loss factor for domestic equipment


Discussion on 62305 2 cont2

Discussion on 62305-2 (cont)

  • Therefore I think SG 5 needs to review the use of loss versus probability

  • If loss is retained the values should be carefully selected and rationale provided

  • Loss factors for domestic equipment need to be developed


Future work

Future work

  • Consider

    • the use of 62305-2

    • The factor Lc

    • The factor ra

    • Loss factors


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