international telecommunication union itu-t sg 5 technical session “lightning protection” 12...
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International Telecommunication Union
ITU-T SG 5 Technical Session “Lightning protection”12 December 2005, ITU Headquarters, Geneva
Risk regarding Risk regarding safetysafetyPhil Day
Protection Specialist, Telstra Corp, Australia
2dates
ITU-T
ITU-T SG 5 Technical Session “Lightning protection”12 December 2005, ITU Headquarters, Geneva
Introduction
o This presentation will introduce:1. Missing risk components2. Risk mechanisms 3. The magnitudes of voltages and
currents relevant to electric shock;
4. Discussion on 62305-25. Future work
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ITU-T
ITU-T SG 5 Technical Session “Lightning protection”12 December 2005, ITU Headquarters, Geneva
Lightning as source of damages
Direct to the
structure
Close to the structure
Direct to the tlc line
Close to the tlc line
RA Injury to people
RB Physical damage
RC Equipment failure
RU Injury to people
RV Physical damage
RW Equipment failure
RM
Equipment failure
RZ
Equipment 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
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ITU-T
ITU-T SG 5 Technical Session “Lightning protection”12 December 2005, ITU Headquarters, Geneva
Missing Risk components
o RA is the risk of electric shock component due to a strike to the structure
1. Does not calculate inside structure• Note in 620305
2. Remote telecommunication earth is a particular risk and not calculated
3. Following figures show mechanisms
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ITU-T
ITU-T SG 5 Technical Session “Lightning protection”12 December 2005, ITU Headquarters, Geneva
Missing Risk components
o RU is the risk of eclectic shock component due to a strike to the services
1. Remote telecommunication earth is a particular risk and not calculated
2. Following figures show mechanisms
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ITU-T
ITU-T SG 5 Technical Session “Lightning protection”12 December 2005, ITU Headquarters, Geneva
Risk mechanisms
Figure 3 - Direct strike to structure (touch potential with respect to the ground outside the structure)
User environment
Power
V
ra
RA1
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ITU-T
ITU-T SG 5 Technical Session “Lightning protection”12 December 2005, ITU Headquarters, Geneva
Risk mechanisms (cont)
User environment
Power
r
V
a
Not covered by 62305-2
Excluded by note in 62305-2
Figure 4 - Direct strike to structure (touch potential with respect to the floor of the structure)
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ITU-T
ITU-T SG 5 Technical Session “Lightning protection”12 December 2005, ITU Headquarters, Geneva
Risk mechanisms (cont)
Figure 5 - Direct strike to structure (touch potential; earthed object to a telecommunication line which is connected to a remote earth)
Telecommunications line
User environment
Power
Vconnected to remote earth
R
Not covered by 62305-2If covered by 62305-2, r = 1a
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ITU-T
ITU-T SG 5 Technical Session “Lightning protection”12 December 2005, ITU Headquarters, Geneva
Risk mechanisms (cont)
Figure 6 - Direct strike to structure (touch potential; floor to a telecommunication line which is connected to a remote earth)
User environment
Power
V
Telecommunications lineconnected to remote earth
ra R
Not covered by 62305-2If covered by 62305-2, r may be 1 in some circumstancesa
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ITU-T
ITU-T SG 5 Technical Session “Lightning protection”12 December 2005, ITU Headquarters, Geneva
Risk mechanisms (cont)
Figure 7 - Direct strike to structure (flashover to internal wiring or plumbing)
Power
RB1
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ITU-T
ITU-T SG 5 Technical Session “Lightning protection”12 December 2005, ITU Headquarters, Geneva
Risk mechanisms (cont)
Figure 8 - Direct strike to structure (flashover to telecommunication line due to EPR)
Power
Telecommication cable
equip
Not covered by 62305-2
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ITU-T
ITU-T SG 5 Technical Session “Lightning protection”12 December 2005, ITU Headquarters, Geneva
Risk mechanisms (cont)
Figure 9 - Direct strike to structure (Damage to telecommunication equipment) (No SPDs)
a)
Source S1
current paths for a strike to the structure,
Strike to the structure
Equipment
b)
Source S1
current paths for a strike to the structure,
Strike to the structure
Equipment
shielded telecommunication cable unshielded telecommunication cable
Covered by 62305-2 but needs modification
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ITU-T
ITU-T SG 5 Technical Session “Lightning protection”12 December 2005, ITU Headquarters, Geneva
Risk mechanisms (cont)
Figure 10 - Direct strike to overhead power line (touch potential with respect to the floor of the structure)
User environment
Power
V
ra
Covered by 62305-2
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ITU-T
ITU-T SG 5 Technical Session “Lightning protection”12 December 2005, ITU Headquarters, Geneva
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)
Telecommunications line
User environment
Power
Vconnected to remote earth
R
Not covered by 62305-2
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ITU-T
ITU-T SG 5 Technical Session “Lightning protection”12 December 2005, ITU Headquarters, Geneva
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)
User environment
Power
V
Telecommunications lineconnected to remote earth
ra R
Not covered by 62305-2
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ITU-T
ITU-T SG 5 Technical Session “Lightning protection”12 December 2005, ITU Headquarters, Geneva
Risk mechanisms (cont)
Figure 13 - Direct strike to telecommunication line (touch potential with respect to the floor of the structure)
Telecommunications
User environment
Power
V
ra
Covered by 62305-2, but may require change
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ITU-T
ITU-T SG 5 Technical Session “Lightning protection”12 December 2005, ITU Headquarters, Geneva
Risk mechanisms (cont)
Figure 14 - Direct strike to telecommunication line (touch potential with respect to earthed object)
Telecommunications
User environment
Power
V
Not covered by 62305-2
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ITU-T
ITU-T SG 5 Technical Session “Lightning protection”12 December 2005, ITU Headquarters, Geneva
Risk mechanisms (cont)
Figure 15 - Direct strike to power line (flashover to telecommunication line due to EPR)
Power
Telecommication cableequip
Covered by 62305-2 but requires modification
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ITU-T
ITU-T SG 5 Technical Session “Lightning protection”12 December 2005, ITU Headquarters, Geneva
Risk mechanisms (cont)
Figure 16 - Direct strike to telecommunication line (flashover to structure)
Power
Telecommication cable
equip
Covered by 62305-2 but requires modification
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ITU-T
ITU-T SG 5 Technical Session “Lightning protection”12 December 2005, ITU Headquarters, Geneva
Risk mechanisms (cont)
Figure 17 - Direct strike to power line/cable (Damage to telecommunication equipment)
a) current paths for a strike to the power line,
Source S3Strike to the power line
Equipment
b) current paths for a strike to the power line,
Source S3Strike to the power line
Equipment
shielded telecommunication cable unshielded telecommunication cable
Covered by 62305-2 but requires change
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ITU-T
ITU-T SG 5 Technical Session “Lightning protection”12 December 2005, ITU Headquarters, Geneva
Risk mechanisms (cont)
Figure 18 - Direct strike to telecommunication line/cable (Damage to telecommunication equipment)
a)current paths for a strike to the telecommunications line,
Equipment
Source S3Strike to the telecommunication line
shielded telecommunication cableb)current paths for a strike to the telecommunications
Equipment
Source S3Strike to the telecommunication line
line, unshielded telecommunication cable
Covered by 62305-2 but requires change
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ITU-T
ITU-T SG 5 Technical Session “Lightning protection”12 December 2005, ITU Headquarters, Geneva
Magnitudes
Figure 1 - Resistance to ground at strike point
Resistance at strike point
0
50
100
150
200
250
300
0 20 40 60 80 100 120 140 160 180 200
Strike current in kA
Res
ista
nce
in
oh
m
R for 100 ohm-m
R for 1000 ohm-m
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ITU-T
ITU-T SG 5 Technical Session “Lightning protection”12 December 2005, ITU Headquarters, Geneva
Magnitudes (cont)
Figure 2 - EPR at strike point versus current
EPR versus current and resistivity
0
500
1000
1500
2000
2500
3000
3500
4000
4500
0 20 40 60 80 100 120 140 160 180 200
Current in kA
EP
R i
n k
V
EPRV for 100 ohm-m
EPR for 1000 ohm-m
100 kV line
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ITU-T
ITU-T SG 5 Technical Session “Lightning protection”12 December 2005, ITU Headquarters, Geneva
Magnitudes (cont)
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;)
Cable type Limiting voltage
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
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ITU-T
ITU-T SG 5 Technical Session “Lightning protection”12 December 2005, ITU Headquarters, Geneva
Magnitudes (cont)Table 2 – Values of ra
Low voltages only?
Type of soil or floor Contact resistance (kΩ)*
ra and ru
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.
26dates
ITU-T
ITU-T SG 5 Technical Session “Lightning protection”12 December 2005, ITU Headquarters, Geneva
Discussion on 62305-2
o As described by Roberto the Risk of loss = NX * PX * LX
1. 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
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ITU-T
ITU-T SG 5 Technical Session “Lightning protection”12 December 2005, ITU Headquarters, Geneva
Discussion on 62305-2 (cont)
1. Px is the probability of damage. This includes:• Whether SPDs are installed• Shielding factors• Screen resistance
o Some rationale has been provided by Roberto
• IEC have assumed both an LPS and coordinated SPDs (software)o My approach is add one at a time. The
most common protection is an MSPD and possibly a GDT on the telecommunication line
28dates
ITU-T
ITU-T SG 5 Technical Session “Lightning protection”12 December 2005, ITU Headquarters, Geneva
Discussion on 62305-2 (cont)
1. Lx is the consequence of loss. The factors include:• np, nt and t
I 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
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ITU-T
ITU-T SG 5 Technical Session “Lightning protection”12 December 2005, ITU Headquarters, Geneva
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
30dates
ITU-T
ITU-T SG 5 Technical Session “Lightning protection”12 December 2005, ITU Headquarters, Geneva
Future work
o Consider 1. the use of 62305-22. The factor Lc
3. The factor ra
4. Loss factors